The results of investigation of the ${\mathrm{Cr}}_x\mathrm{Nb}{\mathrm{Se}}_2$ chalcogenides $(x=0.33,0.5)$ by the nuclear magnetic resonance (NMR) method on ${}^{53}\mathrm{Cr}$ and ${}^{93}\mathrm{Nb}$ nuclei in the magnetically ordered state at zero external magnetic field have been presented. Ab initio calculations have been performed to theoretically estimate NMR parameters and interpret the experimental data. It has been shown that the intercalation of Cr atoms into $\mathrm{Nb}{\mathrm{Se}}_2$ results in spin and charge redistributions. The lower magnetic moment of chromium nuclei, $2.2{\mu }_{\mathrm{B}}$, compared to the theoretical value $\mu =3{\mu }_{\mathrm{B}}$ for ${\mathrm{Cr}}^{3+}$ is attributed to the high degree of hybridization of the $a_{1g}$ and $e_g$ orbitals of $3d$ Cr electrons with $4d_{z^2}$ and $5s$ niobium orbitals. Such a hybridization also results in the presence of a high local magnetic field in the niobium nuclei location in ${\mathrm{Cr}}_x\mathrm{Nb}{\mathrm{Se}}_2$.

The electronic structures of the heavy-fermion superconductor $\mathrm{Ce}{\mathrm{Rh}}_2{\mathrm{As}}_2$ with local inversion symmetry breaking and the reference material $\mathrm{La}{\mathrm{Rh}}_2{\mathrm{As}}_2$ have been investigated by using experimental optical conductivity $\left[{\sigma }_1\left(\omega \right)\right]$ spectra and first-principles density functional theory calculations. The low-temperature ${\sigma }_1\left(\omega \right)$ spectra of $\mathrm{La}{\mathrm{Rh}}_2{\mathrm{As}}_2$ revealed a broad peak at $\sim 0.1\mathrm{eV}$ and a sharp peak at $\sim 0.5\mathrm{eV}$ after a subtraction of the Drude contribution of free carriers. The peak features and the background intensity were nicely reproduced in calculated ${\sigma }_1\left(\omega \right)$ spectra from DFT calculations, implying a conventional metallic nature. In $\mathrm{Ce}{\mathrm{Rh}}_2{\mathrm{As}}_2$, two mid-IR peaks at $\hslash \omega \sim 0.12$ and 0.4 eV corresponding to the unoccupied Ce $4f_{5/2}$ and $4f_{7/2}$ states, respectively, were strongly developed with decreasing temperature, which suggests the emergence of hybridization states between the conduction and $4f$ electrons. We compared the temperature dependence of the mid-IR peaks of $\mathrm{Ce}{\mathrm{Rh}}_2{\mathrm{As}}_2$ with corresponding data from $\mathrm{Ce}{\mathrm{Cu}}_2{\mathrm{Si}}_2$ and $\mathrm{Ce}{\mathrm{Ni}}_2{\mathrm{Ge}}_2$ in a $\mathrm{Th}{\mathrm{Cr}}_2{\mathrm{Si}}_2$-type structure to examine the possible impact of local inversion symmetry breaking on electronic structures.

The compound ${\mathrm{ZrTe}}_5$ has recently been connected to a charge-density-wave (CDW) state with intriguing transport properties. Here, we investigate quantum oscillations in ultrasound measurements that microscopically originate from electron-phonon coupling and analyze how these would be affected by the presence or absence of a CDW. We calculate the phonon self-energy due to electron-phonon coupling, and from there deduce the sound-velocity renormalization and sound attenuation. We find that the theoretical predictions for a metallic Dirac model resemble the experimental data on a quantitative level for magnetic fields up to the quantum-limit regime.

Atomically thin two-dimensional (2D) magnets have given rise to emergent phenomena due to magnetic exchange and spin-orbit coupling showing great promise for realizing ultrathin device structures. In this paper, we critically examine the magnetic properties of 2D ${\mathrm{FeS}}_2$, a non van der Waals magnet, which has been recently claimed to exhibit room-temperature ferromagnetism in the (111) orientation. Our ab initio study based on collinear density functional theory has revealed the ground state as an antiferromagnetic one with an ordering temperature of around 100 K along with a signature of spin-phonon coupling, which may trigger a ferromagnetic coupling via strain. Moreover, our calculations based on spin spirals indicate the possibility of noncollinear magnetic structures, which is also supported by Monte Carlo simulations based on ab initio magnetic exchange parameters. This opens up an excellent possibility to manipulate magnetic structures by the application of directional strain.

