We study the topological properties of a twisted superconducting bilayer with spin-singlet pairings and Rashba spin-orbital coupling. By introducing the chirality basis, we obtain the effective odd-parity superconductors with the help of spin-orbital coupling. For the twisted bilayer with $d$-wave pairings, two non-Abelian topological phases with Chern numbers $C=-1$ and $C=-5$ are identified, and the analytical expressions for the boundary of non-Abelian phase are derived as well within the circular Fermi surface approximation. We perform numerical calculations at the twist angle of the moiré lattice which further verify the topological phase diagram from the effective odd-parity Hamiltonian. For the bilayer with $d$-wave and $s_{\pm }$-wave pairings, we reveal the second-order topological superconductor with a Majorana zero mode at each corner by analyzing the relative configuration of the pairing nodes of superconductors and the Fermi surface of the normal state. We find that the regions of second-order topological phase are narrowed when the bilayer is twisted.

URhGe is a ferromagnetic superconductor with a distinctive magnetic behavior. In a field $H\parallel b$ applied perpendicular to the easy axis, URhGe exhibits an abrupt orientational transition of the magnetization with a reentrant superconducting phase emerging close to the transition field $H_m$. We develop a theoretical description of the magnetic properties of URhGe by considering a spin model with competing magnetic anisotropies. The model is analyzed both analytically at zero temperature and with Monte Carlo simulations at finite temperatures. The constructed $H_b$–$T$ phase diagram features a tricritical point on the line $H_m\left(T\right)$ and is in a good quantitative agreement with the experimental diagram of URhGe. We demonstrate that the asymptotic tricritical behavior of the order parameter and the correlation length is described by the mean-field critical exponents. The derived microscopic parameters suggest that URhGe is an $XY$-like ferromagnet with an additional weak in-plane anisotropy in the $bc$ plane.

Kondo-lattice systems are recognized for potentially hosting a variety of rich topological phases. Several pioneering studies have demonstrated significant anomalous Hall and anomalous Nernst effects in these systems, attributed to the Berry curvature of the hybridization bands. In this paper, we investigate UBiTe, a ferromagnetic Kondo-lattice system. Our findings reveal that the intrinsic contribution to the anomalous Hall conductivity is closely tied to the Kondo coherence temperature. Moreover, we demonstrate that slight shifts in the Fermi level across three different samples significantly influence this intrinsic contribution, aligning with the Berry curvature localized within the narrow hybridization bands. This provides a stark contrast to the less pronounced sensitivity observed in weakly correlated Weyl semimetals, underscoring the distinctive electronic properties of Kondo-lattice systems. The anomalous Hall conductivity of one sample ranks among the highest reported for topological magnetic materials.

This paper proposes an innovative approach to improve Bragg coherent diffraction imaging (BCDI) microscopy applied to time evolving crystals and/or nonhomogeneous crystalline strain fields, identified as two major limitations of BCDI microscopy. Speckle BCDI (spBCDI), introduced here, rests on the ability of a strongly nonuniform illumination to induce a convolution of the three-dimensional (3D) frequency content associated with the finite-size crystal and a kernel acting perpendicularly to the illumination beam. In the framework of Bragg diffraction geometry, this convolution is beneficial as it encodes some 3D information about the sample in a single two-dimensional (2D) measurement, i.e., in the detector plane. With this approach, we demonstrate that we can drastically reduce the sampling frequency along the rocking curve direction and still obtain datasets with enough information to be inverted by a traditional phase retrieval algorithm. Numerical simulations, performed for a highly distorted crystal, show that spBCDI allows a gain in the sampling ratio ranging between 4 and 20 along the rocking curve scan, for a speckle illumination with individual speckle size of 50 nm at the sample position. Furthermore, spBCDI allows working at low intensity levels, leading to an additional gain for the total scanning time. Reductions of a factor of about 40 were numerically observed. Thus, full 3D datasets measured in the 0.2 s time scale at fourth-generation synchrotrons become feasible, with a remarkable potential for the imaging of strongly distorted crystals. Practical details on the implementation of the method are also discussed.

We study the dynamics and thermalization of the Fredkin spin chain, a system with local three-body interactions, particle conservation, and explicit kinetic constraints. We consider deformations away from its stochastic point in order to tune between regimes where kinetic energy dominates and those where potential energy does. By means of exact diagonalization, perturbation theory, and variational matrix product states, we show there is a sudden change of behavior in the dynamics that occurs, from one of fast thermalization to one of slow metastable (prethermal) dynamics near the stochastic point. This change in relaxation is connected to the emergence of additional kinetic constraints, which lead to the fragmentation of Hilbert space in the limit of a large potential energy. We also show that this change can lead to thermalization being evaded for special initial conditions because of nonthermal eigenstates (akin to quantum many-body scars). We provide clear evidence for the existence of these nonthermal states for large system sizes even when far from the large-potential-energy limit, and explain their connection to the emergent kinetic constraints.

