Found 30 papers in cond-mat
Date of feed: Mon, 31 Jul 2023 00:30:00 GMT

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Chiral Tunneling through Double Barrier Structure in Twisted Graphene Bilayer. (arXiv:2307.15159v1 [cond-mat.mes-hall])
A. Bahlaoui, Y. Zahidi

The paper discusses the chiral tunnelling of charge carriers through double barrier structure in twisted graphene bilayer. The theoretical analysis investigates the transmission probability for various system parameters under both symmetric and asymmetric barrier conditions. The results reveal that the transmission probability of quasiparticles in the $K$ cone is mirror symmetric to that of $K_{\theta}$ cone about $\varphi =0$. Furthermore, the study shows that the transmission changes gradually from perfect transmission to perfect reflection in the normal direction by increasing the incident energy and the barrier height, which is different from the case of monolayer and AB-stacked bilayer graphene. It is also found that the double barrier structure remains, only in certain cases, perfectly transparent for normal or near-normal incidence. The chiral nature of the quasiparticles in graphene causes the tunneling to be highly dependent on the direction and also on the double barrier structure. Interestingly, this characteristic provides additional parameter that allows us to tune the electronic properties of the twisted graphene bilayer. Additionally, we found that the transmission exhibits some sharp resonance peaks, the number and amplitude of which depend on the system parameters. Our results provide a better understanding of the chiral tunnelling in twisted graphene bilayer through double barrier structures and can help in designing efficient electronic devices.

Majorana bound states in d-wave superconductor planar Josephson junction. (arXiv:2307.15162v1 [cond-mat.supr-con])
Hamed Vakili, Moaz Ali, Mohamed Elekhtiar, Alexey A. Kovalev

We study phase-controlled planar Josephson junction comprising a two-dimensional electron gas with strong spin-orbit coupling and d-wave superconductors, which have an advantage of high critical temperature. We show that a region between the two superconductors can be tuned into topological state by the in-plane Zeeman field, and can host Majorana bound states. The phase diagram as a function of the Zeeman field, chemical potential, and the phase difference between superconductors exhibits the appearance of robust Majorana bound states for a wide range of parameters. We further investigate the behavior of the topological gap and its dependence on the type of d-wave pairing, i.e., d, d+is, or d+id', and note the difficulties that can arise due to the presence of gapless excitations in pure d-wave superconductors. On the other hand, the planar Josephson junctions based on superconductors with d+is and d+id' pairings can potentially lead to realizations of Majorana bound states. Our proposal can be realized in twisted bilayer d-wave superconductors realizable in mechanically exfoliated van der Waals copper oxide heterostructures.

Increasing the Rate of Magnesium Intercalation Underneath Epitaxial Graphene on 6H-SiC(0001). (arXiv:2307.15214v1 [cond-mat.mtrl-sci])
Jimmy C. Kotsakidis, Marc Currie, Antonija Grubišić-Čabo, Anton Tadich, Rachael L. Myers-Ward, Matthew DeJarld, Kevin M. Daniels, Chang Liu, Mark T. Edmonds, Amadeo L. Vázquez de Parga, Michael S. Fuhrer, D. Kurt Gaskill

Magnesium intercalated 'quasi-freestanding' bilayer graphene on 6H-SiC(0001) (Mg-QFSBLG) has many favorable properties (e.g., highly n-type doped, relatively stable in ambient conditions). However, intercalation of Mg underneath monolayer graphene is challenging, requiring multiple intercalation steps. Here, we overcome these challenges and subsequently increase the rate of Mg intercalation by laser patterning (ablating) the graphene to form micron-sized discontinuities. We then use low energy electron diffraction to verify Mg-intercalation and conversion to Mg-QFSBLG, and X-ray photoelectron spectroscopy to determine the Mg intercalation rate for patterned and non-patterned samples. By modeling Mg intercalation with the Verhulst equation, we find that the intercalation rate increase for the patterned sample is 4.5$\pm$1.7. Since the edge length of the patterned sample is $\approx$5.2 times that of the non-patterned sample, the model implies that the increased intercalation rate is proportional to the increase in edge length. Moreover, Mg intercalation likely begins at graphene discontinuities in pristine samples (not step edges or flat terraces), where the 2D-like crystal growth of Mg-silicide proceeds. Our laser patterning technique may enable the rapid intercalation of other atomic or molecular species, thereby expanding upon the library of intercalants used to modify the characteristics of graphene, or other 2D materials and heterostructures.

