Competing magnetic interactions and coupling to lattice degrees of freedom can stabilize complex spin orders in type-II multiferroic materials, leading to magnetically induced ferroelectricity. Here, we investigate the low-temperature crystal and magnetic structures of the spin-driven multiferroic ${\mathrm{FeVO}}_4$ using high-resolution synchrotron x-ray and neutron powder diffraction, complemented by macroscopic measurements. ${\mathrm{FeVO}}_4$ exhibits two successive antiferromagnetic transitions: an incommensurate collinear phase below $T_{\mathrm{N}1}\approx 21\mathrm{K}$, followed by an incommensurate noncollinear (NC) helical phase below $T_{\mathrm{N}2}\approx 15\mathrm{K}$. The magnetic order in these two phases is characterized by closely related incommensurate propagation vectors refined from powder neutron diffraction, indicating only a weak temperature dependence of the magnetic modulation. While both magnetic structures break inversion symmetry at the level of the magnetic modulation, ferroelectricity emerges only in the helical phase, where NC allows a finite spin chirality, consistent with spin-driven ferroelectricity commonly discussed within an inverse Dzyaloshinskii-Moriya framework. Subtle anomalies in lattice parameters observed near both magnetic transitions provide qualitative evidence of weak spin-lattice coupling, without detectable lowering of crystallographic symmetry. Together, these results establish a bulk-sensitive, temperature-dependent picture of how magnetic frustration, weak lattice responses, and NC spin order cooperate to stabilize the multiferroic ground state in ${\mathrm{FeVO}}_4$.

The reversal of the anomalous Hall effect (AHE) via low-power ferroelectric (FE) switching has recently attracted significant interest. However, a general symmetry-based design principle for such control remains absent. Here, we establish effective symmetry criteria for FE-switchable AHE in two-dimensional (2D) multiferroics without altering the magnetic configuration. By analyzing the transformation properties of Berry curvature under magnetic space group (MSG) symmetry operations associated with FE switching, we show that FE-switchable AHE in 2D multiferroics requires the following conditions (i) The MSG of the FE phase contains none of the symmetry operations belonging to the Berry curvature reversing set $S=\{T,2_{\parallel },n_{001}T,PT,m_{\perp },m_{001}T,S_{n}T\}$, thereby allowing a nonzero AHE. (ii) The MSG of the paraelectric phase contains at least one symmetry operation that not only belongs to the set $S$, but also maps the two symmetry-related FE states onto each other by reversing the FE polarization, thereby ensuring the simultaneous switching of both FE polarization and AHE. These criteria are validated by first-principles calculations in the in-plane FE VOBrI and out-of-plane FE ${\mathrm{Co}}_2{\mathrm{NF}}_2$ single layers, and further confirmed using a modified Kane–Mele model. Our results provide a practical symmetry-based guideline for designing and screening 2D multiferroics with FE-switchable AHE and Chern number $C$.

The transition from very weak to ultrastrong plasmon-polariton-phonon coupling in (surface) doped ${\mathrm{HfS}}_2$ multilayers has been investigated. A plasmon-polariton (PP) in a single-layer ${\mathrm{HfS}}_2$ interacts weakly with polar phonons, however in ${\mathrm{HfS}}_2$ multilayers ($N>25$) the PP-phonon splitting becomes ${\mathrm{\Omega }}_{\text{PP-Ph}}\ge {\omega }_{\text{LOx}}/3$, indicating ultrastrong PP-phonon coupling. A particularly interesting electrodynamic effect appears for $d>10\text{−}\mu \text{m}$-thick ${\mathrm{HfS}}_2$ slabs. Then the absorption spectrum is dominated by a series of infrared active cavity resonances that spatially and by frequency resemble ${\mathrm{HfS}}_2$ cavity modes; they are standing waves confined to the ${\mathrm{HfS}}_2$ film but also radiate into the surrounding vacuum. The intensity of cavity resonances is comparable with the intensity of evanescent surface plasmon polaritons, while their number and frequency can be tuned by changing the ${\mathrm{HfS}}_2$ surface doping and/or thickness $d$. These are also very robust modes, so they may be very useful for the development of multifunctional nanoscale and mesoscale photonic devices.

