We consider sample to sample fluctuations of the waiting time between the detection of two consecutive electrons in quasi-one-dimensional disordered conductors at zero temperature. We compute the full distribution of the mean waiting time along the crossover from ballistic to localized transport in the framework of the Dorokhov-Mello-Pereyra-Kumar theory for an arbitrary number of conduction channels. In particular, we show that its variance, with respect to disorder, displays universal fluctuations similar to the universal conductance fluctuations in the metallic regime. We further discuss the statistical properties of the jitter associated to quantum fluctuations of the waiting time and compare it to predictions given by full counting statistics.

We report transport studies on the layered van der Waals topological crystalline insulator ${\mathrm{Ta}}_2{\mathrm{Pd}}_3{\mathrm{Te}}_5$. The temperature-dependent resistance at high temperature is dominated by a bulk insulating gap and tends to saturate at low temperatures. Low-temperature magnetotransport shows that ${\mathrm{Ta}}_2{\mathrm{Pd}}_3{\mathrm{Te}}_5$ exhibits weak antilocatization (WAL) effect in both perpendicular orientation and parallel orientation, suggesting a contribution of the WAL effect from both topological edge states and bulk states. By measuring the anisotropic magnetoconductance and then subtracting the contribution of bulk states, the WAL effect associated with topological edge states can be revealed and analyzed quantitatively based on the two-dimensional Hikami-Larkin-Nagaoka model. Our results have important implications in understanding the WAL phenomena in ${\mathrm{Ta}}_2{\mathrm{Pd}}_3{\mathrm{Te}}_5$.

The spin-orbit coupled electronic structure of two representative nonpolar half-Heusler alloys, namely 18-electron compound CoZrBi and 8-electron compound SiLiIn, has been studied in detail. An excursion through the Brillouin zone of these alloys from one high-symmetry point to the other revealed rich local symmetry of the associated wave vectors resulting in nontrivial spin splitting of the bands and consequent diverse spin textures in the presence of spin-orbit coupling. Our first-principles calculations supplemented with the low-energy $\mathit{k}·\mathit{p}$ model Hamiltonian revealed the presence of the linear Dresselhaus effect at the $X$ point having $D_{2d}$ symmetry, and the Rashba effect with both linear and nonlinear terms at the $L$ point with $C_{3v}$ point group symmetry. Interestingly we have also identified nontrivial Zeeman spin splitting at the non-time-reversal invariant $W$ point and a pair of nondegenerate bands along the path $\mathrm{\Gamma }$ to $L$ displaying vanishing spin polarization due to the non-pseudo-polar point group symmetry of the wave vectors. Further, a comparative study of CoZrBi and SiLiIn suggests, in addition to the local symmetry of the wave vectors, the important role of the participating orbitals in deciding the magnitude of the spin splitting of the bands. Our calculations suggest that half-Heusler compounds with heavy elements displaying diverse spin textures may be ideal candidates for spin valleytronics, where spin textures can be controlled by accessing different valleys around the high-symmetry $k$-points.

We assess the accuracy of ghost-rotationally-invariant slave-boson (g-RISB) theory in multiorbital systems by applying it to both the three-orbital degenerate Hubbard model and a realistic ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ model extracted from first-principle simulations and comparing the results to those obtained using dynamical mean-field theory (DMFT). Our findings indicate that g-RISB's accuracy can be systematically improved toward the exact DMFT limit in infinite-dimensional multiorbital models by increasing the number of ghost orbitals. This allows for a more precise description of aspects of Hund metal physics and Mott physics compared with the original RISB approach. We also demonstrate that g-RISB reliably captures the quasiparticle weights, Fermi surface, and low-energy spectral function for the realistic ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ model compared with DMFT. Moreover, we showcase the potential of using the density matrix renormalization group method as an impurity solver within the g-RISB framework to study systems with a larger number of ghost orbitals. These results show the potential of g-RISB as a reliable tool for simulating correlated materials. The connection between the g-RISB and DMFT self-energy is also discussed.

