We study the electronic, magnetic, and spin-transport properties of the orthorhombic ${\mathrm{Mn}}_5{\mathrm{Si}}_3$ compound in the AF2 phase using symmetry analysis and ab initio calculations. Our ground-state energy calculations align with experimental observations, demonstrating that the collinear antiferromagnetic (AFM) order, with the Néel vector in the [010] direction, is the most stable magnetic configuration both with and without spin-orbit coupling (SOC) in bulk lattice geometry. We identified an unconventional eightfold degenerate Dirac nodal line (DNL) close to the Fermi level, characterized by negligible SOC. This DNL is robustly protected by a unique combination of pure-spin and lattice symmetries together with magnetic space-group (MSG) symmetries. Upon introducing SOC, this degeneracy is reduced to two fourfold DNLs, being protected by the combination of time-reversal, partial translation, and nonsymmorphic symmetries within the MSG. We also predict a large intrinsic spin Hall conductivity which correlates with the presence of SOC-induced splitting of these eightfold degenerate DNLs near the Fermi level. These intriguing characteristics position the collinear AFM ${\mathrm{Mn}}_5{\mathrm{Si}}_3$ as a compelling candidate for spintronic applications, particularly in the generation and detection of spin currents, while remaining compatible with modern silicon technology.

We report the discovery of multiple topological phase transitions induced by the photonic quantum spin Hall effect (PQSHE) in a non-Hermitian photonic crystal (PhC). When increasing the magnitude of the non-Hermitian terms, the system undergoes transitions from topological corner states to topological edge states and subsequently to topological bulk states. The angular momentum of the wave function of the out-of-plane electric field excited by the chiral source acts as the pseudospin degree of freedom in the PQSHE. Therefore, we consider the introduction of chiral sources with different circular polarizations into non-Hermitian PhCs and observe the emergence of asymmetric field responses. These results are expected to enable the multidimensional manipulation of topological states, offering an avenue for the detection of chiral sources.

Periodically driven (Floquet) systems can exhibit possibilities beyond what can be obtained in equilibrium. Both in Floquet systems and in the related problems of discrete-time quantum walks and quantum cellular automata, a basic distinction arises among unitary time evolution operators: while all physical operators are local, not all are locally generated (i.e., generated by some local Hamiltonian). In this paper, we define the notion of equivalence up to a locally generated unitary in all Altland-Zirnbauer symmetry classes. We then classify noninteracting unitaries in all dimensions on this basis by showing that equivalence up to a locally generated unitary is identical to homotopy equivalence.

We present the basic properties of a physical system: an individual ${\mathrm{V}}^{2+}$ ion embedded into an individual quantum dot. The system is realized utilizing molecular beam epitaxy and it is observed using a low-temperature polarization-resolved magnetophotoluminescence. The nature of the system is confirmed by observation of the excitonic lines split due to the interactions of a vanadium ion with carriers confined in a CdTe/ZnTe quantum dot. Observed data are explained by the numerical modeling which includes an $s,p\text{−}d$ exchange interaction, Zeeman splitting of the exciton and the ion, a diamagnetic shift, and the presence of shear strain within the quantum dot. The fundamental state of vanadium exhibits a spin $\pm \frac{1}{2}$, making this system a textbook localized qubit.

When interacting with an environment, the entanglement within quantum many-body systems is rapidly transferred to the entanglement between the system and the bath. For systems with a large local Hilbert space dimension, this leads to a first-order entanglement transition for the reduced density matrix of the system. On the other hand, recent studies have introduced a new paradigm for classifying density matrices, with particular focus on scenarios where a strongly symmetric density matrix undergoes spontaneous symmetry breaking to a weak symmetry phase. This is typically characterized by a finite Rényi-2 correlator or a finite Wightman correlator. In this Letter, we study the entanglement transition from the perspective of strong-to-weak symmetry breaking, using solvable complex Brownian Sachdev-Ye-Kitaev models. We perform analytical calculations for both the early-time and late-time saddles. The results show that while the Rényi-2 correlator indicates a transition from a symmetric to symmetry-broken phase, the Wightman correlator becomes finite even in the early-time saddle due to the single-replica limit, demonstrating that the first-order transition occurs between a near-symmetric phase and a deeply symmetry-broken phase in the sense of a Wightman correlator. Our results provide another viewpoint on the entanglement transition under symmetry constraints and can be readily generalized to systems with repeated measurements.