An effective model of a two-band superconductor with full interband pairing is established based on doubly coupled Kitaev chains with a $\pi$-phase difference. Tunable Andreev bound states and quantized Andreev reflection are demonstrated. A hybrid qubit architecture is constructed, leveraging these bound states to synergize ultrafast microwave-driven Rabi oscillations in Andreev qubits with topologically protected quantum memory via Majorana zero modes. The resulting theoretically derived quantum memory and nontrivial fusion could offer supporting signatures for topological superconductivity. All theoretical results of our base model are directly reproduced within a realistic theoretical material model of an altermagnet-proximitized topological superconducting nanowire system.

We investigate analytically and numerically the effects of disorder on the helical edge of a two-dimensional topological insulator in the presence of a Zeeman field and superconductivity. Employing bosonization and a renormalization-group analysis, we study how impurity potentials modify charge- and spin-density wave correlations as well as superconducting pair correlations. Our results reveal that the Zeeman field controls the competition: in the attractive regime, it amplifies the superconducting gap, while in the repulsive regime, it stabilizes impurity effects by keeping the system longer in the relevant regime for disorder. We also find that disorder induces logarithmic suppression of density-wave correlations, while at the same time introducing positive logarithmic corrections that enhance superconducting pairing correlations and contribute to their stability. These effects directly modify the scaling of spin conductance, providing experimentally accessible signatures of the interplay between disorder and superconductivity in topological edge channels.

Surface-enhanced Raman scattering (SERS) has been considered as a powerful trace-level analytical technique for a diversity of fields. However, a molecule in the real world inevitably interacts with other molecules or external stimuli, which often results in obvious changes of its SERS spectrum, e.g., relative intensity, broadening/narrowing, shifting, splitting/merging of the peaks, emergence of new peaks and/or disappearance of existed peaks, etc. These bring fundamental challenges to SERS in solving real-world problems through recognition of the molecule's fingerprints, which has long been an open question in the field. We proposed here a virtual molecules (VMs) and virtual spectra method to deal with the molecule's interactions, and reformulated SERS with two concepts, i.e., cross-section function and relative scattering ability of molecules, which are valid for molecular systems with/without interactions. We established an approach to experimentally obtain the cross-section function and the relative scattering ability of VMs, by which the SERS behavior of molecular systems can be explicitly described by our formulation, with no need to recognize the molecule's fingerprints. These efforts consolidate the foundation of SERS, and push forward its applications as a powerful trace-level analytical technique in solving real-world problems.

We study topological effects in a one-dimensional plasmonic crystal formed by the screened plasmons emerging in a periodically modulated graphene sheet, placed on top of a metallic substrate. We develop the theory of quantization of screened plasmons, as appropriate for lossless graphene described by a Drude conductivity. By analyzing the resulting band structure, we show that the crystal sustains nontrivial topological bands, with quantized geometric phase. We further show that in a finite open system, edge states appear within the band gap, which undergo a topological phase transition and merge with bulk states as the modulation increases. Our work provides a robust theoretical framework for the study of band structure and topology of layered media and extends the possibilities for engineering two-dimensional materials with external modulation.

We uncover a previously overlooked contribution to the electro-optic Kerr rotation of reflected light, arising from the interplay of matter, the static electric field, and the magnetic component of light. This contribution remains nonzero even in isotropic, nonmagnetic, homogeneous systems. We derive analytical expressions for the Kerr rotation in both two-dimensional layers and semi-infinite systems. Within the relaxation-time approximation, we predict experimentally accessible signal magnitudes in metals. This inherent mechanism thereby opens opportunities for probing electronic properties in materials through Kerr spectroscopy.

Resonant parametric modulation is a major tool for studying magnetic systems. For a spin-1/2 chain in a strong magnetic field, the resulting excitations can be mapped onto fermionic excitations in the Kitaev chain. We show that the response to turning on the modulation reveals dynamical bulk aspects of the nontrivial topology of the closed chain. In the topological regime, depending on the turn-on rate, the system displays an absence of frequency dispersion of the time-averaged magnetization and an absence or a suppression of its spatial correlations near resonance. The transition between the topological and trivial regimes is controlled by the modulation frequency.

