Found 45 papers in cond-mat

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Long-lived Topological Flatband Excitons in Semiconductor Moir\'e Heterostructures: a Bosonic Kane-Mele Model Platform
Ming Xie, Mohammad Hafezi, Sankar Das Sarma
arXiv:2403.00052v1 Announce Type: new Abstract: Moir\'e superlattices based on two-dimensional transition metal dichalcogenides (TMDs) have emerged as a highly versatile and fruitful platform for exploring correlated topological electronic phases. One of the most remarkable examples is the recently discovered fractional quantum anomalous Hall effect (FQAHE) under zero magnetic field. Here we propose a minimal structure that hosts long-lived excitons -- a ubiquitous bosonic excitation in TMD semiconductors -- with narrow topological bosonic bands. The nontrivial exciton topology originates from hybridization of moir\'e interlayer excitons, and is tunable by controlling twist angle and electric field. At small twist angle, the lowest exciton bands are isolated from higher energy bands, and provides a solid-state realization of bosonic Kane-Mele model with topological flatbands, which could potentially support the bosonic version of FQAHE.

Crystalline axion electrodynamics in charge-ordered Dirac semimetals
Julian May-Mann, Mark R. Hirsbrunner, Lei Gioia, Taylor L. Hughes
arXiv:2403.00055v1 Announce Type: new Abstract: Three-dimensional Dirac semimetals can be driven into an insulating state by coupling to a charge density wave (CDW) order. Here, we consider the quantized crystalline responses of such charge-ordered Dirac semimetals, which we dub Dirac-CDW insulators, in which charge is bound to disclination defects of the lattice. Using analytic and numeric methods we show the following. First, when the CDW is lattice-commensurate, disclination-line defects of the lattice have a quantized charge per length. Second, when the CDW is inversion-symmetric, disclinations of the lattice have a quantized electric polarization. Third, when the CDW is lattice-commensurate and inversion-symmetric, disclinations are characterized by a "disclination filling anomaly" -- a quantized difference in the total charge bound to disclination-lines of Dirac-CDW with open and periodic boundaries. We construct an effective response theory that captures the topological responses of the Dirac-CDW insulators in terms of a total derivative term, denoted the $R\wedge F$ term. The $R\wedge F$ term describes the crystalline analog of the axion electrodynamics that are found in Weyl semimetal-CDW insulators. We also use the crystalline responses and corresponding response theories to classify the strongly correlated topological phases of three-dimensions Dirac-semimetals.

Non-Abelian fractionalization in topological minibands
Aidan P. Reddy, Nisarga Paul, Ahmed Abouelkomsan, Liang Fu
arXiv:2403.00059v1 Announce Type: new Abstract: Motivated by the recent discovery of fractional quantum anomalous Hall states in moir\'e systems, we consider the possibility of realizing non-Abelian phases in topological minibands. We study a family of moir\'e systems, skyrmion Chern band (SCB) models, which can be realized in two-dimensional semiconductor/magnetic skyrmion heterostructures and also capture the essence of twisted transition metal dichalcogenide (TMD) homobilayers. We show using many-body exact diagonalization that, in spite of strong Berry curvature variations in momentum space%and real-space emergent magnetic field, , the non-Abelian Moore-Read state can be realized at half filling of the second miniband. These results demonstrate the feasibility of non-Abelian fractionalization in moir\'e systems without Landau levels and shed light on the desirable conditions for their realization. In particular, we discuss the prospect of realizing the Moore-Read state at filling factor $\nu=3/2$ in twisted semiconductor bilayers.

Quantum transport properties of the topological Dirac Semimetal $\alpha$-Sn
Md Shahin Alam, Alexandr Kazakov, Mujeeb Ahmad, Rajibul Islam, Fei Xue, Marcin Matusiak
arXiv:2403.00083v1 Announce Type: new Abstract: We report measurements of the electrical resistivity ($\rho$) and thermoelectric power (S) in a thin film of strained single-crystalline $\alpha$-Sn grown by molecular beam epitaxy on an insulating substrate. The temperature (T) dependence of the resistivity of $\alpha$-Sn can be divided into two regions:below T* $\approx$ 135 K $\rho$(T) shows a metallic-like behaviour, while above this temperature an increasing contribution from thermally excited holes to electrical transport is observed. However, it is still dominated by highly mobile electrons, resulting in a negative sign of the Seebeck coefficient above T = 47 K. In the low temperature limit, a small positive S likely reflects the persistent contribution from low-mobility holes or the positive phonon-drag thermopower. In the presence of the magnetic field (B) applied along an electric field or thermal gradient, we note a negative magnetoresistance or a negative slope of S(B), respectively. The theoretical prediction for the former (calculated using density functional theory) agrees well with the experiment. However, these characteristics quickly disappear when the magnetic field is deviated from an orientation parallel to the electrical field or the thermal gradient. We indicate that the behaviour of the electrical resistivity and thermoelectric power can be explained in terms of the chiral current arising from the topologically non-trivial electronic structure of $\alpha$-Sn. Its decay at high temperature is a consequence of the decreasing ratio between the intervalley Weyl relaxation time to the Drude scattering time.

A moment tensor potential for lattice thermal conductivity calculations of alpha and beta phases of Ga2O3
Nikita Rybin, Alexander Shapeev
arXiv:2403.00113v1 Announce Type: new Abstract: Calculations of heat transport in crystalline materials have recently become mainstream, thanks to machine-learned interatomic potentials that allow for significant computational cost reductions while maintaining the accuracy of first-principles calculations. Moment tensor potentials (MTP) are among the most efficient and accurate models in this regard. In this study, we demonstrate the application of MTP to the calculation of the lattice thermal conductivity of alpha and beta Ga2O3. Although MTP is commonly employed for lattice thermal conductivity calculations, the advantages of applying the active learning methodology for potential generation is often overlooked. Here, we emphasize its importance and illustrate how it enables the generation of a robust and accurate interatomic potential while maintaining a moderate-sized training dataset.

Ab initio modelling of quantum dot qubits: Coupling, gate dynamics and robustness versus charge noise
Hamza Jnane, Simon C Benjamin
arXiv:2403.00191v1 Announce Type: new Abstract: Electron spins in semiconductor devices are highly promising building blocks for quantum processors (QPs). Commercial semiconductor foundries can create QPs using the same processes employed for conventional chips, once the QP design is suitably specified. There is a vast accessible design space; to identify the most promising options for fabrication, one requires predictive modeling of interacting electrons in real geometries and complex non-ideal environments. In this work we explore a modelling method based on real-space grids, an ab initio approach without assumptions relating to device topology and therefore with wide applicability. Given an electrode geometry, we determine the exchange coupling between quantum dot qubits, and model the full evolution of a $\sqrt{\text{SWAP}}$ gate to predict qubit loss and infidelity rates for various voltage profiles. Moreover we explore the impact of unwanted charge defects (static and dynamic) in the environment, and test robust pulse sequences. As an example we exhibit a sequence correcting both systematic errors and (unknown) charge defects, observing an order of magnitude boost in fidelity. The technique can thus identify the most promising device designs for fabrication, as well as bespoke control sequences for each such device.