We investigate the electronic properties of a hybrid system that comprises single-bilayer graphene structures subjected to a perpendicular magnetic field. Specifically, our focus is on the behavior exhibited by the zigzag boundaries of the junction, namely, zigzag-1 (ZZ1) and zigzag-2 (ZZ2), using the continuum Dirac model for rigorous analysis. Our findings reveal a striking dependence of conductance on the width of the bilayer graphene at ZZ1, providing essential insights into the transport behavior of this boundary. Moreover, we observe a captivating phenomenon where the conductance at ZZ2 exhibits prominent maxima, demonstrating a robust correlation with the applied magnetic field. Additionally, our investigation uncovers the profound impact of interfaces on transmission probability, with ZZ1 being notably more affected compared to ZZ2. The variation of the Fermi energy further highlights the significant influence of magnetic field strength on the system's conductive properties, resulting in distinct conductance characteristics between the two regions. The combined results of ZZ1 and ZZ2 provide valuable insights into the system's transport properties. Notably, a clear exponential-like trend in conductance variation with the applied magnetic field underscores the system's strong sensitivity to magnetic changes.

Valley coupling is proposed to construct a spatially separated two-parameter pump based on the O- or Y-shaped Kekulé (Kek) graphene superlattices (GSs) with a sandwiched graphene layer. It is shown that for the O-shaped Kek GS pumping structure, pumped charges with an integer number can be obtained in a pumping cycle at the Fermi energy residing in the effective energy gap. Particularly, this quantization only from the contribution of intervalley reflection is thoroughly different from the one in previous two-parameter pumps only with the intravalley reflection. This stems from the Hamiltonian of an antiunitary symmetry, leading to a phase analogous to a topological superconductor and thus a perfect pseudo-Andreev reflection in the valley version. The quantization also can be attributed to the topological interfacial state (TIS) arising in between the two pumping sources due to different quantum valley Hall insulator (QVHI) phases. However, for the Y-shaped Kek GS one, the current coming from both the intravalley and intervalley reflections is nonquantized. This is due to the time-dependent coupling term between two valleys only emerging in the $A$ sublattice, which induces no QVHI and no resultant TISs. Our findings may not only pave a new road to design the quantized charge pump device based on the GS, but also provide a sharp experimental signature to detect the O-shaped one and distinguish between the two GSs.

We study a quasistatically driven random-field Ising model (RFIM) at zero temperature with interactions mediated by the long-range anisotropic Eshelby kernel. Analogously to amorphous solids at their yielding transition, and differently from ferromagnetic and dipolar RFIMs, the model shows a discontinuous magnetization jump associated with the appearance of a band-like structure for weak disorder and a continuous magnetization growth, yet punctuated by avalanches, for strong disorder. Through a finite-size scaling analysis in two and three dimensions we find that the two regimes are separated by a finite-disorder critical point, which we characterize. We discuss similarities and differences between the present model and models of sheared amorphous solids.

Quantum antiferromagnets on geometrically frustrated lattices have long attracted interest for the formation of quantum disordered states and the possible emergence of quantum spin liquid (QSL) ground states. Here we turn to the nearest-neighbor spin-$1/2$ Heisenberg antiferromagnet on the maple-leaf lattice, which is known to relieve frustration by the formation of canted ${120}^{\circ }$ magnetic order or valence bond crystal order when varying the bond anisotropy. Employing a pseudofermion functional renormalization group approach to assess its ground state phase diagram in detail, we present evidence for a QSL regime sandwiched between these two limiting phases. The formation of such a QSL might signal proximity to a possible deconfined quantum critical point from which it emerges, and that is potentially accessible by tuning the exchange couplings. Our conclusions are based on large-scale simulations involving a careful finite-size scaling analysis of the behavior of magnetic susceptibility and spin-spin correlation functions under renormalization group flow.

