Alkali metals undergo an electride transition with excess electrons localized in interstices and acting as anionic interstitial quasi-atoms (ISQs). Less is known about the role of electride transition in changing their thermophysical properties. Here, taking potassium as an example, we investigated the thermodynamic and dynamic properties in the face-centered cubic (fcc) phase region where an electride transition occurs when increasing pressure. With the help of machine-learning-enhanced molecular dynamic simulations and density functional theory calculations, we show property anomalies over a wide pressure range of 10–20 GPa but no accompanying structural transformations. Furthermore, we find that these anomalies in solid potassium are stronger at lower temperatures due to the more electron-localized nature of ISQs. Our findings unveil the rich phenomena in electrides and could deepen our understanding on electride phase transition.

We study the lattice dynamics of group IV semiconductors using the fully ab initio extended Hubbard functional. The on-site and intersite Hubbard interactions are determined self-consistently with recently developed pseudohybrid functionals and included in force calculations. We analyze the Pulay forces with the choice of atomic orbital projectors and the force contribution of the on-site and intersite Hubbard terms. The phonon dispersions, Grüneisen parameters, and lattice thermal conductivities of diamond, silicon, and germanium, which are the most representative covalent-bonding semiconductors, are calculated and compared with the results using local, semilocal, and hybrid functionals. The extended Hubbard functional produces increased phonon velocities and lifetimes, and thus lattice thermal conductivities compared to local and semilocal functionals, agreeing with experiments very well. Considering that our computational demand is comparable to simple local functionals, this work thus suggests a way to perform high-throughput electronic and structural calculations with higher accuracy.

We theoretically demonstrate microwave-induced dynamical switching of magnetic topology in centrosymmetric itinerant magnets by taking the Kondo-lattice model on a triangular lattice, which is known to exhibit two types of skyrmion lattices with different magnetic topological charges of $|N_{\mathrm{sk}}|=1$ and 2. Our numerical simulations reveal that intense excitation of a resonance mode with circularly polarized microwave field can switch the magnetic topology, i.e., from the skyrmion lattice with $|N_{\mathrm{sk}}|=1$ to another skyrmion lattice with $|N_{\mathrm{sk}}|=2$ or to a nontopological magnetic order with $|N_{\mathrm{sk}}|=0$ depending on the microwave frequency. This magnetic-topology switching shows various distinct behaviors, that is, deterministic irreversible switching, probabilistic irreversible switching, and temporally random fluctuation depending on the microwave frequency and the strength of the external magnetic field, the variety of which is attributable to different energy landscapes in the dynamical regime. The obtained results are also discussed in light of time-evolution equations based on an effective model derived using perturbation expansions.

Motivated by the recent advancements in experimental techniques in the cold atomic systems, we study the dependence of the conductivity on momentum in a system of strongly interacting bosons in an optical lattice. By employing the quantum rotor approach to the Bose-Hubbard model we calculate the current-current correlation function and subsequently obtain the analytic formula for the momentum-dependent longitudinal conductivity. We analyze the behavior of the conductivity for the square and cubic lattices in both, the superfluid and Mott insulator phases. As a consequence of the particle-hole symmetry, the conductivity for a uniformly filled lattice in the superfluid phase exhibits a linear dependence for a surprisingly wide range of momenta around $\mathbf{k}=0$. This allows us to predict the value of the group velocity of the particle excitations. We also consider the impact of finite temperature and discover that it leads to an additional conductivity channel, which is aligned along the direction of the probe field and located within the energy gap.

Even-parity interorbital spin-triplet pairing emerges as an intriguing candidate in multiorbital superconductors with significant Hund's and spin-orbit coupling. Within such a state, the pairing is dominated by the intraband pseudospin-singlet component via the spin-orbit coupling, distinguishing it from a pure spin triplet and motivating the name, shadowed triplet. With atomic spin-orbit coupling, it was shown that this pairing exhibits an anisotropic $s$-wave character, while higher angular momentum pairing symmetries such as $d$- or $g$-wave have been proposed based on phenomenological analyses in candidate systems. A natural question is then whether higher angular momentum pairings may arise with this form of spin-triplet pairing. Here, we examine the interplay between spin-orbit coupling and the electronic dispersions in correlated metals and demonstrate how they can be realized. We apply this idea to ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and determine the competition among different pairing states as multiple spin-orbit coupling parameters are tuned. The presence of both $d$- and $g$-wave pairings, including a $d+ig$ state, are found when momentum-dependent spin-orbit coupling with $d$-wave character is increased. Implications of the theory and future directions are also discussed.

