Due to its strong magneto-optical response, plasmons in graphene can be actively tuned by a static magnetic field, resulting in another quasiparticle called graphene magnetoplasmon (GMP). In this work, we theoretically investigate GMPs in graphene disks with their two halves subject to two magnetic fields. As the two magnetic fields are identical (case I), the well-known symmetric mode splitting is observed for a larger chemical potential ${\mu }_c$, with two GMPs ($\mathrm{GM}{\mathrm{P}}_{\pm }$) being circularly polarized with different chirality; with decreasing ${\mu }_c$, the lower-energy $\mathrm{GM}{\mathrm{P}}_{-}$ will become an edge mode with a significantly reduced damping rate. As the two magnetic fields are opposite (case II), the magnetic field effect is completely absent for a larger ${\mu }_c$, e.g., $\mathrm{GM}{\mathrm{P}}_{\pm }$ are degenerate and linear polarized, while for a smaller ${\mu }_c$, $\mathrm{GM}{\mathrm{P}}_{\pm }$ will be circularly polarized again, and $\mathrm{GM}{\mathrm{P}}_{-}$ is circulating unidirectionally along the magnetic border. However, if two magnetic fields are different in magnitude, both $\mathrm{GM}{\mathrm{P}}_{\pm }$ will exhibit field circulating along the border, and more interestingly, in the same direction as case II, namely, the opposite field circulating is prohibited. Having a small defect, the unidirectional field circulating is not broken, which will pass around the defect smoothly. Finally, we propose a feasible scheme, graphene folding, for producing specified magnetic fields, in which two halves of the disk are folded with different angles to a uniform magnetic field. In spite of structural deformation, the main features of $\mathrm{GM}{\mathrm{P}}_{\pm }$ are shown to be well maintained. Our work provides a better understanding of magnetoplasmons in graphene, which could be of interest to plasmonic and magneto-optic device applications.

Spectroscopy experiments are routinely used to characterize the behavior of strongly correlated systems. An in-depth understanding of the different spectral features is thus essential. Here, we show that the spectrum of the multiorbital Hubbard model exhibits unique Hund bands that occur at energies given only by the Hund coupling $J_{\mathrm{H}}$, as distinct from the Hubbard satellites following the interaction $U$. We focus on experimentally relevant single-particle and optical spectra that we calculate for a model related to iron chalcogenide ladders. The calculations are performed via the density-matrix renormalization group and Lanczos methods. The generality of the implications is verified by considering a generic multiorbital model within dynamical mean-field theory.

We show that pure spin injection from a magnetic electrode into an inversion symmetry-broken system composed of a tunnel barrier and a metallic region generates a transverse charge current. Such a tunneling spin galvanic conversion is robust to disorder and nonlocal, i.e., injection and detection contacts do not coincide, and is strongly anisotropic whenever the internal spin-orbit field has a nontrivial angular dependence. The anisotropy shows up in linear response, contrary to what happens in bulk conversion setups lacking tunneling elements. This is particularly relevant for spin-charge conversion at oxide interfaces, where both the tunnel barrier and the receiving low-dimensional metallic system host effective spin-orbit fields with complex angular symmetries.

Magnetic anisotropy and the controllability of the magnetic order of two-dimensional magnetic materials are of great importance for the development of next-generation spintronics. Here, first-principles calculations are performed to study these two properties of a topical van der Waals antiferromagnetic (AFM) semiconductor CrSBr. Both the intralayer and interlayer exchange interactions are found nearly isotropic because of the weak $p\text{−}d$ hybridization between Cr and anion atoms. Magnetic anisotropy is determined by single-ion anisotropy, which is originated from the spin-orbit coupling of both Cr and Br atoms. Such results are distinct from previous works where anisotropic exchange interaction is supposed to be the origin of the exhibited uniaxial magnetic anisotropy in this material. Moreover, the AFM ground state of bilayer CrSBr is found to be originated from the competition between different orbital-dependent ferromagnetic (FM) and AFM exchange interactions via two inequivalent super-superexchange pathways. Importantly, the magnetic ground state of bilayer CrSBr can be switched from AFM to FM when the applied out-of-plane electric field exceeds a threshold value of 0.046 eV/Å. This can be explained by the orbital overlap variation between interlayer nearest-neighbor Cr pairs upon application of the electric field. Our results will provide a comprehensive understanding of the magnetic behavior in layered CrSBr and suggest bilayer CrSBr as an appealing candidate for electric-field-driven miniaturized spintronic devices.

