We investigate low-energy magnon excitations above the noncollinear flux state and noncoplanar canted flux state in a Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interaction (DMI) on a Sashtry-Sutherland lattice. While previous studies have shown the presence of topological magnetic excitation in the dimer and ferromagnetic phases on the Shastry-Sutherland lattice, our results establish the nontrivial topology of magnons in the antiferromagnetic flux and canted flux states. Our results uncover the existence of a multitude of band topology transitions in the magnon sector—evidenced by the changing Chern numbers of the single magnon bands—as the Hamiltonian parameters are varied, even when the ground state remains unchanged. The thermal Hall conductivity is calculated and its derivative is shown to exhibit a logarithmic divergence at the boundaries of band topology transitions, independent of the type of band touching involved. A simple analytical form of the temperature dependence of a logarithmic peak is derived for a generic spin model. This may provide a useful means to identify the energy at which the band topological transition of magnon bands occurs. We also propose the way to realize the studied model in a practical material.

We analyze the zero temperature phase diagrams of the spin $S$ quantum antiferromagnet on square and triangular lattices with competing nearest and next-nearest exchange interactions as well as biquadratic couplings. We approach the problem from the large $S$ limit. Our primary focus is on determining the extent to which the existence and character of any quantum disordered phases can be inferred from this approach.

Single crystals of monoclinic ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ were grown using a self-flux method and were characterized by room-temperature powder x-ray diffraction, anisotropic temperature- and field-dependent magnetization, temperature-dependent resistivity, specific heat, and muon spin rotation. ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ has a Curie temperature ($T_{\mathrm{C}}$) of 3.8 K and clear signatures of ferromagnetism in magnetization and $\mu \mathrm{SR}$ data, as well as a clear loss of spin disorder scattering in resistivity data and a sharp specific heat anomaly. The magnetism associated with ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ is itinerant has a change in the entropy at $T_{\mathrm{C}}$ of $\simeq 0.05Rln2$ per mol Co and has a low-field saturated moment of $\sim 0.1{\mu }_{\mathrm{B}}/\mathrm{Co}$, making it a rare, itinerant, small moment, low-$T_{\mathrm{C}}$ compound.

Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of ${\mathrm{LaH}}_{10}$ under megabar pressure. Specifically, the isotope effect of $T_{\mathrm{c}}$ was measured by the replacement of hydrogen (H) with deuterium (D), demonstrating a driving role of phonons in the observed room-temperature SC. Herein, based on the first-principles calculations within the harmonic approximation, we reveal that (i) the identical electron-phonon coupling constants of fcc ${\mathrm{LaH}}_{10}$ and ${\mathrm{LaD}}_{10}$ decrease monotonously with increasing pressure and (ii) the isotope effect of $T_{\mathrm{c}}$ is nearly proportional to $M^{-\alpha }$ ($M$: ionic mass) with $\alpha \approx$ 0.465, irrespective of pressure. The predicted value of $\alpha$ agrees well with the experimental one ($\alpha =0.46$) measured at around 150 GPa. Thus, our findings provide a theoretical confirmation of the conventional electron-phonon coupling mechanism in a recently discovered room-temperature superconductor of compressed ${\mathrm{LaH}}_{10}$.

For the skyrmion-hosting intermetallic ${\mathrm{Gd}}_2{\mathrm{PdSi}}_3$ with centrosymmetric hexagonal lattice and triangular net of rare earth sites, we report a thorough investigation of the magnetic phase diagram. Our work reveals a magnetic phase with an isotropic value of the critical field for all orientations, where the magnetic ordering vector $\mathbf{q}$ is depinned from its preferred directions in the basal plane. The bulk nature of the skyrmion lattice and of other magnetic phases was evidenced by specific-heat measurements. Resistivity anisotropy, likely originating from partial gapping of the density of states along $\mathbf{q}$ in this Ruderman-Kittel-Kasuya-Yosida magnet, is picked up via the planar Hall effect (PHE). The PHE confirms the single-$\mathbf{q}$ nature of the magnetic order when the field is in the hexagonal plane, and allows one to detect the preferred directions of $\mathbf{q}$. Several scenarios for the depinned phase, such as tilted conical order, are discussed on the basis of the data.

