Critical current density and vortex pinning dynamics have been studied in the superconductor ${\mathrm{Sn}}_{0.55}{\mathrm{In}}_{0.45}\mathrm{Te}$. Analysis of the temperature-dependent lower critical field shows that it has a weakly anisotropic single energy gap. The critical current density $J_c\left(0\right)$ and pinning potential $U_0\left(H\right)$ values reach as high as $2.56\times {10}^3\mathrm{A}/{\mathrm{cm}}^2$ at 1.8 K and $2.1\times {10}^3$ K at ${\mu }_{0}H=0.01\mathrm{T}$, respectively. Based on the collective pinning model, we demonstrate the coexistence of vortex pinning regimes in ${\mathrm{Sn}}_{0.55}{\mathrm{In}}_{0.45}\mathrm{Te}$. One is a $\delta T_{\mathrm{c}}$ pinning regime induced by the spatial fluctuations of the transition temperature in a low field. The other is a dominantly $\delta l$ pinning regime associated with the spatial variations of the charge-carrier mean free path in a higher field. This causes a nonconstant exponent of the power-law behavior $J_c\left(T\right)\propto H^n$. A very weak vortex fluctuation is unveiled by a narrow separation between the irreversibility field ${\mu }_0{H}_{\mathrm{irr}}\left(T\right)$ and upper critical field ${\mu }_0{H}_{\mathrm{c}2}\left(T\right)$ in the vortex phase diagram. We discuss the potential application in superconducting electronics like the single-photon detector in thin film form.

We present an unconventional mechanism for Raman scattering of phonons, which is based on the linear magnetoelastic coupling present in non-Kramers magnetic ions. This provides a direct coupling of Raman-active phonons to the magnet's quasiparticles. We propose to use this mechanism to probe the emergent magnetic monopoles, electric charges, and photons of the emergent quantum electrodynamics (eQED) of the U(1) quantum spin liquid known as quantum spin ice. Detecting this eQED in candidate rare-earth pyrochlore materials, or indeed signatures of topological magnetic phases more generally, is a challenging task. We show that the Raman scattering cross section of the phonons directly yields relevant information, with the broadening of the phonon linewidth, which we compute, exhibiting a characteristic frequency dependence reflecting the two-particle density of states of the emergent excitations. Remarkably, we find that the Raman linewidth is sensitive to the details of the symmetry fractionalization and hence can reveal information about the projective implementation of symmetry in the quantum spin liquid, thereby providing a diagnostic for a $\pi$-flux phase. The Raman scattering of the phonons thus provides a useful experimental tool to probe the fractionalization in quantum spin liquids that turns out to closely mirror pair production in quantum electrodynamics and the deep inelastic scattering of quantum chromodynamics. Indeed, the difference to the latter is conceptual more than technical: the partons (quarks) emerge from the hadrons at high energies due to asymptotic freedom, while those in eQED arise from fractionalization of the spins at low energies.

We study the full distribution of quantum work in generic, noninteracting, disordered fermionic nanosystems at finite temperature. We derive an analytical determinant formula for the characteristic function of work statistics for quantum quenches starting from a thermal initial state. For work small compared to the thermal energy of the Fermi gas, work distribution is Gaussian, and the variance of work is proportional to the average work, while in the low-temperature or large-work limit, a non-Gaussian distribution with superdiffusive work fluctuations is observed. Similarly, the time dependence of the probability of adiabaticity crosses over from an exponential to a stretched exponential behavior. For large enough average work, the work distribution becomes universal, and depends only on the temperature and the mean work. Apart from initial low-temperature transients, work statistics are well captured by a Markovian energy-space diffusion process of hardcore particles, starting from a thermal initial state. Our findings can be verified by measurements on nanoscale circuits or via single qubit interferometry.

