We analyze the collective excitations of a magnetoelectric multiferroic material and show that the coupling between magnetization and polarization fluctuations gives rise to hybrid modes—electromagnons—resulting from the mixing of magnons (oscillations of the magnetization field) and polarization waves (ferrons). We characterize their main properties and discuss their potential applications in multiferroic-based technologies. Additionally, we provide a phenomenological framework for these systems, which will be invaluable for describing the dynamics of the multiferromagnetic state.

Bulk polycrystalline double perovskite oxides ${\mathrm{La}}_2{\mathrm{Ni}}_{1-x}{\mathrm{Cu}}_x{\mathrm{MnO}}_6$ (with nominal $x=0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, \text{and} 1.0)$ samples were synthesized by the standard solid-state reaction method. The Cu/Ni content in the final samples was estimated using energy-dispersive spectroscopy (EDS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The structural properties of the samples characterized using powder x-ray diffraction technique indicate systematic expansion of lattice parameters and unit-cell volume with increasing Cu content. Raman spectral analysis indicates increased lattice disorder with increasing Cu content. Both x-ray photoelectron spectroscopy (XPS) and x-ray absorption near edge spectroscopy (XANES) measurements carried out on selected compositions indicate the presence of ${\mathrm{Mn}}^{4+}$, ${\mathrm{Ni}}^{2+}$, and/or ${\mathrm{Cu}}^{2+}$ oxidation states. The extended x-ray absorption fine structure (EXAFS) measurements carried out on selected compositions suggest lattice/crystalline disorder in the higher Cu containing samples. The isofield and isothermal magnetization measurements indicate gradual and systematic variation from simple ferromagnetism to a Griffiths phase to spin glass behavior with increasing Cu content. Based on the experimental results, the temperature $\left(T\right)$ versus composition $\left(x\right)$ phase diagram for the ${\mathrm{La}}_2{\mathrm{Ni}}_{1-x}{\mathrm{Cu}}_x{\mathrm{MnO}}_6$ system, comprising paramagnetic, ferromagnetic, Griffiths, and spin-glass phases is proposed. Detailed analysis using mean-field theory and Monte Carlo simulations using an Ising model Hamiltonian indicates that the decrease in ferromagnetic transition temperature (Curie temperature) with increasing Cu content is owing to magnetic dilution by the lower magnetic moment of the ${\mathrm{Cu}}^{2+}$ ions $(S=1/2)$ compared to the ${\mathrm{Ni}}^{2+}$ ions $(S=1)$. For the ferromagnetic compositions of ${\mathrm{La}}_2{\mathrm{Ni}}_{1-x}{\mathrm{Cu}}_x{\mathrm{MnO}}_6$ samples, the magnetocaloric properties were also evaluated from experimental isothermal magnetization data. The results show a maximum isothermal magnetic entropy change of 1.0–2.7 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ and a refrigerant capacity of 110–200 J/kg, both values for field changes from 0 to 70 kOe, over a relatively wide temperature range of 100–300 K depending on the chemical composition.

The classical Heisenberg model is one of the most fundamental models in statistical and condensed matter physics. Extensive theoretical and numerical studies suggest that, in two dimensions, this model does not exhibit a finite-temperature phase transition but instead manifests asymptotic freedom. However, some research has also proposed the possibility of a Berezinskii-Kosterlitz-Thouless (BKT) phase transition over the years. In this study, we revisit the classical two-dimensional (2D) Heisenberg model through large-scale simulations with linear system sizes up to $L=16384$. Our Monte Carlo data, without any extrapolation, clearly reveal an exponential divergence of the correlation length $\xi$ as a function of the inverse temperature $\beta$, a hallmark of asymptotic freedom. Moreover, extrapolating $\xi$ to the thermodynamic limit in the low-temperature regime achieves close agreement with the three-loop perturbative calculations. We further propose a finite-size scaling (FSS) ansatz for $\xi$, demonstrating that the pseudocritical point ${\beta }_L$ diverges logarithmically with $L$. The thermodynamic and finite-size scaling behaviors of the magnetic susceptibility $\chi$ are also investigated and corroborate the predictions of asymptotic freedom. Our paper provides solid evidence for asymptotic freedom in the 2D Heisenberg model and advances understanding of finite-size scaling in such systems.