Despite much effort over the past two decades, the pairing symmetry of a ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ superconductor is still unclear. Motivated by the recent rapid progress in fabrication techniques for ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ thin films, we propose a promising strategy for identifying the spin-triplet superconductivity in the thin-film geometry by employing an antisymmetric spin-orbit-coupling potential and a Zeeman potential due to an external magnetic field. We demonstrate that a spin-triplet superconducting thin film undergoes a phase transition from a helical state to a chiral state by increasing the applied magnetic field. This phase transition is accompanied by a drastic change in the property of surface Andreev bound states. As a consequence, the helical-chiral phase transition, which is unique to the spin-triplet superconductors, can be detected through a sudden change in a tunneling conductance spectrum of a normal-metal/superconductor junction. Importantly, our proposal is constructed by combining fundamental and rigid concepts regarding the physics of spin-triplet superconductivity.

We evidenced by means of optical microscopy the long-range character of the interactions acting in spin crossover (SCO) single crystals through a study of the optical density (OD) variation during the spin transition between high-spin (HS) and low-spin (LS) states. The time evolution of the local OD, measured in four single crystals, revealed the existence of precursor phenomena, which are manifest through the appearance of significant changes in the OD of the probed area well before the arrival of the front interface in the case of HS to LS transition and after the passage of the interface in the case of LS to HS transition. These two effects are attributed to the manifestation of long-range interactions that develop during the propagation of the HS/LS interface, which is accompanied by a volume change, generating elastic stresses in the material that deploy far from the sources. Interestingly, the experimental investigations indicate that the precursor and the after effect phenomena occur mostly in the HS phase, which is softer than the LS phase. These original experimental results are well reproduced using an electroelastic modeling in which we considered, in addition to the lattice misfit between HS and LS states, the existence of different elastic constants in the HS and LS phases.

We study a transition between a homogeneous and an inhomogeneous phase in a system of one-dimensional, Raman tunnel-coupled Bose gases. The homogeneous phase shows a flat density and phase profile, whereas the inhomogeneous ground state is characterized by periodic density ripples and a soliton staircase in the phase difference. We show that under experimentally viable conditions the transition can be tuned by the wave-vector difference $Q$ of the Raman beams and can be described by the Pokrovsky-Talapov model for the relative phase between the two condensates. Local imaging available in atom chip experiments allows us to observe the soliton lattice directly, while modulation spectroscopy can be used to explore collective modes, such as the phonon mode arising from breaking of translation symmetry by the soliton lattice. In addition, we investigate regimes where the cold atom experiment deviates from the Pokrovsky-Talapov field theory. We predict unusual mesoscopic effects arising from the finite size of the system, such as quantized injection of solitons upon increasing $Q$, or the system size. For moderate values of $Q$ above criticality, we find that the density modulations in the two gases interplay with the relative phase profile and introduce novel features in the spatial structure of the mode wave functions. Using an inhomogeneous Bogoliubov theory, we show that spatial quantum fluctuations are intertwined with the emerging soliton staircase. Finally, we comment on the prospects of the ultracold atom setup.

We have studied the compression behavior of ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures in comparison with pure ${\mathrm{H}}_2$ and He using powder synchrotron x-ray diffraction, and we present the pressure-volume (PV) compression data of ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures to 160 GPa. The results indicate that both ${\mathrm{H}}_2$ and He in ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures remain in hcp to the maximum pressure studied, yet they develop a substantial level of lattice distortion in the (100) plane, most profound in He-rich solids and below 66 GPa. The measured PV data also indicate the softening of an He (or ${\mathrm{H}}_2$) -rich lattice upon increasing the level of the guest ${\mathrm{H}}_2$ (or He) concentration. We suggest that the observed softening and lattice distortion are due to a substitutional incorporation of ${\mathrm{H}}_2$ (guest) molecules into the basal plane of the hcp-He (host) lattice, and thereby reflect the miscibility between ${\mathrm{H}}_2$ and He in ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures. Interestingly, solid He exhibits a lesser degree of preferred orientation in ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures than in pure He, likely due to the presence of solid ${\mathrm{H}}_2$ disturbing the crystalline ordering of He-rich solids. Finally, the present PV compression data of ${\mathrm{H}}_2$-rich and He-rich solids to 160 GPa deviate from those of pure ${\mathrm{H}}_2$ and pure He above ∼70 and 45 GPa respectively, providing new constraints for the development of the equation of state for ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures for planetary models.

