Found 35 papers in cond-mat


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Edge currents as probe of topology in twisted cuprate bilayers
Vedangi Pathak, Oguzhan Can, Marcel Franz
arXiv:2403.14851v1 Announce Type: new Abstract: Bilayers made of high-$T_c$ cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ assembled with a twist angle close to $45^\circ$ have been recently shown to spontaneously break time reversal symmetry $\mathcal{T}$, consistent with theoretical predictions for emergent chiral topological $d_{x^2-y^2}+id_{xy}$ phase in such twisted $d$-wave superconductors. Here we use a minimal microscopic model to estimate the size of spontaneous chiral edge currents expected to occur in the $\mathcal{T}$-broken phase. In accord with previous theoretical studies of chiral $d$-wave superconductors we find small but non-vanishing edge currents which we nevertheless predict to be above the detection threshold of the state-of-the-art magnetic scanning probe microscopy. In addition, by deriving a simple relation between the edge current and the electron spectral function we help elucidate the longstanding disparity between the size of edge currents in chiral $d$-wave and $p$-wave superconductors.

Nonmonotonic relaxation of Campbell penetration depth from creep-enhanced vortex pinning
Sunil Ghimire, Filippo Gaggioli, Kamal R. Joshi, Marcin Konczykowski, Romain Grasset, Elizabeth H. Krenkel, Amlan Datta, Makariy A. Tanatar, Shuzhang Chen, Cedomir Petrovic, Vadim B. Geshkenbein, Ruslan Prozorov
arXiv:2403.14891v1 Announce Type: new Abstract: We study the effects of flux creep on the linear AC response of the vortex lattice in a low-pinning Ca$_3$Ir$_4$Sn$_13$ superconductor by measuring the Campbell penetration depth, $\lambda_\rm \scriptscriptstyle C(T,H,t)$. Thermal fluctuations release vortices from shallow pinning sites, only for them to become re-trapped by deeper potential wells, causing an initial increase of the effective Labusch parameter, which is proportional to the pinning well depth. This effect cannot be detected in conventional magnetic relaxation measurements but is revealed by our observation of a nonmonotonic time evolution of $\lambda_\rm \scriptscriptstyle C(T,H,t)$, which directly probes the average curvature of the occupied pinning centers. The time evolution of $\lambda_\rm \scriptscriptstyle C(T,H,t)$ was measured at different temperatures in samples with different densities of pinning centers produced by electron irradiation. The $\lambda_\rm \scriptscriptstyle C(T,H,t)$ is hysteretic with a zero-field-cool warmed (ZFCW) state that exhibits a noticeable nonmonotonic relaxation but shows a monotonic change in the field-cooled (FC) state. The curves, measured at different temperatures, can be collapsed together when plotted on a logarithmic time scale $t \to T\ln(t/t_0)$, quantitatively corroborating the proposed picture of vortex creep based on the strong pinning theory.

An investigation on electronic and magnetic properties of Cr substituted MoS$_2$ monolayer and multilayers-Hybrid functional calculations
Aloka Ranjan Sahoo, Sharat Chandra
arXiv:2403.14945v1 Announce Type: new Abstract: With help of ab initio density functional theory calculation, DFT+U, and hybrid functional HSE06, we revisit the layer dependent electronic structure and magnetic properties of pristine and 3d transition metal Cr doped MoS$_2$ monolayer and multilayers. Our results show that the dopant Cr atoms prefer to stay at nearest neighbor distances. In the multilayers, they prefer to remain in the outermost surface layers. Matching with the experimental band gap, the optimized U parameter we report is 4 eV. The band gap of the Cr doped monolayer is indirect, confirming the experimental observation from photoluminescence experiments. The HSE06 calculation for Cr doped monolayer shows that the band gap of doped Cr MoS$_2$ monolayer is indirect and no magnetism is observed. From the DFT studies, the band gap for the multilayers is indirect, and doping with Cr does not induce magnetic moments in MoS$_2$ layers. The band gap is observed to decrease with the multilayer thickness. The strain induced by substitutional Cr doping at the Mo site transforms the band gap in monolayer MoS$_2$ from direct to indirect. The defect states are produced within the band gap region close to the conduction band minimum.

Quantum spin driven Yu-Shiba-Rusinov multiplets and fermion-parity-preserving phase transition in K$_3$C$_{60}$
Shu-Ze Wang, Xue-Qing Yu, Li-Xuan Wei, Li Wang, Qiang-Jun Cheng, Kun Peng, Fang-Jun Cheng, Yu Liu, Fang-Sen Li, Xu-Cun Ma, Qi-Kun Xue, Can-Li Song
arXiv:2403.14970v1 Announce Type: new Abstract: Magnetic impurities in superconductors are of increasing interest due to emergent Yu-Shiba-Rusinov (YSR) states and Majorana zero modes for fault-tolerant quantum computation. However, a direct relationship between the YSR multiple states and magnetic anisotropy splitting of quantum impurity spins remains poorly characterized. By using scanning tunneling microscopy, we resolve systematically individual transition-metal (Fe, Cr and Ni) impurities induced YSR multiplets as well as their Zeeman effects in K$_3$C$_{60}$ superconductor. The YSR multiplets show identical $d$ orbital-like wave functions that are symmetry-mismatched to the threefold K$_3$C$_{60}$(111) host surface, breaking point-group symmetries of the spatial distribution of YSR bound states in real space. Remarkably, we identify an unprecedented fermion-parity-preserving quantum phase transition between ground states with opposite signs of the uniaxial magnetic anisotropy that can be manipulated by an external magnetic field. These findings can be readily understood in terms of anisotropy splitting of quantum impurity spins, and thus elucidate the intricate interplay between the magnetic anisotropy and YSR multiplets.