The determination of the nature of phase transitions, especially those that involve two symmetry-breaking order parameters, is a fundamental issue in condensed matter physics. For the Laves-phase rare-earth–transition-metal intermetallic compounds, their phase transitions involve both magnetic ordering and structural ordering. As a typical material of the Laves-phase intermetallics, ${\mathrm{TbCo}}_2$ has been studied extensively for its transition around 230 K. However, the understanding on the nature of this transition has remained controversial (first/second order) for decades. Here, in this paper, based on the criteria that determine first-order and second-order transitions for magnetic materials, which are (1) latent heat, (2) thermal hysteresis, (3) coexistence of phases, and (4) the Banerjee criterion, we show direct evidence to reveal the first-order nature of the transition in ${\mathrm{TbCo}}_2$, which is further interpreted by a Landau theory based phenomenological approach. Our work reconciles the lasting arguments on the transition of ${\mathrm{TbCo}}_2$ and may pave the way for deepening the understanding on the transitions of magnetic materials that involve both magnetic and structural transitions.

In this work, we report the propagating spin waves hybridized between first-order and quasiuniform modes in a $\mathrm{Co}_{20}\mathrm{Fe}_{60}\mathrm{B}_{20}$ thin film capped by $\mathrm{Ir}_{25}\mathrm{Mn}_{75}$. The anticrossing gaps are observed at room temperature both in the reflection and transmission spectra, where the coupling strength can be tuned by varying the value of the in-plane wave vector at which the dispersion curves cross. The key mechanism behind this feature is theoretically ascribed to the dipole-dipole interaction by a model which accounts for many features of our experimental results. The strong coupling with a cooperativity up to 2.0 is achieved with taking the dissipation rates of two coupled branches into account. A reference CoFeB sample without IrMn reveals that the interfacial pinning effect also plays a role in the magnon-magnon hybridization. Tunable hybridization of magnons may foster the field of magnonics in information processing.

Motivated by the recent discovery of ferromagnetic quantum criticality in the heavy fermion compound ${\mathrm{CeRh}}_6{\mathrm{Ge}}_4$, we develop a numerical algorithm of infinite projected entangled pair states for the anisotropic ferromagnetic Kondo-Heisenberg model in two dimensions and study the ferromagnetic quantum phase transitions with varying magnetic and hopping anisotropy. Our calculations reveal a continuous ferromagnetic quantum phase transition in the large anisotropic region and first-order quantum phase transitions for smaller anisotropy. Our results highlight the importance of magnetic anisotropy on ferromagnetic quantum criticality in Kondo lattice systems and provide a possible explanation for the experimental observation in ${\mathrm{CeRh}}_6{\mathrm{Ge}}_4$ with a quasi-one-dimensional magnetic structure. Our work opens the avenue for future studies of the rich Kondo lattice physics using state-of-the-art tensor network approaches.

SiC polytypes have been studied for decades, both experimentally and with atomistic simulations, yet no consensus has been reached on the factors that determine their stability and growth. Proposed governing factors are temperature-dependent differences in the bulk energy, biaxial strain induced through point defects, and surface properties. In this work, we investigate the thermodynamic stability of the 3C, 2H, 4H, and 6H polytypes with density functional theory (DFT) calculations. The small differences of the bulk energies between the polytypes can lead to intricate changes in their energetic ordering depending on the computational method. Therefore, we employ and compare various DFT codes, i.e., vasp, cp2k, and fhi-aims; exchange-correlation functionals, i.e., LDA, PBE, PBEsol, PW91, HSE06, SCAN, and RTPSS; and nine different van der Waals (vdW) corrections. At $T=0$ K, 4H-SiC is marginally more stable than 3C-SiC, and the stability further increases with temperature by including entropic effects from lattice vibrations. Neither the most advanced vdW corrections nor strain on the lattice have a significant effect on the relative polytype stability. We further investigate the energies of the (0001) polytype surfaces that are commonly exposed during epitaxial growth. For Si-terminated surfaces, we find 3C-SiC to be significantly more stable than 4H-SiC. We conclude that the difference in surface energy is likely the driving force for 3C-nucleation, whereas the difference in the bulk thermodynamic stability slightly favors the 4H and 6H polytypes. In order to describe the polytype stability during crystal growth correctly, it is thus crucial to take into account both of these effects.

