The universal statistics of density fluctuations of localized quantum states may offer unprecedented opportunities to probe and understand quantum transport in connection with dimensionality, coherence, symmetry, and disorder. To date, the possible role of topological phase transitions in the fluctuation statistics is not studied yet. Using a Su-Schrieffer-Heeger chain subject to off-diagonal disorder (so that chiral symmetry is preserved), this work investigates how a disorder-driven topological phase transition impacts on the spatial fluctuations of the logarithmic wave-packet density $lnP\left(r\right)$ at distance $r$ from the initial excitation. Away from the transition, in both topological and trivial localized phases, the standard deviation follows the conventional one-dimensional scaling $\sigma [lnP\left(r\right)]\sim r^{\theta }$ with $\theta \simeq \frac{1}{2}$. Near the transition, however, the fluctuation growth is enhanced: the fitted exponent $\theta$ increases above $\frac{1}{2}$ in a nonmonotonic manner before returning close to $\frac{1}{2}$ at criticality. We interpret this behavior from the energy-resolved density of states and localization length. Near the transition, several energy sectors carry appreciable spectral weight and exhibit competitive decay rates, preventing a single localization scale from dominating the accessible wave-packet tail and thereby enhancing the fluctuations of $lnP\left(r\right)$. Our results establish wave-packet fluctuation statistics as a dynamical indicator of disordered chiral topological transitions and motivate broader studies of fluctuation phenomena in disordered topological quantum systems.

We report a systematic study of the composition-dependent bulk properties in $\mathrm{C}{\mathrm{o}}_{1/3\left(1\pm \delta \right)}\mathrm{Nb}{\mathrm{S}}_2$ single crystals across a series of precisely controlled cobalt compositions with $-4\%\le \delta \le 8\%$. By tuning the cobalt stoichiometry, we find that the topological Hall effect is critically sensitive to the intercalant cobalt composition and is completely suppressed when the cobalt composition exceeds $\delta =+4\%$. We observe that the longitudinal conductivity is also strongly influenced by the cobalt composition, reaching its maximum value just before the disappearance of the topological Hall effect. Furthermore, heat capacity measurements reveal distinct Sommerfeld coefficients ($\gamma$) across different compositions, which exhibit a clear linear scaling with the inverse of the ordinary Hall coefficient ($R_H^{-1}$). These results demonstrate that composition tuning in $\mathrm{C}{\mathrm{o}}_{1/3\left(1\pm \delta \right)}\mathrm{Nb}{\mathrm{S}}_2$ systematically modifies the low-energy electronic degree of freedom, moving beyond a simple dilute impurity picture. Finally, we use the microscopic spin Hamiltonian to explain the stability of the experimentally observed M-point modulation vector and the corresponding triple-Q magnetic order. Our findings highlight that the topological properties of this system are highly tunable through precise control of the intercalant concentration, offering a new perspective on the competition between electronic and magnetic orders in intercalated transition-metal dichalcogenides.

The growing interest in quantum magnonics is driving the development of advanced techniques for generating, controlling, and detecting nonclassical magnonic states. Here, we explore the potential of an ensemble of solid-state spin defects coupled to a shared magnetic bath as a source of such states. We establish a theoretical framework to characterize the quantum correlations among magnons emitted by the ensemble into the bath and investigate how these correlations depend on experimentally tunable parameters. Our findings show that the emitted magnons retain the quantum correlations inherent to the solid-state emitters, paving the way for the deterministic generation of quantum many-body magnonic states.

Domain-wall (DW) motion is a crucial process involved in magnetization reversal, be it under a magnetic field or spin-polarized current stimulus. In most cases the DW speed does not exceed $\sim 100\mathrm{m}\text{/}\mathrm{s}$ and collapses above a given threshold of the stimulus, an effect known as Walker breakdown. A few specific material properties have been identified to delay the breakdown of speed by increasing the energy barrier preventing internal precession. We show that in a three-dimensional nanomagnetic system, here with vortex-state domains in nanowires, the topology of the magnetization distribution may intrinsically and robustly delay the Walker breakdown due to an exchange-spring effect. However, in contrast to cases in lower dimension, the motion remains steady state. In addition, curvature induces a major nonreciprocal effect, delaying or not the Walker breakdown depending on the sequence of chiralities of the azimuthal domains on both sides of the DW, independent of its direction of motion.