Room-temperature quantum emission from interface excitons in mixed-dimensional heterostructures. (arXiv:2307.15399v1 [cond-mat.mes-hall])
N. Fang, Y. R. Chang, S. Fujii, D. Yamashita, M. Maruyama, Y. Gao, C. F. Fong, D. Kozawa, K. Otsuka, K. Nagashio, S. Okada, Y. K. Kato

The development of van der Waals heterostructures has introduced unconventional phenomena that emerge at atomically precise interfaces. For example, interlayer excitons in two-dimensional transition metal dichalcogenides show intriguing optical properties at low temperatures. Here we report on room-temperature observation of interface excitons in mixed-dimensional heterostructures consisting of two-dimensional tungsten diselenide and one-dimensional carbon nanotubes. Bright emission peaks originating from the interface are identified, spanning a broad energy range within the telecommunication wavelengths. The effect of band alignment is investigated by systematically varying the nanotube bandgap, and we assign the new peaks to interface excitons as they only appear in type-II heterostructures. Room-temperature localization of low-energy interface excitons is indicated by extended lifetimes as well as small excitation saturation powers, and photon correlation measurements confirm single-photon emission. With mixed-dimensional van der Waals heterostructures where band alignment can be engineered, new opportunities for quantum photonics are envisioned.

Magnetic-field periodic quantum Sondheimer oscillations in thin-film graphite. (arXiv:2307.15418v1 [cond-mat.mes-hall])
Toshihiro Taen, Andhika Kiswandhi, Toshihito Osada

Materials with the mesoscopic scales have provided an excellent platform for quantum-mechanical studies. Among them, the periodic oscillations of the electrical resistivity against the direct and the inverse of the magnetic fields, such as the Aharonov-Bohm effect and the Shubnikov-de Haas effect, manifest the interference of the wavefunction relevant to the electron motion perpendicular to the magnetic field. In contrast, the electron motion along the magnetic field also leads to the magnetic-field periodicity, which is the so-called Sondheimer effect. However, the Sondheimer effect has been understood only in the framework of the semiclassical picture, and thereby its interpretation at the quasiquantum limit was not clear. Here, we show that thin-film graphite exhibits clear sinusoidal oscillations with a period of about 1-3 T over a wide range of the magnetic fields (from around 10 T to 30 T), where conventional quantum oscillations are absent. In addition, the sample with a designed step in the middle for eliminating the stacking disorder effect verifies that the period of the oscillations is inversely proportional to the thickness, which supports the emergence of the Sondheimer oscillations in the quasiquantum limit. These findings suggest that the Sondheimer oscillations can be reinterpreted as inter-Landau-level resonances even at the field range where the semiclassical picture fails. Our results expand the quantum oscillation family, and pave the way for the exploration of the out-of-plane wavefunction motion.

Non-Hermitian phase-biased Josephson junctions. (arXiv:2307.15472v1 [cond-mat.supr-con])
Jorge Cayao, Masatoshi Sato

We study non-Hermitian Josephson junctions formed by conventional superconductors with a finite phase difference under non-Hermiticity naturally appearing due to coupling to normal reservoirs. Depending on the structure of non-Hermiticity, captured here in terms of retarded self-energies, the low-energy spectrum hosts topologically stable exceptional points either at zero or finite real energies as a function of the superconducting phase difference. Interestingly, we find that the corresponding phase-biased supercurrents acquire divergent profiles at such exceptional points, an instance that turns out to be a natural and unique non-Hermitian effect that signals a possible way to enhance the sensitivity of Josephson junctions. Our work thus opens the way for realizing unique non-Hermitian phenomena due to the interplay between non-Hermitian topology and the Josephson effect.

Tunable topological phase transition in soft Rayleigh beam system with imperfect interfaces. (arXiv:2307.15509v1 [cond-mat.soft])
Tao Feng, Letian Gan, Shiheng Zhao, Zheng Chang, Siyang Li, Yaoting Xue, Xuxu Yang, Tuck-Whye Wong, Tiefeng Li, Weiqiu Chen

Acoustic metamaterials, particularly the topological insulators, exhibit exceptional wave characteristics that have sparked considerable research interest. The study of imperfect interfaces affect is of significant importance for the modeling of wave propagation behavior in topological insulators. This paper models a soft Rayleigh beam system with imperfect interfaces, and investigates its topological phase transition process tuned by mechanical loadings. The model reveals that the topological phase transition process can be observed by modifying the distance between imperfect interfaces in the system. When a uniaxial stretch is applied, the topological phase transition points for longitudinal waves decrease within a limited frequency range, while they increase within a larger frequency scope for transverse waves. Enhancing the rigidity of the imperfect interfaces also enables shifting of the topological phase transition point within a broader frequency range for longitudinal waves and a confined range for transverse waves. The transition of topologically protected interface modes in the transmission performance of a twenty-cell system is verified, which include altering frequencies, switching from interface mode to edge mode. Overall, this study provides a new approach and guideline for controlling topological phase transition in composite and soft phononic crystal systems.