The tenfold classification of topological phases enumerates all strong topological phases for both clean and disordered systems. These strong topological phases are connected to the existence of robust edge states. However, in addition to the strong topological phases in the tenfold classification, there exist weak topological phases whose properties under disorder are less well understood. It is unknown if the weak topological indices can be generalized for arbitrary disorder, and the physical signatures of these indices is not known. In this paper, we study disordered models of the two-dimensional weak AIII insulator. We demonstrate that the weak invariants can be defined at arbitrary disorder, and that these invariants are connected to the presence or absence of bound charge at dislocation sites.

We report a global effect induced by the local complex field associated with the spin-exchange interaction. High-order exceptional point up to ($N+1$)-level coalescence is created at the critical local complex field applied to the $N$-size quantum spin chain. The ($N+1$)-order coalescent level is a saturated ferromagnetic ground state in the isotropic spin system. Remarkably, the final state always approaches the ground state for an arbitrary initial state with any number of spin flips, even if the initial state is orthogonal to the ground state. Furthermore, the switch of macroscopic magnetization is solely driven by the time and forms a hysteresis loop in the time domain. The retentivity and coercivity of the hysteresis loop mainly rely on the non-Hermiticity. Our findings highlight the cooperation of non-Hermiticity and the interaction in the quantum spin system, suggest a dynamical framework to realize magnetization, and thus pave the way for the non-Hermitian quantum spin system.

Magnetic damping plays a crucial role in the dynamics of magnetic systems. Hence, control over the damping is highly desirable for the development of magnetic devices. One of the possible ways to manipulate magnetic damping in a ferromagnetic material is the injection of spin currents generated by the spin Hall effect. The generated spin currents can be used to manipulate magnetic moments as well as the effective damping of the ferromagnetic material. In this paper, we demonstrate that the influence of the spin current on the damping is highly sensitive to the relative direction of the spin polarization and the precessional axis of the magnetization. The observations are important for various applications in magnetic storage devices and in microwave signal processing.

Magnetic first-order phase transitions are key for the emergence of functionalities of fundamental and applied significance, including magnetic shape memory as well as magnetostrictive and magnetocaloric effects. Such transitions are usually associated with thermomagnetic hysteresis. We report the observation of a first-order transition in $\mathrm{P}{\mathrm{r}}_2\mathrm{In}$ from a paramagnetic to a ferromagnetic state at $T_C=57\mathrm{K}$ without a detectable thermomagnetic hysteresis, which is also accompanied by a large magnetocaloric effect. The peculiar electronic structure of $\mathrm{P}{\mathrm{r}}_2\mathrm{In}$ exhibiting a large density of states near the Fermi energy explains the highly responsive magnetic behavior of the material. The magnetic properties of $\mathrm{P}{\mathrm{r}}_2\mathrm{In}$ are reported, including observation of another (second-order) magnetic transition at 35 K.

Thermodynamic properties, ${}^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) measurements, and density-functional band-structure calculations for $\varepsilon \text{−}{\mathrm{LiVOPO}}_4$ are reported. This quantum magnet features a singlet ground state and comprises two types of alternating spin-$\frac{1}{2}$ chains that manifest themselves by the double maxima in the susceptibility and magnetic specific heat, and by the two-step magnetization process with an intermediate $\frac{1}{2}$-plateau. From thermodynamic data and band-structure calculations, we estimate the leading couplings of $J_1\simeq 20$ K and $J_2\simeq 60$ K and the alternation ratios of ${\alpha }_1=J_1^{\prime }/J_1\simeq 0.6$ and ${\alpha }_2=J_2^{\prime }/J_2\simeq 0.3$ within the two chains, respectively. The zero-field spin gap ${\mathrm{\Delta }}_0/k_{\mathrm{B}}\simeq 7.3$ K probed by thermodynamic and NMR measurements is caused by the $J_1\text{−}{J}_1^{\prime }$ spin chains and can be closed in the applied field of ${\mu }_0{H}_{\mathrm{c}1}\simeq 5.6$ T, giving rise to a field-induced long-range order. The NMR data reveal predominant three-dimensional spin-spin correlations at low temperatures. Field-induced magnetic ordering transition observed above $H_{\text{c}1}$ is attributed to the Bose-Einstein condensation of triplons in the sublattice formed by the $J_1\text{−}{J}_1^{\prime }$ chains with weaker exchange couplings.