Van der Waals transition-metal dichalcogenides (TMDCs) form a vast family that has garnered significant attention in various fields. Among these, ${\mathrm{TiS}}_2$ has complex and controversial electronic properties at ambient and high pressures that need clarification, such as its semiconductor/metal nature, ambiguous high pressure structures, disputed electronic behaviors under pressure, etc. In this work, we confirm the anomalous metal-semiconductor-metal transition and reveal the emergence of superconductivity in ${\mathrm{TiS}}_2$. This metal-semiconductor transition near 15 GPa is clarified as an intrinsic property of single-crystal ${\mathrm{TiS}}_2$ due to the self-Ti-doping and an isostructural transition. Re-metallization occurs at 31 GPa, and superconductivity emerges above 88 GPa. The critical temperature $T_c$ increases monotonically with pressure, reaching 4.1 K at 136.6 GPa, and is still not saturated. As the lightest TMDC and the first superconducting layered fourth-period transition-metal disulfide, ${\mathrm{TiS}}_2$ offers valuable insights into its unique electronic properties. This research not only reveals the anomalous metal-semiconductor transition and superconductivity but also inspires further investigation into the evolution of electronic properties in other TMDCs under pressure.

Calcite, a ${\mathrm{CaCO}}_3$ polymorph, is one of the most significant materials in nature. In addition to its fundamental role in the global carbon cycle, it fills an unparalleled range of applications, both as a natural biomineral and more directly engineered materials. One of the most notable characteristics of calcite is its tendency to form twins, the boundaries of which are expected to determine key attributes of the host mineral at mesoscopic scales. Using a classical molecular dynamics simulation performed with a thermodynamically consistent rigid-ion force field, we show that the walls between the two twin domains aligned along the hexagonal $\left(10\overline{1}4\right)$ plane of calcite have some unexpected properties: (1) rather than monoatomic planes, these twin walls are composed of two layers with fundamentally different distortions, (2) atomic shifts within the twin walls create strong polarity while the bulk remains centrosymmetric, and (3) the temperature evolution of the structural order parameter is mostly, but not completely, related to the tilt and rotation of ${{\mathrm{CO}}_3}^{2-}$ molecules. Molecular dynamics simulations using thermodynamically accurate interatomic potentials demonstrate that the temperature evolution of twin walls is different from that of the bulk material. We show that kinks in twin walls have a low energy and generate high structural disorder near the kink position. Our methods are applicable to other molecular systems and emphasize the dominance of twin walls in materials.

Many estimates for the magnetic relaxation time of magnetic nanoparticle systems neglect the effect of the applied field strength. This is despite many applications of magnetic nanoparticles involving relaxation dynamics under the influence of applied fields. Here, an analytic approximation for the field-dependent Brownian relaxation time of single-domain, spherical magnetic nanoparticles in an external applied field is developed mathematically. This expression is validated by comparison with existing empirically derived expressions and by comparison to particle-level simulations that allow particle rotations. Our approximation works particularly well for larger particles. We then use the developed expression to analytically calculate the total magnetic relaxation time when both Brownian and Néel relaxation mechanisms are at play. Again, we show that the results match those found using particle-level simulations, this time with both particle rotations and internal magnetization dynamics allowed. However, for some particle parameters and for large field strengths, our simulations reveal that the Brownian and Néel relaxation mechanisms are decoupled and it is not appropriate to combine these to calculate a total relaxation time.

The magnonic excitations of a dimerized, one-dimensional, antiferromagnetic chain can be trivial or topological depending on the signs and magnitudes of the alternating exchange couplings and the anisotropy. The topological phase that occurs when the signs of the two different exchange couplings alternate is qualitatively different from that of the Su-Schrieffer-Heeger model. A material that may exhibit these properties is the quasi-one-dimensional material ${\mathrm{MoI}}_3$ that consists of dimerized chains weakly coupled to adjacent chains. The magnetic ground state and its excitations are analyzed both analytically and numerically using exchange and anisotropy parameters extracted from density functional theory calculations.