La$_4$Co$_4$X (X = Pb, Bi, Sb): a demonstration of antagonistic pairs as a route to quasi-low dimensional ternary compounds
Tyler J. Slade, Nao Furukawa, Matthew Dygert, Siham Mohamed, Atreyee Das, Weiyi Xia, Cai-Zhuang Wang, Sergey L. Budko, Paul C. Canfield
arXiv:2403.00204v1 Announce Type: new Abstract: We outline how pairs of strongly immiscible elements, referred to here as antagonistic pairs, can be used to synthesize ternary compounds with quasi-reduced dimensional motifs. By identifying third elements that are compatible with a given antagonistic pair, ternary compounds can be formed in which the third element segregates the immiscible atoms into spatially separated substructures. Quasi-low dimensional structural units are a natural consequence of the immiscible atoms seeking to avoid contact in the solid-state. As proof of principle, we present the discovery and physical properties of La$_4$Co$_4$X (X = Pb, Bi, Sb), a new family of intermetallics based on the antagonistic pairs Co-Pb and Co-Bi. La$_4$Co$_4$X adopts a new orthorhombic crystal structure (space group Pbam) containing quasi-2D Co slabs and La-X layers that stack along the a-axis. Consistent with our proposal, the La atoms separate the Co and X substructures, ensuring there are no direct contacts between immiscible atoms. Within the Co slabs, the atoms occupy the vertices of corner sharing tetrahedra and triangles, and this motif produces flat electronic bands near the Fermi level that favor magnetism. The Co is moment bearing in La$_4$Co$_4$X, and we show that whereas La$_4$Co$_4$Pb behaves as a three dimensional antiferromagnet with T$_N$ = 220 K, La$_4$Co$_4$Bi and La$_4$Co$_4$Sb have behavior consistent with low dimensional magnetic coupling and ordering, with T$_N$ = 153 K and 143 K respectively. In addition to the Pb, Bi, and Sb based La$_4$Co$_4$X compounds, we were likely able to produce an analogous La$_4$Co$_4$Sn in polycrystalline form, although we were unable to isolate single crystals. We anticipate that using mutually compatible third elements with an antagonistic pair represents a generalizable design principle for discovering new materials and structure types containing low-dimensional substructures.

Critical slowing of the spin and charge density wave order in thin film Cr following photoexcitation
Sheena K. K. Patel, Oleg Yu. Gorobtsov, Devin Cela, Stejpan B. Hrkac, Nelson Hua, Rajasekhar Medapalli, Anatoly G. Shabalin, James Wingert, James M. Glownia, Diling Zhu, Matthieu Chollet, Oleg G. Shpyrko, Andrej Singer, Eric E. Fullerton
arXiv:2403.00267v1 Announce Type: new Abstract: We report on the evolution of the charge density wave (CDW) and spin density wave (SDW) order of a chromium film following photoexcitation with an ultrafast optical laser pulse. The CDW is measured by ultrafast time-resolved x-ray diffraction of the CDW satellite that tracks the suppression and recovery of the CDW following photoexcitation. We find that as the temperature of the film approaches a discontinuous phase transition in the CDW and SDW order, the time scales of recovery increase exponentially from the expected thermal time scales. We extend a Landau model for SDW systems to account for this critical slowing with the appropriate boundary conditions imposed by the geometry of the thin film system. This model allows us to assess the energy barrier between available CDW/SDW states with different spatial periodicities.

Lattice dynamics study of electron-correlation-induced charge density wave in antiferromagnetic kagome metal FeGe
Andrzej Ptok, Surajit Basak, Aksel Kobia{\l}ka, Ma{\l}gorzata Sternik, Jan {\L}a\.zewski, Pawe{\l} T. Jochym, Andrzej M. Ole\'s, Przemys{\l}aw Piekarz
arXiv:2403.00297v1 Announce Type: new Abstract: Electron-correlation-driven phonon soft modes have been recently reported in the antiferromagnetic kagome FeGe compound and associated with the observed charge density wave (CDW). In this paper, we present a systematic investigation of the CDW origin in the context of the ab initio lattice dynamics study. Performing the group theory analysis of the mentioned soft mode, we found that the stable structure has the Immm symmetry and can be achieved by the small shift of Ge atoms. Additionally, we show that the final structure realizes a distorted honeycomb Ge lattice as well as a non-flat kagome-like Fe net. For completeness, we present the electronic properties calculations. From the theoretical STM topography simulation, we indicate that the observed CDW occurs in the deformed honeycomb Ge sublattice.

Surface Chern-Simons theory for third-order topological insulators and superconductors
Zhi-Hao Huang, Yi Tan, Wei Jia, Long Zhang, Xiong-Jun Liu
arXiv:2403.00316v1 Announce Type: new Abstract: Three-dimensional 3rd-order topological insulators (TOTIs) and superconductors (TOTSCs), as the highestorder topological phases hosting zero corner modes in physical dimension, has sparked extensive research interest. However, such topological states have not been discovered in reality due to the lack of experimental schemes of realization. Here, we propose a novel surface Chern-Simons (CS) theory for 3rd-order topological phases, and show that the theory enables a feasible and systematic design of TOTIs and TOTSCs. We show that the emergence of zero Dirac (Majorana) corner modes is entirely captured by an emergent $\mathbb{Z}_{2}$ CS term that can be further characterized by a novel two-particle Wess-Zumino (WZ) term uncovered here in the surfaces of three-dimensional topological materials. Importantly, our proposed CS term characterization and two-particle WZ term mechanism provide a unique perspective to design TOTIs (TOTSCs) in terms of minimal ingredients, feasibly guiding the search for underlying materials, with promising candidates being discussed. This work shall advance both the theoretical and experimental research for highest-order topological matters.

Superconductivity and metallic behavior in heavily doped bulk single crystal diamond and graphene/diamond heterostructure
Shisheng Lin, Xutao Yu, Minhui Yang, Huikai Zhong, Jiarui Guo
arXiv:2403.00359v1 Announce Type: new Abstract: Owing to extremely large band gap of 5.5 eV and high thermal conductivity, diamond is recognized as the most important semiconductor. The superconductivity of polycrystalline diamond has always been reported, but there are also many controversies over the existence of superconductivity in bulk single crystal diamond and it remains a question whether a metallic state exists for such a large band gap semiconductor. Herein, we realize a single crystal superconducting diamond with a Hall carrier concentration larger than 3*1020 cm-3 by co-doped of boron and nitrogen. Furthermore, we show that diamond can transform from superconducting to metallic state under similar carrier concentration with tuned carrier mobility degrading from 9.10 cm2 V-1 s-1 or 5.30 cm2 V-1 s-1 to 2.66 cm2 V-1 s-1 or 1.34 cm2 V-1 s-1. Through integrating graphene on a nitrogen and boron heavily co-doped diamond, the monolayer graphene can be superconducting through combining Andreev reflection and exciton mediated superconductivity, which may intrigue more interesting superconducting behavior of diamond heterostructure.

Quasi-one-dimensional spin transport in antiferromagnetic Z3 nodal net metals
Tingli He, Lei Li, Chaoxi Cui, Run-Wu Zhang, Zhi-Ming Yu, Guodong Liu, Xiaoming Zhang
arXiv:2403.00371v1 Announce Type: new Abstract: In three dimensions, the quasi-one-dimensional (Q1D) transport is commonly thought to only appear in the systems with Q1D chain structure. Here, based on first-principle calculations, we go beyond the common belief to show that the Q1D transport can also be realized in many 3D antiferromagnetic (AFM) metals with topological node structure but without Q1D chain structure, including the existing compounds \b{eta}-Fe2(PO4)O and Co2(PO4)O, and LiTi2O4. All these materials have an AFM ground state and exhibit an ideal crossed Z3 Weyl nodal line in each spin channel, formed by three straight and flat nodal lines traversing the whole Brillouin zone. These nodal lines eventually lead to an AFM Z3 nodal net. Surprisingly, we find that the longitudinal conductivity {\sigma}xx in these topological nodal net metals is dozens of times larger than {\sigma}yy and {\sigma}zz in the up-spin channel, while {\sigma}yy dominates the transport in the down-spin channel. This means that each spin channel has a Q1D transport signature, and the principal moving direction for the two spin channels is orthogonal, leading to Q1D direction-dependent spin transport. This novel phenomenon can not be found in both conventional 3D bulk materials and Q1D chain materials, and may solely be induced by the Z3 nodal net, as it gradually disappears when the Fermi level moves away from the nodal net. Our work not only enhances the comprehension of topological physics in antiferromagnets, but also opens a new direction for the exploration of topological spintronics.