The enriched finite-element basis—wherein the finite-element basis is enriched with atom-centered numerical functions—has recently been shown to be a computationally efficient basis for systematically convergent all-electron density functional theory (DFT) ground-state calculations. In this work, we present the expressions to compute variationally consistent ionic forces and stress tensor for all-electron DFT calculations in the enriched finite-element basis. In particular, we extend the formulation of configurational forces [P. Motamarri and V. Gavini, Phys. Rev. B 97, 165132 (2018)] to the enriched finite-element basis and elucidate the additional contributions arising from the enrichment functions. We demonstrate the accuracy of the formulation by comparing the computed forces and stresses for various benchmark systems with those obtained from finite differencing the ground-state energy. Further, we also benchmark our calculations against the Gaussian basis for molecular systems and against the linearized augmented plane wave with local orbitals basis for periodic systems.

A remarkable feature of the trimer Su-Schrieffer-Heeger (SSH3) model is that it supports localized edge states. However, in contrast to the dimer version of the model, a change in the total number of edge states in SSH3 without mirror-symmetry is not necessarily associated with a phase transition, i.e., a closing of the band gap. As such, the topological invariant predicted by the 10-fold way classification does not always coincide with the total number of edge states present. Moreover, although Zak's phase remains quantized for the case of a mirror-symmetric chain, it is known that it fails to take integer values in the absence of this symmetry and thus it cannot play the role of a well-defined bulk invariant in the general case. Attempts to establish a bulk-edge correspondence have been made via Green's functions or through extensions to a synthetic dimension. Here we propose a simple alternative for SSH3, utilizing the previously introduced sublattice Zak's phase, which also remains valid in the absence of mirror symmetry and for noncommensurate chains. The defined bulk quantity takes integer values, is gauge invariant, and can be interpreted as the difference of the number of edge states between a reference and a target Hamiltonian. Our derivation further predicts the exact corrections for finite open chains, is straightforwardly generalizable, and invokes a chiral-like symmetry present in this model.

Recent work has demonstrated that quantum Fisher information (QFI), a witness of multipartite entanglement, and magnetic Van Hove correlations $G(r,t)$, a probe of local real-space real-time spin dynamics, can be successfully extracted from inelastic neutron scattering on spin systems through accurate measurements of the dynamical spin structure factor $S(k,\omega )$. Here we apply theoretically these ideas to the half-filled Hubbard chain with nearest-neighbor hopping, away from the strong-coupling limit. This model has nontrivial redistribution of spectral weight in $S(k,\omega )$ going from the noninteracting limit ($U=0$) to strong coupling ($U\to \infty$), where it reduces to the Heisenberg quantum spin chain. We use the density matrix renormalization group to find $S(k,\omega )$, from which QFI is then calculated. We find that QFI grows with $U$. With realistic energy resolution it becomes capable of witnessing bipartite entanglement above $U=2.5$ (in units of the hopping), where it also changes slope. This point is also proximate to slope changes of the bandwidth $W\left(U\right)$ and the half-chain von Neumann entanglement entropy. We compute $G(r,t)$ by Fourier transforming $S(k,\omega )$. The results indicate a crossover in the short-time short-distance dynamics at low $U$ characterized by ferromagnetic light-cone wavefronts, to a Heisenberg-type behavior at large $U$ featuring antiferromagnetic light cones and spatially period-doubled antiferromagnetism. We find this crossover has largely been completed by $U=3$. Our results thus provide evidence that, in several aspects, the strong-coupling limit of the Hubbard chain is reached qualitatively already at a relatively modest interaction strength. We discuss experimental candidates for observing the $G(r,t)$ dynamics found at low $U$.

We propose a heat current analog of the shift current, “shift heat current.” We study nonlinear heat current responses to an applied ac electric field by a diagrammatic method and derive a microscopic expression for the second-order dc heat current response. As a result, we find that the shift heat current is related to the shift vector, a geometric quantity that also appears in the expression for the shift current. The shift heat current directly depends on and can be controlled through the chemical potential. In addition, we apply the diagrammatic method to electron-phonon coupled systems, and we find that even if only the phonons are excited by an external field, the amplitude of the shift heat current is determined by the energy scale of electrons, not of phonons.