We have conducted dielectric measurements of ice VII at pressures up to 12.2 GPa, and verified a dominant-dynamics change from a molecular rotation to a proton translation at approximately 10 GPa, using a newly developed high-pressure cell. Based on relaxation times of the two motions, which have a crossover point between 9 and 10 GPa, we show that the change in the disordered states in ice VII can be characterized by the time scale of the motions. Our results provide a suitable explanation of the long-standing problem of the anomalous behavior of ice VII at around 10 GPa.

The spin-$\frac{3}{2}$ Heisenberg antiferromagnet on the bilayer honeycomb lattice is a minimal model to describe the magnetic behavior of ${\mathrm{Bi}}_3{\mathrm{Mn}}_4{\mathrm{O}}_{12}\left({\mathrm{NO}}_3\right)$. We study this model with frustrating interlayer second-neighbor couplings taking into account quantum and thermal fluctuations. We use a path integral formulation in terms of coherent states to describe the low-energy physics of the model. We show that for a particular point in the parameter space, close to the experimental estimated couplings, a continuum classical degeneracy is lifted by both quantum and thermal fluctuations, and a collinear state is then selected by an order by disorder mechanism. Our results provide a global perspective in the understanding of the experimental observations.

We study magnetic properties of a periodically driven Mott insulator with strong spin-orbit coupling and show some properties characteristic of linearly polarized light. We consider a $t_{2g}$-orbital Hubbard model driven by circularly or linearly polarized light with strong spin-orbit coupling and derive its effective Hamiltonian in the strong-interaction limit for a high-frequency case. We show that linearly polarized light can change not only the magnitudes and signs of the exchange interactions, but also their bond anisotropy even without the bond-anisotropic hopping integrals. Because of this property, the honeycomb-network spin system could be transformed into weakly coupled zigzag or step spin chains for the light field polarized along the $b$ or $a$ axis, respectively. Then, analyzing how the light fields affect several magnetic states in a mean-field approximation, we show that linearly polarized light can change the relative stability of the competing magnetic states, whereas such a change is absent for circularly polarized light. We also analyze the effects of both the bond anisotropy of nearest-neighbor hopping integrals and a third-neighbor hopping integral on the magnetic states and show that the results obtained in a simple model, in which the bond-averaged nearest-neighbor hopping integrals are considered, remain qualitatively unchanged except for the stability of zigzag states in the nondriven case and the degeneracy lifting of the zigzag or stripy states.

Majorana bound states are zero-energy states predicted to emerge in topological superconductors and intense efforts seeking definitive proof of their observation are still ongoing. A standard route to realize them involves antagonistic orders: a superconductor in proximity to a ferromagnet. Here, we show that this issue can be resolved using antiferromagnetic rather than ferromagnetic order. We propose to use a chain of antiferromagnetic skyrmions, in an otherwise collinear antiferromagnet, coupled to a bulk conventional superconductor as a novel platform capable of supporting Majorana bound states that are robust against disorder. Crucially, the collinear antiferromagnetic region neither suppresses superconductivity nor induces topological superconductivity, thus allowing for Majorana bound states localized at the ends of the chain. Our model introduces a new class of systems where topological superconductivity can be induced by editing antiferromagnetic textures rather than locally tuning material parameters, opening avenues for the conclusive observation of Majorana bound states.

In the framework of the dynamic facilitation model, a glass former is structured with local cooperative excitations in space and time when approaching the glass transition, which is closely related to dynamic relaxations. We investigate the structure of excitation fields in supercooled ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ glass former, and reveal that the excitation fields feature the vortexlike structure beyond the well-known stringlike excitations. The vortex is developed from the stringlike excitations and frequently annihilates via the interactions between vortex and antivortex. The region favored by vortices exhibits percolationlike morphology. We find that the probability distributions of vortex core number are characterized by the discrete multiple mode, which is very analogous to the quantized mode of the slow-β type relaxation. Furthermore, the relaxation time derived from the formation rate of vortices as well as the corresponding activation energy coincide with the characteristic values of the slow-β relaxation in metallic glasses. Therefore, it is concluded that the vortex excitation is the origin of the slow-β relaxation in dynamic space. We further find that the activation energy and relaxation time associated with individual excitations agree well with the Johari-Goldstein β relaxation. It manifests a more intrinsic structural sign of the Johari-Goldstein β relaxation than the interpretation based on stringlike excitations.