We use the entanglement negativity, a bipartite measure of entanglement in mixed quantum states, to study how multipartite entanglement constrains the real-space structure of the ground-state wave functions of $(2+1)$-dimensional topological phases. We focus on the (Abelian) Laughlin and (non-Abelian) Moore-Read states at filling fraction $\nu =1/m$. We show that a combination of entanglement negativities, calculated with respect to specific cylinder and torus geometries, determines a necessary condition for when a topological state can be disentangled, i.e., factorized into a tensor product of states defined on cylinder subregions. This condition, which requires the ground state to lie in a definite topological sector, is sufficient for the Laughlin state. On the other hand, we find that a general Moore-Read ground state cannot be disentangled even when the disentangling condition holds.

We describe a systematic procedure for determining the identity of a 2D bosonic symmetry-protected topological (SPT) phase from the properties of its edge excitations. Our approach applies to general bosonic SPT phases with either unitary or antiunitary symmetries, and with either continuous or discrete symmetry groups, with the only restriction being that the symmetries must be on-site. Concretely, our procedure takes a bosonic SPT edge theory as input, and produces an element $\omega$ of the cohomology group $H^3(G,U_T\left(1\right))$. This element $\omega \in H^3(G,U_T\left(1\right))$ can be interpreted as either a label for the bulk 2D SPT phase or a label for the anomaly carried by the SPT edge theory. The basic idea behind our approach is to compute the $F$ symbol associated with domain walls in a symmetry-broken edge theory; this domain-wall $F$ symbol is precisely the anomaly we wish to compute. We demonstrate our approach with several SPT edge theories, including both lattice models and continuum field theories.

In the $GW$ approximation, the screened interaction $W$ is a nonlocal and dynamical potential that usually has a complex frequency dependence. A full description of such a dependence is possible but often computationally demanding. For this reason, it is still common practice to approximate $W\left(\omega \right)$ using a plasmon pole (PP) model. Such an approach, however, may deliver an accuracy limited by its simplistic description of the frequency dependence of the polarizability, i.e., of $W$. In this work, we explore a multipole approach (MPA) and develop an effective representation of the frequency dependence of $W$. We show that an appropriate sampling of the polarizability in the frequency complex plane and a multipole interpolation can lead to a level of accuracy comparable with full-frequency methods at a much lower computational cost. Moreover, both accuracy and cost are controllable by the number of poles used in MPA. Eventually, we validate the MPA approach in selected prototype systems, showing that full-frequency quality results can be obtained with a limited number of poles.

Nodal-line semimetals (NLSMs) contain Dirac-Weyl-type band-crossing nodes extending into shapes of lines, loops, and chains in the reciprocal space, leading to band topology and transport responses. Robust NLSMs against spin-orbit coupling typically occur in three-dimensional and in-plane isotropic materials which have more symmetry operations to protect the line nodes of band crossing, while the possibilities in exfoliatable materials with in-plane anisotropy are rarely discussed. Here, we demonstrate a robust NLSM phase in an exfoliatable in-plane anisotropic nonmagnetic semimetal $\mathrm{TaNi}{\mathrm{Te}}_5$. Combining angle-resolved photoemission spectroscopy measurements and first-principles calculations, we reveal multiple Dirac-type nodal lines with fourfold degeneracy in $\mathrm{TaNi}{\mathrm{Te}}_5$. Our findings suggest rich physics in structurally anisotropic topological materials and call for further functional exploitation based on them.

Dynamical quantum phase transitions (DQPTs) feature singular temporal behavior in transient quantum states during nonequilibrium real-time evolution. In this work we show that DQPTs in random Ising chains exhibit critical behavior with nontrivial exponents that are not integer valued and not of mean-field type. By means of an exact renormalization group transformation we estimate the exponents with high accuracy eliminating largely any finite-size effects. We further discuss how the considered dynamical phenomena can be made accessible in current Rydberg atom platforms. In this context we explore signatures of the DQPTs in the statistics of spin configuration measurements available in such architectures. Specifically, we study the statistics of clusters of consecutively aligned spins and observe a marked influence of the DQPT on the corresponding distribution.

