Among the FeSe-based superconductors, $\left({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x\mathrm{OH}\right)\mathrm{FeSe}$ has been discovered as an air-stable superlattice structure harboring both high transition temperature (high-$T_{\mathrm{c}}$) superconductivity and intriguing topological superconducting properties. Here, we use first-principles approaches to identify a chemically isovalent and structurally identical counterpart of $\left({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x\mathrm{OH}\right)\mathrm{FeSe}$, namely, $\left({\mathrm{Li}}_{1-x}{\mathrm{Co}}_x\mathrm{OH}\right)\mathrm{CoSb}$, which not only is an attractive candidate to harbor high-$T_{\mathrm{c}}$ superconductivity, but also exhibits two distinct features surrounding topology and magnetism. The rationale of this predictive design is based on the recent identification of CoSb as a layered high-$T_{\mathrm{c}}$ superconductor stabilized on ${\mathrm{SrTiO}}_3$. We first show that the superlattice structures of $\left({\mathrm{Li}}_{1-x}{\mathrm{Co}}_x\mathrm{OH}\right)\mathrm{CoSb}$ $(x=0 \mathrm{or} 0.25)$ are dynamically and thermodynamically stable. Next, we demonstrate that $\left({\mathrm{Li}}_{1-x}{\mathrm{Co}}_x\mathrm{OH}\right)\mathrm{CoSb}$ possesses superior superconducting properties to $\left({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x\mathrm{OH}\right)\mathrm{FeSe}$, offering an appealing platform for realizing high-$T_{\mathrm{c}}$ superconductivity beyond the Cu- and Fe-based superconducting systems. More strikingly, we find that (LiOH)CoSb is already topologically nontrivial even without extrinsic doping in the spacer layers, thereby offering a cleaner and more ideal candidate system for realizing topological superconductivity. Furthermore, $\left({\mathrm{Li}}_{1-x}{\mathrm{Co}}_x\mathrm{OH}\right)\mathrm{CoSb}$ exhibits weaker elemental magnetic moments than $\left({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x\mathrm{OH}\right)\mathrm{FeSe}$, which may provide a different angle for elucidating the microscopic mechanisms of superconductivity in these and related systems.

Nitride perovskites are supposed to exhibit excellent properties as oxide analogs and may even have a better performance in specific fields for their more covalent characters. However, until now, very limited nitride perovskites have been reported. In this Rapid Communication, a nitride perovskite ${\mathrm{LaMoN}}_3$ has been systematically studied by first-principles calculations. The most interesting physical property is its ferroelectric $R3c$ phase, which can be stabilized under a moderate hydrostatic pressure ($\sim 1.5$ GPa) and probably remain metastable under an ambient condition. Its ferroelectric polarization is considerably large, $80.3\mu \mathrm{C}/{\mathrm{cm}}^2$, driven by the nominal $4d^0$ rule of ${\mathrm{Mo}}^{6+}$, and the covalent hybridization between Mo's $4d$ and N's $2p$ orbitals is very strong. Our calculation not only predicts a ferroelectric material with prominent properties, but also encourages more studies on the pressure engineering of functional nitrides.

Thin-film antiferromagnets (AFs) with Rashba spin-orbit coupling are theoretically investigated. We demonstrate that the relativistic Dzyaloshinskii-Moriya interaction (DMI) produces a large surface magnetization and a boundary-driven twist state in the antiferromagnetic Néel vector. We predict a magnetization on the order of $2.3\times {10}^4$ A/m, which is comparable to the magnetization of ferromagnetic semiconductors. Importantly, the magnetization is characterized by ultrafast terahertz dynamics and provides different approaches for efficiently probing and controlling the spin dynamics of AFs as well as detecting the antiferromagnetic DMI. Notably, the magnetization does not lead to any stray magnetic fields except at the corners where weak magnetic monopole fields appear.

Direct optical ferroelectric switching (FE switch) has the advantage of being ultrafast over the traditional FE switch, which relies on domain nucleation and growth. However, how to realize nonvolatility in such an optical FE switch poses a serious challenge. Time-dependent density-functional theory molecular dynamics study reveals that subpicosecond nonvolatile FE switches can be realized in GeTe and ${\mathrm{PbTiO}}_3$. While optical tuning of the transition barrier and initiation of a directional atomic motion are crucial, the dephasing of the excited state holds the key for the realization of nonvolatility.