Quantum magnonics is an emerging research field, with great potential for applications in magnon based hybrid systems and quantum information processing. Quantum correlation, such as entanglement, is a central resource in many quantum information protocols that naturally comes about in any study toward quantum technologies. This applies also to quantum magnonics. Here, we investigate antiferromagnetic coupling of two ferromagnetic sublattices that can have two different magnon modes. We show how this may lead to experimentally measurable bipartite continuous-variable magnon-magnon entanglement. The entanglement can be fully characterized via a single squeezing parameter or, equivalently, entanglement parameter. The clear relation between the entanglement parameter and the Einstein, Podolsky, and Rosen (EPR) function of the ground state opens up for experimental quantification magnon-magnon continuous-variable entanglement and EPR nonlocality. We propose a practical experimental realization to measure the EPR function of the ground state, in a setting that relies on magnon-photon interaction in a microwave cavity.

In this letter, we study the origin of the anomalous Hall effect (AHE) in ferrimagnetic insulator ${\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TmIG)/Pt heterostructures. A monotonic decrease of the anomalous Hall resistivity ($\mathrm{\Delta }{\rho }_{\mathrm{AHE}}$) with decreasing temperature is observed for TmIG/Pt, and a sign reversal of $\mathrm{\Delta }{\rho }_{\mathrm{AHE}}$ occurs at around 80 K. With the addition of a Cu interlayer, the $\mathrm{\Delta }{\rho }_{\mathrm{AHE}}$ similarly decreases as a function of temperature, but maintains the same sign across the full temperature range. This indicates that both the magnetic-proximity effect and spin Hall effect in the TmIG/Pt bilayer contribute to the AHE signal with opposing signs. The spin-Hall contribution to the AHE is dominant at room temperature but decreases with decreasing temperature. Meanwhile, the magnetic-proximity contribution to the AHE becomes dominant with decreasing temperatures, leading to a change of sign for $\mathrm{\Delta }{\rho }_{\mathrm{AHE}}$. We exclude a dominant influence of a ferrimagnetic compensation point in the temperature region by complementary magnetic hysteresis and neutron diffraction measurements. Our work, based on a simple method, sheds light on the origin of the AHE in magnetic insulator heterostructures, where the competition between the magnetic-proximity effect and spin Hall effect governs the sign and amplitude of the AHE.

We report the effect of magnetic dilution on the physical properties of $\left({\mathrm{Gd}}_{1-x}{\mathrm{Y}}_x\right){\mathrm{Cd}}_6$ approximant crystals (ACs), close siblings of their corresponding quasicrystal (QC). Compared to the pure system ${\mathrm{GdCd}}_6$, we observe remarkable changes in the thermodynamic and magnetic bulk properties near and below the static-ordering temperatures from diluting the magnetic Gd atoms with nonmagnetic Y atoms by only 1–3% $(x=0.01–0.03)$. On the other hand, the corresponding QC system exhibits a monotonic change in its spin-glass behavior upon the magnetic dilution. We discuss the origin of the magnetic-dilution behavior in the present AC system in terms of possible magnetic frustration and short-range magnetic correlation that can be linked to its peculiar structure.

We report the nanoscale spin detection and electron paramagnetic resonance (EPR) spectrum of copper $\left({\mathrm{Cu}}^{2+}\right)$ ions via double electron-electron resonance (DEER) with single spins in diamond at room temperature and low magnetic fields. We measure unexpectedly narrow EPR resonances with linewidths $\sim 2-3$ MHz from copper-chloride molecules dissolved in polylysine. We also observe coherent Rabi oscillations and hyperfine splitting from single ${\mathrm{Cu}}^{2+}$ ions, which could be used for dynamic nuclear spin polarization and higher sensitivity of spin detection. We interpret and analyze these observations using both spin Hamiltonian modeling of the copper-chloride molecules and numerical simulations of the predicted DEER response, and obtain a sensing volume $\sim {\left(250\text{nm}\right)}^3$. This work will open the door for copper-labeled EPR measurements under ambient conditions in biomolecules and nanomaterials.