In this work, we theoretically investigate the false vacuum decay process in a ferromagnetic quantum spin-1/2 chain. We develop a many-body theory describing the nucleation and the coherent dynamics of true-vacuum bubbles that is analytically tractable and agrees with numerical matrix product state calculations in all parameter regimes up to intermediate times. This theory allows us to identify different regimes in the parameter space and unravel the underlying physical mechanisms, thus offering conceptual insight into the microscopic quantum dynamics of metastable states. In particular, analogies and differences with the cosmological false vacuum decay picture are highlighted and characterized in terms of experimentally observable quantities.

When a quantum system exhibiting a second-order phase transition is quenched across the critical point in a large but finite time, the dynamics are not adiabatic in the critical region, and the Kibble–Zurek (KZ) mechanism provides a framework to determine local observables such as the mean defect density. However, to find higher-point functions, one has to go beyond the KZ paradigm, as shown in recent works on the one-dimensional transverse field Ising model (TFIM) following a linear quench. It has been found that (i) besides the KZ scale, the quench dynamics depend on another length scale that arises because of the finite phase difference between the low-energy modes, and (ii) contrary to the expectations based on the KZ mechanism, in general, the correlation functions do not decay exponentially with distance. Motivated by these results for the linear quench, we are interested in understanding if these properties are universal, and consider the 1D TFIM when the transverse field varies algebraically in the vicinity of the critical field. We focus on the equal-time, longitudinal kink-kink correlation function at the end of the quench from the paramagnetic to the ferromagnetic phase, and find that (i) the correlator depends only on the KZ length for superlinear quenches, otherwise an additional dephasing length is required to describe it, and (ii) the dephased correlator decays as a compressed exponential with an exponent that changes continuously with the quench exponent. Our results are obtained using adiabatic perturbation theory, analytical arguments, and exact numerical integration of the relevant equations.

We examine the structural, vibrational, and transport properties of ${\mathrm{EuAg}}_4{\mathrm{As}}_2$ single crystals under pressures up to 28.8–41.8 GPa, aiming to trace the evolution of the structural distortion near $T_{\mathrm{S}}\sim 130\mathrm{K}$ and the two magnetic transitions at $T_{\mathrm{N}1}\sim 15\mathrm{K}$ and $T_{\mathrm{N}2}\sim 9\mathrm{K}$. Under ambient conditions, a Raman-active phonon mode centered at $\sim 157\mathrm{c}{\mathrm{m}}^{-1}$ is observed and identified as having $A_{1g}$ symmetry, and its temperature evolution shows no discernible anomaly across these three transitions. Under pressure, combined synchrotron x-ray diffraction and Raman measurements reveal two structural distortions at $P_{\mathrm{C}1}\sim 7$ GPa and $P_{\mathrm{C}2}\sim 17$ GPa. Structural refinements and bond-valence-sum analysis suggest that these transitions mainly involve successive discontinuous modifications of the Ag-As tetrahedra, without changing the average crystal symmetry. Distinct transport and magnetic responses accompany these structural distortions: For $P<P_{\mathrm{C}1}, T_{\mathrm{S}}$ increases while its resistivity anomaly is suppressed and $T_{\mathrm{N}1}$ and $T_{\mathrm{N}2}$ gradually increases; for $P_{\mathrm{C}1}<P<P_{\mathrm{C}1}$, high-temperature ferromagneticlike and low-temperature antiferromagneticlike states emerge; and for $P>P_{\mathrm{C}2}$, the resistivity becomes metalliclike, with only a faint broad kink and very weak magnetoresistance comparable to that of traditional metals.

Spin-torque vortex oscillators (STVOs) have been shown to exhibit rich and complex dynamical regimes, which are strongly dependent on the configuration of the polarizer. Here, we give an overview of the dynamics in an STVO comprising two vortex free layers, where each layer serves as a dynamic polarizer for the other, increasing the number of degrees of freedom and, therefore, the complexity of the system. The dynamics are studied through extensive micromagnetic simulations, performed using our own implementation of the coupled equations of motion, implemented in the open-source micromagnetics code $\mathrm{MUMAX3}$. We explore the roles of relative vortex configurations and layer asymmetry on the current-driven dynamics and find several complex regimes, including self-modulated gyration, the emergence of C-state dynamics, as well as chaotic transitions between regular gyration and this C state.

