The quasiparticles (QPs) or quasiholes (QHs) of fractional quantum Hall states have been predicted to obey fractional braid statistics, which refers to the Berry phase (in addition to the usual Aharonov-Bohm phase) associated with an exchange of two QPs or two QHs or, equivalently, to half of the phase associated with a QP or QH going around another. Certain phase slips in interference experiments in the fractional quantum Hall regime have been attributed to fractional braid statistics, where the interference probes the Berry phase associated with a closed path which has segments along the edges of the sample as well as through the bulk (where tunneling occurs). Noting that QPs and QHs with sharply quantized fractional charge and fractional statistics do not exist at the edge of a fractional quantum Hall state due to the absence of a gap there, we provide arguments that the existence of composite fermions at the edge is sufficient for understanding the primary experimental observations; unlike QPs and QHs, composite fermions are known to be well defined in compressible states without a gap. We further propose that transport through a closed tunneling loop contained entirely in the bulk can, in principle, allow measurement of the braid statistics in a way that the braiding object explicitly has a fractionally quantized charge over the entire loop. Optimal parameters for this experimental geometry are determined from quantitative calculations.

In frustrated magnets, a variety of novel phenomena arise due to their peculiar magnetic states, whose excitations usually reside in the GHz to THz range. Intense THz lasers, therefore, lead to examining nonlinear optical effects in such magnets. Employing an unbiased numerical method, we calculate the laser-pulse driven harmonic spectra of the Shastry-Sutherland magnets, which are well known as the model of a quantum frustrated magnet $\mathrm{SrCu}{}_2$($\mathrm{BO}{}_3$)${}_2$. As a result, nonlinear responses of triplons and a two-triplon bound state are numerically shown to emerge through the Zeeman or magnetoelectric couplings between the laser and the electron spin. Furthermore, the dynamical symmetries and selection rules of harmonic spectra for the Shastry-Sutherland model realized in $\mathrm{SrCu}{}_2$($\mathrm{BO}{}_3$)${}_2$, are derived. The selection rules tell us that one can obtain information on magnetic anisotropy and symmetry from the spectra by manipulating external fields or two-color lasers. Our results indicate that laser-driven harmonic spectra are useful as a probe of less-detectable quantum many-body states in frustrated magnets.

Motivated by by the recent discovery of dielectric relaxation by quantum critical magnons in ${\mathrm{Cs}}_2{\mathrm{Cu}}_2{\mathrm{Mo}}_3{\mathrm{O}}_{12}$, we conduct a detailed analysis of its dielectric response and compare it to that in the isostructural compound ${\mathrm{Rb}}_2{\mathrm{Cu}}_2{\mathrm{Mo}}_3{\mathrm{O}}_{12}$. Measurements in the vicinity of the field-induced magnon softening show that its description in terms of a three-dimensional Bose-Einstein condensation quantum critical point is unaltered by the presence of dielectric relaxation. We also demonstrate the existence of dielectric relaxation anomalies at 19 K in ${\mathrm{Rb}}_2{\mathrm{Cu}}_2{\mathrm{Mo}}_3{\mathrm{O}}_{12}$ and discuss the implications for the microscopic origin of dielectric activity in two compounds.

In recent years, the nonlinear Hall effect has attracted great attention with three different terms contributed by the Drude effect, Berry curvature dipole, and Berry connection polarizability. In this paper, we theoretically predict an intrinsic second-order spin current induced by spin-dependent Berry curvature polarizability based on time-independent perturbation theory. We show two other second-order spin conductivities contributed by the group velocity and spin-dependent Berry curvature dipole. A two-dimensional Rashba-Dresselhaus spin-orbit coupled system is studied as an example. and it is found that the intrinsic second-order contribution plays a major role when the chemical potential $\mu$ is greater than zero, while current mainly comes from the extrinsic terms when $\mu <0$. Our calculation provides a theoretical basis for understanding the nonlinear spin transport.