Raman Spectroscopy of Monolayer to Bulk PtSe2 Exfoliated Crystals. (arXiv:2307.15520v1 [cond-mat.mtrl-sci])
Marin Tharrault, Eva Desgué, Dominique Carisetti, Bernard Plaçais, Christophe Voisin, Pierre Legagneux, Emmanuel Baudin

Raman spectroscopy is widely used to assess the quality of 2D materials thin films. This report focuses on $\rm{PtSe_2}$, a noble transition metal dichalcogenide which has the remarkable property to transit from a semi-conductor to a semi-metal with increasing layer number. While polycrystalline $\rm{PtSe_2}$ can be grown with various cristalline qualities, getting insight into the monocrystalline intrinsic properties remains challenging. We report on the study of exfoliated 1 to 10 layers $\rm{PtSe_2}$ by Raman spectroscopy, featuring record linewidth. The clear Raman signatures allow layer-thickness identification and provides a reference metrics to assess crystal quality of grown films.

Low-Rank Decompositions of Three-Nucleon Forces via Randomized Projections. (arXiv:2307.15572v1 [nucl-th])
A. Tichai, P. Arthuis, K. Hebeler, M. Heinz, J. Hoppe, T. Miyagi, A. Schwenk, L. Zurek

Ab initio calculations for nuclei and nuclear matter are limited by the computational requirements of processing large data objects. In this work, we develop low-rank singular value decompositions for chiral three-nucleon interactions, which dominate these limitations. In order to handle the large dimensions in representing three-body operators, we use randomized decomposition techniques. We study in detail the sensitivity of different three-nucleon topologies to low-rank matrix factorizations. The developed low-rank three-nucleon interactions are benchmarked in Faddeev calculations of the triton and ab initio calculations of medium-mass nuclei. Exploiting low-rank properties of nuclear interactions will be particularly important for the extension of ab initio studies to heavier and deformed systems, where storage requirements will exceed the computational capacities of the most advanced high-performance-computing facilities.

Self-organized states of solutions of active ring polymers in bulk and under confinement. (arXiv:2307.15579v1 [cond-mat.soft])
Juan Pablo Miranda-López, Emanuele Locatelli, Chantal Valeriani

In the presented work we study, by means of numerical simulations, the behaviour of a suspension of active ring polymers in the bulk and under lateral confinement. When changing the separation between the confining planes and the polymers' density, we detect the emergence of a self-organised dynamical state, characterised by the coexistence of slowly diffusing clusters of rotating disks and faster rings moving in between them. This system represents a peculiar case at the crossing point between polymer, liquid crystals and active matter physics, where the interplay between activity, topology and confinement leads to a spontaneous segregation of a one component solution.

Nonlinear optical diode effect in a magnetic Weyl semimetal. (arXiv:2307.15603v1 [cond-mat.mes-hall])
Christian Tzschaschel, Jian-Xiang Qiu, Xue-Jian Gao, Hou-Chen Li, Chunyu Guo, Hung-Yu Yang, Cheng-Ping Zhang, Ying-Ming Xie, Yu-Fei Liu, Anyuan Gao, Damien Bérubé, Thao Dinh, Sheng-Chin Ho, Yuqiang Fang, Fuqiang Huang, Johanna Nordlander, Qiong Ma, Fazel Tafti, Philip J.W. Moll, Kam Tuen Law, Su-Yang Xu

Weyl semimetals have emerged as a promising quantum material system to discover novel electrical and optical phenomena, due to their combination of nontrivial quantum geometry and strong symmetry breaking. One crucial class of such novel transport phenomena is the diode effect, which is of great interest for both fundamental physics and modern technologies. In the electrical regime, giant electrical diode effect (the nonreciprocal transport) has been observed in Weyl systems. In the optical regime, novel optical diode effects have been theoretically considered but never probed experimentally. Here, we report the observation of the nonlinear optical diode effect (NODE) in the magnetic Weyl semimetal CeAlSi, where the magnetic state of CeAlSi introduces a pronounced directionality in the nonlinear optical second-harmonic generation (SHG). By physically reversing the beam path, we show that the measured SHG intensity can change by at least a factor of six between forward and backward propagation over a wide bandwidth exceeding 250 meV. Supported by density-functional theory calculations, we establish the linearly dispersive bands emerging from Weyl nodes as the origin of the extreme bandwidth. Intriguingly, the NODE directionality is directly controlled by the direction of magnetization. By utilizing the electronically conductive semimetallic nature of CeAlSi, we demonstrate current-induced magnetization switching and thus electrical control of the NODE in a mesoscopic spintronic device structure with current densities as small as 5 kA/cm$^2$. Our results advance ongoing research to identify novel nonlinear optical/transport phenomena in magnetic topological materials. The NODE also provides a way to measure the phase of nonlinear optical susceptibilities and further opens new pathways for the unidirectional manipulation of light such as electrically controlled optical isolators.