A semiconducting nanowire proximitized by an $s$-wave superconductor can be tuned into a topological state by an applied magnetic field. This quantum phase transition is marked by the emergence of Majorana zero modes at the ends of the wire. The fusion of Majorana modes at a junction between two nanowires results in a $4\pi$-periodic Josephson effect. We elucidate how the $4\pi$ periodicity arises across the topological phase transition in a highly-transparent short nanowire junction. Owing to a high transmission coefficient, Majorana zero modes coming from different wires are strongly coupled, with an energy scale set by the proximity-induced, field-independent pairing potential. At the same time, the topological spectral gap—defined by competition between superconducting correlations and Zeeman splitting—becomes narrow in the vicinity of the transition point. The resulting hybridization of the fused Majorana states with the spectral continuum strongly affects the electron density of states at the junction and its Josephson energy. We study the manifestations of this hybridization in the energy spectrum and phase dependence of the Josephson current. We pinpoint the experimentally observable signatures of the topological phase transition, focusing on junctions with weak backscattering.

Unconventional superconductivity has recently been discovered in the iron-based superconducting silicide LaFeSiH. By using the complementary techniques of muon spin rotation, tunneling diode oscillator, and density-functional theory, we investigate the magnetic penetration depth and thereby the superconducting gap of this high-temperature superconductor. We find that the magnetic penetration depth displays a sub-$T^2$ behavior in the low-temperature regime below $T_c/3$, which evidences a nodal structure of the gap (or a gap with very deep minima). Even if the topology of the computed Fermi surface is compatible with the $s_{\pm }$-wave case with accidental nodes, its nesting and orbital-content features may eventually result in a $d$-wave state, which is more unusual for high-temperature superconductors of this class.

We describe the inclusion of electrodynamic fields in time-dependent density functional theory (TDDFT) by incorporating both the induced scalar and vector potentials within the time-dependent Kohn-Sham equation. The Hamiltonian is described in both the Coulomb and Lorenz gauges, and the advantages of the latter are outlined. Integral expressions are defined for the retarded potentials of each gauge and a methodological approach to evaluate these nontrivial expressions with low computational cost is adopted. Various molecular structures of relatively small sizes are studied, including water, benzene, and conductive carbon chains. Dipole strengths resulting from both pulse and boost excitations suggest a preserved gauge invariance of the proposed formal approach to TDDFT in the weak magnetic field limit.

We propose a mechanism of spin-triplet superconductivity at the edge of $d$-wave superconductors. Recent theoretical research on $d$-wave superconductors predicted that strong ferromagnetic (FM) fluctuations are induced by a high density of states due to edge Andreev bound states (ABSs). Here, we construct a linearized gap equation for the edge-induced superconductivity and perform a numerical study based on a large cluster Hubbard model with a bulk $d$-wave superconducting (SC) gap. We find that ABS-induced strong FM fluctuations mediate the $d\pm ip$-wave SC state, in which the time-reversal symmetry is broken. The edge-induced $p$-wave transition temperature $T_{cp}$ is slightly lower than the bulk $d$-wave one $T_{cd}$, and a Majorana bound state may be created at the end point of the edge.

We study the level-spacing statistics in the entanglement spectrum of output states of random universal quantum circuits where qubits are subject to a finite probability of projection to the computational basis at each time step. We encounter two phase transitions with increasing projection rate. The first is the volume-to-area law transition observed in quantum circuits with projective measurements. We identify a second transition within the area law phase by repartioning the system randomly into two subsystems and probing the entanglement level statistics. This second transition separates a pure Poisson level statistics phase at large projective measurement rates from a regime of residual level repulsion in the entanglement spectrum, characterized by nonuniversal level spacing statistics that interpolates between the Wigner-Dyson and Poisson distributions. By applying a tensor network contraction algorithm introduced in [Z.-C. Yang et al., Phys. Rev. E 97, 033303 (2018)] to the circuit spacetime, we identify this second projective-measurement-driven transition as a percolation transition of entangled bonds. The same behavior is observed in both circuits of random two-qubit unitaries and circuits of universal gate sets, including the set implemented by Google in its Sycamore circuits.