Artificial spin ice (ASI) represents a class of uniquely structured superlattices comprising geometrically arranged interacting nanomagnets. This arrangement facilitates the exploration of magnetic frustration phenomena and related spin wave dynamics, contributing to the field of magnonics. In this paper, we present a comprehensive study of spin-wave dynamics in square ASI lattices using micromagnetic simulations, explicitly focusing on ferromagnetic resonance (FMR) and oscillation modes. We investigate how variations in the aspect ratio of nanomagnet dimensions influence magnetic excitations in both saturated and remanent states. We analyze the frequency variations of FMR peaks corresponding to edges and bulk oscillation modes in relation to both magnetic configuration and nanomagnets dimensions. We emphasize the remanent state of square ASI vertex configurations, particularly focusing on their characteristic energy states (types I–IV), while detailing how symmetries influence oscillation modes. We observe distinct FMR responses originating from vertices, exhibiting unique characteristics for each energy state. Our results offer a potential method of utilizing the FMR technique to identify energy states in ASI systems.

Controlling the spin orientation of magnetic systems is crucial for various quantum technologies. In this work, applying first-principle studies, we have investigated how interfacial interactions between a single-molecule magnet (SMM), chromocene $\left({\mathrm{CrCp}}_2\right)$, and substrates (magnetic and nonmagnetic) could control the magnetization of the SMM. Due to magnetic anisotropy, an isolated chromocene molecule exhibits the magnetization direction aligned parallel to the principal molecular axis. Typically, molecule-substrate interactions quench the magnetic anisotropy in the SMMs. In the current work, we observed a switch in the magnetization direction from out-of-plane to in-plane direction while ${\mathrm{CrCp}}_2$ is deposited on Au(111), graphene, hexagonal closed packed–Co(0001) and face-centered cubic–Co(111) substrates. The resulting interface formations induce structural and electronic structure changes in the SMMs. We realized that only the structural change enhanced the SMM behaviors of ${\mathrm{CrCp}}_2$ compared to the isolated systems. Unfortunately, this is inseparable from the electronic structural changes at the interface. The charge density redistribution at the interfaced molecule modulates the magnetic anisotropy of SMMs and switches their magnetization directions. Finally, we explored the complex nature of the magnetic interactions between the SMM and magnetic substrate, accounting for the Dzyaloshinski-Moriya and symmetric/antisymmetric exchange interactions.

We develop a theory of focusing of a THz Gaussian laser beam by a layered superconducting slab of finite thickness in the presence of an external dc magnetic field in a nonlinear regime. We show that focusing abilities of the slab, which originate from the specific nonlinearity of the medium, can be flexibly tuned by the external magnetic field providing a way to control THz waves. We analytically study the main characteristics of the Gaussian beam transmitted through such a nonlinear lens, namely, a beam waist and a focusing distance, as functions of radiation frequency, beam intensity, and dc field magnitude. The results of analytic calculations are supported by the numerical simulation of the electromagnetic field distribution in the beam propagating through the superconducting slab.

A unique type of tantalum hydride was synthesized by exposing tantalum dihydride to the high hydrogen pressure of 9 GPa and a temperature of $580{}^{\circ }\mathrm{C}$ using toroid-type high-pressure chambers. The samples of this hydride were cooled down to 100 K, recovered to ambient pressure, and studied in a metastable state by hot extraction, powder x-ray and neutron diffraction, and inelastic neutron scattering. X-ray diffraction demonstrated that this hydride had an A15-type crystal structure of metal lattice (space group $Pm\text{−}3n$, Ta atoms at the $2a$ and $6c$ Wyckoff positions) and a lattice parameter of $a=5.510\left(5\right)\AA$ at $T=85$ K. The hydrogen content determined by hot extraction was $\mathrm{H}/\mathrm{Ta}=1.23\left(5\right)$. Hydrogen desorption during heating the sample in vacuum proceeded in two steps—first, $\mathrm{\Delta }\mathrm{H}/\mathrm{Ta}=0.2$ was desorbed at around $-70{}^{\circ }\mathrm{C}$, and then the rest of the hydrogen was desorbed between $100{}^{\circ }\mathrm{C}$ and $390{}^{\circ }\mathrm{C}$. The $\mathrm{A}15\text{-type}$ metal lattice was preserved upon hydrogen removal, leaving a unique polymorph of tantalum. Neutron diffraction of $\mathrm{A}15\text{−}{\mathrm{TaH}}_{1.23\left(5\right)}$ demonstrated that hydrogen atoms occupy the $24k$ and $16i$ Wyckoff sites in the crystal structure, and annealing at 250 K resulted in a decrease of the $24k$ and an increase of the $16i$ site occupancies. Inelastic neutron scattering revealed four vibrational modes in the fundamental band of $\mathrm{A}15\text{−}{\mathrm{TaH}}_{1.23\left(5\right)}$ at 72, 135, 145, and $166\mathrm{meV}$, the first three and the last one of which were tentatively assigned to the vibrations of H atoms at the $24k$ and $16i$ sites, respectively. No superconductivity was found in $\mathrm{A}15\text{−}{\mathrm{TaH}}_{1.1}$ and hydrogen-free A15-Ta at temperatures down to 1.5 K.

