EuAuSb is a triangular-lattice Dirac semimetal in which a topological Hall effect has been observed to develop in association with a magnetically ordered phase. Our single-crystal neutron diffraction measurements have identified an incommensurate helical order in which individual ferromagnetic ${\mathrm{Eu}}^{2+}$ layers rotate in-plane by $\sim {120}^{\circ }$ from one layer to the next. An in-plane magnetic field distorts the incommensurate order, eventually leading to a first order transition to a state that is approximately commensurate and that is continuously polarized as the bulk magnetization approaches saturation. From an analysis of the magnetic diffraction intensities versus field, we find evidence for a dip in the ordered in-plane moment at the same field where the topological Hall effect is a maximum, and we propose that this is due to field-induced quantum spin fluctuations. Our electronic structure calculations yield exchange constants compatible with the helical order and show that the bands near the Fermi level lose their spin degeneracy via a mechanism similar to that in the collinear altermagnets. We find that, unlike the even symmetry seen in the altermagnets, the spin splitting in EuAuSb has odd-wave symmetry similar to that recently found in a number of coplanar magnetic materials.

The Mpemba effect, where a system initially farther from equilibrium relaxes faster than one closer to equilibrium, has been extensively studied in classical systems and recently explored in quantum settings. While previous studies of the quantum Mpemba effect (QME) have largely focused on isolated systems with global symmetries, we argue that the QME is ubiquitous in generic, nonintegrable many-body systems lacking such symmetries, including U(1) charge conservation, spatial symmetries, and even energy conservation. Using paradigmatic models such as the quantum Ising model with transverse and longitudinal fields, we show that the QME can be understood through the energy density of initial states and their inverse participation ratio in the energy eigenbasis. Our findings provide a unified framework for the QME, linking it with classical thermal relaxation.

We investigate the quantum Mpemba effect (QME) in isolated, nonintegrable quantum systems, where relaxation dynamics depend on structure of the initial states. By analyzing the distribution of initial states across symmetrical subspaces, we identify a tunable mechanism that influences the emergence of QME, showing faster relaxation from certain out-of-equilibrium states. Additionally, we propose an experimentally realizable quantum circuit, which requires no complex controls on quantum simulator platforms and serves to verify our theoretical predictions. These results establish symmetry-resolved state engineering as a practical tool for manipulating nonequilibrium quantum dynamics.

Magneto-optical techniques have become essential tools in spintronics, enabling the investigation of spin dynamics in the ultrafast regime. A key challenge in this field has been to accurately isolate the contributions to magneto-optical signals of spin transport phenomena from the local magnetization dynamics. The contribution of transported and accumulated spins was long believed to be orders of magnitude smaller than that of the magnetization and thus previous approaches to disentangle these signals have relied on specific experimental designs, usually including thick metal layers. Here, we present experimental evidence demonstrating that the magneto-optical signal from ultrafast spin accumulations can, under certain conditions, be comparable to or even exceed that of the magnetic layer in a standard ultrafast demagnetization experiment. Our findings provide a framework for accessing and isolating these spin accumulations, allowing for time- and depth-dependent probing of transported spin and/or orbital angular momentum.

Skyrmions have been proposed as new information carriers in racetrack memory devices. To realize such devices, a small size, high speed of propagation, and minimal skyrmion Hall angle are required. Synthetic antiferromagnets (SAFs) present the ideal materials systems to realize these aims. In this work, we use micromagnetic simulations to propose a new method for manipulating them using exclusively global magnetic fields. An out-of-plane microwave field induces oscillations in the skyrmion radius, which in turn emits spin waves. When a static in-plane field is added, this breaks the symmetry of the skyrmions and causes asymmetric spin wave emission. This in turn drives the motion of the skyrmions, with the fastest velocities observed at the frequency of the intrinsic out-of-phase breathing mode of the pair of skyrmions. This behavior is investigated over a range of experimentally realistic antiferromagnetic interlayer exchange coupling strengths, and the results are compared to previous works. Through this we demonstrate the true effect of varying the exchange coupling strength and gain greater insight into the mechanism of skyrmion motion. In an attempt to more accurately reproduce experimental SAF samples, we investigate the effect of changing the ratio between the layer magnetizations in the SAF, and demonstrate that maximum velocity can be achieved when there is 100% compensation. We also investigate the differences between excitation mechanisms, using both electric fields and spin transfer torques to excite skyrmion motion. These results will help to inform the design of future novel computing architectures based on the dynamics of skyrmions in synthetic antiferromagnets.

