To establish the microscopic P-T phase diagram of recent 112-type iron-pnictides $\mathrm{Eu}\left({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x\right){\mathrm{As}}_2$ (x = 0, 0.04), high-pressure synchrotron Mössbauer spectroscopy experiments in ${}^{151}\mathrm{Eu}$ and ${}^{57}\mathrm{Fe}$ have been performed. In ${\mathrm{EuFeAs}}_2$ application of pressure completely suppresses the itinerant electron magnetism from the Fe sublattice and the local-moment magnetism in Eu ions at $\sim 10$ and $\sim 11.6\mathrm{GPa}$, respectively. High-pressure x-ray diffraction experiments in ${\mathrm{EuFeAs}}_2$ reveal an anomalous change in the lattice parameters and a discontinuity in volume around 10 GPa, suggesting an isostructural transition at this pressure. With Ni-doping (x = 0.04), a collapse of local magnetic order occurs at $\sim 8\mathrm{GPa}$, a lower critical pressure compared with the parent compound. In both systems, the suppression of local-moment magnetism is associated with a significant increase of mean valence in Eu ions.

The topological phonon state of quantum matter is an emerging field that has been attracting considerable interest. For instance, Weyl phonons in transition-metal monosilicides have been proposed theoretically and identified experimentally. However, topological phonon nodal net states are not well studied due to the lack of realistic materials. Here, based on first-principles calculations and effective model analysis, we propose an existing material—cuprous oxide—to host the nodal net phonons. The nontrivial phonon surface states and uncovered phononic arcs are clearly visible on $k$-resolved phonon spectra, which are amenable to experimental detection. Our findings offer a possible platform for realizing topologically nontrivial phonon states and their applications.

Using the local moment counter charge (LMCC) method to accurately represent the asymptotic electrostatic boundary conditions within density functional theory supercell calculations, we present a comprehensive analysis of the atomic structure and energy levels of point defects in cubic silicon carbide ($3C$-SiC). Finding that the classical long-range dielectric screening outside the supercell induced by a charged defect is a significant contributor to the total energy. we describe and validate a modified Jost screening model to evaluate this polarization energy. This leads to bulk-converged defect levels in finite size supercells. With the LMCC boundary conditions and a standard Perdew-Burke-Ernzerhof (PBE) exchange correlation functional, the computed defect level spectrum exhibits no band gap problem: the range of defect levels spans $\sim 2.4\mathrm{eV}$, an effective defect band gap that agrees with the experimental band gap. Comparing with previous literature, our LMCC-PBE defect results are in consistent agreement with the hybrid-exchange functional results of Oda et al. [J. Chem. Phys. 139, 124707 (2013)] rather than their PBE results. The difference with their PBE results is attributed to their use of a conventional jellium approximation rather than the more rigorous LMCC approach for handling charged supercell boundary conditions. The difference between standard dft and hybrid functional results for defect levels lies not in a band gap problem but rather in solving a boundary condition problem. The LMCC-PBE entirely mitigates the effect of the band gap problem on defect levels. The more computationally economical PBE enables a systematic exploration of $3C$-SiC defects, where, most notably, we find that the silicon vacancy undergoes Jahn-Teller-induced distortions from the previously assumed $T_d$ symmetry, and that the divacancy, like the silicon vacancy, exhibits a site-shift bistability in $p$-type conditions.

Interference is the cornerstone of Huygens source design for reshaping and controlling scattering patterns. The conventional underpinning principle, such as for the Kerker effect, is the interference of electric and magnetic dipole and quadrupole modes. Here a route to realize transverse Kerker scattering through employing only the interference between the electric dipole and magnetic quadrupole is demonstrated. The proposed approach is numerically validated in an ultrathin Silicon square nanoplate metasurface, and is further verified by multipole decomposition. The metasurface is shown to be invisible for near-infrared wavelengths and with an enhanced electric field in the region of the nanoparticle. Additionally, we develop further the proposed approach with practical implementation for invisibility applications by exploring the effects of the aspect ratio of the square plate nanoresonator, the interparticle separation, and the presence of a substrate. Further it is demonstrated that invisibility can be observed at oblique incidence up to ${60}^{\circ }$ for a transverse magnetic plane wave. The results are relevant for Huygens metasurface design for perfect reflectors, invisibility, and devices for harmonic generation manipulation.

While established neural network approaches based on restricted Boltzmann machine architectures and Metropolis sampling methods are well suited for symmetric open quantum systems, they result in poor scalability and systematic errors for setups without symmetries of translational invariance, independent of training parameters such as the sample size. To overcome this representational limit, we present a hybrid sampling strategy which takes asymmetric properties explicitly into account, achieving fast convergence times and high scalability for asymmetric open systems, underlining the universal applicability of artificial neural networks.