Defects in a material can significantly tune properties and enhance utility. Hybrid functionals like HSE06 are often used to describe solids with such defects. However, geometry optimization (including accounting for effects such as Jahn-Teller distortion) using hybrid functionals is challenging for the large supercells needed for defect study. The proposed ${\mathrm{r}}^2\mathrm{SCAN}+\mathrm{rVV}10+$U$+U_d$ method, which is computationally much cheaper and faster than hybrid functionals, can successfully describe defects in materials with the proper choice of U (for the $d$ orbitals of the host atom) and $U_d$ (for those of the defect atom), as shown here for small polaron defects in layered transition-metal oxides. For a range of U and $U_d$ around literature values (from solid-state reaction energies) for a given transition-metal ion and its oxidation state, we find that this approach predicts localized polaronic states in band gaps, as hybrid functionals do. The layered materials birnessite $({\mathrm{K}}_{\mathit{n}}{\mathrm{MnO}}_2,n=0.03)$ and ${\mathrm{K}}_{\mathit{n}}{\mathrm{NiO}}_2,n=0.03$, with one K atom intercalated between layers in a supercell, are found to have one localized occupied $e_g$ polaronic state on the transition metal ion reduced by the insertion of the K atom, when the geometry is calculated as above using published U values. The expected Jahn-Teller distortion is not observed when $U=U_d=0$. Layered cobalt oxide with additional potassium ions intercalated $({\mathrm{K}}_{\mathit{n}}{\mathrm{CoO}}_2,n=1.03)$ is different due to a dramatic difference in electronic configuration of the defected Co(II) ion: A single extra K atom in the supercell leads to four localized electrons in the band gap, using standard U values, and even for $U=U_d=0$.

Controlling magnetic anisotropy energy (MAE) in two-dimensional ferromagnetic materials is crucial for designing novel spintronic devices. Using first-principles calculations, we systematically investigate the magnetic properties of monolayer ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ (F5GT) under two scenarios: (I) Co and Ni doping and (II) compressive and tensile strains. Our results show that the F5GT monolayer exhibits a weak in-plane MAE, which can be significantly enhanced by Co doping. Additionally, a $1\%$ compressive strain switches the magnetic easy axis from in plane to out of plane, while $4\%$ compressive strain can further enhance the out-of-plane MAE. Spin-orbit coupling matrix analysis reveals that the enhancement of in-plane MAE in Co-doped F5GT arises from changes in $\langle {\mathit{p}}_x\left|L_z\right|{\mathit{p}}_y\rangle$ of Te and $\langle {\mathit{d}}_{xy}\left|L_z\right|{\mathit{d}}_{x^2+y^2}\rangle$ of Fe(2) and Fe(3). The effect of compressive strain is primarily attributed to a substantial increase in the positive contribution from $\langle {\mathit{d}}_{xy}\left|L_z\right|{\mathit{d}}_{x^2+y^2}\rangle$ of Fe(1).

Recent case-by-case studies revealed that the dispersion of low-energy excitations in gapless frustration-free Hamiltonians is often quadratic or softer. In this paper, we argue that this is actually a general property of such systems. By combining the previous study by Bravyi and Gosset and the min-max principle, we prove this hypothesis for models with local Hilbert spaces of dimension two that contains only nearest-neighbor interactions on cubic lattice. This may be understood as a no-go theorem realizing gapless phases with linearly dispersive excitations in frustration-free Hamiltonians. We also provide examples of frustration-free Hamiltonians in which the plane-wave state of a single spin flip does not constitute low-energy excitations.

