Weyl materials exhibit topologically nontrivial electronic or phonon energy-band crossings, offering promising conditions for fabricating novel topological devices and investigating exotic electrical and thermal transport properties. Here, we employ first-principles calculations to analyze the phonon dispersion of the experimentally synthesized boron arsenate $\left({\mathrm{BAsO}}_4\right)$ material, revealing the presence of four ideal type-I Weyl points with topological charge $\mathcal{C}=\pm 1$ within the first Brillouin zone. These Weyl points are precisely located in the $k_z=0.0$ plane and are constrained by the $S_4$ symmetry. Notably, both the O-atom and As-atom terminated surfaces exhibit clean and distinct surface arcs, connecting a pair of Weyl points with opposite chirality. These surface arcs maintain considerable separation in momentum space and span a length of approximately $0.687{\AA }^{-1}$. Furthermore, we construct a three-band effective Hamiltonian to capture the Weyl-related phonon branches in ${\mathrm{BAsO}}_4$ and to discuss the conditions governing the generation of Weyl points. Our results present an operational material platform for exploring the intrinsic properties of phononic Weyl-related phenomena.

The electrical conductivity of one-dimensional (1D) disordered solids exhibits exponential decay with respect to their length, a well-known manifestation of the localization phenomenon. In this study, we investigate alterations in the conductivity resulting from the insertion of 1D semiconductors into single-mode electromagnetic cavities, focusing specifically on the regime of nondegenerate doping. Our approach employs the Green's function technique adapted for the nonperturbative consideration of cavity-excited states. This encompasses coherent electron-cavity effects, such as electron motion within the zero-point fluctuating field, as well as incoherent photon emission processes during tunneling. The energy spectrum of electron transmission across the cavity develops Fano-type resonances linked to virtual photon emission, passage along a resonant level, and photon reabsorption. The quality factor of the Fano resonance depends on whether the intermediate state is coupled to the leads, reaching its maximum when this state is deeply localized within the disorder potential. Coupling to the cavity also raises the energies of shallow bound states, bringing them close to the conduction band bottom. This effect results in an enhancement of the conductance at low temperatures.

The ability to control the Gilbert damping which determines the lifetime of spin information is crucial for designing spintronic and magnonic devices. Thus, controlling the Gilbert damping parameter α has been a significant research target for several decades. Although numerous approaches have been explored to control α, few reports of large changes of this parameter have been presented. Herein, we demonstrate significant change of α in 2-nm-thick ${\mathrm{Co}}_{25}{\mathrm{Fe}}_{75}$ films originating from uniaxial surface magnetic anisotropy, which affects the two-magnon scattering. We report a change in α by approximately 0.02, or 300%. The value for α and its change are comparable to those observed in a previous study using a film that is one order of magnitude thicker. Our results achieved with ${\mathrm{Co}}_{25}{\mathrm{Fe}}_{75}$ can be directly transferred to other ultrathin ferromagnetic materials, which are a promising platform for spin information processing, and thus represents a versatile approach to modulate the Gilbert damping.

Topological flat bands, which are regarded as the cornerstone of various topological states induced by the many-body interaction, have aroused great interest in the fields of physics and material science. To date, most of the established topological flat bands have been employed in Euclidean space. Here, we report on an observation of hyperbolic topological flat bands in non-Euclidean space. By introducing magnetic flux into the hyperbolic octagon-kagome lattice, energy bands in four-dimensional $k$ space with the nontrivial Chern vector can be created via the formalism of hyperbolic band theory. The bandwidth of hyperbolic topological bands can be significantly reduced by tuning the next-nearest-neighbor coupling strength. Numerical results of finite hyperbolic models with fully and partially open boundary conditions clearly demonstrate the existence of topological boundary states induced by hyperbolic topological flat bands. Moreover, we design and fabricate electric circuits to observe hyperbolic topological flat bands in experiments. Site-resolved impedance responses and robust voltage dynamics demonstrate the coexistence of flat-band dispersion and topological boundary states. This letter may act as a foundation for exploring exotic hyperbolic fractional Chern insulators.

We show that short-range interactions are irrelevant around gapless ground-state delocalization-localization transitions driven by quasiperiodicity in interacting fermionic chains. In the presence of interactions, these transitions separate Luttinger liquid and Anderson glass phases. Remarkably, close to criticality, we find that excitations become effectively noninteracting. By formulating a many-body generalization of a recently developed method to obtain single-particle localization phase diagrams, we carry out precise calculations of critical points between Luttinger liquid and Anderson glass phases and find that the correlation length critical exponent takes the value $\nu =1.001\pm 0.007$, compatible with $\nu =1$ known exactly at the noninteracting critical point. We also show that other critical exponents, such as the dynamical exponent $z$ and a many-body analog of the fractal dimension are compatible with the exponents obtained at the noninteracting critical point. Noteworthy, we find that the transitions are accompanied by the emergence of a many-body generalization of previously found single-particle hidden dualities. Finally, we show that in the limit of vanishing interaction strength, all finite-range interactions are irrelevant at the noninteracting critical point.