One of the key issues in the physics of topological insulators is whether the topologically nontrivial properties survive at finite temperatures and, if so, whether they disappear only at the temperature of topological gap closing. Here, we study this problem, using quantum fidelity as a measure, by means of ab initio methods supplemented by an effective dissipative theory built on the top of the ab initio electron and phonon band structures. In the case of SnTe, the prototypical crystal topological insulator, we reveal the presence of a characteristic temperature, much lower than the gap-closing one, that marks a loss of coherence of the topological state. The transition is not present in a purely electronic system but it appears once we invoke coupling with a dissipative bosonic bath. Features in the dependence with temperature of the fidelity susceptibility can be related to changes in the band curvature, but signatures of a topological phase transition appear in the fidelity only though the nonadiabatic coupling with soft phonons. Our argument is valid for valley topological insulators, but in principle can be generalized to the broader class of topological insulators which host any symmetry-breaking boson.

Neon (Ne), as the fifth most abundant element in the universe, is rare to react with other elements by forming stable solid compounds. It is well known that pressure is a powerful tool to generate the compounds that are inaccessible at ambient pressure. In this work, we performed structure-searching simulations to examine stable compounds of Ne and ${\mathrm{H}}_2\mathrm{O}$ at a wide pressure range of 0–600 GPa. Our simulations identified two phases of ${\mathrm{H}}_2\mathrm{ONe}$ and ${\mathrm{H}}_2{\mathrm{ONe}}_2$ under high pressure. By employing chemical-bonding analysis, interestingly, we found that Ne-O interactions are comparable in strength to that of conventional hydrogen bond. Moreover, our molecular dynamic simulations indicate the diffusion behavior of hydrogen atoms within a fixed Ne-O lattice framework of ${\mathrm{H}}_2{\mathrm{ONe}}_2$ at high pressure and high temperature. These results provide the implications for the possible existence of pressure-stabilized ${\mathrm{H}}_2\mathrm{ONe}$ and ${\mathrm{H}}_2{\mathrm{ONe}}_2$ compounds viable in a variety of astronomical objects.

We present an extension of the classical Johnson-Nyquist theorem for multiport classical electrical passive linear networks by Twiss [J. Appl. Phys. 26, 599 (1955)] to the quantum case. Conversely, we extend the quantum fluctuation-dissipation result for one port electrical systems to the multiport case, both reciprocal and nonreciprocal, performing a detailed quantum analysis of the canonical Foster lossless immittance expansions. Our results are extended to lossy systems by depicting resistive components as continuous limits of purely lossless lumped-element networks. Simple circuit examples are analyzed, including a linear system lacking a direct impedance representation.

The upper critical field $H_{c2}$, the field $H_{c3}$ for nucleation of the surface superconductivity, and the thermodynamic field $H_c$ are evaluated within the weak-coupling theory for the isotropic s-wave case with arbitrary transport, and pair-breaking scattering. We find that, for the standard geometry of a half-space sample in a magnetic field parallel to the surface, the ratio $\mathcal{R}=H_{c3}/H_{c2}$ is within the window $1.55\lesssim \mathcal{R}\lesssim 2.34$, regardless of temperature or the scattering type. While the nonmagnetic impurities tend to flatten the $\mathcal{R}\left(T\right)$ variation, magnetic scattering merely shifts the maximum of $\mathcal{R}\left(T\right)$ to lower temperatures. Surprisingly, while reducing the transition temperature, magnetic scattering has a milder impact on $\mathcal{R}$ than nonmagnetic scattering. The surface superconductivity is quite robust; in fact, the ratio $\mathcal{R}\approx 1.7$ even in the gapless state. We used Eilenberger's energy functional to evaluate the condensation energy $F_c$ and the thermodynamic critical field $H_c$ for any temperature and scattering parameters. By comparing $H_{c2}$ and $H_c$, we find that, unlike transport scattering, the pair-breaking pushes materials toward type-I behavior. We find a peculiar behavior of $F_c$ as a function of the pair-breaking scattering parameter at the low-$T$ transition from gapped to gapless phases, which has recently been associated with the topological transition in the superconducting density of states.