We analyze the transport properties of curved, three-dimensional graphite samples in strong magnetic fields. Focusing on a millimeter-scale graphite cylinder as a prototypical curved object, we perform longitudinal and Hall voltage measurements while applying quantizing magnetic fields. These measurements are investigated as a function of field strength and angles. Most importantly, we find that angle-dependent Shubnikov-de Hass oscillations are superimposed with angle-independent features. Reproducing the experimental observations, we introduce a network model that accounts for the cylindrical geometry effect by conceptualizing the cylinder as composed of strips of planar graphite in an effectively inhomogeneous magnetic field. Our work highlights how the interplay between geometric curvature and quantizing magnetic fields can be leveraged to engineer tunable spatial current densities within solid-state systems, and paves the way for understanding transport properties of curved and bent three-dimensional samples more generally.

${\mathrm{PtTe}}_2$ and ${\mathrm{PdTe}}_2$ are among the first transition metal dichalcogenides that were predicted to host type-II Dirac fermions, exotic particles prohibited in free space. These materials are layered and air stable, which makes them top candidates for technological applications that take advantage of their anisotropic magnetotransport properties. Here, we provide a detailed characterization of the electronic structure of ${\mathrm{PtTe}}_2$ and ${\mathrm{PdTe}}_2$ using angle-resolved photoemission spectroscopy (ARPES) and density functional theory calculations, offering an alternative interpretation for one of the Dirac-like dispersions in these materials. Through the use of circularly polarized light, we report a different behavior of such dispersion in ${\mathrm{PdTe}}_2$ compared to ${\mathrm{PtTe}}_2$, that we relate to a symmetry analysis of the dipole matrix element. Such analysis reveals a link between the observed circular dichroism and the different momentum-dependent terms in the dispersion of these two compounds, despite their close similarity in crystal structure. Additionally, our data show a clear difference in the circular dichroic signal for the type-II Dirac cones characteristic of these materials, compared to their topologically protected surface states. Our paper provides a useful reference for the ARPES characterization of other transition metal dichalcogenides with topological properties and illustrates the use of circular dichroism as a guide to identify the topological character and attributes of two otherwise equivalent band dispersions.

We report measurements of the low-temperature magnetization $M$ and specific heat $C$ as a function of temperature and magnetic field of the quasi-one-dimensional spin chain, heavy-fermion compound ${\mathrm{YbFe}}_5{\mathrm{P}}_3$, which resides close to a quantum critical point. The results are compared to the predictions of scaling laws obtained from a generalized free-energy function expected near an antiferromagnetic quantum critical point (AFQCP). The scaling behavior depends on the dimensionality $d$ of the fluctuations, the coherence length exponent $\nu$, and the dynamic exponent $z$. The free energy treats the magnetic field as a relevant renormalization group variable, which leads to a new exponent $\varphi =\nu z_h$, where $z_h$ is a dynamic exponent expected in the presence of a magnetic field. When $z_h=z,T/H$ scaling is expected, as observed in several compounds close to a QCP; whereas in ${\mathrm{YbFe}}_5{\mathrm{P}}_3$, a $T/H^{3/4}$ dependence of the scaling is observed. This dependence reflects the relationship $z_h=(4z/3)$ and a field exponent $\varphi =4/3$. A feature of the scaling law is that it restricts the possible values of the exponents to two cases for ${\mathrm{YbFe}}_5{\mathrm{P}}_3$: $d=1$, $\nu =1$, $z=1$, and $d=2$, $\nu =1/2$, $z=2$.