We continue our exploration of exotic, gapless lattice and continuum field theories with subsystem global symmetries. In an earlier paper, we presented free lattice models enjoying all the global symmetries (except continuous translations), dualities, and anomalies of the continuum theories. Here, we study in detail the relation between the lattice models and the corresponding continuum theories. We do that by analyzing the spectrum of the theories and several correlation functions. These lead us to uncover interesting subtleties in the way the continuum limit can be taken. In particular, in some cases, the infinite volume limit and the continuum limit do not commute. This signals a surprising UV/IR mixing, i.e., long-distance sensitivity to short-distance details.

We investigate non-Hermitian spectrum and multistability of exciton-polariton condensates excited by a nonresonant pump. An increase in pumping power moves the system away from non-Hermitian spectrum degeneracy toward bifurcation through an exceptional point, which induces a transition from monostability to multistability. The spectrum can be used as a universal method for detecting this transition. In the region of multistability, the system contains one steady and two metastable states. The analyses of stability show that metastable states maintain a finite lifetime and eventually evolve into steady states, which are induced by non-Hermitian skin effects. We also discover a steady state with multipeak soliton for attractive polariton-polariton interaction, which is different from general single-peak soliton for repulsive interaction. Our results open up exciting possibilities for controlling non-Hermitian quantum multistable states, which may be useful for designing polariton-based devices exploiting optical multistability.

We propose here a counterdiabatic (CD) strategy for the fast preparation of a state with long-range topological order by magnetic field tuning of an initial separable state. For concreteness, we consider the ground state of the honeycomb Kitaev model whose long-range topological order together with the anyonic excitations make it an interesting candidate for fault-tolerant universal quantum computation and storage. We implement an approximate local CD perturbation having the form of the off-diagonal exchange interactions in Kitaev Hamiltonians. The counterdiabatically produced state is found to have a high fidelity $(\gtrsim 0.5)$ and retains numerous desired entanglement properties while giving a speed-up of the order of ${10}^6$. In our study of up to 24-spin clusters we found the fidelity is constrained by the spectral gap rather than the system size.

Detailed analysis of the defect-related photoluminescence (PL) in semi-insulating and $n$-type Be-doped GaN samples grown by molecular beam epitaxy is presented. The dominant PL bands in these samples are the ultraviolet $\left({\mathrm{UVL}}_{\mathrm{Be}}\right)$, yellow $\left({\mathrm{YL}}_{\mathrm{Be}}\right)$, red $\left({\mathrm{RL}}_{\mathrm{Be}}\right)$, and green (GL2) bands. The ${\mathrm{UVL}}_{\mathrm{Be}}$ band is caused by electron transitions via the $0/-$ level of the ${\mathrm{Be}}_{\mathrm{Ga}}$ acceptor located at 113 meV above the valence band. The ${\mathrm{UVL}}_{\mathrm{Be}}$ band is quenched above 60 K, and the quenching is tunable by excitation intensity. The quenching of the ${\mathrm{YL}}_{\mathrm{Be}}$ above 200 K is likely related to an acceptor level at 0.3 eV. In semi-insulating samples, the quenching temperature is tunable with the intensity of the excitation laser. Based on the first-principles calculations, the ${\mathrm{YL}}_{\mathrm{Be}}$ band is preliminarily attributed to the ${\mathrm{Be}}_{\mathrm{Ga}}\text{−}{\mathrm{V}}_{\mathrm{N}}\text{−}{\mathrm{Be}}_{\mathrm{Ga}}$ complex. The new ${\mathrm{RL}}_{\mathrm{Be}}$ band is attributed to the internal transition in the ${\mathrm{Be}}_{\mathrm{Ga}}\text{−}{\mathrm{V}}_{\mathrm{N}}$ complex with a deep $+/0$ transition level at about 0.95 eV.

Material-dependent signs of the spin Hall conductivity are a useful tool to distinguish the spin Hall effect from other spin phenomenon. Similarly, material-dependent signs of the orbital Hall effect (OHE) can be a useful tool to distinguish the OHE from other effects. But previous theoretical calculations of the orbital Hall conductivity (OHC) found mostly positive sign, making difficult the OHE detection based on the material dependence of the OHC sign. We investigate the intrinsic OHE in elemental group XIV materials Si, Ge, and $\alpha$-Sn with diamond cubic structures. We find that the OHC in these materials are gigantic $\sim {10}^3(\hslash /e){\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$ and negative. These materials have two pairs of valence bands interacting with each other to generate negative orbital Berry curvature. Further, we suggest the usage of these materials to measure the OHE.