Majorana zero-modes in a dissipative Rashba nanowire
Arnob Kumar Ghosh, Annica M. Black-Schaffer
arXiv:2403.00419v1 Announce Type: new Abstract: Condensed matter systems are continuously subjected to dissipation, which often has adverse effects on quantum phenomena. We focus on the impact of dissipation on a superconducting Rashba nanowire. We reveal that the system can still host Majorana zero-modes (MZMs) with a finite lifetime in the presence of dissipation. Most interestingly, dissipation can also generate two kinds of dissipative boundary states: four robust zero-modes (RZMs) and two MZMs, in the regime where the non-dissipative system is topologically trivial. The MZMs appear via bulk gap closing and are topologically characterized by a winding number. The RZMs are not associated with any bulk states and possess no winding number, but their emergence is instead tied to exceptional points. Further, we confirm the stability of the dissipation-induced RZMs and MZMs in the presence of random disorder. Our study paves the way for both realizing and stabilizing MZMs in an experimental setup, driven by dissipation.

The first law of thermodynamics in hydrodynamic steady and unsteady flows
Konrad Gi\.zy\'nski, Karol Makuch, Jan Paczesny, Pawe{\l} \.Zuk, Anna Macio{\l}ek, Robert Ho{\l}yst
arXiv:2403.00463v1 Announce Type: new Abstract: We studied planar compressible flows of ideal gas as models of a non-equilibrium thermodynamic system. We demonstrate that internal energy $U(S^{*},V,N)$ of such systems in stationary and non-stationary states is the function of only three parameters of state, i.e. non-equilibrium entropy $S^{*}$, volume $V$ and number of particles $N$ in the system. Upon transition between different states, the system obeys the first thermodynamic law, i.e. $dU=T^{*}dS^{*}-p^{*}dV+{\mu}^{*}dN$, where $U=3/2 NRT^{*}$ and $p^{*}V=NRT^{*}$. Placing a cylinder inside the channel, we find that U depends on the location of the cylinder $y_{c}$ only via the parameters of state, i.e. $U(S^{*}(y_{c}),V,N(y_{c}))$ at V=const. Moreover, when the flow around the cylinder becomes unstable, and velocity, pressure, and density start to oscillate as a function of time, t, U depends on t only via the parameters of state, i.e. $U(S^{*}(t),V,N(t))$ for V=const. These examples show that such a form of internal energy is robust and does not depend on the particular boundary conditions even in the unsteady flow.

Robustness of the pyrochlore structure in rare-earth A2Ir2O7 iridates and pressure-induced structural transformation in IrO2
Daniel Sta\v{s}ko, Kristina Vl\'a\v{s}kov\'a, Andrej Kancko, Daniel M. T\"obbens, Dominik Daisenberger, Gaston Garbarino, Ross Harvey Colman, Milan Klicpera
arXiv:2403.00477v1 Announce Type: new Abstract: A comprehensive study of the structural properties of the heavily investigated rare-earth A2Ir2O7 series under extreme conditions is presented. The series is covered by studying iridates with A = Pr, Sm, Dy-Lu. Temperature- and pressure-dependent synchrotron X-ray powder diffraction experiments reveal robustness of the pyrochlore structure throughout the rare-earth series, down to 4 K and up to 20 GPa. The thermal expansivity and pressure compressibility are determined, including Debye temperature, bulk modulus and Gr\"uneisen parameter. Temperature and pressure evolution of the fractional coordinate of oxygen at 48f Wyckoff position, the sole free atomic position parameter, is investigated and discussed regarding the antiferromagnetic ordering of the Ir magnetic moments. In addition, the pressure evolution of the crystal structure of an IrO2 minority phase is followed. The tetragonal rutile-type structure is orthorhombically distorted at 15 GPa, and the orthorhombic structure is not fully stabilised up to 20 GPa.

Nonlinear optical responses in superconductors under magnetic fields: quantum geometry and topological superconductivity
Hiroto Tanaka, Hikaru Watanabe, Youichi Yanase
arXiv:2403.00494v1 Announce Type: new Abstract: Noncentrosymmetric superconductors offer fascinating phenomena of quantum transport and optics such as nonreciprocal and nonlinear responses. Time-reversal symmetry breaking often plays an essential role in the emergence and enhancement of nonreciprocal transport. In this paper, we show the nonreciprocal optical responses in noncentrosymmetric superconductors arising from time-reversal symmetry breaking by demonstrating them in $s$-wave superconductors with a Rashba spin-orbit coupling and a magnetic field. Numerical results reveal the superconductivity-induced bulk photocurrent and second harmonic generation, which are forbidden at the zero magnetic field. We discuss the properties and mechanisms of the superconducting nonlinear responses emerging under the magnetic field. In particular, we investigate the magnetic-field dependence of the photocurrent conductivity and clarify the essential ingredients which give a contribution unique to superconductors under the magnetic field. This contribution is dominant in the low carrier density regime although the corresponding joint density of states is tiny. We attribute the enhancement to the quantum geometry. Moreover, the nonlinear conductivity shows peculiar sign reversal at the transition to the topological superconducting state. We propose a bulk probe of topological transition and quantum geometry in superconductors.

Minority magnons and mode branching in monolayer Fe$_3$GeTe$_2$
Thorbj{\o}rn Skovhus, Thomas Olsen
arXiv:2403.00525v1 Announce Type: new Abstract: In this letter, we predict the existence of minority magnons in a monolayer of Fe$_3$GeTe$_2$ using first principles calculations. Minority magnons constitute a new type of collective magnetic excitations which increase the magnetic moment rather than lower it, contrary to ordinary (majority) magnons. The presence of such quasi-particles is made possible by the nontrivial ferromagnetic band structure of Fe$_3$GeTe$_2$ originating from its nonequivalent Fe sublattices. The result is a strong peak in the dynamic spin-raising susceptibility $\chi^{-+}(\omega)$ in the long wavelength limit, which is the hallmark of minority magnon physics. We calculate the susceptibility using time-dependent density functional theory and perform a detailed mode analysis, which allows us to separate and investigate the individual magnon modes as well as the Stoner excitations that constitute the many-body spectrum. For minority as well as majority magnons, the analysis reveals a plethora of magnetic excitations, which in addition to the standard main magnon branches include both satellite, valley and spin-inversion magnons, originating from the itinerancy of the ferromagnetic order. The physics underlying this analysis is in no way restricted to Fe$_3$GeTe$_2$, and minority magnons are expected to be observable in many complex ferromagnetic materials.

Extended Hubbard corrected tight-binding model for rhombohedral few-layer graphene
Dongkyu Lee, Wooil Yang, Young-Woo Son, Jeil Jung
arXiv:2403.00530v1 Announce Type: new Abstract: Rhombohedral multilayer graphene (RnG) featuring partially flat bands has emerged as an important platform to probe strong Coulomb correlation effects. Theoretical consideration of local electron-electron interactions are of particular importance for electronic eigenstates with a tendency to spatially localize. We present a method to incorporate mean-field electron-electron interaction corrections in the tight-binding hopping parameters of the band Hamiltonian within the extended Hubbard model that incorporates ab initio estimates of on-site ($U$) and inter-site ($V$) Hubbard interactions for the $\pi$ bands of RnG. Our Coulomb-interaction renormalized band structures feature electron-hole asymmetry, band flatness, band gap, and anti-ferromagnetic ground states in excellent agreement with available experiments for $n \geq 4$. We reinterpret the putative gaps proposed in $n=3$ systems in terms of shifting electron and hole density of states peaks depending on the range of the Coulomb interaction models.

Comment on "Controlled Bond Expansion for Density Matrix Renormalization Group Ground State Search at Single-Site Costs" (Extended Version)
Ian P McCulloch, Jesse Osborne
arXiv:2403.00562v1 Announce Type: new Abstract: In a recent Letter [Phys. Rev. Lett. 130, 246402 (2023)], Gleis, Li, and von Delft present an algorithm for expanding the bond dimension of a Matrix Product State wave function, giving accuracy similar to 2-site DMRG, but computationally more efficient, closer to the performance of 1-site DMRG. The Controlled Bond Expansion (CBE) algorithm uses the Hamiltonian projected onto two sites, and then further projected onto the two-site tangent space, to extract a set of $k$ vectors that are used to expand the basis between the two sites. CBE achieves this with a complicated sequence of five singular value decompositions (SVDs), in order to project onto the 2-site tangent space and reduce the bond dimension of the tensor network such that the contraction can be done in time $O(dwD^3)$. In this Comment, we show that (1) the projection onto the 2-site tangent space is unnecessary, and is generally not helpful; (2) the sequence of 5 SVDs can be replaced by a single $QR$ decomposition (optionally with one SVD as well), making use of the randomized SVD (RSVD) with high accuracy and significantly improved efficiency, scaling as $O(dwkD^2)$ i.e., the most expensive operations are only quadratic in the bond dimension $D$ and linear in the number of expansion vectors $k$; (3) several statements about the variational properties of the CBE algorithm are incorrect, and the variational properties are essentially identical to existing algorithms including 2-site DMRG and single-site subspace expansion (3S); (4) a similar RSVD approach can be applied to the 3S algorithm, which leads to many advantages over CBE, especially in systems with long range interactions. We also make some comments on the benchmarking MPS algorithms, and the overall computational efficiency with respect to the accuracy of the calculation.