Using an extended Su-Schrieffer-Heeger model including spin-orbit coupling and a nonadiabatic dynamics method, the dynamic picture of spin Hall effect (SHE) from interchain hopping of polarons is revealed in a finite organic polymer ladder. The results demonstrate that the transverse hopping of the polaron between chains under an electric field causes a spin-resolved longitudinal motion of the polaron along the chain. The direction of longitudinal transport remains opposite for the initial spin-up and spin-down polarons, which induces a pure spin current carried by polarons. By means of the statistical average over two kinds of polarons with different initial spins, an obvious oscillating SHE is achieved. Spectrum analysis from Fourier transform of spin signal shows a low-frequency part and a high-frequency part in the spectrum. The low-frequency part is attributed to the intrinsic electron dynamic oscillation in the finite-size system in the presence of polarons and the adopted periodic boundary, and the high-frequency part is due to the spin-flip spin dynamics. In addition, we found that the charge-spin conversion efficiency from the interchain polaron hopping may be larger than that from the intrachain polaron transport by one order, which confirms the enhancement of charge-spin conversion efficiency by organic anisotropy. This work deepens our understanding on the mechanism of organic SHE from polarons hopping, as well as the merit of organic anisotropy in the realization of a large SHE.

In the framework of the general phase diagram published recently for a pseudospin $S=1/2$ on a hyperkagome network [Kibalin et al., Phys. Rev. Res. 2, 033509 (2020)], four ${\mathrm{Dy}}_3{B}_2{C}_3{\mathrm{O}}_{12}$ garnets with different species on the $B$ and $C$ sites, namely, ${\mathrm{Dy}}_3{\mathrm{Sc}}_2{\mathrm{Al}}_3{\mathrm{O}}_{12}$ (DyScAl), ${\mathrm{Dy}}_3{\mathrm{Te}}_2{\mathrm{Li}}_3{\mathrm{O}}_{12}$ (DyTeLi), ${\mathrm{Dy}}_3{\mathrm{Sc}}_2{\mathrm{Ga}}_3{\mathrm{O}}_{12}$ (DyScGa), and ${\mathrm{Dy}}_3{\mathrm{In}}_2{\mathrm{Ga}}_3{\mathrm{O}}_{12}$ (DyInGa), have been studied by neutron powder diffraction and inelastic neutron scattering, to investigate the impact of $B$ and $C$ substitutions on the ${\mathrm{Dy}}^{3+}$ dodecahedral oxygen environment and crystal field, and thus on the ${\mathrm{Dy}}^{3+}$ spin magnetic anisotropy. In the four compounds, the magnetic ground state is a multiaxis antiferromagnetic order similar to that of ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$, characterized by an ordered moment close to the theoretical maximum, $\sim 6{\mu }_{\mathrm{B}}$. The gap between the ground state and the first excited crystal electric field level varies from $\sim 3.2$ meV (DyInGa) up to 11.2 meV (DyScAl), confirming the rather strong Ising character of the ${\mathrm{Dy}}^{3+}$ moment in those garnets. For a better understanding of the impact of the distortion of the oxygen environment on the ${\mathrm{Dy}}^{3+}$ magnetic anisotropy, point-charge calculations were then performed, mapping a magnetic anisotropy diagram versus a wide range of distortions. Results show that Ising-like behaviors mostly predominate, associated with large $g_x, g_y$, or $g_z$ Landé values, whose stable area is determined by the shape of the $\mathrm{Dy}{\mathrm{O}}_8$ cage. Magnetic entropy calculations confirm that the magnetocaloric effect increases sharply near those boundaries and validate the use of dysprosium garnets for low temperature, low magnetic field adiabatic demagnetization refrigeration cryostats.