We use ${}^{51}\mathrm{V}$ nuclear magnetic resonance (NMR) spectroscopy to investigate the magnetic ground state of the lacunar spinel ${\mathrm{GeV}}_4{\mathrm{S}}_8$, which undergoes a structural distortion at $T_{\text{JT}}\approx 30\mathrm{K}$ followed by an antiferromagnetic (AFM) ordering at $T_N\approx 15\mathrm{K}$. According to our zero- and finite-field NMR data, the four V-sites of ${\mathrm{V}}_4$ clusters become magnetically inequivalent in the AFM state: Two of them share the same internal field, while the other two sites are characterized by different internal fields. The angular dependence of the ${}^{51}\mathrm{V}$ NMR lines, upon rotation of an external magnetic field about the pseudocubic [110] and [100] axes, reveals that the internal fields are either parallel to the orthorhombic $a$ axis at all four V-sites of the ${\mathrm{V}}_4$ tetrahedra, or they form an orthogonal pattern, where two V-sites have internal field along the $a$ axis and the other two along the $b$ axis. Based on these results, further supported by the observation of distinct spin-echo modulations of the inequivalent V-sites, we conclude that the magnetic space group of the AFM state is $P_{b}mn{2}_1$ or $Pm{n}^{\prime }{2}_1^{\prime }$.

We introduce a computational framework for the efficient modeling of nonlinear optical responses in solids under nonresonant excitation. Utilizing the Semiconductor Bloch Equations, our approach captures multiband carrier dynamics across the entire Brillouin zone. A significant simulation speedup is achieved through a learned single-particle Hamiltonian optimized for an extremely coarse numerical grid. Notably, this method maintains the high accuracy in current densities and carrier populations required for coupling with Maxwell's equations, thereby enabling the multiscale simulation of complex light-matter interactions, where macroscopic pulse propagation directly couples to the quantum dynamics of the optically excited material.

The emergence of altermagnetism, a collinear magnetic phase characterized by momentum-dependent spin-split bands but zero net magnetization, has fundamentally reshaped the classification of magnetic order. We propose an altermagnetic (AM) order in a repulsive Hubbard model on the Lieb-5 lattice. Considering only nearest-neighbor hoppings within the lattice, we show a phase transition from the nonmagnetic phase to a unique AM isolated band metal phase (AMIM), allowing clear identification of spin-split states. Additionally, the AM metallic phase (AMM) is also shown to appear as an intermediate phase during the transition from the normal metal to the AMIM in the presence of diagonal hopping within each unit cell of the Lieb-5 lattice. The manifestation of distinct AM phases and the phase transitions, driven by the Hubbard interaction and hopping integrals, has been explored in terms of the spin-resolved band structure, spectral function, and behavior of the AM order parameter. The stability of these AM phases against the spin–orbit coupling and temperature is also established.

We report the electronic structure of the kagome compound ${\mathrm{LuNb}}_6{\mathrm{Sn}}_6$ using high-field torque magnetometry and first-principles calculations. This compound hosts a kagome lattice of Nb atoms and undergoes a charge density wave (CDW) transition below 70 K, accompanied by the formation of a $\sqrt{3}\times \sqrt{3}\times 3$ superlattice modulation [B. R. Ortiz et al., J. Am. Chem. Soc. 147, 5279 (2025)]. Torque measurements up to 41 T reveal pronounced de Haas-van Alphen (dHvA) oscillations for magnetic fields applied along both polar (ac-plane) and azimuthal (ab-plane) directions. The frequency spectra exhibit multiple branches, with the highest frequency reaching nearly 2500 T when the field is applied along the $c$ direction. To map the Fermi surface topology, we performed angle-dependent measurements with the magnetic field rotated in both polar and azimuthal directions. The frequencies vary systematically with polar angle while remaining nearly unchanged with azimuthal angle, indicating a quasi-two-dimensional Fermi surface. To further understand the experimental results, we carried out density functional theory calculations of the electronic structure and Fermi surface for both the pristine and CDW phases. While the dHvA frequencies calculated for the pristine structure fail to reproduce the experimental spectrum, those obtained for the CDW phase are in good agreement with the measured frequencies. These results establish a direct link between the observed quantum oscillations and the reconstructed Fermi surface of ${\mathrm{LuNb}}_6{\mathrm{Sn}}_6$ and provide important insights into the electronic structure of this and related kagome materials.