Vanishing of Resistivity upon Freezing of Vortex Liquid in Clean Superconductors
Naratip Nunchot, Ryusuke Ikeda
arXiv:2403.14992v1 Announce Type: new Abstract: Superconducting transition, defined as vanishing of the resistivity, under a magnetic field in a clean bulk type II superconductor with weak sample disorder is believed to be a reflection of freezing of the vortex liquid to a kind of vortex solids. This fundamental issue on superconductivity is examined in detail. Based on the Ginzburg-Landau fluctuation theory for a three-dimensional (3D) system and through a supplementary study in 2D case, we find that the resistivity in the weakly disordered 3D case vanishes in a nearly discontinuous way, reflecting growth of the Bragg peaks on approaching the vortex lattice melting transition. In contrast, such a sharp decrease of the resistivity does not clearly appear in the corresponding 2D case. The consequences of this difference in the vanishing behavior of the resistivity between the 2D and 3D systems are discussed in relation to available experimental facts.

All van der Waals three-terminal SOT-MRAM realized by topological ferromagnet Fe3GeTe2
Jingyuan Cui, Kai-Xuan Zhang, Je-Geun Park
arXiv:2403.15020v1 Announce Type: new Abstract: Magnetic van der Waals (vdW) materials have attracted massive attention because of their academic interest and application potential for the past few years. Its main advantage is the intrinsic two-dimensionality, enabling much smaller devices of novel concepts. One particular exciting direction lies in the current-driven spin-orbit torque (SOT). Here, we, for the first time, realize an all vdW three-terminal SOT memory, employing the unique physics principle of gigantic intrinsic SOT of Fe3GeTe2 (FGT) and the well-known industry-adopted tunnelling magnetoresistance (TMR) effect. We designed the device operation procedure and fabricated the FGT/h-BN/FGT vdW heterostructure as a proof of concept. This device exhibits a classical TMR effect and unambiguously demonstrates the conception by precise performance as expected: the magnetic information of the top-FGT is written by current-driven SOT and read out by TMR separately. The writing and reading current paths are physically decoupled, enhancing the design and optimization flexibility substantially and further strengthening the device's endurance naturally. Our work would prompt more expansive use of vdW magnets for spintronic applications.

Super-Planckian radiative heat transfer between coplanar two-dimensional metals
Tao Zhu, Yong-Mei Zhang, Jian-Sheng Wang
arXiv:2403.15036v1 Announce Type: new Abstract: We use the nonequilibrium Green's function formalism to investigate the radiative heat transfer (RHT) between coplanar two-dimensional (2D) metals via a tight-binding square lattice model and the Drude model. Our results reveal that the RHT between coplanar 2D metals is significantly larger than black-body radiation in both the near and far fields, leading to a global super-Planckian RHT. As the separation distance increases, the heat flux density exhibits a rapid decrease in the near field, followed by a slower decrease and eventual $1/d$ dependence in the far field, while maintaining a much higher magnitude than black-body radiation. Evanescent waves dominate the heat transfer in the near field, while propagating waves dominate the far field. Surprisingly, the propagating heat flux remains almost constant over a wide range of distances, resulting in a super-Planckian behavior in the far field. The dispersion relation of the spectrum function reveals distinct contributions from propagating and evanescent waves, with possible origins from surface plasmon resonance. These findings provide insights into the unique characteristics of RHT between coplanar 2D metals and highlight the potential for achieving enhanced heat transfer beyond the black-body limit, with implications for thermal management and energy conversion applications.

Growth of membranes formed by associating polymers at interfaces
Elena N. Govorun (SIMM), Julien Dupr\'e de Baubigny (SIMM), Patrick Perrin (SIMM), Mathilde Reyssat (PMMH), Nad\`ege Pantoustier (SIMM), Thomas Salez (LOMA), C. Monteux (SIMM)
arXiv:2403.15041v1 Announce Type: new Abstract: Polymer association at liquid-liquid interfaces is a promising way to spontaneously obtain soft self-healing membranes. In the case of reversible bonding between two polymers, the macromolecules are mobile everywhere within the membrane and they can be absorbed into it at both boundaries due to binding to macromolecules of the other type. In this work, we develop the theoretical model of membrane growth based on these assumptions. The asymptotic dependence of membrane thickness on time as h ~ t^(1/2), as typically observed in experiments in a stationary regime, reveals an interdiffusion-controlled process, where the polymer fluxes sustain the polymer absorption at the membrane boundaries. The membrane growth rate is mainly determined by the difference in equilibrium compositions at the boundaries, the association constant, the polymer lengths and mobilities. This model is further used to describe the growth of hydrogel membranes formed via H-bonding of polymers at the interface between a solution of poly(propylene oxide) (PPO) in isopropyl myristate and an aqueous solution of poly(methacrylic acid) (PMAA). The film thickness is measured by reflectometric methods. The dependence of thickness on time can be approximated by the power law t^(beta), where beta= 1/2 for the PMAA solution at pH=3 and decreases with increasing pH and, hence, ionization degree. The growth rate slows down about 25 times for 500-nm-thick films at pH = 5.1 compared to the case of pH = 3. The ionization degree of PMAA solutions was studied by potentiometric methods. Even a small change in ionization was found to influence the growth rate of the film. A slowdown of the film growth for the ionized polymer can be explained by a drop in the composition gradient in the membrane, as is predicted by the proposed model.