A quantitative phase-field model for void evolution in defect supersaturated environments: a novel introduction of defect reaction asymmetry. (arXiv:2307.15626v1 [cond-mat.mtrl-sci])
Sreekar Rayaprolu, Kyle Starkey, Anter El-Azab

Voids develop in crystalline materials under energetic particle irradiation, as in nuclear reactors. Understanding the underlying mechanisms of void nucleation and growth is of utmost importance as it leads to dimensional instability of the metallic materials. In the past two decades, researchers have adopted the phase-field approach to study the phenomena of void evolution under irradiation. The approach involves modeling the boundary between the void and matrix with a diffused interface. However, none of the existing models are quantitative in nature. This work introduces a thermodynamically consistent, quantitative diffuse interface model based on KKS formalism to describe the void evolution under irradiation. The model concurrently considers both vacancies and self-interstitials in the description of void evolution. Unique to our model is the presence of two mobility parameters in the equation of motion of the phase-field variable. The two mobility parameters relate the driving force for vacancy and self-interstitial interaction to the interface motion, analogous to dislocation motion through climb and glide processes. The asymptotic matching of the phase-field model with the sharp-interface theory fixes the two mobility parameters in terms of the material parameters in the sharp-interface model. The Landau coefficient, which controls the height of the double-well function in the phase field variable, and the gradient coefficient of the phase field variable are fixed based on the interfacial energy and interface width of the boundary. With all the parameters in the model determined in terms of the material parameters, we thus have a new phase field model for void evolution. Simple test cases will show the void evolution under various defect supersaturation to validate our new phase-field model.

Pressure-induced Superconductivity in Zintl Topological Insulator SrIn2As2. (arXiv:2307.15629v1 [cond-mat.supr-con])
Weizheng Cao, Haifeng Yang, Yongkai Li, Cuiying Pei, Qi Wang, Yi Zhao, Changhua Li, Mingxin Zhang, Shihao Zhu, Juefei Wu, Lili Zhang, Zhiwei Wang, Yugui Yao, Zhongkai Liu, Yulin Chen, Yanpeng Qi

The Zintl compound AIn2X2 (A = Ca, Sr, and X = P, As), as a theoretically predicted new non-magnetic topological insulator, requires experiments to understand their electronic structure and topological characteristics. In this paper, we systematically investigate the crystal structures and electronic properties of the Zintl compound SrIn2As2 under both ambient and high-pressure conditions. Based on systematic angle-resolved photoemission spectroscopy (ARPES) measurements, we observed the topological surface states on its (001) surface as predicted by calculations, indicating that SrIn2As2 is a strong topological insulator. Interestingly, application of pressure effectively tuned the crystal structure and electronic properties of SrIn2As2. Superconductivity is observed in SrIn2As2 for pressure where the temperature dependence of the resistivity changes from a semiconducting-like behavior to that of a metal. The observation of nontrivial topological states and pressure-induced superconductivity in SrIn2As2 provides crucial insights into the relationship between topology and superconductivity, as well as stimulates further studies of superconductivity in topological materials.

Long-Range Hydrophobic Attraction Between Graphene and Water/Oil Interfaces. (arXiv:2307.15658v1 [cond-mat.soft])
Avishi Abeywickrama, Douglas H. Adamson, Hannes C. Schniepp

Long-range hydrophobic attractions between mesoscopic surfaces in water play an important role in many colloid and interface phenomena. Despite being studied by several approaches, the origin of these forces has yet to be adequately explained. While previous research has focused on solid/water/solid and solid/water/air scenarios, we investigated a solid/water/liquid situation to gain additional insight. We directly measured the long-range interactions between a solid and a hydrophobic liquid separated by water using force spectroscopy, where colloidal probes were coated with graphene oxide (GO) to interact with immobilized heptane droplets in water. We detected attractions with a range of ~0.5 {\mu}m that cannot be explained by standard Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. When the GO was reduced to rGO to become more hydrophobic, these forces increased in strength and ranged up to 1.2 {\mu}m. This suggests that the observed attractions result from long-range hydrophobic forces. Based on our results, we propose air bubbles attached to the colloidal probe and molecular rearrangement at the water/oil interface as possible origins of the observed interactions. This knowledge will be useful to understand and motivate the formation of emulsions using 2D materials and other amphiphilic/hydrophobic particles.