Three-dimensional (3D) graphene networks (3DGNs) have drawn broad interest recently for their superior physical properties, such as large surface area, high strength, superelasticity, tunable band gaps and topological properties, with potential applications in high-capacity energy storage and novel electronic systems. In this work, giant negative Poisson ratios (NPRs) up to $-8.5$ and colossal auxetic transverse contraction (or expansion) of more than 40% (or 20%) in 3DGNs are predicted by first-principles calculations, adding another extraordinary mechanical property to 3DGNs. A mechanism dominated by ${sp}^3$-carbon bond angle distortion and in-plane anisotropy variation is revealed that can explain such exceptional NPRs in 3DGNs. Furthermore, easy manipulation and enhancement of NPRs are achieved by applying biaxial stresses which increase the in-plane anisotropy of 3DGNs, providing a way for the rational design and application of NPR materials. These discoveries will deepen our understandings of 3DGNs and broaden their technological applications as multifunctional materials.

Although previous molecular dynamics studies proposed the existence of Zr-centered Frank-Kasper Z16 structures in Cu-Zr metallic glasses, it cannot be concluded yet, owing to the degeneracy problem of the Voronoi index and the artifact in sets of potentials for Cu-Zr systems. We solve both problems by combining a recently developed Finnis-Sinclair potentials to generate realistic atomic structures and the $p_3$ code to properly differentiate local structures. In previous studies, the Voronoi index $〈0,0,12,4〉$ was typically associated with Frank-Kasper Z16 local structures. However, we demonstrate that this index includes two types of polyhedra, only one of which is associated with the Frank-Kasper Z16 structures. We reveal that the Z16 structures are more frequent than the other structures and that the two have different behaviors. The tendency of Zr-centered Z16 local structures to be neighbors of Cu-centered icosahedral local structures is also confirmed. Our findings illustrate the importance of properly differentiating local structures in order to elucidate the behavior of metallic glasses at the atomic scale.

Photoinduced phase transitions can have complex and intriguing behaviors more than material ground-state dynamics. Understanding the underlying mechanism can help us to design new ways to manipulate the materials. A variety of mechanisms has been proposed to explain the photoinduced phase transitions of $\mathrm{Ir}{\mathrm{Te}}_2$, but a consensus has yet to be reached. Here, we study the photo-induced phase transitions of $\mathrm{Ir}{\mathrm{Te}}_2$ by performing the real-time time-dependent density functional theory (rt-TDDFT) simulations in combination with the occupation constrained DFT method. We reveal that the microscopic driving force for the photo-induced phase transitions arises from the tendency to lower the energy levels occupied by the excited carriers, through the increase or decrease of the associated atomic pair distances, depending on whether the newly occupied states are antibonding or bonding states, respectively. The geometric constraints between different bonds represented by the Poisson ratio can bring together different tendencies from different atomic pairs, thus forming a complex intriguing dynamic picture depending on the intensity of the excitation. We also find that phonons don’t play a primary role, but can assist the phase transition. These findings imply that one can control the structural phase transitions by selectively exciting photocarriers into designated atomic states using appropriate photon sources.

Understanding heat transfer in the earth mantle region is of great scientific interest but highly challenging due to dissimilar conditions from our daily lives. Thermal conductivity of highly pressured and thermally activated materials can be completely different from that at ambient condition. In this study we calculate the equation of state and thermal conductivity of cubic crystalline MgO, a major component of the mantle, in such an environment. It is shown that the material properties are not accurately captured unless rigorous treatment of anharmonicity of phonon vibrational motion is explicitly applied. To predict renormalized phonon dispersion relations, interatomic force constants of high-order expansion are required, especially at elevated temperature. The anharmonicity plays an increasingly substantial role for regulating volume expansion as temperature rises, because the Gibbs free energy of MgO considerably deviates from what was predicted by the quasiharmonic approximation. We find that the lattice thermal conductivity of MgO and the heat transfer of the earth's mantle are reliably estimated only when both the temperature-dependent renormalization of phonon frequencies and four-phonon scattering effects are taken into consideration. We map the characteristics at Geotherm into contour diagrams in which equilibrium volumes and the thermal conductivities are described as functions of temperature and pressure. The thermal conductivity values of MgO in this study are smaller than those in previous theoretical studies due to the additional incorporation of four-phonon scatterings in the calculations. Specifically, deviation between the values in previous studies and in this study becomes larger as thermodynamic variables reach those near the core-mantle boundary. For instance, thermal conductivities of 52.15 and 23.67 ${\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ are estimated at ambient and extreme conditions ($T=4000\mathrm{K}$ and $P=135\mathrm{GPa}$), respectively.