Quantum Valley Hall effect without Berry curvature
Rasoul Ghadimi, Chiranjit Mondal, Sunje Kim, Bohm-Jung Yang
arXiv:2403.15050v1 Announce Type: new Abstract: The quantum valley Hall effect (QVHE) is characterized by the valley Chern number (VCN) in a way that one-dimensional (1D) chiral metallic states are guaranteed to appear at the domain walls (DW) between two domains with opposite VCN for a given valley. Although in the case of QVHE, the total BC of the system is zero, the BC distributed locally around each valley makes the VCN well-defined as long as inter-valley scattering is negligible. Here, we propose a new type of valley-dependent topological phenomenon that occurs when the BC is strictly zero at each momentum. Such zero Berry curvature (ZBC) QVHE is characterized by the valley Euler number (VEN) which is computed by integrating the Euler curvature around a given valley in two-dimensional (2D) systems with space-time inversion symmetry. 1D helical metallic states can be topologically protected at the DW between two domains with the opposite VENs when the DW configuration preserves either the mirror symmetry with respect to the DW or the combination of the DW space-time inversion , and chiral symmetries. We establish the fundamental origin of ZBC-QVHE. Also, by combining tight-binding model study and first-principles calculations, we propose stacked hexagonal bilayer lattices including h-BX (X=As, P) and large-angle twisted bilayer graphenes as candidate systems with robust helical DW states protected by VEN.

Luminescence properties and phase transformation of broadband NIR emitting A2(WO4)3:Cr3+ (A=Al3+, Sc3+) phosphors toward NIR spectroscopy applications
Shuai Yang, Yongjie Wang, Guotao Xiang, Sha Jiang, Li Li, Faling Ling, Huanhuan Hu, Yuanyuan Zhang, Xianju Zhou, Andrzej Suchocki
arXiv:2403.15148v1 Announce Type: new Abstract: The synthesis, structural, and luminescence properties have been carried out for Cr3+-activated Al2(WO4)3 (AWO) and Sc2(WO4)3 (SWO) phosphors for application in pc-NIR LED. Upon blue excitation, these compounds are capable of exhibiting broadband NIR emission stems primarily from 4T2-->4A2 transition in the range of 670-1200 nm (maxima ~808 nm, FWHM ~140 nm) for AWO:Cr and of 700-1300 nm (maxima ~870 nm, FWHM ~164 nm) for SWO:Cr. The significant shift of NIR emission is attributed to the substitution of AlO6 with larger ScO6 octahedrons. To gain insight into the luminescence the crystal field strength, Racah parameters, nephelauxetic effect, and electron-phonon coupling have been analyzed based on spectroscopic results. The electron-phonon coupling parameter S for SWO:Cr was determined to be 11.5, twice as large as that for AWO:Cr, which is in accordance with its strong thermal quenching. The abrupt changes occurring at 275 K in temperature-dependent luminescence spectra and decay lifetime of AWO:Cr is associated with temperature-driven phase transformation from low-temperature monoclinic to high-temperature orthorhombic phase. Pressure induced amorphization of AWO:Cr at pressures higher than 25 kbar was confirmed by employing high pressure evolution of Raman spectra. A high-power NIR pc-LED, fabricated by coating AWO:0.04Cr on a commercial 470 nm LED chip, shows good performance with an output power of 17.1 mW driven by a current of 320 mA, revealing potential application of studied materials for NIR light source.

Spin Hall Effect: Symmetry Breaking, Twisting, and Giant Disorder Renormalization
David T. S. Perkins, Alessandro Veneri, Aires Ferreira
arXiv:2403.15229v1 Announce Type: new Abstract: Atomically-thin materials based on transition metal dichalcogenides and graphene offer a promising avenue for unlocking the mechanisms underlying the spin Hall effect (SHE) in heterointerfaces. Here, we develop a microscopic theory of the SHE for twisted van der Waals heterostructures that fully incorporates twisting and disorder effects, and illustrate the critical role of symmetry breaking in the generation of spin-Hall currents. We find that an accurate treatment of vertex corrections leads to a qualitatively and quantitatively different SHE than that obtained from popular approaches like the ``$i\,\eta$'' and ladder approximations. A pronounced oscillatory behavior of skew-scattering processes with twist angle, $\theta$, is predicted, reflecting a non-trivial interplay of Rashba and valley-Zeeman effects and yields a vanishing SHE for $\theta = 30^\circ$ and, for graphene-WSe$_2$, an optimal SHE for $\theta \approx 17^\circ$. Our findings reveal disorder and broken symmetries as important knobs to optimize interfacial SHEs.

Single-layer of Bi$_{1-x}$Sb$_x$ grown on Ag(111)
Javier D. Fuhr, J. Esteban Gayone, Hugo Ascolani
arXiv:2403.15242v1 Announce Type: new Abstract: In this work, we report the growth of a single mixed Bi$_{1-x}$Sb$_x$ layer, with diverse stoichiometries, on a Ag(111) substrate. The atomic geometry has been thoroughly investigated by low energy electron diffraction, scanning tunneling microscopy, and X-ray photoelectron spectroscopy experiments, as well as calculations based on density functional theory (DFT). We first determined that both pure systems (Bi/Ag(111) and Sb/Ag(111)) show similar behaviors: they form surface alloys with ($\sqrt{3}\times\sqrt{3}$)R30$^\circ$ periodicity for coverages lower than 1/3 ML, and undergo a dealloying transition for higher coverages up to 2/3 ML. We then established a simple preparation procedure to obtain a mixed Bi-Sb overlayer on Ag(111): it is essential to start with a surface completely covered by either of the two pure surface alloys and then deposit the other element on it. The energetics derived from DFT calculations provide insight into the systems preference towards the formation of this phase, and also predict a pathway to the formation of Bi-rich non-alloyed phases. The obtained mixed Bi-Sb phase has a lateral atomic arrangement very similar to the one in the non-alloyed phase observed for Sb on Ag(111), with Sb and Bi atoms distributed disorderly, and presents a significant vertical corrugation, promising considerable Rashba effects.