The square-kagome lattice Heisenberg antiferromagnet is a highly frustrated Hamiltonian whose material realizations have been scarce. We theoretically investigate the recently synthesized ${\mathrm{Na}}_6{\mathrm{Cu}}_7{\mathrm{BiO}}_4{\left(\mathrm{PO}\right)}_4{)}_4{\mathrm{Cl}}_3$ where a ${\mathrm{Cu}}^{2+}$ spin-$1/2$ square-kagome lattice (with a six site unit cell) is decorated by a seventh magnetic site alternatingly above and below the layers. The material does not show any sign of long-range magnetic order down to 50 mK despite a Curie-Weiss temperature of $-212\mathrm{K}$ indicating a quantum paramagnetic phase. Our DFT energy mapping elicits a purely antiferromagnetic Hamiltonian that features longer range exchange interactions beyond the pure square-kagome model and, importantly, we find the seventh site to be strongly coupled to the plane. We combine two variational Monte Carlo approaches, pseudofermion/Majorana functional renormalization group and Schwinger-Boson mean field calculations to show that the complex Hamiltonian of ${\mathrm{Na}}_6{\mathrm{Cu}}_7{\mathrm{BiO}}_4{\left(\mathrm{PO}\right)}_4{)}_4{\mathrm{Cl}}_3$ still features a nonmagnetic ground state. We explain how the seventh ${\mathrm{Cu}}^{2+}$ site actually aids the stabilization of the disordered state. We predict static and dynamic spin structure factors to guide future neutron scattering experiments.

This study conducts experimental exploration into a system of two-dimensional Dirac fermions utilizing a critical-thickness HgTe quantum well in weak magnetic fields. The formation and evolution of Shubnikov–de Haas oscillations in the magnetotransport and the capacitive response are studied, complemented by calculations of Landau levels (LLs). It is shown that the behavior of the LLs is influenced not only by the linear dispersion law of the carriers and the Zeeman splitting, but also by the splitting of the Dirac cones in zero magnetic field caused by interface inversion asymmetry. The measured value of the splitting is 1.5 meV. The behavior of the zero LL is studied and its spin splitting is demonstrated. It is shown that the broadening of the zero LL is several times higher than that of the other levels due to the lack of charge impurity screening.

We study theoretically and experimentally how to reduce the backscattering of water waves in a channel with multiple turns. We show that it is possible not only to cancel backscattering but also to achieve a remarkable transmission in such geometries. In order to avoid the reflection that naturally arises at each turn of the waveguide, an anisotropic metamaterial made of closely spaced thin vertical plates is used. The efficiency of the metamaterial arrangement depends only slightly on the frequency of the incident wave, as long as its wavelength is much larger than the periodicity of the array. This phenomenon is applies not only to water wave channels but also to any type of waves with Neumann boundary conditions.

We propose a method to determine the magnetic exchange interaction and onsite anisotropy tensors of extended Heisenberg spin models from density functional theory including relativistic effects. The method is based on the Liechtenstein-Katsnelson-Antropov-Gubanov torque formalism, whereby energy variations upon infinitesimal rotations are performed. We assume that the Kohn-Sham Hamiltonian is expanded in a nonorthogonal basis set of pseudoatomic orbitals. We define local operators that are both Hermitian and satisfy relevant sum rules. We demonstrate that in the presence of spin-orbit coupling a correct mapping from the density functional total energy to a spin model that relies on the rotation of the exchange field part of the Hamiltonian can not be accounted for by transforming the full Hamiltonian. We derive a set of sum rules that pose stringent validity tests on any specific calculation. We showcase the flexibility and accuracy of the method by computing the exchange and anisotropy tensors of both well-studied magnetic nanostructures and of recently synthesized two-dimensional magnets. Specifically, we benchmark our approach against the established Korringa-Kohn-Rostoker Green's function method and show that they agree well. Finally, we demonstrate how the application of biaxial strain on the two-dimensional magnet $\mathrm{T}\text{−}{\mathrm{CrTe}}_2$ can trigger a magnetic phase transition.