The scalar spin chirality (SSC), defined as a triple product of spins, is essential for describing noncoplanar spin structures and understanding chiral physics in magnetic systems. Traditionally, SSC has been discussed primarily in the context of noncoplanar ground-state spin configurations at zero temperature, as collinear spin systems are generally thought to lack SSC. Consequently, whether the SSC can emerge at finite temperatures in spin systems with collinear ground states remains an open question and has yet to be fully understood. In this study, we theoretically demonstrate that thermally excited magnons can induce SSC even in collinear spin systems. By considering two-dimensional ferromagnets on kagome and honeycomb lattices, we demonstrate that the Dzyaloshinskii-Moriya interactions (DMI), which break effective time-reversal symmetry of the system, lead to the emergence of finite SSC fluctuations at finite temperatures. Using a simple spin model, we show both numerically and analytically that the SSC increases with the magnitude of DMI and temperature. Furthermore, calculations based on realistic material parameters reveal that the magnon-induced SSC can achieve a magnitude comparable to those observed in noncoplanar spin configurations. These findings suggest that SSC plays a significant role even in collinear spin systems, providing insights into the chiral physics of magnetic materials.

Multiwavefunction overlaps—generalizations of the quantum mechanical inner product for more than two quantum many-body states—are valuable tools for studying many-body physics. In this paper, we investigate the multiwavefunction overlap of ($2+1$)-dimensional gapped ground states, focusing particularly on symmetry-protected topological (SPT) states. We demonstrate how these overlaps can be calculated using the bulk-boundary correspondence and ($1+1$)-dimensional edge theories, specifically conformal field theory. When applied to SPT phases, we show that the topological invariants, which can be thought of as discrete higher Berry phases, can be extracted from the multiwavefunction overlap of four ground states with appropriate symmetry actions. Additionally, we find that the multiwavefunction overlap can be expressed in terms of the realignment of reduced density matrices. Furthermore, we illustrate that the same technique can be used to evaluate the multientropy—a quantum information theoretical quantity associated with multipartition of many-body quantum states –for ($2+1$)-dimensional gapped ground states. Combined with numerics, we show that the difference between multientropy for tripartition and second Rényi entropies is bounded from below by $(c_{\mathrm{tot}}/4)ln2$, where $c_{\mathrm{tot}}$ is the central charge of ungappable degrees of freedom. To calculate multientropy numerically for free fermion systems (such as Chern insulators), we develop the correlator method for multientropy.

We present angle-resolved reflected electron spectroscopy data for the three molybdenum-based transition-metal dichalcogenides (TMDs) ${\mathrm{MoS}}_2, {\mathrm{MoSe}}_2$, and ${\mathrm{MoTe}}_2$. To follow the changes as the series moves from S to Se to Te in more detail, we determine accurate IV spectra for monolayers and bulk TMDs. These experimental data sets are then compared with theoretical predictions for both the unoccupied band structure and the scattering density of states. We find good agreement, especially for lower energies where inelastic effects are relatively unimportant. Furthermore, we identify a series of interlayer resonances for which the dependence of the hybridization effects on the layer count is observed. Although these resonances bear a similarity to interlayer resonances in hBN and graphene, they differ in their character, being dominated by unoccupied $d$-states of the chalcogen atoms. The unoccupied states studied and analyzed here play a key role in all processes that require an electron to temporarily reside in a state above the vacuum level, such as in photoemission and secondary electron emission experiments.

The entanglement spectra for a subsystem in a spin chain fine-tuned to a quantum-critical point contains signatures of the underlying quantum field theory that governs its low-energy properties. For an open chain with given boundary conditions described by a two-dimensional (2D) conformal field theory (CFT), the entanglement spectrum of the left/right half of the system coincides with a boundary CFT spectrum, where one of the boundary conditions arise due to the “entanglement cut.” The latter has been argued to be conformal and has been numerically found to be the “free” boundary condition for Ising, Potts, and free boson theories. For these models, the free boundary condition for the lattice degree of freedom has a counterpart in the continuum theory. However, this is not true in general. Here, this question is analyzed for the unitary minimal models of 2D CFTs using the density matrix renormalization group technique. The entanglement spectra are computed for blocks of spins in open chains of $A$-type restricted solid-on-solid models with identical boundary conditions at the ends. The imposed boundary conditions are realized exactly for these lattice models due to their integrable nature. The obtained entanglement spectra are in good agreement with certain boundary CFT spectra. The boundary condition for the entanglement cut is found to be conformal and to coincide with the one with the highest boundary entropy. This identification enables determination of the exponents governing the unusual corrections to the entanglement entropy from the CFT partition functions. These are compared with numerical results.