Bipartite Sachdev-Ye Models with Read-Saleur Symmetries
J. Classen-Howes, P. Fendley, A. Pandey, S. A. Parameswaran
arXiv:2403.15270v1 Announce Type: new Abstract: We introduce an SU(M)-symmetric disordered bipartite spin model with unusual characteristics. Although superficially similar to the Sachdev-Ye model, it has several markedly different properties for M>2. In particular, it has a large non-trivial nullspace whose dimension grows exponentially with system size. The states in this nullspace are frustration-free, and are ground states when the interactions are ferromagnetic. The exponential growth of the nullspace leads to Hilbert-space fragmentation and a violation of the eigenstate thermalization hypothesis. We demonstrate that the commutant algebra responsible for this fragmentation is a non-trivial subalgebra of the Read-Saleur commutant algebra of certain nearest-neighbour models such as the spin-1 biquadratic spin chain. We also discuss the low-energy behaviour of correlations for the disordered version of this model in the limit of a large number of spins and large M, using techniques similar to those applied to the SY model. We conclude by generalizing the Shiraishi-Mori embedding formalism to non-local models, and apply it to turn some of our nullspace states into quantum many-body scars.

Quantum Fluctuations Suppress the Critical Fields in BaCo$_2$(AsO$_4$)$_2$
Shiva Safari, William Bateman-Hemphill, Asimpunya Mitra, F\'elix Desrochers, Emily Z. Zhang, Lubuna Shafeek, Austin Ferrenti, Tyrel M. McQueen, Arkady Shekhter, Zolt\'an K\"oll\"o, Yong Baek Kim, B. J. Ramshaw, K. A. Modic
arXiv:2403.15315v1 Announce Type: new Abstract: Early efforts to realize exotic quantum ground states in frustrated magnets focused on frustration arising from the lattice geometry alone. Attention has shifted to bond-dependent anisotropic interactions, as well as further-neighbor interactions, on non-geometrically-frustrated lattices due to their greater versatility. The honeycomb magnet BaCo$_2$(AsO$_4$)$_2$ recently emerged as a candidate host for both bond-dependent (e.g. Kitaev) and third-neighbor ($J_3$) interactions, and has become a model experimental system due to its relatively low levels of disorder. Understanding the relative importance of different exchange interactions holds the key to achieving novel ground states, such as quantum spin liquids. Here, we use the magnetotropic susceptibility to map out the intermediate and high-field phase diagram of BaCo$_2$(AsO$_4$)$_2$ as a function of the out-of-plane magnetic field direction at $T = 1.6$ K. We show that the experimental data are qualitatively consistent with classical Monte Carlo results of the XXZ-$J_1$-$J_3$ model with small Kitaev and off-diagonal exchange couplings included. However, the calculated critical fields are systematically larger than the experimental values. Infinite-DMRG computations on the quantum model reveal that quantum corrections from a nearby ferromagnetic state are likely responsible for the suppressed critical fields. Together, our experiment and theory analyses demonstrate that, while quantum fluctuations play an important role in determining the phase diagram, most of the physics of BaCo$_2$(AsO$_4$)$_2$ can be understood in terms of the classical dynamics of long-range ordered states, leaving little room for the possibility of a quantum spin liquid.

Photonic cross noise spectroscopy of Majorana bound states
Lena Bittermann, Fernando Dominguez, Patrik Recher
arXiv:2403.15340v1 Announce Type: new Abstract: We propose a route to detect Majorana bound states (MBSs) by coupling a topological superconductor to quantum dots (QDs) in a $pnp$ junction. Here, two MBSs are coherently coupled to electrons on two QDs, which recombine with holes to photons. We focus on the spectroscopy of cross-correlated shot noise and the polarization of the emitted photons. Our detection scheme allows us to probe the necessary condition for the emergence of MBSs, specifically, the existence of non-local triplet superconducting correlations and also the fundamental property that two MBSs comprise a single complex fermion. We compare our results to the ones obtained from non-topological quasi-MBSs (qMBSs) and establish a correspondence between the number of peaks in the cross-correlation with the number of MBSs in the system. Here, we can identify a tunneling regime that facilitates differentiation between topological MBSs and trivial qMBSs. Additionally, we test the robustness of the detection scheme by the addition of uncorrelated particles.

Topological analysis and experimental control of transformations of domain walls in magnetic cylindrical nanowires
L. \'Alvaro-G\'omez, J. Hurst, S. Hegde, S. Ruiz-G\'omez, E. Pereiro, L. Aballe, J. C Toussaint, L. P\'erez, A. Masseboeuf, C. Thirion, O. Fruchart, D. Gusakova
arXiv:2403.15343v1 Announce Type: new Abstract: Topology is a powerful tool for categorizing magnetization textures, highlighting specific features in both 2D systems, such as thin films or curved surfaces, and in 3D bulk systems. In the emerging field of 3D nanomagnetism within confined geometries, the contributions from both volume and surface must be considered, requiring appropriate topological analysis to obtain a complete view of the system. Here, we consider domain walls in cylindrical magnetic nanowires to illustrate the use of topological invariants. We begin with micromagnetic simulations of domain wall transformation under the stimulus of an \OErsted field, tracking bulk and surface topological signatures, and analyzing the interplay between multiple micromagnetic objects. For instance, the extensive analysis allowed us to highlight mechanisms of domain wall type conversion from topologically non-trivial to trivial states, a phenomenon disregarded in previous studies. Additionally, we provide experimental evidence of the transient states predicted to occur during the dynamical process.