We report magnetic and transport properties of single-crystalline ${\mathrm{EuZn}}_2{\mathrm{P}}_2$, which has trigonal ${\mathrm{CaAl}}_2{\mathrm{Si}}_2$-type crystal structure and orders antiferromagnetically at $\approx 23\mathrm{K}$. Easy $ab$-plane magneto-crystalline anisotropy was confirmed from the magnetization isotherms, measured with a magnetic field applied along different crystallographic directions ($ab$ plane and $c$ axis). Positive Curie-Weiss temperature indicates dominating ferromagnetic correlations. Electrical resistivity displays insulating behavior with a band gap of $\approx 0.35$ eV, which decreases to $\approx 0.26$ eV upon application of a high magnetic field. We explain the intriguing presence of magnetic interactions in an intermetallic insulator by the mechanism of extended superexchange, with phosphorus as an anion mediator, which is further supported by our analysis of the charge and spin-density distributions. We constructed the effective Heisenberg model, with exchange parameters derived from the ab initio DFT calculations, and employed it in Monte Carlo simulations, which correctly reproduced the experimental value of the Néel temperature.

We discuss the macroscopic behavior of the superfluid ${}^3\mathrm{He}$ phase (pair density wave phase) with a spatially modulated pair density wave recently observed experimentally. As an order parameter we assume, based on the experimental results and a Landau-type model, a variation of the phase of the macroscopic wave function coupled to spatially modulated plane waves of the macroscopic wave function in the plane perpendicular to the confinement. As a result we find only one true Goldstone mode in orbit space coupling the superfluid aspects to the spatial modulations of the order parameter in the plane of the sample. This coupling is predicted to lead to a propagating mode sharing aspects of second sound and acoustic waves arising from the spatial variations of the order parameter. Due to the coupling of the phase of the order parameter to in-plane spatial modulations, the velocity of first sound becomes anisotropic. In addition, the velocities of first and second sound reflect the static and dynamic coupling terms to the order parameter. Fourth sound in contrast, the velocity of which also becomes anisotropic, couples only to one static cross coupling associated with density variations and not to any dynamic cross-coupling terms. Therefore measurements of the fourth sound velocity could be used to measure quite directly a static cross-coupling term. The situation studied here is thus qualitatively different from that suggested for supersolid ${}^4\mathrm{He}$ for which one has a solid phase with broken translational symmetry associated with a density wave as in a usual solid. As for spin space we obtain, neglecting the tiny magnetic dipole interaction and in the absence of a magnetic field, three pairs of spin waves closely resembling the results of the planar distorted $B$ phase. Excitations in spin space in the presence of the magnetic dipole interaction and/or an external magnetic field are also investigated briefly.

Thermal conductivity measurements can provide key and experimentally verifiable insight into the electronic transport of unconventional superconductors. In this paper, electronic thermal transport of two-dimensional tight-binding metallic systems with coexisting $d$-wave superconducting (SC) and antiferromagnetic spin density wave (SDW) orders with nesting vector $\mathbf{Q}=(\pi /2,\pi /2)$ or $(\pi ,0)$ are considered. The coexisting SC and SDW orders are modeled at the mean-field level. Thermal conductivities are numerically calculated within Boltzmann kinetic theory in the weak impurity scattering (Born) limit. These SDW nesting vectors are chosen for their unique property of reconstructing the Fermi surface parallel to $\mathbf{Q}$ and preserving the metallic FS perpendicular to $\mathbf{Q}$. This leads to anisotropic electronic thermal conductivities parallel and perpendicular to $\mathbf{Q}$, which also depend on the presence or absence of additional gapless excitations exclusive to the coexistence phase. It was found that the $\mathbf{Q}=(\pi /2,\pi /2)$ and $(\pi ,0)$ SDW systems exhibit equivalent electron transport relative to $\mathbf{Q}$. These systems also had equivalent electron transport when coexisting with a $d$-wave SC gap when ${\mathrm{\Delta }}_{\mathbf{k}}$ had the same symmetry class under translations of $\mathbf{Q}$.