One of the most important tasks in the development of high-performance spintronic devices is the preparation of two-dimensional (2D) magnetic layers with long-range exchange interactions. ${\mathrm{MN}}_4$ embedded graphene $\left({\mathrm{MN}}_4\text{−}\mathrm{G}\right)$ layers, with $\mathrm{M}$ being transition metal elements, are experimentally accessible 2D layers which exhibit interesting magnetic properties. In this paper, by employing the spin-polarized density functional theory (SP-DFT), we study ${\mathrm{MN}}_4\text{−}\mathrm{G}$ layers with a special focus on the behavior of the indirect $\mathrm{M}\text{−}\mathrm{M}$ exchange interactions and demonstrate that the ${\mathrm{MN}}_4\text{−}\mathrm{G}$ layers with $\mathrm{M}=\mathrm{Fe}$, Mn, and Co, are 2D anisotropic magnetic layers with Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. By examining the electronic configurations of the $\mathrm{M}$ atoms for various $\mathrm{M}\text{−}\mathrm{M}$ spacers, we demonstrate that the RKKY interaction in such layers are tunable and exhibit an unusual, prolonged decay ($r^{-n}$, with $0.5\le n\le 2)$. In addition, we isnvestigate the influence of the ${\mathrm{CuN}}_4$ moiety in the graphene host, and show that, in contrary to the other ${\mathrm{MN}}_4\text{−}\mathrm{G}$ layers, the 2D ${\mathrm{CuN}}_4\text{−}\mathrm{G}$ layer behaves as decoupled one-dimensional spin chains, regardless of the spacer lengths.

We present flatspin, a novel simulator for systems of interacting mesoscopic spins on a lattice, also known as artificial spin ice (ASI). A generalization of the Stoner-Wohlfarth model is introduced, and combined with a well-defined switching protocol to capture realistic ASI dynamics using a point-dipole approximation. Temperature is modelled as an effective thermal field, based on the Arrhenius-Néel equation. Through GPU acceleration, flatspin can simulate the dynamics of millions of magnets within practical time frames, enabling exploration of large-scale emergent phenomena at unprecedented speeds. We demonstrate flatspin's versatility through the reproduction of a diverse set of established experimental results from literature. In particular, the field-driven magnetization reversal of “pinwheel” ASI is reproduced, for the first time, in a dipole model. Finally, we use flatspin to explore aspects of “square” ASI by introducing dilution defects and measuring the effect on the vertex population.

We investigate the ground state phase diagram of an extended Hubbard model with a $\pi$-flux hopping term at half filling on a square lattice, with unbiased large-scale auxiliary-field quantum Monte Carlo simulations. As a function of interaction strength, there emerges an intermediate phase which realizes two interaction-driven quantum critical points, with the first between the Dirac semimetal and an insulating phase of weak valence bond solid (VBS) order, and the second separating the VBS order and an antiferromagnetic insulating phase. These intriguing quantum critical points are respectively bestowed with Gross-Neveu and deconfined quantum criticalities, and the critical exponents ${\eta }_{\text{VBS}}=0.6\left(1\right)$ and ${\eta }_{\text{AFM}}=0.58\left(3\right)$ at a deconfined quantum critical point satisfy the conformal field theory bootstrap bound. We also investigate the dynamical properties of the spin excitation and find the spin gap open near the first transition and closed at the second. The relevance of our findings in realizing deconfined quantum criticality in fermion systems and the implication to lattice models with further extended interactions such as those in quantum moiré systems, are discussed.

In this paper, we explore the possibility for the non-Hermiticity of the system originating from the curved space. We obtain a duality between a generalized non-Hermitian Hatano-Nelson model in $d$-dimensional flat space and a Hermitian system in $2d$-dimensional curved space, and give the metric of the curved space analytically. This duality shows the possibility of non-Hermiticity coming from the metric of the space, and provides a perspective on exploring non-Hermitian or Hermitian systems.