Exciton-activated effective phonon magnetic moment in monolayer MoS2
Chunli Tang, Gaihua Ye, Cynthia Nnokwe, Mengqi Fang, Li Xiang, Masoud Mahjouri-Samani, Dmitry Smirnov, Eui-Hyeok Yang, Tingting Wang, Lifa Zhang, Rui He, Wencan Jin
arXiv:2403.15347v1 Announce Type: new Abstract: Optical excitation of chiral phonons plays a vital role in studying the phonon-driven magnetic phenomena in solids. Transition metal dichalcogenides host chiral phonons at high symmetry points of the Brillouin zone, providing an ideal platform to explore the interplay between chiral phonons and valley degree of freedom. Here, we investigate the helicity-resolved magneto-Raman response of monolayer MoS2 and identify a doubly degenerate Brillouin-zone-center chiral phonon mode at ~270 cm-1. Our wavelength- and temperature-dependent measurements show that this chiral phonon is activated through the resonant excitation of A exciton. Under an out-of-plane magnetic field, the chiral phonon exhibits giant Zeeman splitting, which corresponds to an effective magnetic moment of 2.5mu_B. Moreover, we carry out theoretical calculations based on the Morphic effects in nonmagnetic crystals, which reproduce the linear Zeeman splitting and Raman cross-section of the chiral phonon. Our study provides important insights into lifting the chiral phonon degeneracy in an achiral covalent material, paving a new route to excite and control chiral phonons.

Crossover from relativistic to non-relativistic net magnetization for MnTe altermagnet candidate
N. N. Orlova, A. A. Avakyants, A. V. Timonina, N. N. Kolesnikov, E. V. Deviatov
arXiv:2403.15348v1 Announce Type: new Abstract: We experimentally study magnetization reversal curves for MnTe single crystals, which is the altermagnetic candidate. Above 85~K temperature, we confirm the antiferromagnetic behavior of magnetization $M$, which is known for $\alpha$--MnTe. Below 85~K, we observe anomalous low-field magnetization behavior, which is accompanied by the sophisticated $M(\alpha)$ angle dependence with beating pattern as the interplay between $M(\alpha)$ maxima and minima: in low fields, $M(\alpha)$ shows ferromagnetic-like 180$^\circ$ periodicity, while at high magnetic fields, the periodicity is changed to the 90$^\circ$ one. This angle dependence is the most striking result of our experiment, while it can not be expected for standard magnetic systems. In contrast, in altermagnets, symmetry allows ferromagnetic behavior only due to the spin-orbit coupling. Thus, we claim that our experiment shows the effect of weak spin-orbit coupling in MnTe, with crossover from relativistic to non-relativistic net magnetization, and, therefore, we experimentally confirm altermagnetism in MnTe.

Doped stabilizer states in many-body physics and where to find them
Andi Gu, Salvatore F. E. Oliviero, Lorenzo Leone
arXiv:2403.14912v1 Announce Type: cross Abstract: This work uncovers a fundamental connection between doped stabilizer states, a concept from quantum information theory, and the structure of eigenstates in perturbed many-body quantum systems. We prove that for Hamiltonians consisting of a sum of commuting Pauli operators (i.e., stabilizer Hamiltonians) and a perturbation composed of a limited number of arbitrary Pauli terms, the eigenstates can be represented as doped stabilizer states with small stabilizer nullity. This result enables the application of stabilizer techniques to a broad class of many-body systems, even in highly entangled regimes. Building on this, we develop efficient classical algorithms for tasks such as finding low-energy eigenstates, simulating quench dynamics, preparing Gibbs states, and computing entanglement entropies in these systems. Our work opens up new possibilities for understanding the robustness of topological order and the dynamics of many-body systems under perturbations, paving the way for novel insights into the interplay of quantum information, entanglement, and many-body systems.

Mott insulating states of the anisotropic SU(4) Dirac fermions
Han Xu, Yu Wang, Zhichao Zhou, Congjun Wu
arXiv:1912.11791v3 Announce Type: replace Abstract: We employ the large-scale quantum Monte-Carlo simulations to investigate the Mott-insulating states of the half-filled SU(4) Hubbard model on the square lattice with a staggered-flux pattern. The noninteracting band structure that evolves from a nested Fermi surface at zero flux to isotropic Dirac cones at $\pi$ flux, exhibits anisotropic Dirac cones as the flux varies in between. Our simulations show transitions between the three phases of Dirac semimetal, antiferromagnet and valence-bond solid. A direct continuous transition between the antiferromagnetic phase and the valence-bond-solid phase is realized via varying the flux in the Mott regime. The simulated critical exponents remarkably agree with those of SU(4) $J$-$Q$ model. Inside the valence-bond-solid phase induced by the flux, the plaquette valence-bond state with vanishing single-particle gap is identified. At strong coupling, the valence-bond-solid phase disappears and the Mott-insulating state is always accompanied by antiferromagnetic ordering, regardless of the magnitude of the flux.

A Generic Topological Criterion for Flat Bands in Two Dimensions
Alireza Parhizkar, Victor Galitski
arXiv:2301.00824v2 Announce Type: replace Abstract: We show that the continuum limit of moir\'e graphene is described by a $(2+1)$-dimensional field theory of Dirac fermions coupled to two classical vector fields: a periodic gauge and spin field. We further show that the existence of a flat band implies an effective dimensional reduction, where the time dimension is ``removed.'' The resulting two-dimensional Euclidean theory contains the chiral anomaly. The associated Atiyah-Singer index theorem provides a self-consistency condition for flat bands. In the Abelian limit, where the spin field is disregarded, we reproduce a periodic series of quantized magic angles known to exist in twisted bilayer graphene in the chiral limit. However, the results are not exact. If the Abelian field has zero total flux, perfectly flat bands can not exist, because of the leakage of edge states into neighboring triangular patches with opposite field orientations. We demonstrate that the non-Abelian spin component can correct this and completely flatten the bands via an effective renormalization of the Abelian component into a configuration with a non-zero total flux. We present the Abelianization of the theory where the Abelianized flat band can be mapped to that of the lowest Landau level. We show that the Abelianization corrects the values of the magic angles consistent with numerical results. We also use this criterion to prove that an external magnetic field splits the series into pairs of magnetic field-dependent magic angles associated with flat moir\'e-Landau bands. The topological criterion and the Abelianization procedure provide a generic practical method for finding flat bands in a variety of material systems including but not limited to moir\'e bilayers.