${\mathrm{CaSb}}_2$ is a bulk superconductor and a topological semimetal, making it a great platform for realizing topological superconductivity. In this work, we investigate the superconducting upper and lower critical field anisotropies using magnetic susceptibility and study the superconducting state using muon spin relaxation. The temperature dependence of the transverse-field relaxation rate can be fitted with a single-gap model or two-gap model. Zero-field relaxation shows little temperature dependence when the muon spin is parallel to the $c*$ axis, while an increase in relaxation appears below 1 K when the muon spin is parallel to the $ab$ plane. We conclude an $s+is$ order parameter considering the breaking of time-reversal symmetry (TRS), which originates from competing interband interactions between the three bands of ${\mathrm{CaSb}}_2$. To explain the direction-dependent breaking of TRS we suggest loop currents developing in the plane of a distorted square net of Sb atoms.

Lithium-based electrides with interstitial anionic electrons (IAEs) have recently garnered a great deal of attention, since these materials were found to host intriguing properties such as multiple IAE arrangements and potential superconductivity. In this study, we here conducted comprehensive simulations on the pressure-induced stable Li-abundant germanides leveraging the advanced first-principles structure predictions. As a consequence, our simulations identified several metallic Li-Ge electride phases with robust stability, i.e., $\mathrm{L}{\mathrm{i}}_5\mathrm{Ge}, \mathrm{L}{\mathrm{i}}_6\mathrm{Ge}, \mathrm{L}{\mathrm{i}}_7\mathrm{Ge}, \mathrm{L}{\mathrm{i}}_8\mathrm{Ge}$, and $\mathrm{L}{\mathrm{i}}_{10}\mathrm{Ge}$. Strikingly, the evolution from connected one-dimensional (1D) to zero-dimensional (0D) electride states of $\mathrm{L}{\mathrm{i}}_5\mathrm{Ge}$ was identified concurrent with an orthorhombic $Cmcm$ to triclinic $C2/c$ phase transition on account of compression-induced volume reduction, whereas $\mathrm{L}{\mathrm{i}}_{10}\mathrm{Ge}$ possesses the unusual coexistent 0D and 1D IAEs. Electron-phonon coupling (EPC) calculations uncover that the superconductivity of $Cmcm \mathrm{L}{\mathrm{i}}_5\mathrm{Ge}$ is superior to that of $C2/c \mathrm{L}{\mathrm{i}}_5\mathrm{Ge}$ at 50 GPa, which is due to the larger EPC strength, higher density of states at the Fermi level, and more pronounced softened phonon modes of $Cmcm \mathrm{L}{\mathrm{i}}_5\mathrm{Ge}$. Remarkably, $\mathrm{L}{\mathrm{i}}_{10}\mathrm{Ge}$ was calculated to have the highest superconducting critical temperature ($T_c$) of 8.5 K below 50 GPa compared to other lithium-carbon family electrides, which is ascribed to the fact that the Li $2p$ electron states near the Fermi energy are strongly coupled with phonon modes associated with the vibrations of Li atoms. Our findings provide insights into lithium-bearing electride systems with implications for the pursuit of distinguished electride superconductors.

The photoinduced dynamics of ${\mathrm{Ti}}_2{\mathrm{O}}_3$ with a corundum structure have been investigated by pump-probe optical spectroscopy. It is found that a peak in the optical spectrum corresponding to excitations within Ti-Ti dimers is suppressed when a laser pulse is applied at room temperature, indicating a photoinduced phase transition from the low-temperature insulating state to the high-temperature conducting state in ${\mathrm{Ti}}_2{\mathrm{O}}_3$. In addition, the oscillation of reflectivity with time is observed, which can be explained by a strain wave generated by a laser pulse applied to the sample surface. The dependence of the oscillation on the direction of the surface indicates that the change in the $c$ lattice constant parallel to the Ti-Ti dimers plays an important role in the phase transition.