Topologically ordered phases exhibit further complexity in the presence of global symmetries: Their anyonic excitations may exhibit different transformation patterns under these symmetries, leading to a classification in terms of symmetry-enriched topological orders. We develop a generic scheme to study an analogous situation for three-dimensional fracton phases by means of isometric tensor network states (isoTNS) with finite bond dimension, which allow us to tune phase transitions between different symmetry fractionalization patterns. We focus on the X-Cube model, a paradigmatic fracton model hosting two types of excitations: lineons, which are mobile in a single direction only, and fractons that are immobile on their own. By deforming the local tensors of the fixed point ground state, we find a family of exact wavefunctions for which the symmetry fractionalization under an anti-unitary symmetry on both types of excitations is directly visible. These wavefunctions are nonstabilizer states and have nonvanishing correlation lengths. They even exhibit power-law correlations at criticality between two symmetry-enriched topological orders. Furthermore, the isoTNS description allows for the explicit construction of a linear-depth quantum circuit to sequentially realize these exotic 3D states on a quantum processor, including a holographic scheme using only a pair of two-dimensional qubit arrays alongside measurements. Our approach provides a construction to enrich phases with exotic topological or fracton order and to study 3D quantum phase transitions with exact wavefunctions, and offers a tractable route to implement and characterize fracton order on quantum devices.

Quasiparticles are central to condensed matter physics, but their stability can be undermined by quantum many-body interactions. Magnons, i.e., quasiparticles in quantum magnets, are particularly intriguing because their properties are governed by both real and spin space. While crystal symmetries may be low, spin interactions often remain approximately isotropic, limiting spontaneous magnon decay. Textbook wisdom holds that collinear Heisenberg magnets follow a dichotomy: ferromagnets host stable magnons, while antiferromagnetic magnons may decay depending on dispersion curvature. Up to now, relativistic spin-orbit coupling and noncollinear order that connect spin space to real space were shown to introduce more complex magnon instability mechanisms. Here, we show that even in nonrelativistic isotropic collinear systems, this conventional dichotomy is disrupted in altermagnets. Altermagnets, a newly identified class of collinear magnets, exhibit compensated spin order with nonrelativistic time-reversal symmetry breaking and even-parity band splitting. Using kinematic analysis, nonlinear spin-wave theory, and quantum simulations, we reveal that even weak band splitting opens a decay phase space, driving quasiparticle breakdown. Additionally, $d$-wave altermagnets form a rare “island of stability” at the Brillouin-zone center. Our findings establish a quasiparticle stability trichotomy in collinear Heisenberg magnets and position altermagnets as a promising platform for unconventional spin dynamics.

The recently discovered lithium-rich antiperovskites $\left({\mathrm{Li}}_2\mathrm{Fe}\right)\mathrm{SeO}$ and $\left({\mathrm{Li}}_2\mathrm{Fe}\right)\mathrm{SO}$ host lithium and iron ions on the same atomic position which octahedrally coordinates to central oxygens. In a cubic antiperovskite these sites form kagome planes stacked along the $\langle 111\rangle$ directions which triangular motifs induce high geometric frustration in the diluted magnetic sublattice for antiferromagnetic interactions. Despite their compelling properties as high-capacity Li-ion battery cathode materials, very little is known about the electronic and magnetic properties of lithium-rich antiperovskites. We report static magnetization, Mössbauer, and NMR studies on both compounds. Our data reveal a Pauli paramagnetic-like behavior, a long-range antiferromagnetically ordered ground state below $\approx 50$ K, and a regime of short-range magnetic correlations up to 100 K. Our results are consistent with a random Li-Fe distribution on the shared lattice position. In addition, Li-hopping is observed above 200 K with an activation energy of $E_{\mathrm{a}}=0.47$ eV. Overall, our data elucidate static magnetism in a disordered magnetically frustrated and presumably semimetallic system with thermally induced ion diffusion dynamics.