Competing charge and magnetic order in the candidate centrosymmetric skyrmion host EuGa$_2$Al$_2$
A. M. Vibhakar, D. D. Khalyavin, J. M. Moya, P. Manuel, F. Orlandi, S. Lei, E. Morosan, A. Bombardi
arXiv:2304.07903v2 Announce Type: replace Abstract: Eu(Ga$_{1-x}$Al$_x$)$_4$ are centrosymmetric systems that have recently been identified as candidates to stabilise topologically non-trivial magnetic phases, such as skyrmion lattices. In this Letter, we present a high-resolution resonant x-ray and neutron scattering study on EuAl2Ga2 that provides new details of the complex coupling between the electronic ordering phenomena. Our results unambiguously demonstrate that the system orders to form a spin density wave with moments aligned perpendicular to the direction of the propagation vector, and upon further cooling, a cycloid with moments in the ab plane, in contrast to what has been reported in the literature. We show that concomitant with the onset of the spin density wave is the suppression of the charge order, indicative of a coupling between the localised 4$f$ electrons and itinerant electron density. Furthermore we demonstrate that the charge density wave order breaks the four-fold symmetry present in the I4/mmm crystal structure, thus declassifying these systems as square-net magnets.

An algorithm for exact analytical solutions for tilted anisotropic Dirac materials
Julio A. Mojica-Z\'arate, Daniel O-Campa, Erik D\'iaz-Bautista
arXiv:2305.00913v2 Announce Type: replace Abstract: In this article, we obtain the exact solutions for bound states of tilted anisotropic Dirac materials under the action of external electric and magnetic fields with translational symmetry. In order to solve the eigenvalue equation that arises from the effective Hamiltonian of these materials, we describe an algorithm that allow us to decouple the differential equations that are obtained for the spinor components.

Manipulation of Weyl Points in Reciprocal and Nonreciprocal Mechanical Lattices
Mingsheng Tian, Ivan Velkovsky, Tao Chen, Fengxiao Sun, Qiongyi He, Bryce Gadway
arXiv:2308.07853v2 Announce Type: replace Abstract: We introduce feedback-measurement technologies to achieve flexible control of Weyl points and conduct the first experimental demonstration of Weyl type I-II transition in mechanical systems. We demonstrate that non-Hermiticity can expand the Fermi arc surface states from connecting Weyl points to Weyl rings, and lead to a localization transition of edge states influenced by the interplay between band topology and the non-Hermitian skin effect. Our findings offer valuable insights into the design and manipulation of Weyl points in mechanical systems, providing a promising avenue for manipulating topological modes in non-Hermitian systems.

Single-hole spectra of Kitaev spin liquids: from dynamical Nagaoka ferromagnetism to spin-hole fractionalization
Wilhelm Kadow, Hui-Ke Jin, Johannes Knolle, Michael Knap
arXiv:2309.15157v2 Announce Type: replace Abstract: The dynamical response of a quantum spin liquid upon injecting a hole is a pertinent open question. In experiments, the hole spectral function, measured momentum-resolved in angle-resolved photoemission spectroscopy (ARPES) or locally in scanning tunneling microscopy (STM), can be used to identify spin liquid materials. In this study, we employ tensor network methods to simulate the time evolution of a single hole doped into the Kitaev spin-liquid ground state. Focusing on the gapped spin liquid phase, we reveal two fundamentally different scenarios. For ferromagnetic spin couplings, the spin liquid is highly susceptible to hole doping: a Nagaoka ferromagnet forms dynamically around the doped hole, even at weak coupling. By contrast, in the case of antiferromagnetic spin couplings, the hole spectrum demonstrates an intricate interplay between charge, spin, and flux degrees of freedom, best described by a parton mean-field ansatz of fractionalized holons and spinons. Moreover, we find a good agreement of our numerical results to the analytically solvable case of slow holes. Our results demonstrate that dynamical hole spectral functions provide rich information on the structure of fractionalized quantum spin liquids.

Chiral symmetry breaking and topological charge of graphene nanoribbons
Hyun Cheol Lee, S. -R. Eric Yang
arXiv:2312.05487v3 Announce Type: replace Abstract: We explore the edge properties of rectangular graphene nanoribbons featuring two zigzag edges and two armchair edges. Although the self-consistent Hartree-Fock fields break chiral symmetry, our work demonstrates that graphene nanoribbons maintain their status as short-range entangled symmetry-protected topological insulators. The relevant symmetry involves combined mirror and time-reversal operations. In undoped ribbons displaying edge ferromagnetism, the band gap edge states with a topological charge form on the zigzag edges. An analysis of the anomalous continuity equation elucidates that this topological charge is induced by the gap term. In low-doped zigzag ribbons, where the ground state exhibits edge spin density waves, this topological charge appears as a nearly zero-energy edge mode. Our system is outside the conventional calssification for topological insulators.