Phase diagram of one-dimensional driven-dissipative exciton-polariton condensates. (arXiv:2307.15664v1 [cond-mat.stat-mech])
Francesco Vercesi, Quentin Fontaine, Sylvain Ravets, Jacqueline Bloch, Maxime Richard, Léonie Canet, Anna Minguzzi

We consider a one-dimensional driven-dissipative exciton-polariton condensate under incoherent pump, described by the stochastic generalized Gross-Pitaevskii equation. It was shown that the condensate phase dynamics maps under some assumptions to the Kardar-Parisi-Zhang (KPZ) equation, and the temporal coherence of the condensate follows a stretched exponential decay characterized by KPZ universal exponents. In this work, we determine the main mechanisms which lead to the departure from the KPZ phase, and identify three possible other regimes: (i) a soliton-patterned regime at large interactions and weak noise, populated by localized structures analogue to dark solitons; (ii) a vortex-disordered regime at high noise and weak interactions, dominated by point-like phase defects in space-time; (iii) a defect-free reservoir-textured regime where the adiabatic approximation breaks down. We characterize each regime by the space-time maps, the first-order correlations, the momentum distribution and the density of topological defects. We thus obtain the phase diagram at varying noise, pump intensity and interaction strength. Our predictions are amenable to observation in state-of-art experiments with exciton-polaritons.

Thomson problem in the disk. (arXiv:2307.15683v1 [cond-mat.soft])
Paolo Amore, Ulises Zarate

We investigate the classical ground state of a large number of charges confined inside a disk and interacting via the Coulomb potential. By realizing the important role that the peripheral charges play in determining the lowest energy solutions, we have successfully implemented an algorithm that allows us to work with configurations with a desired number of border charges. This feature brings a consistent reduction in the computational complexity of the problem, thus simplifying the search of global minima of the energy. Additionally, we have implemented a divide and conquer approach which has allowed us to study configurations of size never reached before (the largest one corresponding to $N=40886$ charges). These last configurations, in particular, are seen to display an increasingly rich structure of topological defects as $N$ gets larger.

Engineering entanglement geometry via spacetime-modulated measurements. (arXiv:2307.15689v1 [quant-ph])
Aditya Cowsik, Matteo Ippoliti, Xiao-Liang Qi

We introduce a general approach to realize quantum states with holographic entanglement structure via monitored dynamics. Starting from random unitary circuits in $1+1$ dimensions, we introduce measurements with a spatiotemporally-modulated density. Exploiting the known critical properties of the measurement-induced entanglement transition, this allows us to engineer arbitrary geometries for the bulk space (with a fixed topology). These geometries in turn control the entanglement structure of the boundary (output) state. We demonstrate our approach by giving concrete protocols for two geometries of interest in two dimensions: the hyperbolic half-plane and a spatial section of the BTZ black hole. We numerically verify signatures of the underlying entanglement geometry, including a direct imaging of entanglement wedges by using locally-entangled reference qubits. Our results provide a concrete platform for realizing geometric entanglement structures on near-term quantum simulators.

Prevalence of two-dimensional photonic topology. (arXiv:2307.15701v1 [cond-mat.mes-hall])
Ali Ghorashi, Sachin Vaidya, Mikael Rechtsman, Wladimir Benalcazar, Marin Soljačić, Thomas Christensen

The topological characteristics of photonic crystals have been the subject of intense research in recent years. Despite this, the basic question of whether photonic band topology is rare or abundant -- i.e., its relative prevalence -- remains unaddressed. Here, we determine the prevalence of stable, fragile, and higher-order photonic topology in the 11 two-dimensional crystallographic symmetry settings that admit diagnosis of one or more of these phenomena by symmetry analysis. Our determination is performed on the basis of a data set of 550000 randomly sampled, two-tone photonic crystals, spanning 11 symmetry settings and 5 dielectric contrasts, and examined in both transverse electric (TE) and magnetic (TM) polarizations. We report the abundance of nontrivial photonic topology in the presence of time-reversal symmetry and find that stable, fragile, and higher-order topology are generally abundant. Below the first band gap, which is of primary experimental interest, we find that stable topology is more prevalent in the TE polarization than the TM; is only weakly, but monotonically, dependent on dielectric contrast; and that fragile topology is near-absent. In the absence of time-reversal symmetry, nontrivial Chern phases are also abundant in photonic crystals with 2-, 4-, and 6-fold rotational symmetries but comparatively rare in settings with only 3-fold symmetry. Our results elucidate the interplay of symmetry, dielectric contrast, electromagnetic polarization, and time-reversal breaking in engendering topological photonic phases and may inform general design principles for their experimental realization.