Both Kitaev and Dzyaloshinskii-Moriya interactions (DMI) are known to promote intrinsic contributions to the magnon Hall effects such as the thermal Hall and the spin Nernst effects in collinear magnets. Previously, it was reported that a sign change in those transversal transport coefficients only appears in the presence of Kitaev interaction, but not for DMI, which qualitatively distinguishes both kinds of spin-anisotropic interactions in ferromagnets. Herein, we systematically study how the magnon-mediated heat, spin, and orbital transport in longitudinal and transverse geometries evolves with a continuously varying Kitaev-to-DMI ratio, but a fixed magnon band structure. We show that several transport coefficients feature temperature-driven sign changes in the presence of Kitaev interaction, which are absent for DMI. In particular, we find a sign change in longitudinal orbital transport, the magnon orbital Seebeck effect, which is absent in the transverse geometry, the magnon orbital Nernst effect. This sets the orbital transport apart from the heat and spin transport, where we only find sign changes promoted by the Kitaev interaction in transverse, but not in the longitudinal geometry.

Molecular nanomagnets are systems with a vast phenomenology and are very promising for a variety of technological applications, most notably spintronics and quantum information. Their low-energy spectrum and magnetic properties can be modeled using effective spin Hamiltonians, once the exchange coupling parameters between the localized magnetic moments are determined. In this work we employ density functional theory (DFT) to compute the exchange parameters between the atomic spins for two representative ring-shaped molecules containing eight transition-metal magnetic ions: ${\mathrm{Cr}}_8$ and ${\mathrm{V}}_8$. Considering a set of properly chosen spin configurations and mapping their DFT energies on the corresponding expressions from a Heisenberg Hamiltonian, we compute the exchange couplings between magnetic ions which are first, second, and further neighbors on the rings. In spite of their chemical and structural similarities the two systems exhibit very different ground states: antiferromagnetic for ${\mathrm{Cr}}_8$, ferromagnetic for ${\mathrm{V}}_8$, which also features non-negligible couplings between second nearest neighbors. A rationalization of these results is proposed based on the filling of the magnetic centers' $d$ states.

Understanding the behavior of compounds with rich covalent connectivity under high pressure is crucial for advancing superconductor design. In this study, we identify two superconducting S-rich Mg-S compounds, $P6$/mmm $\mathrm{Mg}{\mathrm{S}}_2$ and $I4/m \mathrm{Mg}{\mathrm{S}}_4$, using first-principles structure search calculations under high-pressure conditions. These compounds exhibit unique three-dimensional S covalent networks, featuring honeycomblike and dual-channel structures formed by fivefold-connected trigonal bipyramid and sixfold-connected quasitriangular prism units of S atoms, respectively. The partial occupation of antibonding states and the involvement of S $3d$ orbitals contribute to the formation of weak S-S covalent bonds, which support these high-connectivity motifs. Furthermore, the superconducting properties of these sulfides are largely contributed by their S frameworks, with $P6$/mmm $\mathrm{Mg}{\mathrm{S}}_2$ achieving a $T_{\mathrm{c}}$ of 26.1 K at 300 GPa. This structural arrangement enhances the electronic density of states at the Fermi surface and softens acoustic phonon modes, enabling strong electron-phonon coupling. This work offers valuable insights for designing novel superconductors through precise manipulation of covalent bonding patterns.

The superconducting gap symmetry is investigated by ${}^{125}\mathrm{Te}$ NMR measurements on ${\mathrm{Sc}}_{6}M{\mathrm{Te}}_2$ $(M=\text{Fe,}\text{Co})$ without spatial inversion symmetry. The spin susceptibility obtained from the Knight shift $K$ is suppressed below the superconducting transition temperature, while leaving a finite value down to the lowest temperature $(\simeq 0.4 \mathrm{K})$. The nuclear spin-lattice relaxation rate $1/T_1$ follows a power law against temperature $T$ without showing a coherence peak characteristic of the isotropic gap. The result implies a pairing admixture or a residual density of states under magnetic field. The normal metallic state has a Korringa scaling relation between $1/T_{1}T$ and the Knight shift, reflecting a weak electron correlation.

Josephson junctions constructed from superconductor-semiconductor-superconductor heterostructures have been used to realize a variety of voltage-tunable superconducting quantum devices, including qubits and parametric amplifiers. To date, theoretical descriptions of these systems have been restricted to small quantum fluctuations of the junction phase, making them inapplicable to many experiments. In this paper, we relax this, employing a path-integral formulation where the phase quantum dynamics is obtained self-consistently from an underlying many-body formalism. Our method recovers previously known results for small phase fluctuations, and predicts effects outside of that limit: (i) system capacitances undergo a gate-voltage-dependent renormalization; and (ii) an additional charge offset appears for asymmetric junctions. Our main results can be summarized in terms of a single-particle Hamiltonian, which can be directly compared to that of an ordinary Josephson junction. This more general theory could be a first step towards designing new quantum devices that go qualitatively beyond voltage-tunable variants of previously known circuits.

