Superconductivity in the bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ occurs when the interlayer Ni-O-Ni bond angle becomes straight under pressure, suggesting a strong relationship between the crystal structure and the emergence of superconductivity. In this study, we theoretically propose a way to control the crystal structure of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ toward the tetragonal symmetry via light irradiation instead of pressure using the idea of nonlinear phononics. Here, resonant optical excitation of an infrared-active (IR) lattice vibration induces a nonlinear Raman-mode displacement through the anharmonic phonon-phonon coupling. We calculate the light-induced phonon dynamics on the anharmonic lattice potential determined by first-principles calculation. We find that the interlayer Ni-O-Ni bond angle gets slightly closer to straight when an appropriate IR mode is selectively excited. Our study suggests that light irradiation can be a promising way for structural control of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

Ice phases VII, VIII, and X are all based on a body-centered cubic arrangement of molecules, the differences coming from how molecular orientation breaks the symmetry. It is debatable as to whether these should even be considered distinct phases given that the standard definition of a transition between distinct phases involves a discontinuity in any derivative of the free energy. This can be hard to prove experimentally, and most previous theoretical works have been based on models which either have continuously differentiable free energies or offer no straightforward way to determine the free energy. Here we build a free-energy model based on the common definitions of the phases: ordered ice-VIII, orientationally disordered ice VII, and centered-proton ice X. All transitions in this model might or might not be associated with a discontinuity in the specific heat, depending on parameterization. By comparing with data, we find that a VII-X transition line exists, but it ends in a critical point hidden within the stability field of phase VIII. If the model is correct, there is a discontinuity between VII and X, so they are separate phases. We propose that the hidden phase boundary might be demonstrated experimentally by compression of supercooled ice VII.

The van der Waals ferromagnet ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$ possesses both a high Curie temperature and robust perpendicular magnetic anisotropy, holding promise for practical spintronic applications. In particular, understanding and engineering its Gilbert damping, which determines magnetization dynamics, are crucial for its applications. Here, we investigate the Gilbert damping of bilayer and the twisted bilayer ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$ through first-principles calculations. For the bilayer ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$, we obtain a quite low Gilbert damping when its magnetization is along the $z$ axis at room temperature. In addition, the bilayer ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$ exhibits a large orientational anisotropy of Gilbert damping when its magnetization is rotated from the magnetic easy axis to the hard one. Such anisotropy is attributed to the distinct band structures caused by the anisotropic spin-orbit coupling. Surprisingly, we find that twisting the bilayer ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$ can effectively reduce the Gilbert damping for the perpendicular magnetization and enhance the orientational anisotropy of Gilbert damping up to 635% when rotating the magnetization from the magnetic easy axis to the hard one. These findings open up an entirely new avenue for the manipulation of Gilbert damping and its anisotropy in two-dimensional van der Waals ferromagnets.

We present comprehensive neutron scattering data on polycrystalline samples of a new metastable honeycomb material ${\mathrm{KCoAsO}}_4$. Below $T_N=14$ K, the system orders into a zigzag antiferromagnetic state, with spins ordered into alternating ferromagnetic chains similar to the isostructural sister compound ${\mathrm{KNiAsO}}_4$. In the case of ${\mathrm{KCoAsO}}_4$, we find the moments are robustly canted out of plane closer to the crystallographic $c$ axis. A combination of weak interlayer coupling, lattice strain, and inhomogeneities lead to the coexistence of two magnetic ordering wave vectors $k_1=(1.5 0 0)$ and $k_2=(0.5 0 0.5)$, where the two structures differ only in their layer stacking. Inelastic data show the presence of a spin orbital mode at 24 meV, supporting a pseudospin $\tilde{S}=1/2$ Kramer's doublet ground state of the ${\mathrm{Co}}^{2+}$ ions. We model the low energy excitations using both a conventional XXZ Hamiltonian and generalized Kitaev Heisenberg Hamiltonian within a linear spin wave limit. While either model can qualitatively reproduce the observed spectra, the lack of fine features and observation of disorder prevent a clear-cut determination of the low energy Hamiltonian. In the case of an XXZ-type model, a large easy-axis anisotropy is necessary to reproduce the gapped spectra and canting of the magnetic moments. For the generalized Kitaev model, despite the large canting of the moments away from the honeycomb layers, we find a noticeable if nondominant Kitaev term persists. The contrast of the magnetic properties of ${\mathrm{KCoAsO}}_4$ to other cobalt honeycombs highlights the sensitivity of the low energy magnetic properties of ${\mathrm{Co}}^{2+}$ to fine details of its crystalline environment.