Density-polarity coupling in confined active polar films: asters, spirals, and biphasic orientational phases. (arXiv:2307.15707v1 [cond-mat.soft])
Mathieu Dedenon, Claire A. Dessalles, Pau Guillamat, Aurélien Roux, Karsten Kruse, Carles Blanch-Mercader

Topological defects in active polar fluids can organise spontaneous flows and influence macroscopic density patterns. Both of them play, for example, an important role during animal development. Yet the influence of density on active flows is poorly understood. Motivated by experiments on cell monolayers confined to discs, we study the coupling between density and polar order for a compressible active polar fluid in presence of a +1 topological defect. As in the experiments, we find a density-controlled spiral-to-aster transition. In addition, biphasic orientational phases emerge as a generic outcome of such coupling. Our results highlight the importance of density gradients as a potential mechanism for controlling flow and orientational patterns in biological systems.

Fraunhofer pattern in the presence of Majorana zero modes. (arXiv:2210.02065v2 [cond-mat.mes-hall] UPDATED)
F. Dominguez, E. G. Novik, P. Recher

Majorana bound states (MBSs) emerge as zero energy excitations in topological superconductors. At zero temperature, their presence gives a quantized conductance in NS junctions and a fractional Josephson effect in Josephson junctions when the parity is conserved. However, most of current experiments deviate from the theoretical predictions, yielding for example a non-quantized conductance or the absence of only few odd Shapiro steps. Although these results might be compatible with a topological ground state, it is also possible that a trivial scenario can mimic similar results, by means of accidental zero energy Andreev bound states (ZEABS) or simply by non-adiabatic transitions between trivial Andreev bound states. Here, we propose a new platform to investigate signatures of the presence of MBSs in the Fraunhofer pattern of Josephson junctions featuring quantum spin Hall edge states on the normal part and Majorana bound states at the NS interfaces. We use a tight-binding model to demonstrate a change in periodicity of the Fraunhofer pattern when comparing trivial and non-trivial regimes. We explain these results in terms of local and crossed Andreev bound states, which due to the spin-momentum locking, accumulate different magnetic flux and therefore become distinguishable in the Fraunhofer periodicity. Furthermore, we introduce a scattering model that captures the main results of the microscopic calculations with MBSs and extend our discussion to the main differences found using accidental ZEABS.

Electronic nematicity without charge density waves in titanium-based kagome metal. (arXiv:2211.16477v2 [cond-mat.str-el] UPDATED)
Hong Li, Siyu Cheng, Brenden R. Ortiz, Hengxin Tan, Dominik Werhahn, Keyu Zeng, Dirk Johrendt, Binghai Yan, Ziqiang Wang, Stephen D. Wilson, Ilija Zeljkovic

Layered crystalline materials that consist of transition metal atoms on a kagome network have emerged as a versatile platform to study unusual electronic phenomena. For example, in the vanadium-based kagome superconductors AV3Sb5 (where A can stand for K, Cs, or Rb) there is a parent charge density wave phase that appears to simultaneously break both the translational and the rotational symmetry of the lattice. Here, we show a contrasting situation where electronic nematic order - the breaking of rotational symmetry without the breaking of translational symmetry - can occur without a corresponding charge density wave. We use spectroscopic-imaging scanning tunneling microscopy to study the kagome metal CsTi3Bi5 that is isostructural to AV3Sb5 but with a titanium atom kagome network. CsTi3Bi5 does not exhibit any detectable charge density wave state, but comparison to density functional theory calculations reveals substantial electronic correlation effects at low energies. Comparing the amplitudes of scattering wave vectors along different directions, we discover an electronic anisotropy that breaks the six-fold symmetry of the lattice, arising from both in-plane and out-of-plane titanium-derived d orbitals. Our work uncovers the role of electronic orbitals in CsTi3Bi5, suggestive of a hexagonal analogue of the nematic bond order in Fe-based superconductors.

Absence of mixed valency for Pr in pristine and hole-doped PrNiO$_2$. (arXiv:2302.08460v2 [cond-mat.str-el] UPDATED)
Xingyu Liao, Michael R. Norman, Hyowon Park

Infinite-layer nickelates ($R$NiO$_2$) exhibit some distinct differences as compared to cuprate superconductors, leading to a debate concerning the role of rare-earth ions ($R$=La, Pr, Nd) in the low-energy many-body physics. Although rare-earth $4f$ orbitals are typically treated as inert `core' electrons in studies, this approximation has been questioned. An active participation of $4f$ states is most likely for PrNiO$_2$ based on an analogy to cuprates where Pr cuprates differ significantly from other cuprates. Here, we adopt density functional plus dynamical mean field theory (DFT+DMFT) to investigate the role of Pr $4f$ orbitals and more generally the correlated electronic structure of PrNiO$_2$ and its hole-doped variant. We find that the Pr $4f$ states are insulating and show no evidence for either a Kondo resonance or Zhang-Rice singlet formation as they do not have any hybridization channels near the Fermi energy. The biggest effects of hole doping are to shift the Pr $5d$ and $4f$ states further away from the Fermi energy while enhancing the Ni $3d$ - O $2p$ hybridization, thus reducing correlation effects as the O $2p$ states get closer to the Fermi energy. We again find no evidence for either Kondo or Zhang-Rice physics for the $4f$ states upon hole doping. We conclude by commenting on implications for other reduced valence nickelates.