We study the ground-state phase diagram of Rydberg atoms in a triangular-prism optical tweezer array using the density matrix renormalization group. Unlike two-leg Rydberg ladders with ${\mathbb{Z}}_2$ leg-exchange symmetry, the triangular prism possesses ${\mathbb{D}}_3$ symmetry, giving rise to a richer set of ordered phases and transitions. At relatively small blockade radius, a ${\mathbb{Z}}_2\times {\mathbb{Z}}_3$ density-wave phase appears at large detuning and breaks ${\mathbb{Z}}_2$ translational and ${\mathbb{Z}}_3$ rotational symmetry while preserving the reflection symmetry of the triangular rung. Upon decreasing detuning, it melts via a Berezinskii-Kosterlitz-Thouless (BKT) transition into a critical phase and subsequently enters a disordered phase through a second BKT transition, forming a commensurate regime described at low energies by a ${\mathbb{Z}}_6$ clock model. At larger blockade radius, a ${\mathbb{D}}_3$ phase with one Rydberg excitation per triangle emerges through a first-order transition. When double excitations on neighboring triangles are suppressed, rung-trimerized density waves develop as detuning increases from the disordered phase. These phases break translational symmetry while preserving ${\mathbb{D}}_3$ symmetry, and their melting transitions exhibit critical behaviors similar to those in Rydberg chains and two-leg ladders. In addition, we identify a geometry-dependent crossover within the ${\mathbb{Z}}_2$ rung-trimerized phase, followed by a first-order transition into a ${\mathbb{Z}}_2\times {\mathbb{D}}_3$ phase with complete ${\mathbb{D}}_3$ symmetry breaking. We also find floating phases with incommensurate quasi-long-range order between rung-trimerized states.

Coupling between spin, orbital, charge, and lattice degrees of freedom in transition-metal oxides produces a variety of electronic and magnetic phenomena of importance for future technologies. Here, we explore the electronic band structure of a (111)-oriented ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ thin film through soft x-ray angle-resolved photoemission spectroscopy (ARPES). The measurements agree with the electronic band structure calculated with density functional theory using the Hubbard $U$ correction. Furthermore, we probe the circular dichroism in ARPES and observe a pronounced momentum-resolved magnetic circular dichroism (MCD) in resonant photoemission from the Mn $L$ edge. The momentum distribution of the resonant MCD reproduces that of the Fermi surface, establishing resonant circular dichroism ARPES as a momentum-resolved probe of itinerant Bloch states, with implications for unconventional magnets such as altermagnets and $p$-wave magnets.

We study superconducting instabilities in van der Waals (vdW) heterostructures comprising a honeycomb antiferromagnetic insulator and a transition metal dichalcogenide (TMD). Using a functional renormalization group approach, we demonstrate that interfacial magnon exchange can induce effective attractive interactions among itinerant electrons that can drive unconventional superconducting pairing. The competition between Coulomb-mediated and magnon-mediated interactions is analyzed through the renormalization group flow, revealing that attractive Coulomb interactions naturally favor superconductivity, whereas repulsive interactions require a sufficiently strong magnon-mediated attraction to stabilize pairing. Solving the linearized gap equation with the renormalized effective interaction, we determine the critical temperature and superconducting pairing symmetry. Our results highlight the potential of a broad class of vdW heterostructures as a platform for realizing unconventional superconductivity driven by interfacial magnetic interactions.

Persistent spin helices are a manifestation of symmetry-protected spin textures in systems with balanced spin-orbit coupling. They enable long-lived spin structures that are of interest for spintronics and coherent spin manipulation. The quantum metric has recently emerged as a promising tool for characterizing the geometric structure of quantum states. Here, we demonstrate that the quantum metric provides a sensitive geometric probe of the persistent spin helix. Within the Rashba-Dresselhaus Hamiltonian, we analytically evaluate the quantum metric components and uncover a divergent geometric contribution that emerges precisely at the persistent spin helix condition. We reveal that this divergence originates from a hidden line degeneracy that forms when the strengths of Rashba and Dresselhaus spin-orbit coupling become equal. We further study the role of higher-order cubic spin-orbit interactions and determine how these corrections regularize the geometric response and control the scaling behavior of the quantum metric. Our results establish quantum geometry as a powerful framework for identifying and characterizing persistent spin helices and related symmetry-protected spin textures.