Using a density functional theory based approach, we explore the symmetrization and proton dynamics in ice-VII, for which recent high-pressure NMR experiments indicate significant proton dynamics in the pressure-range of $20–95\mathrm{GPa}$. We directly sample the potential seen by the proton and find a continuous transition from double- to single-well character over the pressure range of 2 to 130 GPa accompanied by proton dynamics, in agreement with the NMR experiments.

Most of the existing research on the dynamics of magnetic solitons such as a domain wall (DW) has focused on the effect of DC forces, where the induced velocity is determined by the force strength. Here we show that AC forces such as an oscillating magnetic field or current are also able to move a DW straight via synchronization between the DW angle and the phase of the AC force. The resulting DW velocity is solely proportional to the driving frequency of the AC force, but the strength of the AC field just affects the frequency range for criteria for the phase-locking behavior. The AC-force-driven DW motion is shown to exhibit a phase locking-unlocking transition, a critical phenomenon akin to the Walker breakdown of a DC-bias-driven DW motion. Our work shows that a DW can be driven straight by synchronizing its angle to AC forces and thereby demonstrates a proof-of-concept of magnetic soliton rectifiers (i.e., DC motion induced by AC forces), shedding a light on the hitherto overlooked utility of internal degree of freedom for driving magnetic textures.

Anisotropic low-temperature properties of the cubic spinel helimagnet $\mathrm{Zn}{\mathrm{Cr}}_2{\mathrm{Se}}_4$ in the single-domain spin-spiral state are investigated by a combination of neutron scattering, thermal conductivity, ultrasound velocity, and dilatometry measurements. In an applied magnetic field, neutron spectroscopy shows a complex and nonmonotonic evolution of the spin-wave spectrum across the quantum-critical point that separates the spin-spiral phase from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of the pseudo-Goldstone magnon mode, observed at wave vectors that are structurally equivalent but orthogonal to the propagation vector of the spin helix, vanishes at this quantum critical point, restoring the cubic symmetry in the magnetic subsystem. The anisotropy imposed by the spin helix has only a minor influence on the lattice structure and sound velocity but has a much stronger effect on the heat conductivities measured parallel and perpendicular to the magnetic propagation vector. The thermal transport is anisotropic at $T\lesssim 2\mathrm{K}$, highly sensitive to an external magnetic field, and likely results directly from magnonic heat conduction. We also report long-time thermal relaxation phenomena, revealed by capacitive dilatometry, which are due to magnetic domain motion related to the destruction of the single-domain magnetic state, initially stabilized in the sample by the application and removal of magnetic field. Our results can be generalized to a broad class of helimagnetic materials in which a discrete lattice symmetry is spontaneously broken by the magnetic order.

The inertial dynamics of magnetization in a ferromagnet is investigated theoretically. The analytically derived dynamic response upon microwave excitation shows two peaks: ferromagnetic and nutation resonances. The exact analytical expressions of frequency and linewidth of the magnetic nutation resonance are deduced from the frequency-dependent susceptibility determined by the inertial Landau-Lifshitz-Gilbert equation. The study shows that the dependence of nutation linewidth on the Gilbert precession damping has a minimum, which becomes more expressive with increase of the applied magnetic field.

We study theoretically NQR and NMR spectra in the presence of odd-parity multipoles originating from staggered antiferromagnetic and antiferroquadrupole orderings. For the $f$-electron metal CeCoSi, which is a candidate hosting odd-parity multipoles, we derive an effective hyperfine field acting on a Co nucleus generated from electronic origin multipole moments of the Ce ion in zero and nonzero magnetic fields. We elucidate that emergent odd-parity multipoles give rise to sublattice-dependent spectral splittings in NQR and NMR through the effective hyperfine coupling in the absence of global inversion symmetry. We mainly examine the behaviors of the NQR and NMR spectra in three odd-parity multipole ordered states: a $y$-type magnetic toroidal dipole order with a staggered $x$-type antiferromagnetic structure, an $xy$-type electric toroidal quadrupole order with a staggered ($x^2-y^2$)-type antiferroquadrupole structure, and a $z$-type electric dipole order with a staggered ($3z^2-r^2$)-type antiferroquadrupole structure. We show that different odd-parity multipole orders lead to different field-dependent spectral splittings in NMR, while only the $xy$-type electric toroidal quadrupole order exhibits the NQR spectral splitting. We also present possible sublattice-dependent spectral splittings for all the odd-parity multipole orders potentially activated in low-energy crystal-field levels, which will be useful to identify odd-parity order parameters in CeCoSi by NQR and NMR measurements.