General scatterings and electronic states in the quantum-wire network of moir\'e systems. (arXiv:2303.00759v4 [cond-mat.mes-hall] UPDATED)
Chen-Hsuan Hsu, Daniel Loss, Jelena Klinovaja

We investigate electronic states in a two-dimensional network consisting of interacting quantum wires, a model adopted for twisted bilayer systems. We construct general operators which describe various scattering processes in the system. In a twisted bilayer structure, the moir\'e periodicity allows for generalized umklapp scatterings, leading to a class of correlated states at certain fractional fillings. We identify scattering processes which can lead to an insulating gapped bulk with gapless chiral edge modes at fractional fillings, resembling the quantum anomalous Hall effect recently observed in twisted bilayer graphene. Finally, we demonstrate that the description can be useful in predicting spectroscopic and transport features to detect and characterize the chiral edge modes in the moir\'e-induced correlated states.

Aperiodic dynamical quantum phase transitions in multi-band Bloch Hamiltonian and its origin. (arXiv:2303.15966v4 [cond-mat.stat-mech] UPDATED)
Kaiyuan Cao, Hao Guo, Guangwen Yang

We investigate the dynamical quantum phase transition (DQPT) in the multi-band Bloch Hamiltonian of the one-dimensional periodic Kitaev model, focusing on quenches from a Bloch band. By analyzing the dynamical free energy and Pancharatnam geometric phase, we show that the critical times of DQPTs deviate from periodic spacing due to the multi-band effect, contrasting with results from two-band models. We propose a geometric interpretation to explain this non-uniform spacing. Additionally, we clarify the conditions needed for DQPT occurrence in the multi-band Bloch Hamiltonian, highlighting that a DQPT only arises when the quench from the Bloch states collapses the band gap at the critical point. Moreover, we establish that the dynamical topological order parameter, defined by the winding number of the Pancharatnam geometric phase, is not quantized but still exhibits discontinuous jumps at DQPT critical times due to periodic modulation. Additionally, we extend our analysis to mixed-state DQPT and find its absence at non-zero temperatures.

Band nonlinearity-enabled manipulation of Dirac nodes, Weyl cones, and valleytronics with intense linearly polarized light. (arXiv:2304.05186v2 [cond-mat.mtrl-sci] UPDATED)
Ofer Neufeld, Hannes Hübener, Gregor Jotzu, Umberto De Giovannini, Angel Rubio

We study low-frequency linearly-polarized laser-dressing in materials with valley (graphene and hexagonal-Boron-Nitride), and topological (Dirac- and Weyl-semimetals), properties. In Dirac-like linearly-dispersing bands, the laser substantially moves the Dirac nodes away from their original position, and the movement direction can be fully controlled by rotating the laser polarization. We prove that this effect originates from band nonlinearities away from the Dirac nodes. We further demonstrate that this physical mechanism is widely applicable, and can move the positions of the valley minima in hexagonal materials to tune valley selectivity, split and move Weyl cones in higher-order Weyl semimetals, and merge Dirac nodes in three-dimensional Dirac semimetals. The model results are validated with ab-initio calculations. Our results directly affect efforts for exploring light-dressed electronic-structure, suggesting that one can benefit from band nonlinearity for tailoring material properties, and highlight the importance of the full band structure in nonlinear optical phenomena in solids.

New insight into tuning magnetic phases of RMn6Sn6 kagome metals. (arXiv:2306.13206v2 [cond-mat.str-el] UPDATED)
Simon X. M. Riberolles, Tianxiong Han, Tyler J. Slade, J. M. Wilde, A. Sapkota, Wei Tian, Qiang Zhang, D. L. Abernathy, L. D. Sanjeewa, S. L. Bud'ko, P. C. Canfield, R. J. McQueeney, B. G. Ueland

Kagome metals with magnetic order offer the possibility of tuning topological electronic states via external control parameters such as temperature or magnetic field. ErMn$_6$Sn$_6$ (Er$166$) is a member of a group of $R166$, $R=$~rare earth, compounds hosting ferromagnetic Mn kagome nets whose magnetic moment direction and layer-to-layer magnetic correlations are strongly influenced by coupling to $R$ magnetic moments in neighboring triangular layers. Here, we use neutron diffraction and magnetization data to examine the temperature-driven transition in Er$166$ from a planar-ferrimagnetic to distorted-triple-spiral magnetic order. These data inform mean-field calculations which highlight the fragile, tunable nature of the magnetism caused by competing Mn-Mn and Mn-Er interlayer magnetic exchange couplings and Mn and Er magnetic anisotropies. This competition results in the near degeneracy of a variety of collinear, non-collinear, and non-coplanar magnetic phases which we show are readily selected and adjusted via changing temperature or magnetic field. Thermal fluctuations of the Er moment direction provide the key to this tunability.