Chiral Spin Liquid on a Shastry-Sutherland Heisenberg Antiferromagnet
Jian-Wei Yang, Wei-Wei Luo, W. Zhu, L. Wang, Bo Yang, Pinaki Sengupta
arXiv:2403.00597v1 Announce Type: new Abstract: We demonstrate the existence of a topological chiral spin liquid in the frustrated Shastry-Sutherland Heisenberg model with an additional spin chirality interaction, using numerically unbiased exact diagonalization and density matrix renormalization group methods. We establish a quantum phase diagram where conventional phases, including dimer singlet, plaquette singlet, N{\' e}el and collinear phase, can be clearly identified by suitable local order parameters. Among them a $SU(2)_1$ chiral spin liquid emerges in the highly frustrated region, which is unambiguously identified by two topologically degenerate ground states, modular matrix, and characteristic level counting in entanglement spectrum, featuring the same topological order of $\nu=1/2$ bosonic Laughlin state. The phase boundaries among the different orders are determined by the energy level crossing analysis and wave function fidelity susceptibility.

Superconductivity Mediated by Nematic Fluctuations in Tetragonal $\textrm{Fe}\textrm{Se}_{1-x}\textrm{S}_{x}$
Pranab Kumar Nag, Kirsty Scott, Vanuildo S. de Carvalho, Journey K. Byland, Xinze Yang, Morgan Walker, Aaron G. Greenberg, Peter Klavins, Eduardo Miranda, Adrian Gozar, Valentin Taufour, Rafael M. Fernandes, Eduardo H. da Silva Neto
arXiv:2403.00615v1 Announce Type: new Abstract: Nematic phases, where electrons in a solid spontaneously break rotational symmetry while preserving the translational symmetry, exist in several families of unconventional superconductors [1, 2]. Although superconductivity mediated by nematic fluctuations is well established theoretically [3-7], it has yet to be unambiguously identified experimentally [8, 9]. A major challenge is that nematicity is often intertwined with other degrees of freedom, such as magnetism and charge order. The FeSe$_{1-x}$S$_x$ family of iron based superconductors provides a unique opportunity to explore this concept, as it features an isolated nematic phase that can be suppressed by sulfur substitution at a quantum critical point (QCP) near $x_c = 0.17$, where nematic fluctuations are the largest [10-12]. Here, we performed scanning tunneling spectroscopy measurements to visualize Boguliubov quasiparticle interference patterns, from which we determined the momentum structure of the superconducting gap near the Brillouin zone $\Gamma$ point of FeSe$_{0.81}$S$_{0.19}$. The results reveal an anisotropic, near nodal gap with minima that are $45^\circ$ rotated with respect to the Fe-Fe direction, characteristic of a nematic pairing interaction, contrary to the usual isotropic gaps due to spin mediated pairing in other tetragonal Fe-based superconductors. The results are also in contrast with pristine FeSe, where the pairing is mediated by spin fluctuations and the gap minima are aligned with the Fe-Fe direction. Therefore, the measured gap structure demonstrates not only a fundamental change of the pairing mechanism across the phase diagram of FeSe$_{1-x}$S$_x$, but it also indicates the existence of superconductivity mediated by nematic fluctuations in FeSe$_{0.81}$S$_{0.19}$.

Harnessing the superconducting diode effect through inhomogeneous magnetic fields
Leonardo Rodrigues Cadorim, Edson Sardella, Cl\'ecio Clemente de Souza Silva
arXiv:2403.00630v1 Announce Type: new Abstract: We propose a superconducting diode device comprising a central superconducting film flanked by two wires carrying an applied DC bias, suitably chosen so as to generate different asymmetric field profiles. Through numerical simulations of the coupled Ginzburg-Landau and heat-diffusion equations, we show that this design is capable of efficiently breaking the reciprocity of the critical current in the central superconductor, thus promoting the diode effect in response to an applied AC current. By adjusting the DC bias in the wires, we find the optimum inhomogeneous field profile that facilitates the entrance of vortices and antivortices in a given polarity of the applied AC current and impede their entrance in the other polarity. This way, the system behaves as an ideal superconducting half-wave rectifier, with diode efficiencies surpassing 70%. Furthermore, we detail the behavior and diode efficiency of the system under different experimental conditions, such as the substrate heat transfer coefficient and the sweep rate of the external current.

Optimal Control of Underdamped Systems: An Analytic Approach
Julia Sanders, Marco Baldovin, Paolo Muratore-Ginanneschi
arXiv:2403.00679v1 Announce Type: new Abstract: Optimal control theory deals with finding protocols to steer a system between assigned initial and final states, such that a trajectory-dependent cost function is minimized. The application of optimal control to stochastic systems is an open and challenging research frontier, with a spectrum of applications ranging from stochastic thermodynamics, to biophysics and data science. Among these, the design of nanoscale electronic components motivates the study of underdamped dynamics, leading to practical and conceptual difficulties. In this work, we develop analytic techniques to determine protocols steering finite time transitions at minimum dissipation for stochastic underdamped dynamics. For transitions between Gaussian states, we prove that optimal protocols satisfy a Lyapunov equation, a central tool in stability analysis of dynamical systems. For transitions between states described by general Maxwell-Boltzmann distributions, we introduce an infinite-dimensional version of the Poincar\'e-Linstedt multiscale perturbation theory around the overdamped limit. This technique fundamentally improves the standard multiscale expansion. Indeed, it enables the explicit computation of momentum cumulants, whose variation in time is a distinctive trait of underdamped dynamics and is directly accessible to experimental observation. Our results allow us to numerically study cost asymmetries in expansion and compression processes and make predictions for inertial corrections to optimal protocols in the Landauer erasure problem at the nanoscale.

Entropy Driven Inductive Response of Topological Insulators
A. Mert Bozkurt, Sofie K\"olling, Alexander Brinkman, \.Inan\c{c} Adagideli
arXiv:2403.00714v1 Announce Type: new Abstract: 3D topological insulators are characterized by an insulating bulk and extended surface states exhibiting a helical spin texture. In this work, we investigate the hyperfine interaction between the spin-charge coupled transport of electrons and the nuclear spins in these surface states. Previous work has predicted that in the quantum spin Hall insulator phase, work can be extracted from a bath of polarized nuclear spins as a resource. We employ nonequilibrium Green's function analysis to show that a similar effect exists on the surface of a 3D topological insulator, albeit rescaled by the ratio between electronic mean free path and device length. The induced current due to thermal relaxation of polarized nuclear spins has an inductive nature. We emphasize the inductive response by rewriting the current-voltage relation in harmonic response as a lumped element model containing two parallel resistors and an inductor. In a low-frequency analysis, a universal inductance value emerges that is only dependent on the device's aspect ratio. This scaling offers a means of miniaturizing inductive circuit elements. An efficiency estimate follows from comparing the spin-flip induced current to the Ohmic contribution. The inductive effect is most prominent in topological insulators which have a large number of spinful nuclei per coherent segment, of which the volume is given by the mean free path length, Fermi wavelength and penetration depth of the surface state.