The complex magnetoelectric (ME) features of the multiferroic manganites ${R\mathrm{Mn}}_2{\mathrm{O}}_5$ (R: rare earth elements, Bi) are of particular interest due to their giving rise to some fascinating phenomena such as topological ME behaviors. Here we systematically report the magnetic and electric properties of orthorhombic ${\mathrm{ErMn}}_2{\mathrm{O}}_5$ single crystals under DC and pulsed magnetic fields. Based on the anomalies in the experimental data along three crystalline axes, the magnetic field-temperature (H-T) phase diagram of ${\mathrm{ErMn}}_2{\mathrm{O}}_5$ is well established and reveals a significant anisotropy. In the case of H//$a$, at 1.6 K, two magnetic transitions occur at $H_{\mathrm{c}1}\sim 12$ T and $H_{\mathrm{c}2}\sim 30$ T, corresponding to the reversal and saturation of ferroelectric polarizations, respectively. As the temperature increases, $H_{\mathrm{c}1}$ slowly shifts towards lower magnetic fields and eventually becomes vague above 10 K. In contrast, $H_{\mathrm{c}2}$ is insensitive to temperature and remains robust up to 40 K. As a result, two field-induced ME phases are clearly identified above 10 T. For H//$b$, the low-temperature modulated incommensurate phase with weak ferroelectricity (ICM2/X) is gradually suppressed with increasing H, and finally replaced by the commensurate phase with a large polarization (CM/FE1) above 20 T. When the magnetic field is applied along the easy $c$ axis, 1/2- and 3/4-like magnetization plateaus induced by $\mathrm{E}{\mathrm{r}}^{3+}$ spins are observed below 5 K, which were not accessed earlier. The corresponding ferroelectric anomalies are triggered by the $4f\text{−}3d$ interaction between the Er and Mn ions, reflecting the rearrangement of the manganese subsystem. Hence, the successive ME phase transitions are well demonstrated in the low-H region, i.e., ICM2/X → CM/FE1 → ICM3/X′. Intriguingly, the CM/FE1 phase reappears instead of the ICM3/X′ phase above 50 T at low temperatures. Possible origins for all ME phases and magnetization plateaus are discussed. These findings could contribute to an in-depth understanding for the effect of rare earth ions in this family of ${R\mathrm{Mn}}_2{\mathrm{O}}_5$.

Heterostructures of superconductors and quantum-Hall insulators are promising platforms for topological quantum computation. However, these two systems are incompatible in some aspects, such as a strong magnetic field, the Meissner effect, and chirality. In this work, we address the condition that the superconducting proximity effect works in the bulk of quantum Hall states, and identify an essential role played by the vortex lattice regardless of pairing symmetry. We extend this finding to a heterostructure between a chiral $p$-wave superconductor in the mixed state and an integer quantum Hall insulator. The proximity effect works selectively in the lowest Landau level, depending on relative chiralities. If the chiralities align, a topological phase transition to a topological superconductor occurs.