Prethermalization and conservation laws in quasi-periodically-driven quantum systems. (arXiv:2306.14022v2 [math-ph] UPDATED)
Matteo Gallone, Beatrice Langella

We study conservation laws of a general class of quantum many-body systems subjected to an external time dependent quasi-periodic driving. We show that, when the frequency of the driving is large enough or the strength of the driving is small enough, the system exhibits a prethermal state for stretched exponentially long times in the perturbative parameter. Moreover, we prove the quasi-conservation of the constants of motion of the unperturbed Hamiltonian and we analyze their physical meaning in examples of relevance to condensed matter and statistical physics.

2D Fractons from Gauging Exponential Symmetries. (arXiv:2306.17121v2 [cond-mat.str-el] UPDATED)
Guilherme Delfino, Claudio Chamon, Yizhi You

The scope of quantum field theory is extended by introducing a broader class of discrete gauge theories with fracton behavior in 2+1D. We consider translation invariant systems that carry special charge conservation laws, which we refer to as exponential polynomial symmetries. Upon gauging these symmetries, the resulting $\mathbb{Z}_N$ gauge theories exhibit fractonic physics, including constrained mobility of quasiparticles and UV dependence of the ground state degeneracy. For appropriate values of theory parameters, we find a family of models whose excitations, albeit being deconfined, can only move in the form of bound states rather than isolated monopoles. For concreteness, we study in detail the low-energy physics and topological sectors of a particular model through a universal protocol, developed for determining the holonomies of a given theory. We find that a single excitation, isolated in a region of characteristic size $R$, can only move from its original position through the action of operators with support on $\mathcal{O}(R)$ sites. Furthermore, we propose a Chern-Simons variant of these gauge theories, yielding non-CSS type stabilizer codes, and propose the exploration of exponentially symmetric subsystem SPTs and fracton codes in 3+1D.

Theory of anomalous Hall effect in transition-metal pentatelluride $\mathrm{ZrTe}_{5}$ and $\mathrm{HfTe}_{5}$. (arXiv:2307.09708v2 [cond-mat.mes-hall] UPDATED)
Huan-Wen Wang, Bo Fu, Shun-Qing Shen

The anomalous Hall effect has considerable impact on the progress of condensed matter physics and occurs in systems with time-reversal symmetry breaking. Here we theoretically investigate the anomalous Hall effect in nonmagnetic transition-metal pentatelluride $\mathrm{ZrTe_{5}}$ and $\mathrm{HfTe}_{5}$. In the presence of Zeeman splitting and Dirac mass, there is an intrinsic anomalous Hall conductivity induced by the Berry curvature in the semiclassical treatment. In a finite magnetic field, the anomalous Hall conductivity rapidly decays to zero for constant spin-splitting and vanishes for the magnetic-field-dependent Zeeman energy. A semiclassical formula is derived to depict the magnetic field dependence of the Hall conductivity, which is beneficial for experimental data analysis. Lastly, when the chemical potential is fixed in the magnetic field, a Hall conductivity plateau arises, which may account for the observed anomalous Hall effect in experiments.

Physical properties of the Hat aperiodic monotile: Graphene-like features, chirality and zero-modes. (arXiv:2307.11054v2 [cond-mat.mes-hall] UPDATED)
Justin Schirmann, Selma Franca, Felix Flicker, Adolfo G. Grushin

The discovery of the Hat, an aperiodic monotile, has revealed novel mathematical aspects of aperiodic tilings. However, the physics of particles propagating in such a setting remains unexplored. In this work we study spectral and transport properties of a tight-binding model defined on the Hat. We find that (i) the spectral function displays striking similarities to that of graphene, including six-fold symmetry and Dirac-like features; (ii) unlike graphene, the monotile spectral function is chiral, differing for its two enantiomers; (iii) the spectrum has a macroscopic number of degenerate states at zero energy; (iv) when the magnetic flux per plaquette ($\phi$) is half of the flux quantum, zero-modes are found localized around the reflected `anti-hats'; and (v) its Hofstadter spectrum is periodic in $\phi$, unlike for other quasicrystals. Our work serves as a basis to study wave and electron propagation in possible experimental realizations of the Hat, which we suggest.