We study the Kitaev model on the trivalent heptagonal Hurwitz hyperbolic tiling. The presence of odd-length loops in the tiling is responsible for a spontaneous time-reversal symmetry breaking. Interestingly, at the isotropic point, the two degenerate ground states (Kramers pair) are shown to be gapped chiral spin liquids and the elementary excitations are non-Abelian Ising anyons.

We show that when a honeycomb antiferromagnetic insulator (AFMI) is sandwiched between two transition-metal dichalcogenide (TMD) monolayers, magnons in the AFMI can mediate an interaction between electrons in the TMDs that gives rise to interlayer Cooper pairing. This interaction opens coexisting extended $s$-wave and chiral $p$-wave superconducting gaps in the energy spectrum of the coupled system. The latter gives rise to topological Majorana edge modes. The mechanism we propose therefore provides a path to realize an intriguing type of topological interlayer pairing in a class of van der Waals heterostructures.

Resonant x-ray diffraction (RXD) provides a unique capability to investigate electronically ordered states in matter. Importantly, circular dichroism in RXD can determine the absolute chirality formed by anisotropic multipole arrangement. Here, we demonstrate that the scattering interference between distinct atomic electric multipoles can create circular contrast in resonant RXD even in a nonchiral crystal. These general considerations are applied to $1T\text{−}\mathrm{TiS}{\mathrm{e}}_2$, where recently reported circular dichroism in RXD was used to claim a chiral charge density wave order. We show that the experimental observations are well reproduced by our ab initio calculations based on the centrosymmetric crystal structure. Our results not only illuminate a way for a better understanding of possible chiral electronic order but also propose a general approach to extract buried high-order atomic multipoles via circular contrast in RXD. Besides, we discuss the difference in the circular dichroism of RXD originated by crystal chirality in chiral crystals and the interference effect in nonchiral crystals.

Compact plasmonic devices have paved a way to achieve highly integrated photonic circuit for the next-generation information technology. In this Letter, we proposed compact and highly efficient plasmonic mode conversion between symmetric and antisymmetric modes in metal slab waveguides containing asymmetric dielectric substructures. We derived intuitive analytical formulations concerning the mode asymmetry and intermode coupling in the asymmetric subwaveguide. And we estimated a conversion efficiency and compactness of the proposed plasmonic mode conversion. As a result, we confirmed the compact and high-efficiency plasmonic mode converter with conversion efficiency as high as $90\%$ and a compact size up to one wavelength. The suggested device will give us potential possibilities to construct on-chip photonic computing networks.

Tungsten oxide $\left({\mathrm{WO}}_x\right)$ films grown on tungsten (W) are characterized by depth-resolved Doppler-broadening spectroscopy (DBS) and positron-annihilation lifetime spectroscopy (PALS) as primary analytical methods. The ${\mathrm{WO}}_x$ films are prepared on W(111) monocrystals using either exposure to air, electrochemical, or thermal oxidation procedures, chosen according to the desired thickness. We calculate the lifetime of positrons in the bulk of ${\mathrm{WO}}_x$ and in different types of vacancies using the atomic superposition (AtSup) method. These give the size required for a multivacancy in ${\mathrm{WO}}_x$ needed for it to be identifiable by PALS. In our experiments, we identified a distinct positron lifetime of $325\mathrm{p}\mathrm{s}$ in the thin oxide layer on W exposed to air. This value overlaps with that of multivacancy sites in W and, hence, should be taken into account in future PALS studies of radiation-induced defects in W.

The exciton-dominated optical response in two-dimensional (2D) materials is significant for basic research and practical applications. Here, carrier dynamics and transient band renormalization in monolayer (ML) ${\mathrm{Cu}}_2\mathrm{Se}$ grown on Cu(111) are explored by time- and angle-resolved photoemission spectroscopy. The lifetime of the excited carriers for ML ${\mathrm{Cu}}_2\mathrm{Se}/\mathrm{Cu}\left(111\right)$ is found to be as long as 620 fs, which is attributed to the fact that the excitons and the hole barrier layer formed at the interface suppress the ultrafast Auger recombination channel and decelerate the relaxation process of the excited carriers. A concurrent transient increase of the band gap and the effective mass of the holes after photoexcitation is observed, suggesting an exciton-driven band renormalization effect occurred in the ML ${\mathrm{Cu}}_2\mathrm{Se}$. These findings provide insights into the photocarrier relaxation process in 2D semiconductors with potential applications in optoelectronic devices.