Colossal negative thermal expansion (CNTE) materials are of significant importance for applications in precision engineering and related fields. However, simultaneously achieving a colossal negative thermal expansion coefficient (CTE) and a broad temperature range remains a central challenge. Using a combination of synchrotron x-ray diffraction, Raman spectroscopy, and density-functional-theory calculations, we find that the $A_2{\mathrm{P}}_2{\mathrm{O}}_7$ ($A=\mathrm{Cu}$, Mg, Zn) series exhibits significant CNTE during the α-β phase transition. Structural analysis indicates that during the phase transition, the pronounced contraction of the axial $\mathrm{A}-\mathrm{O}{4}_{\left(\mathrm{long}\right)}$ bonds drives the lattice volume reduction. Meanwhile, temperature-dependent Raman spectroscopy reveals that the 105 $\mathrm{c}{\mathrm{m}}^{-1}$ vibrational mode, assigned to antisymmetric Cu–O bond stretching, undergoes softening accompanied by significant broadening, indicating strong electron–lattice coupling in the series. Combined with energy pathway calculations, the presence of the pseudo-Jahn–Teller effect destabilizes the high-symmetry β phase and drives its transformation into the low-symmetry α phase, thereby leading to significant volume contraction upon heating. Further analysis indicates that the shallow and flattened potential energy surface at the Cu site in ${\mathrm{Cu}}_2{\mathrm{P}}_2{\mathrm{O}}_7$ enables pronounced anti-off-centering displacement of Cu atoms with increasing temperature, which in turn leads to significant NTE before the phase transition, with a volumetric CTE of $-22.25\times {10}^{-6}{\mathrm{K}}^{-1}$. Furthermore, substituting V at the P site leads to the formation of ${\mathrm{Cu}}_2{\mathrm{V}}_2{\mathrm{O}}_7$, which exhibits a colossal negative CTE ($-858.83\times {10}^{-6}{\mathrm{K}}^{-1}$) and a broad CNTE temperature range of 100–900 K. This study not only reveals a physical driving mechanism of CNTE in the $A_2{\mathrm{P}}_2{\mathrm{O}}_7$ series, but also provides important theoretical guidance for the design of novel functional materials that combine colossal negative thermal expansion coefficients with a broad temperature range.

Recent experimental and theoretical studies have suggested a possible Dirac magnon gap in the two-dimensional ferromagnetic semiconductor ${\mathrm{CrSiTe}}_3$. Detailed neutron scattering measurements were performed to shed light on the existence of the magnon gap, and suggest that the gap is very small or nonexistent, with previous measurements being complicated by experimental factors. During these measurements, it was found that the out-of-plane couplings could explain the usual property of the increase in the magnetic transition temperature when ${\mathrm{CrSiTe}}_3$ is exfoliated to monolayers. Furthermore, the material was shown to have anisotropic magnons along the out-of-plane direction, through the proposed Dirac point. We speculate that this is due to an exchange anisotropy, though Kitaev-like interactions alone cannot explain the spectra.

Chiral magnetic textures, such as skyrmions, are of great interest to the condensed matter community due to their novel transport properties. The stabilization of topologically nontrivial magnetic phases, like the skyrmion lattice in cubic MnSi, is governed by underlying magnetic interactions which can be probed via measurements of spin-wave excitations. Here, we report high-resolution inelastic neutron scattering (INS) measurements of the spin waves in Fe-doped ${\mathrm{Mn}}_{0.9}{\mathrm{Fe}}_{0.1}\mathrm{Si}$ deep within its field-polarized ferromagnetic state. We observe nonreciprocal spin waves with a parabolic dispersion that shifts linearly with magnetic field. Crucially, the spin-wave stiffness is highly anisotropic, with values of 17.2(5) meV ${\text{Å}}^2$ parallel to the applied field and 9.3(3) meV ${\text{Å}}^2$ perpendicular to it. While the applied field fundamentally lowers the systems symmetry from cubic to uniaxial, we demonstrate that the induced spin-wave anisotropy is significantly large, which is not captured within the simple theoretical approximations widely applied up to date.