In this work, we use a mixed quantum-classical (mean-field) many-body approach for simulating the quantum dynamics of excitons and exciton polaritons beyond the single-excitation subspace. We combine the multitrajectory Ehrenfest approach, which propagates slow degrees of freedom classically, with the Gross-Pitaevskii method, which propagates fast degrees of freedom in a mean-field fashion. We use this mean-field many-body Ehrenfest approach to analyze how the phonon-induced dynamic disorder and the many-body interaction affect the incoherent and coherent dynamics of excitons and exciton polaritons. We examine how the number of excitations and the strength of repulsive exciton-exciton interaction nonlinearly influence the transport, Fröhlich scattering, and decoherence.

Quantum paraelectric ${\mathrm{EuTiO}}_3$ is a candidate multiferroic quantum critical material, which displays unique magnetoelectric and magnetoelastic couplings that may be enhanced when tuned towards ferromagnetic and ferroelectric quantum critical points. However, the ground state remains challenging to identify precisely due to the limitations of current techniques. To investigate low temperature magnetism of the compound, we used scanning SQUID microscopy to image local magnetic flux and susceptibility of a ${\mathrm{EuTiO}}_3$ thin film deposited on ${\mathrm{SrTiO}}_3$. We found weak ferromagnetic domains that form below the film's Néel transition. Additionally, we show that magnetic domain texture and dynamics are significantly influenced by how structural domains crystallize. Our results show a novel noncollinear magnetic texture in a ${\mathrm{EuTiO}}_3$ thin film and suggest a potential route to control magnetic domain texture by manipulating structural domains. Such aspects may have implications for multiferroic quantum-critical behavior predicted for this material.

The orthoferrite ${\mathrm{HoFeO}}_3$ exhibits a complex interplay of magnetic interactions between the antiferromagnetically ordered ${\mathrm{Fe}}^{3+}$ spins and the rare-earth ${\mathrm{Ho}}^{3+}$ ions. In this work, we combine superconducting quantum interference device (SQUID) magnetometry studies with electrical spin transport measurements of the spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) on a ${\mathrm{HoFeO}}_3$ single crystal interfaced by a thin Pt layer. Our measurements show that the increase in Ho magnetic susceptibility below the Morin-like spin reorientation transition at $58\mathrm{K}$ affects the magnetic anisotropy of the Fe sublattice and induces a tilting of the easy axis. Below the ordering temperature of Ho at $4\mathrm{K}$, we observe a rapid increase in the SSE signal associated with the emergence of low-energy magnon modes with the onset of Ho-Ho exchange. These findings demonstrate that spin transport techniques can sensitively probe rare-earth–induced modifications of anisotropy and spin dynamics in complex oxides, opening pathways to electrically access low-energy $4f$ excitations.

We address that the stray magnetic field emitted by the excited quantum states of the nitrogen-vacancy (NV) centers is spin-momentum locked, such that the spin transfer to nearby ferromagnetic nanostructures is unidirectional. This may allow the controlled excitation of propagating magnons by NV centers in diamond. A pair of NV spin qubits exchange virtual magnons in a magnetic nanowire in a chiral manner that leads to directional quantum entanglement. A magnon-based “quantum-entanglement isolator” should be a useful device in future quantum information technology.

Two-dimensional (2D) sheets typically have a high Föppl–von Kármán number, that is, their in-plane extent is much greater than thickness, and can be easily bent, much like a paper, making such deformation a novel feasible way to design distinct electronic phases. Through first-principles calculations, we reveal the formation of 1D polarization domains and 1D flat electronic bands by bending-undulation of a 2D bilayer semiconductor. For a 1D sinusoidal deformation of a hexagonal boron nitride ($h\mathrm{BN}$) bilayer as an example, we demonstrate how undulation induces nonuniform shear patterns, creating regions with unique local stacking and vertical polarization akin to sliding-induced ferroelectrics observed in twisted moiré systems. A particular sliding-induced polarization pattern also appears in double-wall BN nanotubes due to curvature differences between inner and outer tubes. Furthermore, undulation generates a shear-induced 1D moiré pattern that perturbs electronic states, confining them into 1D quantum well-like bands with kinetic energy quenched in modulation direction while dispersive in other directions (1D flat bands). This electronic confinement is attributed to modulated shear deformation potential resulting from tangential polarization due to the moiré pattern. Thus, the bending modulation and interlayer shear it causes offer an alternative avenue, termed “curvatronics”, to induce exotic phenomena in 2D bilayer materials.