We present a computational framework to identify Hamiltonians of interacting quantum many-body systems that host nonergodic excited states. We combine quantum Monte Carlo simulations with the recently proposed eigenstate-to-Hamiltonian construction, which maps the ground state of a specified parent Hamiltonian to a single nonergodic excited state of a new derived Hamiltonian. This engineered Hamiltonian contains nontrivial, systematically-obtained, and emergent features that are responsible for its nonergodic properties. We demonstrate this approach by applying it to quantum many-body scar states where we discover a previously unreported family of Hamiltonians with spatially oscillating spin exchange couplings that host scar-like properties, including revivals in the quantum dynamics, and towers in the inverse participation ratio; and to many-body localization, where we find a two-dimensional Hamiltonian with correlated disorder that exhibits nonergodic scaling of the participation entropy and inverse participation ratios of order unity. The method can be applied to other known ground states to discover new quantum many-body systems with nonergodic excited states.

Quantum circuits offer a versatile platform for simulating digital quantum dynamics and uncovering novel states of nonequilibrium quantum matter. One principal example are measurement-induced phase transitions arising from nonunitary dynamics in monitored circuits, which employ midcircuit measurements as an essential building block next to standard unitary gates. Although a comprehensive understanding of the dynamics in generic circuits is still evolving, we contend that monitored quantum circuits give rise to robust phases of dynamic matter, which—akin to Hamiltonian ground-state phases—yield emergent universal behavior, which can be categorized based on circuit symmetries and spatial dimensionality. To illustrate this concept, we focus on measurement-only quantum circuits within symmetry classes BDI and D, which are measurement-only circuit adaptations of the paradigmatic Kitaev and Yao-Kivelson models, embodying particle-hole-symmetric Majorana fermions with or without time reversal. We establish a general framework (Majorana loop models) for both symmetry classes (in arbitrary spatial dimensions) to provide access to the phenomenology of the entanglement dynamics in these circuits, displaying both an area-law phase of localized Majorana loops and a delocalized, highly entangled Majorana liquid phase. The two phases are separated by a continuous transition displaying quantum Lifshitz scaling, albeit with critical exponents of two distinct, non-Hamiltonian universality classes. The loop model framework provides not only analytical understanding of these universality classes in terms of nonlinear sigma models but also allows for highly efficient numerical techniques capable of simulating excessively large circuits with up to ${10}^8$ qubits. We utilize this framework to accurately determine universal probes that distinguish both the entangled phases and the critical points of the two symmetry classes. Our work thereby further solidifies the concept of emergent circuit phases and their phase transitions.

The nonstoichiometric ${\mathrm{Fe}}_2\mathrm{P}$-type ${\mathrm{FeMn}}_{(1-x)}{\mathrm{V}}_x{\left({\mathrm{P}}_{0.5}{\mathrm{Si}}_{0.5}\right)}_{1-x}$ alloys $(x=0,0.01, 0.02, \text{and} 0.03)$ have been investigated as potential candidates for magnetic refrigeration near room temperature. The magnetic ordering temperature decreases with increasing FeV concentration $x$, which can be ascribed to decreased ferromagnetic coupling strength between the magnetic atoms. The strong magnetoelastic coupling in these alloys results in large values of the isothermal entropy change $\left(\mathrm{\Delta }{S}_M\right)$; 15.7 J/(kg K), at 2 T magnetic field for the $x=0$ alloy. $\mathrm{\Delta }{S}_M$ decreases with increasing $x$. Results from Mössbauer spectroscopy reveal that the average hyperfine field (in the ferromagnetic state) and average center shift (in the paramagnetic state) have the same decreasing trend as $\mathrm{\Delta }{S}_M$. The thermal hysteresis $\left(\mathrm{\Delta }{T}_{\mathrm{hyst}}\right)$ of the magnetic phase transition decreases with increasing $x$, while the mechanical stability of the alloys improves due to the reduced lattice volume change across the magnetoelastic phase transition. The adiabatic temperature change $\mathrm{\Delta }{T}_{\mathrm{ad}}$, which highly depends on $\mathrm{\Delta }{T}_{\mathrm{hyst}}$, is 1.7 K at 1.9 T applied field for the $x=0.02$ alloy.