We study the low-energy physics of the critical ($2+1$)-dimensional random transverse-field Ising model. The one-dimensional version of the model is a paradigmatic example of a system governed by an infinite-randomness fixed point, for which many results on the distributions of observables are known via an asymptotically exact renormalization group (RG) approach. In two dimensions, the same RG rules have been implemented numerically and demonstrate a flow to infinite randomness. However, analytical understanding of the structure of this RG has remained elusive due to the development of geometrical structure in the graph of interacting spins. To understand the character of the fixed point, we consider the RG flow acting on a joint ensemble of graphs and couplings. We propose that the RG effectively occurs in two stages: (1) randomization of the interaction graph until it belongs to a certain ensemble of random triangulations of the plane and (2) a flow of the distributions of couplings to infinite randomness while the graph ensemble remains invariant. This picture is substantiated by a numerical RG in which one obtains a steady-state graph degree distribution and subsequently infinite-randomness scaling distributions of the couplings. Both of these aspects of the RG flow can be approximately reproduced in simplified analytical models.

We use stochastic expansion and exact diagonalization to study magic-angle twisted bilayer graphene (TBG) on a disordered substrate. We show that the substrate-induced strong Coulomb disorder in TBG with the chemical potential at the level of the flat bands drives the system to a network of weakly coupled Sachdev-Ye-Kitaev (SYK) bundles, stabilizing an emergent quantum chaotic strange metal (SM) phase of TBG that exhibits the absence of quasiparticles. The Gaussian orthogonal ensemble dominates TBG's long-time chaotic dynamics at strong disorder, whereas fast quantum scrambling appears in the short-time dynamics. In weak disorder, gapped phases of TBG exhibit exponentially decaying specific heat capacity and exponential decay in out-of-time-ordered correlators (OTOCs). This is the system behavior in correlated insulator and superconducting phases, in agreement with the corresponding Larkin-Ovchinnikov result for correlators. The result suggests a low-temperature transition from the superconducting and correlated insulating phases into the strange metal upon increasing the disorder strength. We propose a finite-temperature phase diagram for Coulomb-disordered TBG and discuss the experimental consequences of the emergent SM phase.

Motivated by the potential to suppress antiferromagnetic long-range order in favor of the long-sought-after Kitaev quantum spin liquid state, we study the effect of spin vacancies in the extended Kitaev-Heisenberg model. In particular, we focus on a realistic model obtained from fitting inelastic neutron scattering on $\alpha \text{−}{\mathrm{RuCl}}_3$. We observe that the long-range zigzag magnetic ordered state only survives when the doping concentration is smaller than 5%. Upon further increasing the spin vacancy concentration, the ground state becomes a short-range ordered state at low temperatures. Compared with experiments, our classical solution overstabilizes the zigzag correlation in the presence of spin vacancies. Our theoretical results provide guidance toward interpreting inelastic neutron scattering experiments on magnetically diluted Kitaev candidate materials

Understanding the nature of charge density wave (CDW) and superconductivity in the kagomé metal ${A\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A= \mathrm{Cs},\mathrm{Rb},\mathrm{K})$ is a recent subject of intensive study. Due to the presence of van Hove singularities, electron-electron interaction has been suggested to play an important role in the formation of such broken-symmetry states. Recent experiments show that the CDW order is three dimensional and it is staggered across different kagomé layers. However, the experimental interpretation for the precise structure of CDW varies in terms of whether it is the star of David (SD), inverse star of David (ISD), or the alternation of the two among neighboring layers. In this work, we show that the origin of these distinct CDW orders can be understood in a unified picture by considering intralayer and interlayer electron-electron interactions as well as the coupling between electrons and lattice distortions. Utilizing an effective nine-band model with V $d$ orbitals and out-of-plane Sb $p$ orbitals, it is demonstrated that the repulsive electron-electron interaction favors charge bond order which induces either SD or ISD upon including lattice distortions. As the interlayer interaction is introduced, $\pi$-shifted CDW develops with the staggered ordering along the $c$ axis. We also find that the phase with alternating SD and ISD can be stabilized as the ground state under strong interlayer interaction.