Phenomenology of Majorana zero modes in full-shell hybrid nanowires
Carlos Pay\'a, Samuel D. Escribano, Andrea Vezzosi, Fernando Pe\~naranda, Ram\'on Aguado, Pablo San-Jose, Elsa Prada
arXiv:2312.11613v2 Announce Type: replace Abstract: Full-shell nanowires have been proposed as an alternative nanowire design in the search of topological superconductivity and Majorana zero modes (MZMs). They are hybrid nanostructures consisting of a semiconductor core fully covered by a thin superconductor shell and subject to a magnetic flux. In this work we critically examine this proposal, finding a very rich spectral phenomenology that combines the Little-Parks modulation of the parent-gap superconductor with flux, the presence of flux-dispersing Caroli-de Gennes-Matricon (CdGM) analog subgap states, and the emergence of MZMs across finite flux intervals that depend on the transverse wavefunction profile of the charge density in the core section. Through microscopic simulations and analytical derivations, we study different regimes for the semiconductor core, ranging from the hollow-core approximation, to the tubular-core nanowire appropriate for a semiconductor tube with an insulating core, to the solid-core nanowire. We compute the phase diagrams for the different models in cylindrical nanowires and find that MZMs typically coexist with CdGM analogs at zero energy, rendering them gapless. However, we also find topologically protected parameter regions, or islands, with gapped MZMs. In this sense, the most promising candidate to obtain topologically protected MZMs in a full-shell geometry is the nanowire with a tubular-shaped core. Moving beyond pristine nanowires, we study the effect of mode mixing perturbations. Strikingly, mode mixing can act like a topological $p$-wave pairing between particle-hole Bogoliubov partners, and is therefore able to create new topologically protected MZMs in regions of the phase diagram that were originally trivial. As a result, the phase diagram is utterly transformed and exhibits protected MZMs in around half of the parameter space.

Antipersistent energy current correlations in strong long-ranged Fermi-Pasta-Ulam-Tsingou type models
Daxing Xiong, Jianjin Wang
arXiv:2401.09213v3 Announce Type: replace Abstract: We study heat transfer in one-dimensional Fermi-Pasta-Ulam-Tsingou type systems with long-range (LR) interactions. The strength of the LR interaction between two lattice sites decays as a power $\sigma$ of the inverse of their distance. We focus on the strong LR regime ($0\leq \sigma \leq1$) and show that the thermal transport behaviors are remarkably nuanced. Specifically, we observe that the antipersistent (negative) energy current correlation in this regime is intricately dependent on $\sigma$, displaying a nonmonotonic variation. Notably, a significant qualitative change occurs at $\sigma_c=0.5$, where with respect to other $\sigma$ values, the correlation shows a minimum negative value. Furthermore, our findings also demonstrate that within the long-time range considered, these antipersistent correlations will eventually vanish for certain $\sigma >0.5$. The underlying mechanisms behind these intriguing phenomena are related to the crossover of two diverse space-time scaling properties of equilibrium heat correlations and the various scattering processes of phonons and discrete breathers.

Thermal transport in a 2D amorphous material
Yuxi Wang, Xingxing Zhang, Wujuan Yan, Nianjie Liang, Haiyu He, Xinwei Tao, Ang Li, Fuwei Yang, Buxuan Li, Te-Huan Liu, Jia Zhu, Wu Zhou, Wei Wang, Lin Zhou, Bai Song
arXiv:2402.13471v2 Announce Type: replace Abstract: Two-dimensional (2D) crystals proved revolutionary soon after graphene was discovered in 2004. However, 2D amorphous materials only became accessible in 2020 and remain largely unexplored. In particular, the thermophysical properties of amorphous materials are of great interest upon transition from 3D to 2D. Here, we probe thermal transport in 2D amorphous carbon. A cross-plane thermal conductivity ($\kappa$) down to 0.079 $\rm{Wm}^{-1}K^{-1}$ is measured for van der Waals stacked multilayers at room temperature, which is among the lowest reported to date. Meanwhile, an unexpectedly high in-plane $\kappa$ is obtained for freestanding monolayers which is a few times larger than what is predicted by conventional wisdom for 3D amorphous carbon with similar $\rm{sp}^{2}$ fraction. Our molecular dynamics simulations reveal the role of disorder and highlight the impact of dimensionality. Amorphous materials at the 2D limit open up new avenues for understanding and manipulating heat at the atomic scale.

Novel Dipole-Lattice coupling in the Quantum-Spin-Liquid Material $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$
Jesse Liebman (Johns Hopkins University), Kazuya Miyagawa (University of Tokyo), Kazushi Kanoda (University of Tokyo), Natalia Drichko (Johns Hopkins University)
arXiv:2403.02676v2 Announce Type: replace Abstract: A family of molecular Mott insulators on triangular lattice provided a few S=1/2 triangular quantum spin liquid candidates, with $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ being the most studied material of this group. The large number experimental works present a conflicting set of evidence, with some suggesting spin liquid behavior, while others point towards a valence bond solid with orphan spins. In this work we use Raman scattering spectroscopy to probe both local charge on molecular sites and lattice phonons as a function of temperature down to 6~K. Based on the analysis of the line shape of the BEDT-TTF charge sensitive vibration $\nu_2$ on cooling below 40 K, we suggest a development of disordered fluctuating charge disproportionation on (BEDT-TTF)$_2$ dimers of amplitude as small as 0.06$e$. The lattice phonons show strong anomalous broadening on cooling only in the (c,c) scattering channel, associated with the developing charge disproportionation. We suggest an interpretation, where the coupling of disordered charge dipoles on dimers to the lattice results in anisotropic modulation of charge transfer integrals between dimer lattice sites. Such fluctuations would result in modulation of magnetic coupling between spins which can produce fluctuating charge ordered spin-singlet pairs.