We describe a systematic method to construct models of Chern insulators whose Berry curvature and the quantum volume form coincide and are flat over the Brillouin zone; such models are known to be suitable for hosting fractional Chern insulators. The bands of Chern insulator models where the Berry curvature and the quantum volume form coincide, and are nowhere vanishing, are known to induce the structure of a Kähler manifold in momentum space, and thus we are naturally led to define Kähler bands to be Chern bands satisfying such properties. We show how to construct a geometrically flat Kähler band with Chern number equal to minus the total number of bands in the system, using the idea of Kähler quantization and properties of Bergman kernel asymptotics. We show that, with our construction, the geometrical properties become flatter as the total number of bands in the system is increased; we also show the no-go theorem that it is not possible to construct geometrically perfectly flat Kähler bands with a finite number of bands. We give an explicit realization of this construction in terms of theta functions and numerically confirm how the constructed Kähler bands become geometrically flat as we increase the number of bands. We also show the effect of truncating hoppings at a finite length, which will generally result in deviation from a perfect Kähler band but does not seem to seriously affect the flatness of the geometrical properties.

Elemental monolayers of group 14 with a buckled honeycomb structure, namely, silicene, germanene, stanene, and plumbene, are known to demonstrate spin splitting as a result of an electric field parallel to their high-symmetry axis, which is capable of tuning their topological phase between a quantum spin Hall insulator and an ordinary band insulator. We perform first-principles calculations based on density functional theory to quantify the spin-dependent band gaps and the spin splitting as a function of the applied electric field and extract the main coefficients of the invariant Hamiltonian. Using linear response theory and the Wannier interpolation method, we calculate the spin Hall conductivity in the monolayers and study its sensitivity to an external electric field. Our results show that the spin Hall conductivity is not quantized and, in the case of silicene, germanene, and stanene, degrades significantly as the electric field inverts the band gap and brings the monolayer into the trivial phase. The electric-field-induced band gap does not close in the case of plumbene with a spin Hall conductivity that is robust to the external electric field.

Atomic-scale smooth thin films are keys to successful integration and proper function of many multilayer-structured devices. However, the intrinsic islandlike growth mode prevents human beings from realizing such ultrasmooth films of many important functional materials. To solve this problem, we propose a negative entropy-infusing method that employs evanescent waves to enhance the downward interlayer diffusion of adatoms and thus transform the islandlike growth mode to the layer-by-layer growth mode. The formulas of the optical force and the lowered diffusion barrier were derived, and the application of this theory on a simplified example demonstrates significantly improved surface morphologies through numerical simulations.

We investigate the thermoelectric response of a coherent conductor in contact with a scanning probe. Coupling to the probe has the dual effect of allowing for the controlled local injection of heat currents into the system and of inducing interference patterns in the transport coefficients. This is sufficient to generate a multiterminal thermoelectric effect even if the conductor does not effectively break electron-hole symmetry and the tip injects no charge. Considering a simple model for noninteracting electrons, we find a nonlocal thermoelectric response which is modulated by the position of the hot probe tip, and a nonreciprocal longitudinal response which leads to a thermoelectric diode effect. A separate investigation of the effects of dephasing and of quasielastic scattering gives further insights into the different mechanisms involved.

The quantum phases in a spin-1 skewed ladder system formed by alternately fusing five- and seven-membered rings are studied numerically using the exact diagonalization technique up to 16 spins and using the density matrix renormalization group method for larger system sizes. The ladder has a fixed isotropic antiferromagnetic (AF) exchange interaction ($J_2=1$) between the nearest-neighbor spins along the legs and a varying isotropic AF exchange interaction ($J_1$) along the rungs. As a function of $J_1$, the system shows many interesting ground states (gs) which vary from different types of nonmagnetic and ferrimagnetic gs. The study of various gs properties such as spin gap, spin-spin correlations, spin density, and bond order reveal that the system has four distinct phases, namely, the AF phase at small $J_1$; the ferrimagnetic phase with gs spin $S_G=n$ for $1.44<J_1<4.74$ and with $S_G=2n$ for $J_1>5.63$, where $n$ is the number of unit cells; and a reentrant nonmagnetic phase at $4.74<J_1<5.44$. The system also shows the presence of spin current at specific $J_1$ values due to simultaneous breaking of both reflection and spin parity symmetries.