Hyperbolic phonon-plasmon polaritons in a hBN-graphene van der Waals structure
Yu. V. Bludov, D. A. Bahamon, N. M. R. Peres, C. J. S. de Matos
arXiv:2403.00722v1 Announce Type: new Abstract: In this paper a thorough theoretical study of a new class of collective excitations, dubbed hyperbolic surface phonon plasmon polaritons, is performed. This new type of light-matter excitations are shown to have unique properties that allows to explore them both as the basis of ultra-sensitive devices to the dielectric nature of its surroundings. The system is a van der Waals heterostructure -- a layered metamaterial, composed of different 2D materials in direct contact one with another, namely graphene ribbons and hexagonal boron nitride slabs of nanometric size. In the paper we discuss the spectrum of these new class of excitations, the associated electromagnetic fields, the sensitivity to the dielectric function of its surroundings, and the absorption spectrum. All this is accomplished using an analytical model that considerably diminishes the computational burden, as well as elucidates the underling physical mechanism of the excitations supported by the device.

Carbon-contaminated topological defects in hBN: a potential new class of single photon emitters
Rohit Babar, Igor A. Abrikosov, Gergely Barcza, Viktor Iv\'ady
arXiv:2403.00755v1 Announce Type: new Abstract: Topological defects, such as Stone-Wales defects and grain boundaries, are common in 2D materials. In this exploratory study, we investigate the intricate interplay of carbon contamination and topological defects revealing a new class of color centers in hexagonal boron nitride. We demonstrate that carbon contamination and strain can both stabilize Stone-Wales configurations with desirable optical properties. Inspired by these results, we further demonstrate that carbon atoms at grain boundaries can resolve energetic B-B and N-N bonds and give rise to highly favorable atomic structures potentially leading to the accumulation of carbon contamination at grain boundaries. We identify carbon-contaminated topological defects that give rise to color centers emitting in the visible spectral range with short radiative lifetime and high Debye-Waller factors. Our discoveries shed light on a new class of defects and pave the way towards the identification of color centers and single photon emitters in hBN.

Geometry-free renormalization of directed networks: scale-invariance and reciprocity
Margherita Lalli, Diego Garlaschelli
arXiv:2403.00235v1 Announce Type: cross Abstract: Recent research has tried to extend the concept of renormalization, which is naturally defined for geometric objects, to more general networks with arbitrary topology. The current attempts do not naturally apply to directed networks, for instance because they are based on the identification of (necessarily symmetric) inter-node distances arising from geometric embeddings or on the definition of Hermitian Laplacian operators requiring symmetric adjacency matrices in spectral approaches. Here we show that the Scale-Invariant Model, recently proposed as an approach to consistently model undirected networks at arbitrary (and possibly multi-scale) resolution levels, can be extended coherently to directed networks without the requirement of an embedding geometry or Laplacian structure. Moreover, it can account for nontrivial reciprocity, i.e. the empirically well-documented tendency of links to occur in mutual pairs more or less often than predicted by chance. After deriving the renormalization rules for networks with arbitrary reciprocity, we consider various examples. In particular we propose the first multiscale model of the international trade network with nontrivial reciprocity and an annealed model where positive reciprocity emerges spontaneously from coarse-graining. In the latter case, the renormalization process defines a group, not only a semigroup, and therefore allows to fine-grain networks to arbitrarily small scales. These results strengthen the notion that network renormalization can be defined in a much more general way than required by geometric or spectral approaches, because it needs only node-specific (metric-free) features and can coexist with the asymmetry of directed networks.

Niobium coaxial cavities with internal quality factors exceeding 1.5 billion for circuit quantum electrodynamics
Andrew E. Oriani, Fang Zhao, Tanay Roy, Alexander Anferov, Kevin He, Ankur Agrawal, Riju Banerjee, Srivatsan Chakram, David I. Schuster
arXiv:2403.00286v1 Announce Type: cross Abstract: Group-V materials such as niobium and tantalum have become popular choices for extending the performance of circuit quantum electrodynamics (cQED) platforms allowing for quantum processors and memories with reduced error rates and more modes. The complex surface chemistry of niobium however makes identifying the main modes of decoherence difficult at millikelvin temperatures and single-photon powers. We use niobium coaxial quarter-wave cavities to study the impact of etch chemistry, prolonged atmospheric exposure, and the significance of cavity conditions prior to and during cooldown, in particular niobium hydride evolution, on single-photon coherence. We demonstrate cavities with quality factors of $Q_{\rm int}\gtrsim 1.4\times10^{9}$ in the single-photon regime, a $15$ fold improvement over aluminum cavities of the same geometry. We rigorously quantify the sensitivity of our fabrication process to various loss mechanisms and demonstrate a $2-4\times$ reduction in the two-level system (TLS) loss tangent and a $3-5\times$ improvement in the residual resistivity over traditional BCP etching techniques. Finally, we demonstrate transmon integration and coherent cavity control while maintaining a cavity coherence of \SI{11.3}{ms}. The accessibility of our method, which can easily be replicated in academic-lab settings, and the demonstration of its performance mark an advancement in 3D cQED.

Asymmetrical temporal dynamics of topological edge modes in Su-Schrieffer-Heeger lattice with Kerr nonlinearity
Ghada Alharbi, Stephan Wong, Yongkang Gong, Sang Soon Oh
arXiv:2403.00538v1 Announce Type: cross Abstract: Optical bistability and oscillating phases exist in a Sagnac interferometer and a single ring resonator made of $\chi^{(3)}$ nonlinear medium where the refractive indices are modulated by the light intensity due to the Kerr nonlinearity. An array of coupled nonlinear ring resonators behave similarly but with more complexity due to the presence of the additional couplings.Here, we theoretically demonstrate the bifurcation of topological edge modes which leads to optical bistability in the Su-Schrieffer-Heeger lattice with the Kerr nonlinearity. Additionally, we demonstrate periodic and chaotic switching behaviors in an oscillating phase resulting from the coupling between the topological edge mode and bulk modes with different chiralities, i.e., clockwise and counter-clockwise circulations.

Quantum circuits for toric code and X-cube fracton model
Penghua Chen, Bowen Yan, Shawn X. Cui
arXiv:2210.01682v3 Announce Type: replace Abstract: We propose a systematic and efficient quantum circuit composed solely of Clifford gates for simulating the ground state of the surface code model. This approach yields the ground state of the toric code in $\lceil 2L+2+log_{2}(d)+\frac{L}{2d} \rceil$ time steps, where $L$ refers to the system size and $d$ represents the maximum distance to constrain the application of the CNOT gates. Our algorithm reformulates the problem into a purely geometric one, facilitating its extension to attain the ground state of certain 3D topological phases, such as the 3D toric model in $3L+8$ steps and the X-cube fracton model in $12L+11$ steps. Furthermore, we introduce a gluing method involving measurements, enabling our technique to attain the ground state of the 2D toric code on an arbitrary planar lattice and paving the way to more intricate 3D topological phases.

Electron-optics using negative refraction in two-dimensional inverted-band $pn$ junctions
Yuhao Zhao, Anina Leuch, Oded Zilberberg, Antonio \v{S}trkalj
arXiv:2307.07913v2 Announce Type: replace Abstract: Electron optics deals with condensed matter platforms for manipulating and guiding electron beams with high efficiency and robustness. Common devices rely on the spatial confinement of the electrons into one-dimensional channels. Recently, there is growing interest in electron optics applications in two dimensions, which heretofore are almost exclusively based on graphene devices. In this work, we study band-inverted systems resulting from particle-hole hybridization and demonstrate their potential for electron optics applications. We develop the theory of interface scattering in an inverted-band $pn$ junction using a scattering matrix formalism and observe negative refraction conditions as well as transmission filtering akin to graphene's Klein tunneling but at finite angles. Based on these findings, we provide a comprehensive protocol for constructing electron optic components, such as focusing and bifurcating lenses, polarizers, and mirrors. We numerically test the robustness of our designs to disorder and finite temperatures, and motivate the feasibility of experimental realization. Our work opens avenues for electron optics in two dimensions beyond graphene-based devices, where a plethora of inverted-band materials in contemporary experiments can be harnessed.