Here, pristine and Pd-intercalated $2H\text{−}\mathrm{Ta}{\mathrm{S}}_2$ single crystals with ($00l$) orientation were grown by the chemical vapor transport technique. The superconductivity (SC) and charge density wave (CDW) were characterized by magnetic and electrical transport measurements. We find that SC and CDW in the pristine $2H\text{−}\mathrm{Ta}{\mathrm{S}}_2$ condense respectively at transition temperatures $T_{\mathrm{c}}\sim 0.8\mathrm{K}$ and $T_{\mathrm{CDW}}\sim 78\mathrm{K}$. The CDW order is completely suppressed, and $T_{\mathrm{c}}$ is greatly enhanced to 4.5 K in $2H\text{−}\mathrm{P}{\mathrm{d}}_{0.04}\mathrm{Ta}{\mathrm{S}}_2$, which concludes a competing relation between the two collective electronic states. The positive Hall coefficient $R_{\mathrm{H}}$ for both samples above 78 K indicates that hole-type carriers dominate the transport properties, and almost the same $R_{\mathrm{H}}$ reveals tiny charge transfer between the intercalant Pd and the host $\mathrm{Ta}{\mathrm{S}}_2$. The difference of $R_{\mathrm{H}}$ below 78 K between $\mathrm{Ta}{\mathrm{S}}_2$ and ${\mathrm{Pd}}_{0.04}\mathrm{Ta}{\mathrm{S}}_2$ is attributed to the reconstruction of the Fermi surface by Pd-intercalation-induced collapse of the CDW order. Therefore, the prominently improved $T_{\mathrm{c}}$ in $2H\text{−}\mathrm{P}{\mathrm{d}}_{0.04}\mathrm{Ta}{\mathrm{S}}_2$ is mainly caused by the change of electronic structure due to the suppression of the CDW state rather than charge injection by Pd intercalation.

Crystal-phase semiconductor heterostructures allow for electron confinement without uncertainties caused by chemical intermixing found in material heterostructures and are candidates for next generation optoelectronics devices ranging from single-photon emitters to high efficiency light-emitting diodes. While there has been a great deal of experimental work developing fabrication processes for these structures, theoretical calculations have been limited due to a lack of atomistic models that are able to incorporate the zinc-blende and wurtzite within the same structure. Here, we present calculations of the electronic energies in GaAs nanowires containing various thicknesses of zinc-blende and wurtzite layers using a recently developed tight-binding model for wurtzite III-V semiconductors that is compatible with a zinc-blende model. By comparing results in the flat-band and the unscreened limits, we explain the sensitivity of experimentally observed band gaps on zinc-blende and wurtzite well widths. Our calculations suggest that experiments on devices are likely near the flat-band limit under typical operating conditions.