We study a quantum spin Kitaev model with zigzag edges to clarify the effects of anisotropy in the exchange couplings on spin propagation. We simulate the spin and Majorana dynamics triggered by a magnetic pulse, using the real-space time-dependent Majorana mean-field theory. When the anisotropy is small, the dispersion of the itinerant Majorana fermions remains gapless, where the velocity of the spin propagation matches the group velocity of the itinerant Majorana fermions at the nodal points. On the other hand, in the gapped system with large anisotropy, the spin propagation is strongly suppressed although its nature depends on the shape of the pulse. The spin transport in the junction system described by the Kitaev models with distinct anisotropies is also addressed.

We introduce a type of Wannier functions (WFs) obtained by minimizing the conventional spread functional with a penalty term proportional to the variance of the spread distribution. This modified Wannierization scheme is less prone to produce ineffective solutions featuring one or several poorly localized orbitals, making it well suited for complex systems or high-throughput applications. Furthermore, we propose an automatable protocol for selecting the initial guess and determine the optimal number of bands (or equivalently, WFs) for the localization algorithm. The improved performance and robustness of the approach is demonstrated for a diverse set of test systems including the nitrogen-vacancy center in diamond, metal slabs with atomic adsorbates, spontaneous polarization of ferroelectrics, and 30 inorganic monolayer materials comprising both metals and semiconductors. The methods are implemented in Python as part of the Atomic Simulation Environment.

In the study of correlated systems, approximations based on the dynamical mean-field theory (DMFT) provide a practical way to take local vertex corrections into account, which capture, respectively, particle-particle screening at weak coupling and the formation of the local moment at strong coupling. We show that in both limits the local vertex corrections can be efficiently parametrized in terms of single-boson exchange, such that the two-particle physics described by DMFT and its diagrammatic extensions is recovered to good approximation and at a reduced computational cost. Our investigation highlights the importance of the frequency-dependent fermion-boson coupling (Hedin vertex) for local vertex corrections. Namely, at weak coupling the fermion–spin-boson coupling suppresses the Néel temperature of the DMFT approximation compared with the static mean field, whereas for large interaction it facilitates a huge enhancement of local spin-fluctuation exchange, giving rise to the effective-exchange energy scale $4t^2/U$. We find that parametrizations of the vertex which neglect the nontrivial part of the fermion-boson coupling fail qualitatively at strong coupling.

We construct a three-dimensional (3D), time-reversal symmetric generalization of the Chalker-Coddington network model for the integer quantum Hall transition. In addition to a weak topological insulator phase already accommodated by the network model framework in the preexisting literature, our network model hosts strong topological insulator phases. We unambiguously demonstrate that strong topological insulator phases emerge as intermediate phases between a trivial insulator phase and a weak topological phase. Additionally, we found a duality that relates a trivial insulator phase and a weak topological phase in our network model. Remarkably, strong topological phases are mapped to themselves under this duality. We show that upon adding sufficiently strong disorder, the strong topological insulator phases undergo phase transitions into a metallic phase. We numerically determine the critical exponent of the insulator-metal transition. Our network model explicitly shows how a semiclassical percolation picture of topological phase transitions in two dimensions can be generalized to 3D and opens up a venue for studying 3D topological phase transitions.

The NMR measurements performed on a single orthorhombic crystal of superconducting ferromagnet UCoGe [Y. Ihara et al., Phys. Rev. Lett. 105, 206403 (2010)] demonstrate strongly anisotropic magnetic properties of this material. The presented calculations allow one to establish the dependence of longitudinal spin-lattice relaxation rate from temperature and magnetic field. The value $(1/T_{1}T)$ in field perpendicular to spontaneous magnetization directed along the $c$ axis has a maximum in the vicinity of Curie temperature, whereas it does not reveal similar behavior in a field parallel to the direction of spontaneous magnetization. Also there was shown that the longitudinal spin-lattice relaxation rate is strongly field dependent when the field directed in the $b$-crystallographic direction but field independent if magnetic field is oriented along the $a$ axis.