The creation and manipulation of magnetic skyrmions in magnetic bilayer heterostructures via spin-orbit torque have been intensively studied in spintronics because of their potential application as information carriers in next-generation magnetic memory devices. However, experimental attempts have not always been successful. In this paper, we theoretically elucidate the underlying reasons for these difficulties and propose a practical method to overcome them by employing magnetic bilayer heterostructures that incorporate a chiral ferromagnetic layer hosting Bloch-type skyrmions instead of a conventional ferromagnetic layer hosting Neel-type skyrmions. Our micromagnetic simulations demonstrate that Bloch-type skyrmions can be controllably created in this system via spin-orbit torque exerted by a perpendicular spin current. This finding provides a promising platform and method for realizing skyrmion-based spintronic devices.

In the framework of the Keldysh formalism and the tight-binding model, we investigate spin-orbit phenomena such as the anomalous and spin Hall effects, tunneling anisotropic magnetoresistance, and Rashba-induced spin-orbit torque in single-barrier tunnel junctions. We focus on two configurations: one with a ferromagnetic metal [normal metal (NM)/insulator (I)/ferromagnetic metal (FM)] and the other with a ferromagnetic insulator [NM/ferromagnetic insulator (FI)/NM], both incorporating an asymmetric interfacial Rashba spin-orbit coupling. Using analytical methods and numerical simulations, we derive expressions for these spin-orbit phenomena. We find that while the anomalous Hall effect and spin-orbit torque behave similarly in both configurations, tunneling anisotropic magnetoresistance and the angular dependence of spin Hall effect are significantly enhanced by nearly an order of magnitude when a FI is used. This enhancement remains even for modest exchange splittings, suggesting that FIs such as Eu chalcogenides and spinel oxides are promising for high-efficiency spintronic applications. Additionally, we observe a sign reversal of these effects in NM/I/FM junctions as the system shifts from half-metallic to low-band-filling regimes, while no such reversal occurs in NM/FI/NM due to the spin-filtering effect of the barrier.

As is well known, magnetic impurities adsorbed on superconductors, e.g., of the s-wave type, can introduce a bound gap-state (Yu-Shiba-Rusinov resonance). We here investigate within a minimal model how the impurity moment arranges with respect to a weak homogeneous internal magnetic field employing a fully self-consistent mean-field treatment. Our investigation reveals a critical window of impurity-to-substrate coupling constants, $J$. The width of the critical region, $\delta J$, scales like $\delta J\sim B/\mathrm{\Delta }$, where $B$ is the magnitude of the internal field, that breaks the spin-rotation symmetry, and $\mathrm{\Delta }$ is the bulk order parameter. While tuning $J$ through the window, the energy of the Yu-Shiba-Rusinov (YSR) resonance is pinned to the Fermi energy ${\varepsilon }_{\text{F}}$ and the impurity moment rotates in a continuous fashion. We emphasize the pivotal role of self-consistency: In treatments ignoring self-consistency, the critical window adopts zero width, $\delta J=0$; consequently, there is no pinning of the YSR-resonance to ${\varepsilon }_{\text{F}}$, the impurity orientation jumps and therefore this orientation cannot be controlled continuously by fine-tuning the coupling $J$. In this sense, our study highlights the significance of self-consistency for understanding intricate magnetic interactions between superconductive materials and Shiba chains.

We study the one-dimensional Bose-Hubbard model under the resonant condition, where the nearest-neighbor and on-site interaction strengths are equal. In the strong interaction limit, $n$ bosons occupied in a single site can transfer to neighboring sites in a complete manner, which is referred to as quantum slinky motion. It can be shown that quantum slinky motions can be described by a set of effective noninteracting Hamiltonians. These Hamiltonians are sets of generalized Su-Schrieffer-Heeger chains with an $n$-site unit cell in an auxiliary space, referred to as trimerization, tetramerization, pentamerization, etc., possessing nontrivial Zak phases. The corresponding edge states are demonstrated by the $n$-boson bound states at the ends of the chains. We also investigate the dynamic detection of edge boson clusters through an analysis of quench dynamics. Numerical results indicate that stable edge oscillations clearly manifest the interaction-induced topological features within the extended Bose-Hubbard model.