Particle-hole asymmetric ferromagnetism and spin textures in the triangular Hubbard-Hofstadter model
Jixun K. Ding, Luhang Yang, Wen O. Wang, Ziyan Zhu, Cheng Peng, Peizhi Mai, Edwin W. Huang, Brian Moritz, Philip W. Phillips, Benjamin E. Feldman, Thomas P. Devereaux
arXiv:2309.07876v2 Announce Type: replace Abstract: In a lattice model subject to a perpendicular magnetic field, when the lattice constant is comparable to the magnetic length, one enters the "Hofstadter regime," where continuum Landau levels become fractal magnetic Bloch bands. Strong mixing between bands alters the nature of the resulting quantum phases compared to the continuum limit; lattice potential, magnetic field, and Coulomb interaction must be treated on equal footing. Using determinant quantum Monte Carlo (DQMC) and density matrix renormalization group (DMRG) techniques, we study this regime numerically in the context of the Hubbard-Hofstadter model on a triangular lattice. In the field-filling phase diagram, we find a broad wedge-shaped region of ferromagnetic ground states for filling factor $\nu \leq 1$, bounded below by filling factor $\nu = 1$ and bounded above by half-filling the lowest Hofstadter subband. We observe signatures of SU(2) quantum Hall ferromagnetism at filling factors $\nu=1$ and $\nu=3$. The phases near $\nu=1$ are particle-hole asymmetric, and we observe a rapid decrease in ground state spin polarization consistent with the formation of skyrmions only on the electron doped side. At large fields, above the ferromagnetic wedge, we observe a low-spin metallic region with spin correlations peaked at small momenta. We argue that the phenomenology of this region likely results from exchange interaction mixing fractal Hofstadter subbands. The phase diagram derived beyond the continuum limit points to a rich landscape to explore interaction effects in magnetic Bloch bands.

Generalized Landauer bound from absolute irreversibility
Lorenzo Buffoni, Francesco Coghi, Stefano Gherardini
arXiv:2310.05449v2 Announce Type: replace Abstract: In this work, we introduce a generalization of the Landauer bound for erasure processes that stems from absolutely irreversible dynamics. Assuming that the erasure process is carried out in an absolutely irreversible way so that the probability of observing some trajectories is zero in the forward process but finite in the reverse process, we derive a generalized form of the bound for the average erasure work, which is valid also for imperfect erasure and asymmetric bits. The generalized bound obtained is tighter or, at worst, as tight as existing ones. Our theoretical predictions are supported by numerical experiments and the comparison with data from previous works.

Defect-induced helicity-dependent terahertz emission in Dirac semimetal PtTe2 thin films
Zhongqiang Chen, Hongsong Qiu, Xinjuan Cheng, Jizhe Cui, Zuanming Jin, Da Tian, Xu Zhang, Kankan Xu, Ruxin Liu, Wei Niu, Liqi Zhou, Tianyu Qiu, Yequan Chen, Caihong Zhang, Xiaoxiang Xi, Fengqi Song, Rong Yu, Xuechao Zhai, Biaobing Jin, Rong Zhang, Xuefeng Wang
arXiv:2310.09989v2 Announce Type: replace Abstract: Nonlinear transport enabled by symmetry breaking in quantum materials has aroused considerable interest in condensed matter physics and interdisciplinary electronics. However, the nonlinear optical response in centrosymmetric Dirac semimetals via the defect engineering has remained highly challenging. Here, we observe the helicity-dependent terahertz (THz) emission in Dirac semimetal PtTe2 thin films via circular photogalvanic effect (CPGE) under normal incidence. This is activated by artificially controllable out-of-plane Te-vacancy defect gradient, which is unambiguously evidenced by the electron ptychography. The defect gradient lowers the symmetry, which not only induces the band spin splitting, but also generates the giant Berry curvature dipole (BCD) responsible for the CPGE. Such BCD-induced helicity-dependent THz emission can be manipulated by the Te-vacancy defect concentration. Furthermore, temperature evolution of the THz emission features the minimum of the THz amplitude due to the carrier compensation. Our work provides a universal strategy for symmetry breaking in centrosymmetric Dirac materials for efficient nonlinear transport and facilitates the promising device applications in integrated optoelectronics and spintronics.

Effective interaction between guest charges immersed in 2D jellium
Ladislav \v{S}amaj
arXiv:2310.19517v2 Announce Type: replace Abstract: The model under study is an infinite 2D jellium of pointlike particles with elementary charge $e$, interacting via the logarithmic potential and in thermal equilibrium at the inverse temperature $\beta$. Two cases of the coupling constant $\Gamma\equiv \beta e^2$ are considered: the Debye-H\"uckel limit $\Gamma\to 0$ and the free-fermion point $\Gamma=2$. In the most general formulation, two guest particles, the one with charge $q e$ (the valence $q$ being an arbitrary integer) and the hard core of radius $\sigma>0$ and the pointlike one with elementary charge $e$, are immersed in the bulk of the jellium at distance $d\ge \sigma$. Two problems are of interest: the asymptotic large-distance behavior of the excess charge density induced in the jellium and the effective interaction between the guest particles. Technically, the induced charge density and the effective interaction are expressed in terms of multi-particle correlations of the pure (translationally invariant) jellium system. It is shown that the separation form of the induced charge density onto its radial and angle parts, observed previously in the limit $\Gamma\to 0$, is not reproduced at the coupling $\Gamma=2$. Based on an exact expression for the effective interaction between guest particles at $\Gamma=2$, oppositely ($q=0,-1,-2,\ldots$) charged guest particles always attract one another while likely ($q=1,2,\ldots$) charged guest particles repeal one another up to a certain distance $d$ between them and then the mutual attraction takes place up to asymptotically large (finite) distances.

Hofstadter Butterfly and Broken-Symmetry Quantum Hall States in \alpha-Type Organic Dirac Fermion Systems
Toshihito Osada
arXiv:2312.09413v2 Announce Type: replace Abstract: The electronic state of \alpha-type organic Dirac fermion systems such as \alpha-(ET)_2I_3 or \alpha-(BETS)_2I_3 has been studied under magnetic fields using the four-band tight-binding model with Peierls phase factors. The validity of the Dirac fermion picture in these materials was confirmed by the generated Hofstadter butterfly and its Chern numbers. The four-component envelope function of the N = 0 Landau level with valley degeneracy was studied. It was found that the two degenerate valley states have different weights on A and A' molecules connected by inversion. This feature is also recognized for the N = 0 spin-split Landau levels under the Zeeman effect and the spin-orbit interaction. The spontaneous valley symmetry breaking in the N = 0 Landau levels due to the exchange interaction results in the \nu = 1 and -1 quantum Hall states accompanied by the spatial charge and spin modulations in a unit cell.

Tuning dissipation dilution in 2D material resonators by MEMS-induced tension
M. P. F. Wopereis, N. Bouman, S. Dutta, P. G. Steeneken, F. Alijani, G. J. Verbiest
arXiv:2401.07047v3 Announce Type: replace Abstract: Resonators based on two-dimensional (2D) materials have exceptional properties for application as nanomechanical sensors, which allows them to operate at high frequencies with high sensitivity. However, their performance as nanomechanical sensors is currently limited by their low quality ($Q$)-factor. Here, we make use of micro-electromechanical systems (MEMS) to apply pure in-plane mechanical strain, enhancing both their resonance frequency and Q-factor. In contrast to earlier work, the 2D material resonators are fabricated on the MEMS actuators without any wet processing steps, using a dry-transfer method. A platinum clamp, that is deposited by electron beam-induced deposition, is shown to be effective in fixing the 2D membrane to the MEMS and preventing slippage. By in-plane straining the membranes in a purely mechanical fashion, we increase the tensile energy, thereby diluting dissipation. This way, we show how dissipation dilution can increase the $Q$-factor of 2D material resonators by 91\%. The presented MEMS actuated dissipation dilution method does not only pave the way towards higher $Q$-factors in resonators based on 2D materials, but also provides a route toward studies of the intrinsic loss mechanisms of 2D materials in the monolayer limit.