Spin systems with honeycomb structures have recently attracted a great deal of attention in connection with the Kitaev quantum spin liquid state (QSL) predicted theoretically. One possible Kitaev QSL candidate is ${\mathrm{Na}}_2{\mathrm{Co}}_2\mathrm{Te}{\mathrm{O}}_6$ realizing a honeycomb lattice of pseudospin 1/2. Field-dependent single-crystal neutron diffraction technique allows us to determine the microscopic spin-spin correlations across the field-induced phase transitions for $H\parallel a$ and $H\parallel a^{*}$ in plane field directions. Our results reveal phase transitions, initially to a canted zigzag antiferromagnetic state at approximately 60 kOe, followed by a possible transition to a partially polarized state over the range 90–120 kOe, and finally to a field-induced fully polarized state above 120 kOe. We observe distinct field dependencies of the magnetic peak intensities for $H\parallel a$ and $H\parallel a^{*}$. In addition, low-temperature electron spin resonance in magnetic fields $H\parallel c$ yields a complete softening for one of the antiferromagnetic resonances at $\sim 40$ kOe, revealing a field-induced phase transition. The present work thus provides insights into the field evolution of the important Kitaev-Heisenberg spin system ${\mathrm{Na}}_2{\mathrm{Co}}_2\mathrm{Te}{\mathrm{O}}_6$.

The impact of dynamically encircling an exceptional point (EP) on the low-energy spin excitations in anti-parity-time (anti-$\mathcal{PT}$) symmetric synthetic antiferromagnets is investigated by adopting the quantum adiabatic theorem and numerical simulations. Under adiabatic conditions, the dynamic evolution of the encircling EPs is found to converge toward a low-dissipation state. When the evolution begins from a phase with broken anti-$\mathcal{PT}$ symmetry, the chiral mode switching occurs. On the other hand, a phase with preserved anti-$\mathcal{PT}$ symmetry evolves during the encircling EPs through different magnon states into the same low-dissipation final state. Despite adhering to the adiabatic conditions for evolution parameters, nonadiabatic transitions are still observed in the antiferromagnetic system and can be effectively described by changes in the dynamical and topological aspects of the final magnon state. The results, as validated using full-edged numerical micromagnetic simulations, demonstrate the ability to explore non-Hermitian state transfer in flexible magnetic systems.

Two-dimensional transition metal dichalcogenides (TMDs) are considered a suitable platform to study topological properties such as the quantum anomalous Hall effect. However, this quantum transport property is usually found in systems with a small band gap. For large-band-gap TMDs, the nature of quantum transport is difficult to find. In this work, with the analysis of the $k·p$ model, we investigate the topological phases of ferromagnetic TMDs in the cases of a large gap and small gap. By analyzing the orbital Berry curvature, we reveal that the orbital Hall effect in the system possesses a nontrivial topological invariant $C_L=-1$ when $\mathrm{sgn}\left({\mathrm{\Delta }}_{+1}{\mathrm{\Delta }}_{-1}\right)>0$, where ${\mathrm{\Delta }}_{\tau }$ represents the band gap at the $\tau$ valley (K or $K^{\prime }$ valley). Consequently, the large-gap ferromagnetic TMDs exhibit properties of an orbital Hall insulator. In the case of $\mathrm{sgn}\left({\mathrm{\Delta }}_{+1}{\mathrm{\Delta }}_{-1}\right)<0$, we demonstrate that the small-gap system transforms into a quantum anomalous Hall insulator with a Chern number $C=1$. Both topological phases are valley polarized and robust in the presence of an out-of-plane magnetic moment. Subsequently, we illustrate this transition from an orbital Hall insulator to a quantum anomalous Hall insulator in ${\mathrm{FeCl}}_2$, a representative ferromagnetic TMD, by tuning the Coulomb correction $U_{\mathrm{eff}}$ to manipulate the valley band gaps.

We study magnon-polaron hybrid states, mediated by Dzyaloshinskii-Moriya and magnetoelastic interactions, in a two-dimensional ferromagnetic insulator. The magnetic system consists of both in-plane and flexural acoustic and optical phonon bands, as well as acoustic and optical magnon bands. Through manipulation of the ground-state magnetization direction using a magnetic field, we demonstrate the tunability of Chern numbers and (spin) Berry curvatures of magnon-polaron hybrid bands. This adjustment subsequently modifies two intrinsic anomalous Hall responses of the system, namely, the intrinsic thermal Hall and intrinsic spin Nernst signals. Notably, we find that by changing the magnetic field direction in particular directions, it is possible to completely suppress the thermal Hall signal while maintaining a finite spin Nernst signal. Our finding reveals the intricate interplay between topology and magnetic ordering, offering compelling avenues for on-demand control over emergent nontrivial topological states and quantum transport phenomena in condensed matter systems by potential applications in both classical and quantum information technology.