Bifurcations of inflating balloons and interacting hysterons
Gentian Muhaxheri, Christian D. Santangelo
arXiv:2403.10721v2 Announce Type: replace Abstract: While many materials exhibit a complex, hysteretic response to external driving, there has been a surge of interest in how the complex dynamics of internal materials states can be understood and designed to process and store information. We consider a system of connected rubber balloons that can be described by a Preisach model of non-interacting hysterons under pressure control, but for which the hysterons become coupled under volume control. We study this system by exploring the possible transition graphs, as well as by introducing a configuration space approach which tracks the volumes of each balloon. Changes in the transition graphs turn out to be related to changes in the topology of the configuration space of the balloons, providing a particularly geometric view of how transition graphs can be designed, as well as additional information on the existence of hidden metastable states. This class of systems is more general than just balloons.

Tuning of the ultrafast demagnetization by ultrashort spin polarized currents in multi-sublattice ferrimagnets
Deeksha Gupta, Maryna Pankratova, Matthias Riepp, Manuel Pereiro, Biplab Sanyal, Soheil Ershadrad, Michel Hehn, Niko Pontius, Christian Sch\"u{\ss}ler-Langeheine, Nicolas Bergeard, Anders Bergman, Olle Eriksson, Christine Boeglin
arXiv:2403.11739v2 Announce Type: replace Abstract: Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. Several microscopic mechanisms have been proposed to explain the observations, including the transport of ultrashort spin-polarized hot-electrons (SPHE). Such ultrafast spin currents find growing interest because of the recent challenges in ultrafast spintronics however they are only poorly characterized. One of the key challenges is to characterize the spin-polarized ultrafast currents and the microscopic mechanisms behind SPHE induced manipulation of the magnetization, especially in the case of technologically relevant ferrimagnetic alloys. Here, we have used a combined approach using time- and element-resolved X-ray magnetic circular dichroism and theoretical calculations based on atomistic spin-dynamics simulations to address the ultrafast transfer of the angular momentum from spin-polarized currents into ferrimagnetic Fe74Gd26 films and the concomitant reduction of sub-lattice magnetization. Our study shows that using a Co/Pt multilayer as a polarizer in a spin-valve structure, the SPHE drives the demagnetization of the two sub-lattices of the Fe74Gd26 film. This behaviour is explained based on two physical mechanisms, i.e., spin transfer torque and thermal fluctuations induced by the SPHE. We provide a quantitative description of the heat transfer of the ultrashort SPHE pulse to the Fe74Gd26 films, as well as the degree of spin-polarization of the SPHE current density responsible for the observed magnetization dynamics. Our work finally characterizes the spin-polarization of the SPHEs revealing unexpected opposite spin polarization to the Co magnetization, explaining our experimental results.

Active Nematic Ratchet in Asymmetric Obstacle Arrays
Cody D. Schimming, C. J. O. Reichhardt, C. Reichhardt
arXiv:2403.13733v2 Announce Type: replace Abstract: We numerically investigate the effect of a periodic array of asymmetric obstacles in a two-dimensional active nematic. We find that activity in conjunction with the asymmetry leads to a ratchet effect or unidirectional flow of the fluid along the asymmetry direction. The directional flow is still present even in the active turbulent phase when the gap between obstacles is sufficiently small. We demonstrate that the dynamics of the topological defects transition from flow-mirroring to smectic-like as the gap between obstacles is made smaller, and explain this transition in terms of the pinning of negative winding number defects between obstacles. This also leads to a non-monotonic ratchet effect magnitude as a function of obstacle size, so that there is an optimal obstacle size for ratcheting at fixed activity.

A Noisy Approach to Intrinsically Mixed-State Topological Order
Ramanjit Sohal, Abhinav Prem
arXiv:2403.13879v2 Announce Type: replace Abstract: We propose a general framework for studying two-dimensional (2D) topologically ordered states subject to local correlated errors and show that the resulting mixed-state can display intrinsically mixed-state topological order (imTO) -- topological order which is not expected to occur in the ground state of 2D local gapped Hamiltonians. Specifically, we show that decoherence, previously interpreted as anyon condensation in a doubled Hilbert space, is more naturally phrased as, and provides a physical mechanism for, "gauging out" anyons in the original Hilbert space. We find that gauging out anyons generically results in imTO, with the decohered mixed-state strongly symmetric under certain anomalous 1-form symmetries. This framework lays bare a striking connection between the decohered density matrix and topological subsystem codes, which can appear as anomalous surface states of 3D topological orders. Through a series of examples, we show that the decohered state can display a classical memory, encode logical qubits (i.e., exhibit a quantum memory), and even host chiral or non-modular topological order. We argue that the decohered states represent genuine mixed-state quantum phases of matter and that a partial classification of imTO is given in terms of braided fusion categories.

Topological Data Analysis of Monopoles in $U(1)$ Lattice Gauge Theory
Xavier Crean, Jeffrey Giansiracusa, Biagio Lucini
arXiv:2403.07739v2 Announce Type: replace-cross Abstract: In $4$-dimensional pure compact $U(1)$ lattice gauge theory, we analyse topological aspects of the dynamics of monopoles across the deconfinement phase transition. We do this using tools from Topological Data Analysis (TDA). We demonstrate that observables constructed from the zeroth and first homology groups of monopole current networks may be used to quantitatively and robustly locate the critical inverse coupling $\beta_{c}$ through finite-size scaling. Our method provides a mathematically robust framework for the characterisation of topological invariants related to monopole currents, putting on firmer ground earlier investigations. Moreover, our approach can be generalised to the study of Abelian monopoles in non-Abelian gauge theories.

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NNT-AS1 in CAFs-derived exosomes promotes progression and glucose metabolism through miR-889-3p/HIF-1α in pancreatic adenocarcinoma
Junwei Sun

Scientific Reports, Published online: 24 March 2024; doi:10.1038/s41598-024-57769-6

NNT-AS1 in CAFs-derived exosomes promotes progression and glucose metabolism through miR-889-3p/HIF-1α in pancreatic adenocarcinoma