A Hybrid Machine Learning Framework for Predicting Hydrogen Storage Capacities: Unsupervised Feature Learning with Deep Neural Networks
Satadeep Bhattacharjee, Pritam Das, Swetarekha Ram, Seung-Cheol Lee
arXiv:2401.17587v3 Announce Type: replace Abstract: In this study, we present a sophisticated hybrid machine-learning framework that significantly improves the accuracy of predicting hydrogen storage capacities in metal hydrides. This is a critical challenge due to the scarcity of experimental data and the complexity of high-dimensional feature spaces. Our approach employs the power of unsupervised learning through the use of a state-of-the-art autoencoder. This autoencoder is trained on elemental descriptors obtained from Mendeleev software, enabling the extraction of a meaningful and lower dimensional latent space from the input data. This latent representation serves as the basis for our deep multi-layer perceptron (MLP) model, which consists of five layers and shows good precision in predicting hydrogen storage capacities. Furthermore, our results show very good agreement with the results of density functional theory (DFT). In addition to addressing the limitations caused by limited and unevenly distributed data in the field of hydrogen storage materials, we also focus on discovering new materials that show promising opportunities for hydrogen storage. These materials were identified using both feature-based approaches and predictions generated by a large language model. Finally, our investigation into the effectiveness of transferring weights from the autoencoder to the MLP, in addition to the latent features, suggests that while this strategy slightly improves model performance indicated by a slightly higher R$^2$ value and lower RMSE, it emphasizes the intricate challenge of adapting pre-trained weights for specific supervised tasks.

Linear and Non-Linear Response of Quadratic Lindbladians
Spenser Talkington, Martin Claassen
arXiv:2402.06593v2 Announce Type: replace Abstract: Quadratic Lindbladians encompass a rich class of dissipative electronic and bosonic quantum systems, which have been predicted to host new and exotic physics. In this study, we develop a Lindblad-Keldysh spectroscopic response formalism for open quantum systems that elucidates their steady-state response properties and dissipative phase transitions via finite-frequency linear and non-linear probes. As illustrative examples, we utilize this formalism to calculate the (1) density and dynamic spin susceptibilities of a boundary driven XY model at and near criticality, (2) linear and non-linear optical responses in Bernal bilayer graphene coupled to dissipative leads, and (3) steady state susceptibilities in a bosonic optical lattice. We find that the XY model spin density wavelength diverges with critical exponent 1/2, and there are gapless dispersive modes in the dynamic spin response that originate from the underlying spin density wave order; additionally the dispersing modes of the weak and ultra-strong dissipation limits exhibit a striking correspondence since the boundary dissipators couple only weakly to the bulk in both cases. In the optical response of the Bernal bilayer, we find that the diamagnetic response can decrease with increasing occupation, as opposed to in closed systems where the response increases monotonically with occupation; we study the effect of second harmonic generation and shift current and find that these responses, forbidden in centrosymmetric closed systems, can manifest in these open systems as a result of dissipation. We compare this formalism to its equilibrium counterpart and draw analogies between these non-interacting open systems and strongly interacting closed systems.

Study of superconductivity of very thin $\mathrm{FeSe}_{1-x}\mathrm{Te}_x$ films investigated by microwave complex conductivity measurements
Gaku Matsumoto, Ryo Ogawa, Koji Higasa, Tomoki Kobayashi, Hiroki Nakagawa, Atsutaka Maeda
arXiv:2402.18082v2 Announce Type: replace Abstract: Complex conductivity measurements spanning the entire temperature range, including the vicinity of $T_c$, were conducted on systematically varied FeSe$_{1-x}$Te$_x$ ($x$ = 0 - 0.5) very thin films. By applying a novel cavity measurement technique employing microwave electric fields parallel to FeSe$_{1-x}$Te$_x$ films, we observed distinct temperature-dependent alterations in superfluid fraction and quasiparticle scattering rate at the nematic boundary. These changes in the nematic boundary suggests variations in the superconducting gap structure between samples in the nematic and non-nematic phase. Moreover, fluctuation is visible up to 1.2 $T_c$ irrespective of nematic order, consistent with large superconducting fluctuations in iron chalcogenide superconductors reported previously in [H. Takahashi $\textit{et al}$, Phys. Rev. B 99, 060503(R) (2019)] and [F. Nabeshima $\textit{et al}$, Phys. Rev. B 97, 024504(R) (2018)].

Single Electron Quantum Dot in Two-Dimensional Transition Metal Dichalcogenides
Jaros{\l}aw Paw{\l}owski, Pankaj Kumar, Kenji Watanabe, Takashi Taniguchi, Konstantin S. Novoselov, Hugh O. H. Churchill, Dharmraj Kotekar-Patil
arXiv:2402.19480v2 Announce Type: replace Abstract: Spin-valley properties in two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDC) has attracted significant interest due to the possible applications in quantum computing. Spin-valley properties can be exploited in TMDC quantum dot (QD) with well-resolved energy levels. This requires smaller QDs, especially in material systems with heavy carrier effective mass e.g. TMDCs and silicon. Device architectures employed for TMDC QDs so far have difficulty achieving smaller QDs. Therefore, an alternative approach in the device architecture is needed. Here, we propose a multilayer device architecture to achieve a gate-defined QD in TMDC with a relatively large energy splitting on the QD. We provide a range of device dimensions and dielectric thicknesses and its correlation with the QD energy splitting. The device architecture is modeled realistically. Moreover, we show that all the device parameters used in modeling are experimentally achievable. These studies lay the foundation for future work toward spin-valley qubits in TMDCs. The successful implementation of these device architectures will drive the technological development of 2D materials-based quantum technologies.

Gapped Phases with Non-Invertible Symmetries: (1+1)d
Lakshya Bhardwaj, Lea E. Bottini, Daniel Pajer, Sakura Schafer-Nameki
arXiv:2310.03784v3 Announce Type: replace-cross Abstract: We propose a general framework to characterize gapped infra-red (IR) phases of theories with non-invertible (or categorical) symmetries. In this paper we focus on (1+1)d gapped phases with fusion category symmetries. The approach that we propose uses the Symmetry Topological Field Theory (SymTFT) as a key input: associated to a field theory in d spacetime dimensions, the SymTFT lives in one dimension higher and admits a gapped boundary, which realizes the categorical symmetries. It also admits a second, physical, boundary, which is generically not gapped. Upon interval compactification of the SymTFT by colliding the gapped and physical boundaries, we regain the original theory. In this paper, we realize gapped symmetric phases by choosing the physical boundary to be a gapped boundary condition as well. This set-up provides computational power to determine the number of vacua, the symmetry breaking pattern, and the action of the symmetry on the vacua. The SymTFT also manifestly encodes the order parameters for these gapped phases, thus providing a generalized, categorical Landau paradigm for (1+1)d gapped phases. We find that for non-invertible symmetries the order parameters involve multiplets containing both untwisted and twisted sector local operators, and hence can be interpreted as mixtures of conventional and string order parameters. We also observe that spontaneous breaking of non-invertible symmetries can lead to vacua that are physically distinguishable: unlike the standard symmetries described by groups, non-invertible symmetries can have different actions on different vacua of an irreducible gapped phase. This leads to the presence of relative Euler terms between physically distinct vacua. We also provide a mathematical description of symmetric gapped phases as 2-functors from delooping of fusion category characterizing the symmetry to Euler completion of 2-vector spaces.

Identifying gap-closings in open non-Hermitian systems by Biorthogonal Polarization
Ipsita Mandal
arXiv:2401.12213v2 Announce Type: replace-cross Abstract: We investigate gap-closings in one- and two-dimensional tight-binding models with two bands, containing non-Hermitian hopping terms, and open boundary conditions (OBCs) imposed along one direction. We compare the bulk OBC spectra with the periodic boundary condition (PBC) spectra, pointing out that they do not coincide, which is an intrinsic characteristic of non-Hermitian systems. The non-Hermiticity, thus, results in the failure of the familiar notions of bulk-boundary correspondence found for Hermitian systems. This necessitates the search for topological invariants which can characterize gap-closings in open non-Hermitian systems correctly and unambiguously. We elucidate the behaviour of two possible candidates applicable for one-dimensional slices -- (1) the sum of winding numbers for the two bands defined on a generalized Brillouin zone and (2) the biorthogonal polarization (BP). While the former shows jumps/discontinuities for some of the non-Hermitian systems studied here, at points when an edge mode enters the bulk states and becomes delocalized, it does not maintain quantized values in a given topological phase. On the contrary, BP shows jumps at phase transitions, and takes the quantized value of one or zero, which corresponds to whether an actual edge mode exists or whether that mode is delocalized and absorbed within the bulk (not being an edge mode anymore).