We explore the impact of different materials on orbital-charge conversion in heterostructures with a naturally oxidized copper capping layer. Introducing a thin layer of $\mathrm{Cu}{\mathrm{O}}_x$ (3 nm) to the yttrium iron garnet (YIG)/W heterostructure resulted in a notable decrease in signal when employing the spin pumping (SP) technique. This contrasts with prior findings in YIG/Pt, where the addition of $\mathrm{Cu}{\mathrm{O}}_x$ (3 nm) led to a significant signal enhancement. Conversely, the introduction of the same $\mathrm{Cu}{\mathrm{O}}_x$ (3 nm) layer to YIG/Ti (4 nm) structure showed no change in the SP signal. This lack of change is attributed to the fact that Ti, unlike Pt, does not generate an orbital current at the $\mathrm{Ti}/\mathrm{Cu}{\mathrm{O}}_x$ interface due to its weaker spin-orbit coupling. Notably, incorporating the $\mathrm{Cu}{\mathrm{O}}_x$ (3 nm) layer on top of Si/Py (5 nm)/Pt (4 nm) structures resulted in a substantial increase in the spin pumping signal. However, in $\mathrm{Si}/\mathrm{Cu}{\mathrm{O}}_x$ (3 nm)/Pt (4 nm)/Py (5 nm) structures, the signal exhibited a decrease. Finally, we applied a phenomenological model of the spin (orbital) Hall effect in YIG/heavy-metal systems to refine our data. These discoveries have the potential to advance research in the innovative field of orbitronics and contribute to the development of new technologies based on spin-orbital conversion.

The Rosenzweig-Porter model is a single-parameter random matrix ensemble that supports an ergodic, fractal, and localized phase. The names of these phases refer to the properties of the (midspectrum) eigenstates. This work focuses on the long-range spectral statistics of the recently introduced unitary equivalent of this model. By numerically studying the Thouless time obtained from the spectral form factor, it is argued that long-range spectral statistics can be used to probe the transition between the ergodic and the fractal phases. The scaling of the Thouless time as a function of the model parameters is found to be similar to the scaling of the spreading width of the eigenstates. Provided that the transition between the fractal and the localized phases can be probed through short-range level statistics, such as the average ratio of consecutive level spacings, this work establishes that spectral statistics are sufficient to probe both transitions present in the phase diagram.

In this, the third paper in our series describing the excitations of the higher-lattice gauge theory model for topological phases, we will examine the (3+1)-dimensional case in detail. We will explicitly construct the ribbon and membrane operators which create the topological excitations, and use these creation operators to find the pattern of condensation and confinement. We also use these operators to find the braiding relations of the excitations, and to construct charge measurement operators which project to states of definite topological charge.

We have studied multi-Dirac/Weyl systems with arbitrary topological charge $n$ in the presence of a lattice of local magnetic moments. To do so we propose a multi-Dirac/Weyl Kondo lattice model which is analyzed through a mean-field approach appropriate to the paramagnetic phase. We study both the broken time-reversal and the broken inversion-symmetry Weyl cases. The multi-Dirac and broken time-reversal multi-Weyl cases have similar behavior, which is in contrast to the broken-parity case. For the former, low-energy particle-hole symmetry leads to the emergence of a critical coupling constant below which there is no Kondo quenching, reminiscent of the pseudogap Kondo impurity problem. Away from particle-hole symmetry, there is always Kondo quenching. For the broken inversion symmetry, there is no critical coupling. Depending on the conduction electron filling, Kondo insulator, heavy-fermion metal, or semimetal phases can be realized. In the last two cases, quasiparticle renormalizations can differ widely between opposite chirality sectors, with characteristic dependences on microscopic parameters that could in principle be detected experimentally.

Sb and Bi monolayers, as single-element ferroelectric materials with similar atomic structure, hold intrinsic piezoelectricity theoretically, which makes them highly promising for applications in functional nanodevices such as sensors and actuators. Here, using density functional theory calculations, we systematically explore the piezoelectric response of Sb and Bi monolayers. Our findings reveal that Sb exhibits a negative piezoelectric response, whereas Bi displays a positive one. This discrepancy is attributed to the dominant role of different atomic internal distortions (internal-strain terms) in response to applied strain. Further electron-density distribution analysis reveals that the atomic bonding in Sb tends to be covalent, while the atomic bonding in Bi leans more towards ionic. Compared to the Sb monolayer, the Bi monolayer is distinguished by its more pronounced lone-pair orbitals electrons and associated larger Born effective charges. The Coulomb repulsions between lone-pair orbitals electrons and the chemical bonds lead to the Bi monolayer possessing more prominent atomic folds and, consequently, more significant atomic distortion in the $z$ direction under strain. These differences result in a considerable difference in internal-strain terms, ultimately leading to the reversed piezoelectric response between Sb and Bi monolayers. The present work provides valuable insights into the piezoelectric mechanism of two dimensional ferroelectric materials and their potential applications in nanoelectronic devices.