Two global symmetries are holoequivalent if their algebras of local symmetric operators are isomorphic. A holoequivalent class of global symmetries is described by a topological order (TO) in one higher dimension (called symmetry TO), which leads to a symmetry/topological-order (Symm/TO) correspondence. We establish that (1) for systems with a symmetry described by symmetry TO $\mathcal{M}$, their gapped and gapless states are classified by condensable algebras $\mathcal{A}$, formed by elementary excitations in $\mathcal{M}$ with trivial self-/mutual statistics. These so-called $\mathcal{A}$ states can describe symmetry breaking orders, symmetry protected topological orders, symmetry enriched topological orders, gapless critical points, etc. in a unified way. (2) The local low-energy properties of an $\mathcal{A}$ state can be calculated from its reduced symmetry TO ${\mathcal{M}}_{/\mathcal{A}}$, using holographic modular bootstrap (holoMB) which takes ${\mathcal{M}}_{/\mathcal{A}}$ as an input. Here ${\mathcal{M}}_{/\mathcal{A}}$ is obtained from $\mathcal{M}$ by condensing excitations in $\mathcal{A}$. Notably, an $\mathcal{A}$ state must be gapless if ${\mathcal{M}}_{/\mathcal{A}}$ is nontrivial. This provides a unified understanding of the emergence and symmetry protection of gaplessness that applies to symmetries that are anomalous, higher-form, and/or noninvertible. (3) The relations between condensable algebras constrain the structure of the global phase diagram. We find that, for $1+1\mathrm{D} {\mathbb{Z}}_2\times {\mathbb{Z}}_2^{\prime }$ symmetry with mixed anomaly, there is a stable continuous transition (deconfined quantum critical point) between the ${\mathbb{Z}}_2$-breaking-${\mathbb{Z}}_2^{\prime }$-symmetric phase and the ${\mathbb{Z}}_2$-symmetric-${\mathbb{Z}}_2^{\prime }$-breaking phase. The critical point is the same as a ${\mathbb{Z}}_4$ symmetry breaking critical point. (4) $1+1\mathrm{D}$ bosonic systems with $S_3$ symmetry have four gapped phases with unbroken symmetries $S_3, {\mathbb{Z}}_3, {\mathbb{Z}}_2$, and ${\mathbb{Z}}_1$. We find a duality between two transitions $S_3\leftrightarrow {\mathbb{Z}}_1$ and ${\mathbb{Z}}_3\leftrightarrow {\mathbb{Z}}_2$: they are either both first order or both (stably) continuous, and in the latter case, they are described by the same conformal field theory (CFT). (5) The gapped and gapless states for $1+1\mathrm{D}$ bosonic systems with anomalous $S_3$ symmetries are obtained as well. For example, anomalous $S_3^{\left(1\right)}$ and $S_3^{\left(2\right)}$ symmetries can have symmetry protected chiral gapless states with only symmetric irrelevant and marginal operators.

Modern organic semiconductors frequently adopt a semicrystalline morphology which makes the analysis of charge transport challenging. In this paper, we employ Monte Carlo (MC) simulation to study the charge-carrier mobility in an amorphous layer—typically 100 nm thick—that contains well-ordered nanosized domains (crystallites). The case of a low carrier concentration, typical for applications in photovoltaics and LEDs, is considered. We study the dependence of mobility on temperature, on the amount $\left(V\right)$ of the crystallites, on the energy offset between crystalline and amorphous regions $\left(E_t\right)$, and we compare the results with those for a system with solitary traps. We find that, in a system with solitary traps, the mobility can exceed that of the neat phase if the trap depth is comparable with the standard deviation of the density of states (DOS) of the amorphous phase. Controlled by the electronic overlap in the amorphous phase and the crystallites, the mobility in a system with crystallites can increase by up to two orders of magnitude upon increasing V. It features a pronounced maximum when $E_t$ is close to the standard deviation of the DOS of the amorphous phase, while for large values of $E_t$, the mobility is practically independent of $E_t$. The results can be rationalized in terms of an interplay between percolation at large $E_t$ and hopping transport within the cumulative densities near the transport of the system. We developed a generalized analytic multiple-trapping-release model to rationalize the results of the MC simulations.

The implementation of topology on photonics has opened new functionalities of photonic systems, such as the topologically protected boundary photonic modes. In this study, we investigate topological plasmonics in a graphene lattice arrayed with metal nanoparticles and irradiated by a polarized light. While surface plasmon polaritons are typically excited in such systems, our study shows that the system exhibits a different photonic response with observable edge photonic modes corresponding to distinct topological states. Importantly, we show that the topological phase transition between these states can be easily achieved by controlling the polarization of the external optical field, making it more feasible in experiments than changing the structural parameters. Our system provides a controllable platform for studying topological phenomena in photonics and has potential applications in nanoscale optical devices.

Topological phases are greatly enriched by including non-Hermiticity. While most works focus on the topology of the eigenvalues and eigenstates, how topologically nontrivial non-Hermitian systems behave in dynamics has only drawn limited attention. Here, we consider a breathing honeycomb lattice known to emulate the quantum spin Hall effect and exhibit higher-order corner modes. We find that nonreciprocal intracell couplings introduce gain in one pseudospin subspace while introducing loss with the same magnitude in the other. In addition, nonreciprocal intracell couplings can also suppress the spin mixture of the edge modes at the boundaries and delocalize the higher-order corner mode. Our findings deepen the understanding of non-Hermitian topological phases and bring in the spin degree of freedom in manipulating the dynamics in non-Hermitian systems.