The low-pressure stabilization of superconducting hydrides with high critical temperatures $\left(T_c\mathrm{s}\right)$ remains a significant challenge, and experimentally verified superconducting hydrides are generally constrained to a limited number of structural prototypes. Ternary transition metal complex hydrides (hydrido complexes)—typically regarded as hydrogen storage materials—exhibit a large range of compounds stabilized at low pressure with recent predictions for high-$T_c$ superconductivity. Motivated by this class of materials, we investigated complex hydride formation in the Mg–Pt–H system, which has no known ternary hydride compounds. Guided by ab initio structural predictions, we successfully synthesized a novel complex transition metal hydride, ${\mathrm{Mg}}_4{\mathrm{Pt}}_3{\mathrm{H}}_6$, using laser-heated diamond anvil cells. The compound forms in a body-centered cubic structural prototype at moderate pressures between $\sim 8\text{and}25\mathrm{GPa}$. Unlike the majority of known hydrido complexes, ${\mathrm{Mg}}_4{\mathrm{Pt}}_3{\mathrm{H}}_6$ is metallic, with formal charge described as $4{\left[\mathrm{Mg}\right]}^{2+}·3{\left[{\mathrm{PtH}}_2\right]}^{2-}$. X-ray diffraction measurements obtained during decompression reveal that ${\mathrm{Mg}}_4{\mathrm{Pt}}_3{\mathrm{H}}_6$ remains stable upon quenching to ambient conditions. Magnetic-field and temperature-dependent electrical transport measurements indicate ambient-pressure superconductivity with $T_c$ $(50\%)=2.9\mathrm{K}$, in reasonable agreement with theoretical calculations. These findings clarify the phase behavior in the Mg–Pt–H system, highlight important synergies between computational/experimental approaches, and provide valuable insights for transition metal complex hydrides as a new class of hydrogen-rich superconductors.

We study the low-temperature phase diagram of quantum Kitaev-Heisenberg spin-orbital models with XXZ anisotropy on the honeycomb lattice. Within a parton mean-field theory, we identify three different quantum phases, distinguished by their symmetries. Besides a disordered spin-orbital liquid with unbroken $\mathrm{U}\left(1\right)\times {\mathbb{Z}}_2$ spin rotational symmetry, there are two orbital liquid phases characterized by spin long-range order. In these phases, the spin rotational symmetry is spontaneously broken down to residual U(1) and ${\mathbb{Z}}_2$ symmetries, respectively. The symmetric spin-orbital liquid features three flavors of linearly dispersing gapless Majorana fermions. In the symmetry-broken phases, one of the three Majorana excitations remains gapless, while the other two acquire a band gap. The transitions from the symmetric to the symmetry-broken phases are continuous and fall into the fractionalized Gross-Neveu-${\mathbb{Z}}_2^{*}$ and Gross-Neveu-SO(2)${}^{*}$ universality classes, respectively. The transition between the ordered phases is discontinuous. Using a renormalization group analysis based on the epsilon expansion, we demonstrate that the triple point in the phase diagram features fractionalized fermionic multicriticality with emergent SO(3) symmetry.

The exchange interaction $J$ offers a powerful tool for quantum computation based on semiconductor spin qubits. However, the exchange interaction in two-electron systems in the absence of a magnetic field is usually constrained to be non-negative $J\ge 0$, which inhibits the construction of various dynamically corrected exchange-based gates. In this work, we show that negative exchange $J<0$ can be realized in two-electron Si quantum dot arrays in the absence of a magnetic field due to the presence of the valley degree of freedom. Here, valley phase differences between dots produce a nontrivial ${\mathbb{Z}}_2$ gauge field in the low-energy effective theory, which in turn can lead to a negative exchange interaction. In addition, we show that this ${\mathbb{Z}}_2$ gauge field can break Nagaoka ferromagnetism and be engineered by altering the occupancy of the dot array. Therefore, our work uncovers alternative tools for exchange-based quantum computing and a unique setting for studying quantum magnetism.