Most iron-based superconductors exhibit stripe-type magnetism, characterized by the ordering vector $\mathbf{Q}=(\frac{1}{2},\frac{1}{2})$. In contrast, ${\mathrm{Fe}}_{1+y}\mathrm{Te}$, the parent compound of the ${\mathrm{Fe}}_{1+y}{\mathrm{Te}}_{1-x}{\mathrm{Se}}_x$ superconductors, exhibits double-stripe magnetic order associated with the ordering vector $\mathbf{Q}=(\frac{1}{2},0)$. Here, we use elastic neutron scattering to investigate heavily Cu-substituted ${\left({\mathrm{Fe}}_{1-x}{\mathrm{Cu}}_x\right)}_{1+y}\mathrm{Te}$ compounds and reveal that (1) for $x\gtrsim 0.4$, short-range magnetic order emerges around the stripe-type vector at $\mathbf{Q}=(\frac{1}{2}\pm \delta ,\frac{1}{2}\pm \delta ,\frac{1}{2})$ with $\delta \approx 0.05$; (2) the short-range magnetic order is associated with a superstructure modulation at $\mathbf{Q}=(\frac{1}{3},\frac{1}{3},\frac{1}{2})$, with the magnetic correlation length shorter than that for the superstructure; and (3) for $x\gtrsim 0.55$, we observe an additional intergrown phase with higher Cu content, characterized by a superstructure modulation vector $\mathbf{Q}=(\frac{1}{3},\frac{1}{3},0)$ and magnetic peaks at $\mathbf{Q}=(\frac{2}{3},\frac{1}{3},\frac{1}{2})/(\frac{1}{3},\frac{2}{3},\frac{1}{2})$. The positions of superstructure peaks suggest that relative to the tetragonal unit cell of ${\mathrm{Fe}}_{1+y}\mathrm{Te}$, heavy Cu substitution leads to Fe-Cu orderings that expand the unit cell by $\sqrt{2}\times 3\sqrt{2}$ times in the $ab$ plane, corroborated by first-principles calculations that suggest the formation of spin chains and spin ladders. Our findings show that stripe-type magnetism is common in magnetically diluted iron pnictides and chalcogenides, despite the varying associated atomic orderings.

Landau Fermi liquid theory is a fixed-point theory of metals that includes the forward-scattering amplitudes as exact marginal couplings. However, the fixed-point theory that only includes the strict forward scatterings is nonlocal in real space. In this paper, we revisit the Fermi liquid theory for charge-neutral fermions using the field-theoretic functional renormalization group formalism and show how the scale-invariant fixed point emerges as a local theory, which includes not only the forward scatterings but also nonforward scatterings with small but nonzero momentum transfers. In the low-energy limit, the near-forward scattering and pairing interactions take scale-invariant forms if the momentum transfer and the center-of-mass momentum of Cooper pairs, respectively, are comparable to the energy. The coupling functions fully capture the universal low-energy dynamics of the collective modes and instabilities of Fermi liquids. A runaway flow of the coupling function in the particle-hole channel beyond a critical interaction suggests an instability toward an ordered phase with a wave vector that depends on the interaction strength. At the critical interaction, the instability corresponds to the uniform Pomeranchuk or Stoner instability, but the momentum of the leading instability becomes nonzero for stronger attractive interaction. In the particle-particle channel, the coupling function reveals the dynamics of the unstable mode associated with the BCS instability. When an unstable normal metal evolves into the superconducting state, there exists a period in which a superconducting state with spatially nonuniform phase appears due to the presence of unstable Cooperon modes with nonzero momenta.

The recent discovery of polar vortex textures revealed a new fascinating facet of nanoscale ferroelectric materials with prospects for new interaction pathways with chiral, topological, and photonic materials. Here, we demonstrate how the subterahertz collective response of the ferroelectric vortex lattice enables a coupling to electric and magnetic fields resulting in a novel type of photonic vortex lattice with particular dispersion that we analyze for a wide class of ferroelectric/paraelectric layered heterostructures. General arguments supported by full, material-specific numerics evidence the appearance of polarization-dependent optoelectronic modes and band gaps. The ferroelectric-photonic vorticity coupling renders photonic elements amenable to elastic, electric, and magnetic probes with far-reaching implications for new multifunctional optoelectronics.

Three-terminal coherent conductors are able to perform as quantum thermocouples when the heat absorbed from one terminal is transformed into useful power in the other two. Allowing for a phase coherent coupling to the heat source, we introduce a way to control and improve the thermoelectric response via quantum interference. A simple setup composed of a scanning probe between two resonant tunneling regions is proposed that achieves better performance than incoherent analogs by enhancing the generated power and efficiency and reducing the output current noise.