We developed a quantum eigensolver (QE), which is based on an extension of optimized binary configurations measured by quantum annealing (QA) on a D-Wave quantum annealer (D-Wave QA). This approach performs iterative QA measurements to optimize the eigenstates $|\psi \rangle$ without the derivation of a classical computer. The computational cost is $\eta ML$ for full eigenvalues $E$ and $|\psi \rangle$ of the Hamiltonian $\widehat{H}$ of size $L\times L$, where $M$ and $\eta$ are the number of QA measurements required to reach the converged $|\psi \rangle$ and the total annealing time of many QA shots, respectively. Unlike the exact diagonalization algorithm with $L^3$ iterations on a classical computer, the computation cost is not significantly affected by $L$ and $M$ because $\eta$ represents a very short time within ${10}^{-2}$ seconds on the D-Wave QA. We selected the tight-binding $\widehat{H}$ that contains the exact $E$ values of all energy states in two systems with metallic and insulating phases. We confirmed that the proposed QE algorithm provides exact solutions within the errors of $5\times {10}^{-3}$. Finally, we believe that the newly developed QE algorithm will be widely used for various applications such as material and drug design.

The “blue-green” phosphorescence/thermoluminescence is most commonly observed in diamonds following excitation at or above the indirect band gap and has been explained by a substitutional nitrogen-boron donor-acceptor pair recombination model. “Orange” and “red” phosphorescence have also been frequently observed in laboratory-grown near-colorless high-pressure high-temperature diamonds following optical excitation and their luminescence mechanisms are shown to be different from that of the blue-green phosphorescence. The physics of the orange and red luminescence and phosphorescence bands including the optical-excitation dependency (UV-NIR), temperature dependency ($20\mathrm{K}\text{–}573\mathrm{K}$), and related charge transfer process are investigated by a combination of self-built time-resolved imaging/spectroscopic techniques. In this paper, an alternative model for long-lived phosphorescence based on charge trapping is proposed to explain the orange phosphorescence/thermoluminescence band. Additionally, the red phosphorescence band is attributed to point defect, which possibly has a three-level phosphorescence system.

We theoretically propose an antiferromagnetic silicene/superconductor hybrid structure, which unveils unconventional Andreev reflections (ARs) due to the Rashba spin-orbit and interface couplings. They are characterized by perfect spin- or/and valley-triplet pairing states with the spin or/and valley being fully polarized. Of the most striking is the spin-valley-triplet (intravalley equal-spin) AR induced by the combination of spin-flip and valley-mixing scatterings, which is an alternative pairing process. The tunability of spin and valley polarizations in antiferromagnetic silicene enables a spin-valley pairing switch between three types of triplet (intervalley equal-spin, intravalley opposite-spin, and intravalley equal-spin) pairing AR processes. It is also demonstrated that the corresponding subgap conductance spectra for each type exhibits distinct characteristic features, which can be directly tested experimentally using scanning tunnel microscope measurements and/or point-contact spectroscopy. Our findings may pave the way for the application of silicene in spin-valleytronics.

Magnetic inertia has emerged as a possible way to manipulate ferromagnetic spins at a higher frequency, e.g., terahertz. Theoretical treatments so far have considered the magnetic inertia as a scalar quantity. Here, we explore the magnetic inertial dynamics with a magnetic inertia tensor as macroscopic derivations predicted it to be a tensor. First, the inertia tensor has been decomposed into three terms: (a) scalar and isotropic inertia, (b) anisotropic and symmetric inertia tensor, (c) chiral and antisymmetric tensor. Further, we employ linear response theory to the inertial Landau-Lifshitz-Gilbert equation with the inertia tensor and calculate the effect of chiral and anisotropic inertia on ferromagnets, antiferromagnets, and ferrimagnets. It is established that the precession and nutation resonance frequencies decrease with scalar magnetic inertia. Our results suggest that the nutation resonance frequencies further reduce due to inertia tensor. However, the effective damping of the nutation resonance increases with the chiral and antisymmetric part of the inertia tensor. We show that the precession resonances remain unaffected, while the nutation resonances are modified with the chiral magnetic inertia.

Magnetic damping induces the temporal and spatial decay of spin waves, characterized by the damping factor and attenuating length, both of which can be measured to determine various magnetic and spin-transport parameters. By investigating the dispersion and dissipation of inertial spin waves driven by spin-transfer torques, we find that magnetic inertia modifies the dependence of the damping factor and attenuating length on the electric current and spin wave frequency. This provides a valuable method for probing the inertial relaxation time.