It was presumed that semimetallic bismuth (Bi) would not show superconductivity (SC) even at ultralow temperatures $(<10 \mathrm{mK})$ due to its very low carrier density $(\approx 3\times {10}^{17}{\mathrm{cm}}^{-3})$. Recently, we have established bulk superconductivity in an ultrapure (99.9999%) Bi single crystal at $T_c=0.53 \mathrm{mK}$ with an extrapolated upper critical field $H_c\left(0\right)=5.2\mu \mathrm{T}$ measured along the [0001] (trigonal) crystallographic direction [O. Prakash et al., Science 355, 52 (2017)]. At very low concentrations of the charge carriers, we are dealing with fragile Cooper pairs with an estimated large coherence length ${\xi }_{\text{GL}}\left(0\right)\approx 96\mu \mathrm{m}$. We also stated that one needs to go beyond the conventional electron-phonon coupling (BCS-like) mechanism to understand the SC state in Bi. Bi is a compensated semimetal with electrons and holes as charge carriers. In order to find the charge carriers responsible for the SC, we report the temperature dependence of the anisotropic critical field along the $H\parallel \left[01\overline{1}0\right]$ (bisectrix) crystallographic direction and compare it with the earlier data from measurements along the $H\parallel \left[0001\right]$ (trigonal) axis. Our theoretical analysis of the critical field anisotropy suggests that the light electrons in the three pockets of the Bi Fermi surface are responsible for the SC, which indicates that Bi is an extremely weak type-II (close to type-I) superconductor. Finally, we present a brief review of the current theories proposed to explain the SC in Bi.

The ferromagnetic-metal–superconductor heterostructure with spin-orbit coupling is a promising candidate for topological superconductivity. Inspired by recent experimental progress in layered van der Waals metal–superconductor heterostructures, we study the interplay between the interface Rashba hopping and the intrinsic Dresselhaus spin-orbit coupling and demonstrate rich topological phases with five distinct Chern numbers. In particular, we find a topological state with the Chern number as large as four in a range of parameter space. We calculate the Berry curvatures that construct the Chern numbers and show that these Berry curvatures induce anomalous thermal Hall transport of the superconducting quasiparticles. We reveal chiral edge states in the topological phase and counterpropagating chiral edge states in the topologically trivial phase, and show that the wave functions of these edge states mostly concentrate on the ferromagnetic metal layer of the heterostructure.

We study the competition between the electron liquid and solid phases, such as Wigner crystal and bubbles, in partially filled Landau levels (LLs) of multilayer graphene. Graphene systems offer a versatile platform for controlling band dispersion by varying the number of its stacked layers. The band dispersion determines the LL wave functions, and consequently, the LL-projected Coulomb interaction in graphene and its multilayers is different from that in conventional semiconductors like GaAs. As a result, the energies of the liquid and solid phases are different in the different LLs of multilayer graphene, leading to an alternative phase diagram for the stability of these phases, which we work out. The phase diagram of competing solid and liquid phases in the LLs of monolayer graphene has been studied previously. Here we primarily consider $AB$- or Bernal-stacked bilayer graphene (BLG) and $ABC$-stacked trilayer graphene (TLG) and focus on the Laughlin fractions. We determine the cohesive energy of the solid phase using the Hartree-Fock approximation, and the energy of the Laughlin liquid is computed analytically via the plasma sum rules. We find that at the Laughlin fillings, the electron liquid phase has the lowest energy among the phases considered in the $\mathcal{N}=0,1,2$ LLs of BLG, as well as in the $\mathcal{N}=3,4$ LLs of TLG, while in the $\mathcal{N}>2$ LLs of BLG and $\mathcal{N}>4$ LLs of TLG, the solid phases are more favorable. We also discuss the effect of impurities on the above-mentioned phase diagram.