Quantum simulators have the potential to shed light on the study of quantum many-body systems and materials, offering unique insights into various quantum phenomena. Although adiabatic evolution has been conventionally employed for state preparation, it faces challenges when the system evolves too quickly or the coherence time is limited. In such cases, shortcuts to adiabaticity, such as spatiotemporal quenches, provide a promising alternative. This paper numerically investigates the application of spatiotemporal quenches in the two-dimensional transverse field Ising model with ferromagnetic interactions, focusing on the emergence of the ground state and its correlation properties at criticality when the gap vanishes. We demonstrate the effectiveness of these quenches in rapidly preparing ground states in critical systems. Our simulations reveal the existence of an optimal quench front velocity at the emergent speed of light, leading to minimal excitation energy density and correlation lengths of the order of finite system sizes we can simulate. These findings emphasize the potential of spatiotemporal quenches for efficient ground state preparation in quantum systems, with implications for the exploration of strongly correlated phases and programmable quantum computing.

We propose a multi-impurity method for the bond-weighted tensor renormalization group (BWTRG) to compute the higher-order moment of physical quantities in a two-dimensional system. The replacement of the bond weight with an impurity matrix in a bond-weighted triad tensor network represents a physical quantity such as the magnetization and the energy. We demonstrate that the accuracy of the proposed method is much higher than the conventional tensor renormalization group for the Ising model and the five-state Potts model. Furthermore, we perform the finite-size scaling analysis and observe that the dimensionless quantity characterizing the structure of the fixed point tensor satisfies the same scaling relation in the critical region as the Binder parameter. The estimated critical temperature dependence on the bond dimension indicates that the exponent relating the correlation length to the bond dimension varies continuously with respect to the BWTRG hyperparameter. We find that BWTRG with the optimal hyperparameter is more efficient in terms of computational time than alternative approaches based on the matrix product state in estimating the critical temperature.

Kagome magnets have attracted significant attention due to the interplay between magnetic orders and topological electronic states. The kagome compound ${\mathrm{YMn}}_6{\mathrm{Sn}}_6$ exhibits a helical antiferromagnetic ground state due to the frustrated interlayer exchange interactions, and undergoes successive in-plane field-induced magnetic transitions, resulting in complex magnetotransport properties. In this work, we investigate the magnetic and magnetotransport properties of Tb-substituted ${\mathrm{YMn}}_6{\mathrm{Sn}}_6$ single crystals. Through low-level doping, the interlayer antiferromagnetic exchange is reduced without altering the magnetic structure. Compared to the pristine sample, the doped samples exhibit larger negative magnetoresistance, sharper field-induced resistance transitions, and smaller topological Hall effect. These behaviors can be attributed to the reduction of magnetic fluctuations, which is caused by the shifted balance between the ferromagnetic and antiferromagnetic exchanges. In addition, we analyze the anomalous negative contribution in low-temperature Hall resistivity, which occurs within the same magnetic field range as the negative magnetoresistance in the fanlike magnetic phase. We propose that this phenomenon arises from the magnetization-driven Lifshitz transition.

We investigated the dependence of ${}^{14}\mathrm{N}$ nuclear spin polarization of the nitrogen-vacancy (NV) center on the magnitude (0–1100 G) and orientation of the magnetic field, experimentally using optically detected magnetic resonance and theoretically using the Lindblad equation for the density matrix to model the expected ${}^{14}\mathrm{N}$ nuclear spin polarization. The mechanisms of ${}^{14}\mathrm{N}$ nuclear spin polarization in magnetic field regions away from ground and excited level anticrossing points are explained through the analysis of the interactions of the hyperfine components. We found that in magnetic field regions, where hyperfine mixing is weak, nuclear spin polarization occurs as a result of several thousands of excitation-relaxation cycles. Results show that when the magnetic field is parallel to the NV axis, the polarization profile is mainly determined by the mixing of the excited-state hyperfine components and the mixing of the hyperfine components of the electron spin $m_s=1$ manifold. In addition, an in-depth explanation of the magnetic field transverse component sensitivity around the ground-state level anticrossing has been offered based on hyperfine level mixing analysis and Hamiltonian simulations.