A systematic structural investigation of $\mathrm{F}{\mathrm{e}}_2\mathrm{M}{\mathrm{o}}_3{\mathrm{O}}_8$ as a function of pressure, temperature, and magnetic field reveals that the $P{6}_{3}mc$ space group remains robust over a wide range of conditions. No changes in the long-range crystal structure are observed for pressures up to 10 GPa, temperatures between 11 K and 300 K, and magnetic fields up to 9 T. The magnetostructural response, quantified by $\mathrm{\Delta }c/c$, is determined for magnetic fields applied transverse to the crystallographic $c$ axis, demonstrating strong magnetoelastic coupling. The well-known magnetic-field-induced transition is confirmed to be first order and isostructural, occurring between two distinct altermagnetic states. Importantly, this transition can also be accessed using magnetic fields applied within the $\mathit{ab}$ plane. When expressed in terms of the $c/a$ ratio, the structural evolution under pressure (0–10 GPa) maps continuously onto that observed across the full Zn substitution range in $(\mathrm{F}{\mathrm{e}}_{1-y}\mathrm{Z}{\mathrm{n}}_y{)}_2\mathrm{M}{\mathrm{o}}_3{\mathrm{O}}_8\left(0\le y\le 1\right)$, indicating a common underlying structural control parameter. These results demonstrate that the $c$-axis lattice parameter is the primary structural degree of freedom governing magnetic behavior under external tuning parameters. More broadly, they indicate that magnetic order in this family of complex oxides ($A_2\mathrm{M}{\mathrm{o}}_3{\mathrm{O}}_8, A=\mathrm{Co},\mathrm{Mn},\mathrm{Ni}$) can be systematically tuned via pressure. This tunability highlights these materials as promising platforms for controllable magnetic switching, particularly in thin films integrated with piezoelectric substrates.

Hydrogen doping offers a versatile method to dynamically control the doping level of metal oxides over a wide range, yet it introduces strong lattice modulation whose structural details have been poorly investigated. Here, we elucidate the hydrogen-induced structural modulation in ${\mathrm{NdNiO}}_3$ thin films using synchrotron x-ray diffraction. While the strain relaxed pristine film exhibits a bulklike $\sqrt{2}\times \sqrt{2}\times 2$ structure, the hydrogen-induced insulating phase adopts a $1\times 1\times 2$ structure with some incommensurate modulation. Our results provide the first direct experimental evidence for hydrogen-induced formation of a superstructure in rare-earth nickelates.

${\mathrm{VO}}_2$ features concomitant structural and metal-insulator transitions. This poses a challenge for understanding the underlying mechanism: Is the transition triggered by a structural or by an electronic instability? The two scenarios are expected to produce very different pretransitional fluctuations above $T_{\mathrm{C}}$. By combining magnetic susceptibility, IR reflectivity, and x-ray diffuse scattering measurements, we observe that metallic ${\mathrm{VO}}_2$ features strong electronic and structural fluctuations toward the insulating monoclinic phase. By measuring resonant diffuse x-ray scattering across the vanadium $K$ edge, we search for a potential decoupling between electronic and structural ordering in these fluctuations, finding no evidence of it. While our results do not completely rule out pure electronic fluctuations, they constrain them, favoring the interpretation that the ${\mathrm{VO}}_2$ metal-insulator transition is triggered by a structural instability. Our work offers a unique approach to solve similar problems in other strongly correlated systems.

Several recent x-ray diffraction studies have focused on whether the high-pressure body-centered cubic (bcc) phase of zirconium undergoes an isostructural bcc-bcc transition at 58 GPa. The consensus of these studies is that there is no such transition and that a previous claim by Stavrou et al. resulted from issues with the pressure calibration. However, a close analysis of the data from one of the most recent of these diffraction studies by Anzellini et al. shows unremarked evidence of a discontinuity in both atomic volume and compressibility at 83 GPa indicating an isostructural transition is present. Unfortunately, no other previous studies have reached this pressure, and so the question of the bcc-bcc transition is still open. Here we describe a diffraction study of Zr to 240 GPa looking for a bcc-bcc isostructural transition. Our data show no evidence of any discontinuous change in volume or compressibility at 83 GPa. We observe no evidence of a $\beta \to {\beta }^{\prime }$ transition above 80 GPa, and suggest a possible cause of the discontinuity observed by Anzellini et al.

The atomic structures of ceramics critically govern their thermal properties. However, the atomistic thermal transport mechanisms are poorly understood. Here, we developed novel neural network potentials with near-DFT accuracy, enabling a precise exploration of atomic structural evolution in yttria-stabilized zirconia and its influence on thermal properties. It was found that the monoclinic-to-tetragonal transition is primarily driven by tilt vibrations, whereas the tetragonal-to-cubic transition is mainly governed by octahedral distortions. Yttrium doping and the resulting oxygen vacancies induce local stress and lattice mismatch, thereby shifting the transition temperatures. As the doping concentration increases, the energy barriers between different YSZ phases decrease, thus facilitating phase transitions. Meanwhile, the lattice thermal conductivities are mainly related to low-frequency acoustic branches, exhibit size effects, and are insensitive to anisotropy. Further analysis of phonon lifetimes reveals that yttrium doping and the associated oxygen vacancies enhance lattice anharmonicity and defect scattering. This work provides a theoretical framework for analyzing the structure-dependent thermal properties of advanced oxide ceramics.