Dilute magnetic materials may find applications in spin-dependent applications such as spintronics and spin thermoelectrics. The conventional approach to realizing such materials is by doping a host material with transition-metal and rare-earth elements, which has been widely pursued in developing dilute magnetic semiconductors. However, such an approach could face issues such as solubility and inhomogeneity. Here, we study the dilute magnetic compounds (DMCs), which contain magnetic elements in a relatively small percentage and have the magnetic atoms occupying well-defined (ordered) lattice sites. The diluteness is thus guaranteed by enthalpy, instead of entropy as in the doping approach. By screening the inorganic crystal structure database, we identify two DMCs, ${\mathrm{Mg}}_6{\mathrm{MnO}}_8$ and ${\mathrm{Bi}}_{12}{\mathrm{MnO}}_{20}$. ${\mathrm{Mg}}_6{\mathrm{MnO}}_8$ has a fcc Mn lattice and octahedral coordination. ${\mathrm{Bi}}_{12}{\mathrm{MnO}}_{20}$ has a bcc Mn lattice and tetrahedral coordination. By using first-principles calculations, we calculated magnetic exchange interaction, magnon spectra, and electronic band structures of these materials. The Mn-Mn distance in ${\mathrm{Mg}}_6{\mathrm{MnO}}_8$ and ${\mathrm{Bi}}_{12}{\mathrm{MnO}}_{20}$ is 5.926 and 8.839 Å, respectively. The exchange interaction in ${\mathrm{Mg}}_6{\mathrm{MnO}}_8$ is 4–5 meV, while for ${\mathrm{Bi}}_{12}{\mathrm{MnO}}_{20}$ the largest distance renders the exchange interaction less than 1 meV. ${\mathrm{Mg}}_6{\mathrm{MnO}}_8$ holds promise for realizing the antiferromagnetic spin Seebeck effect. ${\mathrm{Bi}}_{12}{\mathrm{MnO}}_{20}$ has a band gap of 3.5 eV (ignoring the Mn $3d$ states in the band gap) and may be further doped for spintronic applications.

Charge density wave (CDW) is an important physical phenomenon to understand the intrinsic electron-phonon coupling and electron correlations in the low-dimensional systems. Theoretical and experimental studies have shown that there are abundant CDW phases in the two-dimensional transition metal chalcogenides. In this paper, a trimeric CDW phase is predicted by introducing distortion according to the imaginary frequency vibration mode of phonon spectrum in a $1T-M{X}_2$ ($M=\mathrm{Nb}$, Ta; $X=\mathrm{S}$, Se) lattice. In the trimeric $M{X}_2$ (t-$M{X}_2$) the three nearest neighbor $M$ atoms aggregate to form a trimer, accompanied by the asymmetric displacement of the $X$ atoms in the out-of-plane direction. Due to the breaking of inversion symmetry, the ferroelectric polarization occurs in the out-of-plane direction, resulting in the coexistence of magnetism, ferroelectricity, and CDW. More interesting, under the electron doping, t-$M{X}_2$ becomes more stable than the star-of-David phase with the ferromagnetic ground state, which have been predicted theoretically and verified experimentally. In addition, it is found that the ground state of t-$M{X}_2$ monolayer is an antiferromagnetic semiconductor with a direct band gap. Therefore, by the electron doping we can control CDW phase transition from an antiferromagnetic trimeric t-$M{X}_2$ to a ferromagnetic star-of-David phase, realizing the simultaneous electrical control of the CDW and magnetism. Furthermore, the CDW phase transition induced by the electron doping can be explained well by the band alignment theory. This study not only enriches the phase diagram of the transition metal dichalcogenides, but also predicts the possibility of multiferroicity with coexistence and coupling of multiple charge and magnetic orders.

Recently, there has been renewed interest in studies of criticality in the spin quantum Hall effect, realized in the Altland-Zirnbauer symmetry class C of disordered, noninteracting fermions in two spatial dimensions. In our study, we develop a nonperturbative analysis of the replica two-dimensional nonlinear sigma model in class C. We explicitly construct the instanton solution with a unit topological charge. By treating fluctuations around the instanton at the Gaussian level, we calculate the instanton correction to the disorder-averaged logarithm of the partition function. We compute nonperturbative corrections to the anomalous dimensions of pure power-law scaling local operators, which determine the spectrum of generalized multifractality. We also calculate instanton corrections to the renormalized longitudinal and Hall spin conductivities and determine the topology of the phase diagram for class C. Our results demonstrate that the spin quantum Hall effect is indeed a close cousin of the integer quantum Hall effect.

We propose inverse renormalization group transformations to construct approximate configurations for lattice volumes that have not yet been accessed by supercomputers or large-scale simulations in the study of spin glasses. Specifically, starting from lattices of volume $V=8^3$ in the case of the three-dimensional Edwards-Anderson model we employ machine learning algorithms to construct rescaled lattices up to $V^{\prime }={128}^3$, which we utilize to extract two critical exponents. We conclude by discussing how to incorporate numerical exactness within inverse renormalization group methods of disordered systems, thus opening up the opportunity to explore a sustainable and energy-efficient generation of exact configurations for increasing lattice volumes without the use of dedicated supercomputers.