Metasurface spectrometers beyond resolution-sensitivity constraints
Feng Tang, Jingjun Wu, Tom Albrow-Owen, Hanxiao Cui, Fujia Chen, Yaqi Shi, Lan Zou, Jun Chen, Xuhan Guo, Yijun Sun, Jikui Luo, Bingfeng Ju, Jing Huang, Shuangli Liu, Bo Li, Liming Yang, Eric Anthony Munro, Wanguo Zheng, Hannah J. Joyce, Hongsheng Chen, Lufeng Che, Shurong Dong, Tawfique Hasan, Xin Ye, Yihao Yang, Zongyin Yang
arXiv:2402.18996v2 Announce Type: replace-cross Abstract: Optical spectroscopy plays an essential role across scientific research and industry for non-contact materials analysis1-3, increasingly through in-situ or portable platforms4-6. However, when considering low-light-level applications, conventional spectrometer designs necessitate a compromise between their resolution and sensitivity7,8, especially as device and detector dimensions are scaled down. Here, we report on a miniaturizable spectrometer platform where light throughput onto the detector is instead enhanced as the resolution is increased. This planar, CMOS-compatible platform is based around metasurface encoders designed to exhibit photonic bound states in the continuum9, where operational range can be altered or extended simply through adjusting geometric parameters. This system can enhance photon collection efficiency by up to two orders of magnitude versus conventional designs; we demonstrate this sensitivity advantage through ultra-low-intensity fluorescent and astrophotonic spectroscopy. This work represents a step forward for the practical utility of spectrometers, affording a route to integrated, chip-based devices that maintain high resolution and SNR without requiring prohibitively long integration times.

Electron-correlated study of excited states and absorption spectra of some low-symmetry graphene quantum dots
Samayita Das, Alok Shukla
arXiv:2402.19320v2 Announce Type: replace-cross Abstract: We have computed the linear optical absorption spectra of three graphene quantum dots (GQDs), saturated by hydrogens on the edges, using both first-principles time-dependent density-functional theory (TDDFT) and the Pariser-Parr-Pople (PPP) model coupled with the configuration-interaction (CI) approach. To understand the influence of electron-correlation effects, we have also calculated the singlet-triplet energy gap (spin gap) of the three GQDs. Because of the presence of edge hydrogens, these GQDs are effectively polycyclic aromatic hydrocarbons (PAHs) dibenzo[bc,ef]coronene (also known as benzo(1,14)bisanthene, C$_{30}$H$_{14}$), and two isomeric compounds, dinaphtho[8,1,2abc;2,1,8klm]coronene and dinaphtho[8,1,2abc;2,1,8jkl]coronene with the chemical formula C$_{36}$H$_{16}$. The two isomers have different point group symmetries, $C_{2v}$, and $C_{2h}$, therefore, this study will also help us understand the influence of symmetry on optical properties. A common feature of the absorption spectra of the three GQDs is that the first peak representing the optical gap is of low to moderate intensity, while the intense peaks appear at higher energies. For each GQD, PPP model calculations performed with the screened parameters agree well with the experimental results of the corresponding PAH, and also with the TDDFT calculations.

Found 9 papers in nano-lett
Date of feed: Sat, 02 Mar 2024 14:05:39 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

[ASAP] Designer Spin Models in Tunable Two-Dimensional Nanographene Lattices
João Henriques, Mar Ferri-Cortés, and Joaquín Fernández-Rossier

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Nano Letters
DOI: 10.1021/acs.nanolett.3c04915

[ASAP] Emergence of Improper Electronic Ferroelectricity and Flat Band in Twisted Bilayer Tl2S
Zhigang Gui, Wei Li, and Li Huang

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Nano Letters
DOI: 10.1021/acs.nanolett.4c00141

[ASAP] Balancing the Ion/Electron Transport of Graphite Anodes by a La-Doped TiNb2O7 Functional Coating for Fast-Charging Li-Ion Batteries
Yeliang Sheng, Xinyang Yue, Wei Hao, Yongteng Dong, Yakun Liu, and Zheng Liang

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Nano Letters
DOI: 10.1021/acs.nanolett.3c05151

[ASAP] Resonant Tunneling-Enhanced Photoresponsivity in a Twisted Graphene van der Waals Heterostructure
Binghe Xie, Jiaxin Wu, Junning Mei, Shuangxing Zhu, Ruan Zhang, Feifan Gu, Kenji Watanabe, Takashi Taniguchi, and Xinghan Cai

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Nano Letters
DOI: 10.1021/acs.nanolett.3c05131

[ASAP] Quantification of Hybrid Topological Spin Textures and Their Nanoscale Fluctuations in Ferrimagnets
Yuxuan Zhang, Teng Xu, Wanjun Jiang, Rong Yu, and Zhen Chen

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Nano Letters
DOI: 10.1021/acs.nanolett.3c04409

[ASAP] Direct Hot-Electron Transfer at the Au Nanoparticle/Monolayer Transition-Metal Dichalcogenide Interface Observed with Ultrahigh Spatiotemporal Resolution
Jinglin Tang, Yaolong Li, Sheng Ye, Pengzuo Jiang, Zhaohang Xue, Xiaofang Li, Xiaying Lyu, Qinyun Liu, Saisai Chu, Hong Yang, Chengyin Wu, Xiaoyong Hu, Yunan Gao, Shufeng Wang, Quan Sun, Guowei Lu, and Qihuang Gong

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Nano Letters
DOI: 10.1021/acs.nanolett.4c00324

[ASAP] Nonlinear Landau Fan Diagram for Graphene Electrons Exposed to a Moiré Potential
Pilkyung Moon, Youngwook Kim, Mikito Koshino, Takashi Taniguchi, Kenji Watanabe, and Jurgen H. Smet

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Nano Letters
DOI: 10.1021/acs.nanolett.3c04444

[ASAP] Ultralow Auger-Assisted Interlayer Exciton Annihilation in WS2/WSe2 Moiré Heterobilayers
Cheng-Syuan Cai, Wei-Yan Lai, Po-Hsuan Liu, Tzu-Chieh Chou, Ro-Ya Liu, Chih-Ming Lin, Shangjr Gwo, and Wei-Ting Hsu

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Nano Letters
DOI: 10.1021/acs.nanolett.3c04688

[ASAP] Topological Nodal-Point Superconductivity in Two-Dimensional Ferroelectric Hybrid Perovskites
Xiaoyin Li, Shunhong Zhang, Xiaoming Zhang, Zeev Valy Vardeny, and Feng Liu

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Nano Letters
DOI: 10.1021/acs.nanolett.3c04085

Found 3 papers in acs-nano
Date of feed: Sat, 02 Mar 2024 14:03:32 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

[ASAP] Niobium Boride/Graphene Directing High-Performance Lithium–Sulfur Batteries Derived from Favorable Surface Passivation
Yanjuan Li, Zhanzhan Wang, HongFei Gu, Hongpeng Jia, Zhouyang Long, and Xiao Yan

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ACS Nano
DOI: 10.1021/acsnano.3c12076

[ASAP] Dual-Limit Growth of Large-Area Monolayer Transition Metal Dichalcogenides
Zeqin Xin, Xiaolong Zhang, Jing Guo, Yonghuang Wu, Bolun Wang, Run Shi, and Kai Liu

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ACS Nano
DOI: 10.1021/acsnano.3c09222

[ASAP] Atomistic Probing of Defect-Engineered 2H-MoTe2 Monolayers
Odongo Francis Ngome Okello, Dong-Hwan Yang, Seung-Young Seo, Jewook Park, Gunho Moon, Dongwon Shin, Yu-Seong Chu, Sejung Yang, Teruyasu Mizoguchi, Moon-Ho Jo, and Si-Young Choi

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ACS Nano
DOI: 10.1021/acsnano.3c08606