We show that quasiperiodicity can enhance superconductivity in one-dimensional narrow-band systems with $s$-wave pairing. Using a generalized Aubry-André-Harper model featuring quasiperiodic modulations in both the on-site potential and the hoppings, we study superconductivity across the extended, critical, and localized phases present in the noninteracting limit. Our results show that within the critical and localized phases, the superconducting critical temperature exhibits an algebraic scaling with the interaction strength, in contrast to the conventional BCS scaling observed in periodic approximants with a similar density of states. This direct comparison establishes that the enhancement originates from the nature of the single-particle eigenstates, rather than from band flattening alone. Furthermore, we find that the superfluid weight remains finite across all phases, including the localized regime, highlighting that superconducting phase coherence is retained throughout. The effects of quasiperiodicity on the superfluid weight are most pronounced in the weak-coupling regime, indicating the nontrivial role of the localization properties of the parent eigenstates in shaping the superconducting phases.

The correlation properties of the nonaffine elastic response in strongly disordered materials are investigated using the theory of correlated random matrices and supported by numerical models. While the nonaffine displacement field itself predominantly exhibits power-law decay, we demonstrate that its spatial derivatives reveal large-scale, exponentially decaying correlations. Specifically, the correlation functions of the divergence and (for most deformations) the rotor of the nonaffine field are governed by a heterogeneity length scale $\xi$. This length scale is set by the disorder strength and can become indefinitely large, far exceeding the structural correlation length. A notable exception occurs under volumetric deformation, where the rotor correlations lack the exponential tail with the length scale $\xi$. The theory also predicts that the rotor correlations may have small power-law tails. We directly observe the exponential decay, characterized by $\xi$, in numerical studies of a rigidity-percolation model and in molecular dynamics simulations of amorphous polystyrene and the Lennard-Jones glass. The latter example also confirms the existence of the power-law tail in the rotor correlation function at large distances.

Quantum many-body scars (QMBS) are exotic many-body states that exhibit anomalous nonthermal behavior in an otherwise ergodic system. In this work, we demonstrate a simple, scalable, and intuitive construction of QMBS in a kinetically constrained quantum model exhibiting weak Hilbert space fragmentation. We show that exact QMBS can be constructed by injecting a quasiparticle that partially activates the frozen regions in the lattice. Meanwhile, the inelastic collision between multiple quasiparticles allows for the construction of approximate scars, whose damping is governed by an emergent two-body loss. Our findings establish direct connections between quantum many-body scarring and Hilbert space fragmentation, paving the way for systematically constructing exact and approximate QMBS with nontrivial spatial connectivity. The proposed model can be readily implemented in neutral-atom quantum simulators aided by strong Rydberg interactions.

We propose an optimized adiabatic-impulse (OAI) protocol that substantially reduces the evolution time for crossing a quantum phase transition while preserving Kibble–Zurek (KZ) scaling. Near criticality, the control parameter is ramped linearly across the critical point at a rate characterized by a quench time ${\tau }_Q$. Away from criticality, the evolution remains adiabatic and is tuned close to the threshold of adiabatic breakdown, as quantified by an adiabatic coefficient $\zeta$ that scales as ${\tau }_Q^{\alpha }$. As a consequence, the total evolution time exhibits a sublinear power-law dependence on ${\tau }_Q$, and the conventional linear quench is recovered in the limit $\alpha \to \infty$. We apply the OAI protocol to the transverse Ising chain and numerically determine the minimal $\zeta$ required for KZ scaling. We further investigate the nonequilibrium dynamics in the presence of a noisy field that can induce anti-Kibble–Zurek (AKZ) behavior. Within the OAI protocol, noise-induced defects are significantly attenuated because of the shorter evolution time. The optimal quench time at which the defect density is minimized obeys an altered universal power-law scaling with the noise strength. Finally, we generalize the OAI protocol to the nonlinear quenches and numerically demonstrate a marked reduction in noise-induced defects.