The explicit computation of amplitudes for fermionic Gaussian pure states in arbitrary Pauli bases is a long-standing challenge in quantum many-body physics, with significant implications for quantum tomography, experimental studies, and quantum dynamics. These calculations are essential for analyzing complex properties beyond traditional measures, such as formation probabilities, global entanglement, and entropy in nonstandard bases, where exact and computationally efficient methods remain underdeveloped. In addition to these physical applications, having explicit formulas is crucial for optimizing negative log-likelihood functions in quantum tomography, a key task in the NISQ era. In this work, we present an explicit Pfaffian formula (Theorem 1) for determining these amplitudes in arbitrary Pauli bases, utilizing a matrix whose structure reflects the qubit parity. Additionally, we introduce a recursive relation (Theorem 2) that connects amplitudes for systems with varying qubit numbers, enabling scalable computations for large systems. Together, these results provide a versatile framework for studying global entanglement, Shannon-Rényi entropies, formation probabilities, and performing efficient quantum tomography, thereby significantly expanding the computational toolkit for analyzing complex quantum systems. Finally, we utilize our formalism to determine the post-measurement entanglement entropy, reflecting how local measurements alter entanglement, and compare the results with conformal field theory predictions.

Dispersionless flat bands have garnered significant attention due to their unique physical properties. In moiré superlattices, the localization of low-energy electrons arising from interlayer interactions contributes to the formation of flat bands. In this paper, we explore the moiré band of twisted bilayer ${\mathrm{WSe}}_2$ using a continuum model. We identify three distinctive bands slightly detuned from the lowest-energy flat-band regime that can be realized at different twist angles. By calculating the local state distribution in real space and applying the tight-binding method, we reveal that the formation of a frustrated flat band originates from destructive interference in the hopping processes among three nearly degenerate electronic states. Our finding provides a framework for manipulating flat bands in moiré superlattice systems.

Fractals, characterized by self-similarity, complexity, and fractional dimensions, have emerged as a powerful tool for exploring novel physical phenomena in non-integer-dimensional systems. Despite the absence of a conventional “bulk” in fractal lattices, recent research demonstrates that they can host robust topological states, thus posing a challenge to the traditional bulk-edge correspondence in topological physics. In this work, we investigate the topological properties of the two-dimensional Aubry-André-Harper (AAH) model on a fractal lattice, unveiling higher-order corner states induced by the fractal bulk-edge correspondence. We propose a method for implementing the fractal AAH model in an electronic circuit. By analyzing the frequency spectrum of the circuit, we identify the topological features of higher-order corner states in the fractal circuit network. Our research findings enhance the understanding of topological characteristics in non-integer-dimensional systems and provide a practical physical platform for exploring phenomena related to noninteger dimensions.

Dynamic control of topological properties in materials is central to modern condensed matter physics, and Floquet engineering, utilizing periodic light fields, provides a promising avenue. Here, we use Floquet theory to theoretically study the topological response of a $Z_2$ nodal line semimetal (NLSM) when driven by circularly polarized light (CPL). We demonstrate that the direction of CPL irradiation critically dictates the resulting topological phase transitions. Specifically, when light is incident perpendicular to the nodal line plane, increasing the light amplitude induces two successive topological phase transitions: first, from the $Z_2$ NLSM to a vortex NLSM, a rare and intriguing topological state; and second, a transition from the vortex NLSM to a semimetal with a pair of Weyl points (WPs). In stark contrast, irradiation along other directions directly transforms the $Z_2$ nodal line into a pair of WPs. We further investigate the transport properties of the Floquet $Z_2$ NLSM, focusing on the anomalous and planar Hall effects. The anomalous Hall effect exhibits a direction-dependent amplitude variation, deviating from conventional two-band NLSM behavior. Importantly, we reveal a significant and tunable planar Hall effect, a phenomenon largely unexplored in Floquet topological materials, which is highly sensitive to both light amplitude and direction. Our findings not only present a novel route to realize the vortex NLSM, but also establish an efficient way to control Hall transport phenomena in $Z_2$ NLSMs.

Our report paves the way for insight into a structural disorder and its impact on the physical properties of strongly correlated electron systems (SCESs). In a critical regime, each perturbation, e.g., disorder due to structural defects or doping, can have a significant effect on the nature of the quantum macrostate of these materials. For a select group of SCESs, we have empirically documented the Griffiths singularity, as exemplified by CeRhSn, which exhibits non-Fermi-liquid characteristics in susceptibility and specific heat. Our numerical analysis has supported the Griffiths phase scenario for CeRhSn and has revealed that its dc magnetic susceptibility is strongly dependent on the size of inhomogeneous magnetic particles that form in these materials. In the presence of strong disorder, we have proposed a magnetic phase diagram for CeRhSn. The classical Griffiths phase has been identified in the temperature range below the onset temperature of $T_G\sim 220\mathrm{K}$, while the quantum Griffiths phase with non-Fermi-liquid behavior emerges below the quantum critical temperature of $T_Q\sim 6\mathrm{K}$. The phase diagram developed in this study bears notable similarities to the scenario previously proposed by Vojta for magnetic quantum phase transitions in disordered metals.