The absence of intrinsic spin in acoustic waves poses a challenge to realize diverse topological phases, thereby constraining their potential applications in acoustics. In this study, we employ a realistic scheme to synthesize simultaneously the pseudospin and Rashba-Dresselhaus spin-orbit coupling (RDSOC) in acoustic systems and realize multitopological phase modulation. To implement it, we construct laddered acoustic crystals with chiral unitary (AIII) symmetry composing acoustic cavities and coupling tubes. The pseudospin-1/2 is encoded by a ladder consisting of each cylindrical acoustic cavity, and the SOCs are achieved by engineering the couplings between acoustic cavities. Through fine tuning of RDSOC coefficients in acoustic crystals, three distinct symmetry-protected topological phases with pseudospin and a trivial phase are identified based on the analysis of the winding number. Theoretical findings are verified by full-wave simulation results. Thus, our work enables the direct visualization of rich AIII symmetry-protected topological phases and pseudospin-resolved boundary states in acoustic crystals, which will benefit in-depth studies of acoustic coding with pseudospin information.

We investigate the interplay between unitary and nonunitary driven many-body dynam ics in ($1+1$)-dimensional quantum critical systems described by conformal field theory (CFT). By formulating a coherent state approach, we demonstrate that the growth of entanglement entropy and energy can be found analytically for a class of nonunitary driven CFTs, where the evolution alternates between real and imaginary time evolution, the latter corresponding to postselected weak measurements. We find that nonunitary evolution leads to the emergence of steady states at infinite times for the cases of periodic, quasiperiodic, and random drives. In a special class of drives, for mixed initial states, we uncover purification phase transitions that arise as a result of the competition between unitary evolution and weak measurements. We compare the CFT evolution with the corresponding nonunitary dynamics of critical lattice models, finding remarkable agreement.

Two-dimensional (2D) multiferroic materials with the coexistence of spin and electric polarizations are appealing because of their rich fundamental physics and promising technological applications. However, up to now, 2D ferromagnetic (FM) ferroelectric (FE) multiferroic semiconductors are still rather scarce and possess very low Curie temperature ($T_{\mathrm{C}}$). Here, we propose that room-temperature ferromagnetism and electric polarization could exist in a 2D penta-lattice. Based on first-principles calculations, we predict that the penta-CrPS monolayer is a stable room-temperature polar FM semiconductor with $T_{\mathrm{C}}$ up to $\sim 560$ K. The strong FM super-exchange between adjacent Cr ions originates from the small splitting of occupied and empty Cr-3d orbitals induced by the square planar crystal field. The in-plane 4-fold electric polarization can be characterized by the rotation of P-S pairs with a moderate electric polarization transition barrier of $\sim 0.650$ eV. Similar high-temperature ferromagnetism and electric polarization have also been observed in other 2D penta-lattices, e.g., penta-MoPS and penta-RePS monolayers, whose $T_{\mathrm{C}}$ are $\sim 1060$ and $\sim 700$ K, respectively. These findings provide a new direction and potential candidates for realizing room-temperature 2D polar FM semiconductors, which will significantly motivate the research progress of spintronics.

External pressure and associated changes in lattice structures are key to realizing exotic quantum phases such as high-$T_{\mathrm{c}}$ superconductivity. While applying external pressure is a standard method to induce novel lattice structures, its impact on organic molecular crystals has been less explored. Here we report a unique structural phase transition in ${\left(\text{DMET-TTF}\right)}_2{\mathrm{AuBr}}_2$ under pressure. By combining advanced high-pressure techniques and $abinitio$ calculations, we elucidate that ${\left(\text{DMET-TTF}\right)}_2{\mathrm{AuBr}}_2$ undergoes a transition from a quasi-one-dimensional lattice to a nearly perfect rectangular lattice around 0.9 GPa. This transition leads to the realization of an antiferromagnetic Mott insulator with $T_{\mathrm{N}}=66$ K, the highest $T_{\mathrm{N}}$ in low-dimensional molecular crystal solids to date. Upon increasing the pressure, the antiferromagnetic ordering is suppressed, and a superconducting phase with $T_{\mathrm{c}}=4.8$ K emerges around 6 GPa. Our study reveals the significant impact of external pressure on lattice structures of organic molecular crystals and offers insights into how geometrical frustration relates to superconductivity. Our findings also pave the way for realizing functional organic molecular crystals through changes in lattice structures under pressure.