Charge density waves (CDW) in single-layer $1T\text{−}{M\mathrm{Te}}_2$ $(M=\mathrm{Nb},\mathrm{Ta})$ have recently attracted significant attention because of their contrasting structural and physical behavior compared to sulfide and selenide analogs. A first-principles study of fourteen different $1T$-type ${\mathrm{TaTe}}_2$ single layers is reported. The importance of Te to Ta electron transfer and multicenter metal-metal bonding in stabilizing different structural modulations is highlighted. Analysis of the electronic structure of the optimized structures provides insight into what distinguishes $1T\text{−}{\mathrm{TaTe}}_2$ from the related disulfide and diselenide, what are the more stable structural modulations for $1T$-type ${\mathrm{TaTe}}_2$ single layers, the possible role of Fermi surface nesting in some of these CDW instabilities, how the CDW affects the metallic properties of the nondistorted lattice, and the possibility that some of these CDW phases exhibit exotic properties. All CDW phases studied exhibit band structures typical of metallic systems although some display both very flat and dispersive bands at the Fermi level, suggesting that Mott effects could develop. One of the ($4\times 4$) phases studied exhibits a Dirac cone at the Fermi level.

The spin-$\frac{1}{2}$ Heisenberg diamond chain with ferro- and antiferromagnetic exchange interactions is studied. The phase boundary in the parametric space of these interactions is determined, where the transition between the ferromagnetic and other (singlet or ferrimagnetic) ground state phases occurs. On this phase boundary there is a dispersionless (flat) energy band in the one-magnon spectrum and these states can be represented as localized magnons in the trapping cells between neighboring diamonds. The ground state consists of the localized magnons and special magnon complexes and it is macroscopically degenerate. A remarkable feature of the model is the existence, on a certain part of the phase boundary, of two- and three-magnon localized states, forming flat bands in two- and three-magnon spectrum. All these localized states also belong to the ground state manifold, which turns out to be exactly the same as for the system of independent spins-$\frac{3}{2}$. This implies a large macroscopic degeneracy of the ground state $4^n$ ($n$ is number of diamonds in the chain) and a high residual entropy per spin $s_0=\frac{2}{3}ln2$.

Two-dimensional quantum antiferromagnets are believed to host phases of matter whose excitations are more fundamental than those of the ordered phases. When combining two such spin systems in a bilayer, strong interaction between the emergent excitations can produce phases not realized in either of its subsystems. We show that the critical fluctuations of a two-dimensional spin-liquid state can induce a deconfined quantum critical point in a proximate antiferromagnet. The most relevant coupling between the associated effective field theories is given by a mixed Chern-Simons term of the emergent gauge fields in each layer. This describes a topological current-current interaction. In contrast to the local spin-spin interaction, it strongly modifies the renormalization group flow of the theory describing the Néel–valence-bond-solid transition of the antiferromagnet. In particular, the protected coupling constant associated with it implies nontrivial quantum critical scaling characterized by a nonuniversal power-law divergence of the correlation length in the critical domain and Berezinskii-Kosterlitz-Thouless divergence approaching it.

The multiple-spin exchange frequencies of the bilayer Wigner crystal are determined using the semiclassical method, which is asymptotically exact in the limit of dilute electron densities. The evolution of the exchange frequencies with interlayer distances—as the crystal undergoes a series of structural transitions—leads to both ferromagnetic and multisublattice antiferromagnetic phases. Extrapolation of the results to higher densities suggests a rich magnetic phase diagram of the bilayer Wigner crystal, including the possibility of spin-nematic and valence-bond solid phases. The bilayer crystal is stable to higher electron densities than the monolayer, leading to enhanced magnetic energy scales. Our estimates of the exchange energies suggest some of the magnetic phases may be accessible in recently discovered bilayer Wigner crystals in a transition-metal dichalcogenide system.