Machine learning is becoming widely used in analyzing the thermodynamics of many-body condensed matter systems. Restricted Boltzmann machine (RBM) aided Monte Carlo simulations have sparked interest recently, as they manage to speed up classical Monte Carlo simulations. Here we employ the convolutional restricted Boltzmann machine (CRBM) method and show that its use helps to reduce the number of parameters to be learned drastically by taking advantage of translation invariance. Furthermore, we show that it is possible to train the CRBM at smaller lattice sizes, and apply it to larger lattice sizes. To demonstrate the efficiency of CRBM we apply it to the paradigmatic Ising and Kitaev models in two dimensions.

We used resonant x-ray scattering at the $\mathrm{Cu}{L}_3$ and $\mathrm{Dy}{M}_5$ edges to investigate charge order in thin films of underdoped ${\mathrm{DyBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ (DyBCO) epitaxially grown on ${\mathrm{NdGaO}}_3\left(110\right)$ substrates. The films show an orthorhombic crystal structure with short-range ortho-II oxygen order in the charge-reservoir layers. At the Dy $M_5$ edge we observe diffraction peaks with the same planar wave vectors as those of the two-dimensional charge density wave in the ${\mathrm{CuO}}_2$ planes and of the ortho-II oxygen order, indicating the formation of induced ordered states on the rare-earth sublattice. The intensity of the resonant diffraction peaks exhibits a nonmonotonic dependence on an external magnetic field. Model calculations on the modulation of the crystalline electric field at the Dy sites by charge and oxygen order capture the salient features of the magnetic field, temperature, and photon energy dependence of the scattering intensity.

We study a kinetically constrained pair-hopping model that arises within a Landau level in the quantum Hall effect. At filling $\nu =1/3$, the model exactly maps onto the so-called “PXP model,” a constrained model for the Rydberg atom chain that is numerically known to exhibit ETH-violating states in the middle of the spectrum or quantum many-body scars. Indeed, particular charge density wave configurations exhibit the same revivals seen in the PXP model. We generalize the mapping to fillings factors $\nu =p/(2p+1)$, and show that the model is equivalent to nonintegrable spin chains within particular constrained Krylov Hilbert spaces. These lead to new examples of quantum many-body scars which manifest as revivals and slow thermalization of particular charge density wave states. Finally, we investigate the stability of the quantum scars under certain Hamiltonian perturbations motivated by the fractional quantum Hall physics.

The recent proposal of non-Abelian boson-fermion dualities in $2+1$ dimensions, which morally relate $U{\left(k\right)}_N$ to $SU{\left(N\right)}_{-k}$ Chern-Simons-matter theories, presents a new platform for exploring the landscape of non-Abelian quantum Hall states accessible from theories of Abelian composite particles. Here we focus on dualities relating theories of Abelian quantum Hall states of bosons or fermions to theories of non-Abelian “composite fermions” partially filling Landau levels. We show that these dualities predict special filling fractions where both Abelian and non-Abelian composite fermion theories appear capable of hosting distinct topologically ordered ground states, one Abelian and the other a non-Abelian, $U{\left(k\right)}_2$ Blok-Wen state. Rather than being in conflict with the duality, we argue that these results indicate unexpected dynamics in which the infrared and lowest Landau level limits fail to commute across the duality. In such a scenario, the non-Abelian topological order can be destabilized in favor of the Abelian ground state, suggesting the presence of a phase transition between the Abelian and non-Abelian states that is likely to be first order. We also generalize these constructions to other non-Abelian fermion-fermion dualities, in the process obtaining new derivations of a variety of paired composite fermion phases using duality, including the anti-Pfaffian state. Finally, we describe how, in multilayer constructions, excitonic pairing of the composite fermions across $N$ layers can also generate the family of Blok-Wen states with $U{\left(k\right)}_2$ topological order.