A comprehensive first-principles study was performed to investigate the elastic and thermodynamic properties of ${\mathrm{U}}_{1-x}{\mathrm{Th}}_x{\mathrm{O}}_2$ $(x=0, 0.25, 0.5, 0.75, 1)$ solid solutions using the DFT+U method, with ${\mathrm{ThO}}_2$ treated under standard DFT. Despite a slight overestimation relative to experimental data, the predicted lattice constants follow the Vegard's law, providing a robust foundation for in-depth analysis. Consistency between the calculated band gaps and previous experimental and theoretical studies further verifies the effectiveness of our approach. Elastic properties, including bulk, shear, and Young's modulus, as well as Poisson's ratio, were predicted, revealing that ${\mathrm{UO}}_2$ is the most incompressible, whereas ${\mathrm{ThO}}_2$ exhibits superior rigidity. All these solid solutions demonstrate good mechanical stability. Elastic anisotropy was characterized using anisotropic indexes and three-dimensional graphs, which indicate that ${\mathrm{ThO}}_2$ exhibits the highest degree of elastic isotropy, followed by ${\mathrm{U}}_{0.5}{\mathrm{Th}}_{0.5}{\mathrm{O}}_2$, while ${\mathrm{UO}}_2$ shows the highest anisotropy. Furthermore, thermodynamic properties, including vibrational free energy, enthalpy, entropy, and specific heat capacity at constant pressure, were computed over a temperature range from 0 to 2000 K. All the compositions exhibit excellent thermodynamic stability. The calculated thermodynamic functions show overall good agreement with available experimental data, particularly for ${\mathrm{U}}_{0.5}{\mathrm{Th}}_{0.5}{\mathrm{O}}_2$. The parameters obtained from this study provide valuable data for future experimental investigations and illustrate the potential of thorium substitution to modulate the performance of conventional ${\mathrm{UO}}_2$ fuels, laying a foundation for further exploration of advanced nuclear fuels.

We report a comprehensive investigation of the structural, magnetic, vibrational, and optical properties of Fe-doped $\mathrm{Cr}{\mathrm{Cl}}_3$ under varying external pressures. By integrating high-pressure experimental techniques, including Raman spectroscopy, photoluminescence (PL), magnetization, and thermal expansion measurements, with density functional theory (DFT) calculations, we uncover pressure-driven phase and magnetic transitions in this layered van der Waals material. At ambient pressure, Raman spectra exhibit all six expected Raman-active modes, which systematically blueshift with increasing pressure. A distinct change occurs in $A_{\mathrm{g}}^3$ mode near 9.2 GPa, suggesting an isostructural phase transition (IST), similar to that observed in pristine $\mathrm{Cr}{\mathrm{Cl}}_3$ around 11 GPa. PL measurements indicate a band gap of 1.48 eV at approximately 0.6 GPa, which increases with pressure up to 9.2 GPa, followed by a slight decrease beyond this point. This further confirms the occurrence of the IST. Magnetization measurements at ambient pressure under 0.001 T magnetic field reveal two magnetic transitions: $T_{\mathrm{N}}$ at 14.3 K and $T_{\mathrm{C}}$ at 16 K, indicating the coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) phases. Upon applying pressure, $T_{\mathrm{N}}$ and $T_{\mathrm{C}}$ gradually become suppressed, and $T_{\mathrm{N}}$ disappears by 2 GPa. The transition width associated with $T_{\mathrm{C}}$ broadens beyond 0.5 GPa, highlighting the pressure-enhanced FM behavior. Field-dependent magnetization at ambient pressure shows complete suppression of $T_{\mathrm{N}}$ above 0.4 T, with FM ordering dominating at higher fields. At 1.2 GPa, both $T_{\mathrm{N}}$ and $T_{\mathrm{C}}$ shift to lower temperatures. Notably, $T_{\mathrm{N}}$ is suppressed above 0.2 T and only FM order remains. Grüneisen analysis of the uniaxial thermal expansion confirms the competition between FM and AFM interactions and yields very large uniaxial pressure effects of $-143\%/\text{GPa}$ and $+43\%/\text{GPa}$, at TN and TC, respectively. DFT calculations for pure $\mathrm{Cr}{\mathrm{Cl}}_3$ are consistent with experimental data and predict a pressure-induced suppression of interlayer AFM exchange, accompanied by the stabilization of FM intralayer coupling through enhanced Cr–Cl–Cr superexchange pathways. These calculations suggest an AFM-to-FM interlayer stacking transition occurring near 1 GPa. Furthermore, increasing Fe doping appears to support the persistence of AFM character. Our findings establish Fe-doped $\mathrm{Cr}{\mathrm{Cl}}_3$ as a promising platform for pressure-tunable magnetism. The ability to manipulate FM and AFM interactions through external pressure and magnetic fields opens avenues for applications in sensors, spintronic devices, and other functional two-dimensional magnetic systems.

We revisit the relationship between electric polarization modulation $\mathrm{\Delta }P$ in ferroelectrics induced by a low-frequency pulsed electric field and the corresponding second harmonic intensity modulation $\mathrm{\Delta }{I}_{\mathrm{SH}}$. Using nonlinear response theory, we derive their time-domain expressions linear in the pulse amplitude, revealing that not only the electric field but also its time derivative contributes to $\mathrm{\Delta }{I}_{\mathrm{SH}}$. Furthermore, even when the time-derivative component is negligible, $\mathrm{\Delta }{I}_{\mathrm{SH}}$ can be in antiphase with the pulsed field and thus with $\mathrm{\Delta }P$. These theoretical predictions are further supported by real-time simulations of a model for electronic ferroelectrics. Our results demonstrate that the commonly assumed relation $\mathrm{\Delta }P\propto \mathrm{\Delta }{I}_{\mathrm{SH}}$ can break down under certain conditions, reflecting the complex-valued and frequency-dependent nature of nonlinear dynamical susceptibilities.

We theoretically investigate the interplay between Zeeman splitting and transverse-electric–transverse-magnetic (TE-TM)-induced spin-flip tunneling in coupled exciton-polariton condensate systems and its impact on the spin Meissner effect. We demonstrate that although a single condensate exhibits the effect of full paramagnetic screening via spin-anisotropic interactions, the inter-site spin-flip tunneling can dramatically alter this behavior. The geometry of the system is shown to play a crucial role. In particular, in a dyad, the chemical potential reveals quadratic scaling with the magnetic field. In a triangle, the competition between Zeeman and TE-TM splittings produces a rich phase diagram that features asymmetric polarization states corresponding to both positive and negative magnetic susceptibility. In a square configuration, the symmetry of the network can restore the spin Meissner effect, so that the condensate emission frequency becomes magnetic field independent in an extended parameter range. These findings not only shed light on the fundamental physics of polariton lattices but also suggest promising avenues for engineering robust spin-controlled photonic devices and polaritonic simulators.

Floquet engineering via periodic light fields has emerged as a powerful method to control topological phase transitions in quantum materials. However, Floquet-induced two-dimensional (2D) weak topological insulator phases, characterized by nontrivial 2D Zak phases, remain unexplored. In this work, we theoretically investigate two distinct models using Floquet theory: the extended Qi-Wu-Zhang model and Bernevig-Hughes-Zhang model with $d$-wave altermagnetism. For the extended Qi-Wu-Zhang model, we demonstrate that the polarized light can induce a 2D weak topological insulator phase characterized by an emergent 2D Zak phase. In the $d$-wave altermagnetic Bernevig-Hughes-Zhang model, we show that the linearly polarized light can drive more intricate topological phase transitions between weak topological insulator, strong topological insulator, and normal insulator. Furthermore, we find a distinct Floquet-induced topological phase, where one spin component exhibits a floating edge state characterized by the 2D Zak phase and the other spin component hosts a chiral edge state characterized by the Chern number.