Time-reversal-invariant (TRI) topological superfluids (TSFs) and topological superconductors (TSCs) are robust symmetry-protected gapped topological states. In this article, we study the evolution of these topological states in the presence of time-reversal symmetry-breaking (TRB) fields and/or sufficiently large TRI fields. Physically, one of the realizations of TRB fields can be internal spin exchange fields due to background magnetic ordering. We find that the fully gapped TSFs and TSCs are generically separated from other nodal states by various zero temperature quantum critical points that are characterized by generalized quantum Lifshitz Majorana fields with distinct scaling properties. These emergent Lifshitz Majorana fields also define finite temperature properties in quantum critical regimes. Moreover, for a certain subset of TRB fields, there exists a precursor to bulk transitions, where surface states can also exhibit quantum critical behavior near zero fields.

Study of the magnetotransport properties of ScPtBi revealed simultaneously (i) a negative contribution to the longitudinal magnetoresistance, (ii) the planar Hall effect, and (iii) distinct angular narrowing of the longitudinal magnetoresistance—three hallmarks of chiral magnetic anomaly (pumping of axial charge between Weyl nodes), a distinct property of topological semimetals. Electronic structure calculations show that structural defects, such as antisites and vacancies, bring a substantial density of states at the Fermi level of ScPtBi, indicating that it is a semimetal, not a zero-gap semiconductor, as predicted earlier. This is in accord with electrical resistivity in ScPtBi, showing no characteristics of a semiconductor. Moreover, below 0.7 K we observed an onset of a superconducting transition, with the resistivity disappearing completely below 0.23 K.

We propose the construction of thermodynamic ensembles that minimize the Rényi free energy, as an alternative to Gibbs states. For large systems, the local properties of these Rényi ensembles coincide with those of thermal equilibrium and they can be used as approximations to thermal states. We provide algorithms to find tensor network approximations to the 2-Rényi ensemble. In particular, a matrix-product-state representation can be found by using gradient-based optimization on Riemannian manifolds or via a nonlinear evolution which yields the desired state as a fixed point. We analyze the performance of the algorithms and the properties of the ensembles on one-dimensional spin chains.

The Anderson and midgap models are often used in the study of semiconductor heterojunctions, but for van der Waals (vdW) vertical heterostructures they have shown only very limited success. Using the group-IV monochalcogenide vertical heterostructures as a prototypical system, we propose a linear response model and compare the effectiveness of these models in predicting density functional theory (DFT) band alignments, band types, and band gaps. We show that the DFT band alignment is best predicted by the linear response model, which falls in between the Anderson and midgap models. Our proposed model can be characterized by an interface dipole $\alpha \times (E_{m2}-E_{m1})$, where the linear response coefficient $\alpha =0$ and 1 corresponds to the Anderson and midgap model, respectively, and $E_m$ is the midgap energy of the monolayer, which can be viewed as an effective electronegativity. For group-IV monochalcogenides, we show that $\alpha =0.34$ best captures the DFT band alignment of the vdW heterostructure, and we discuss the viability of the linear response model considering other effects such as strains and band hybridization, and conclude with an application of the model to predict experimental band alignments.

We study the photon-dressed electronic band structure of topological insulator thin films doped by magnetic impurities in response to an off-resonance time-periodic electromagnetic field. The thin films irradiated by a circularly polarized light undergo phase transitions, and a fascinating feature of distinct phases emerges in the phase diagram depending on the frequency, intensity, and polarization of the light. As a particular case, the quantum anomalous Hall insulator phase is induced purely by the light-induced mass term with no need for any external magnetic field or even magnetization arising from doping magnetic impurities. Moreover, a quantum pseudo-spin Hall insulator (QPHI) phase emerges in the phase diagram, leading to anisotropic helical edge states with zero total Chern number. We verify these achievements by numerical calculations for a nanoribbon of the thin film for which the edge mode behavior is observed at several points on the phase diagram. The emergence of the mentioned topological phases and the edge modes are further confirmed by both calculating the Hall conductivity by means of the Kubo formula and the Chern number of each band. The effect of light parameters on the Landau-level fan diagram in the presence of a perpendicular magnetic field indicates various topological phases occurring at higher Chern numbers.

The ortho-para conversion of interstitial ${\mathrm{H}}_2$ in single-crystalline natural Si (${}^{\text{nat}}\mathrm{Si}$) and ${}^{29}\mathrm{Si}$ (enrichment 96.2%) is studied by Raman scattering. The conversion process was found to be practically independent of the isotope composition of Si. The characteristic ortho-to-para conversion time at 77 K was found to be $220\pm 35$ and $200\pm 35$ h for ${}^{29}\mathrm{Si}$ and ${}^{\text{nat}}\mathrm{Si}$, respectively, whereas at room temperature the back conversion occurs with a characteristic time of $8.8\pm 1.5$ and $10.5\pm 1.5$ h for ${}^{29}\mathrm{Si}$ and ${}^{\text{nat}}\mathrm{Si}$, respectively. These values agree very well with the transition rates found in previous IR absorption studies by Peng et al. for ${}^{\text{nat}}\mathrm{Si}$ [Phys. Rev. B 80, 125207 (2009)]. Our findings imply that an interaction of ${\mathrm{H}}_2$ with the nuclear spin of nearby ${}^{29}\mathrm{Si}$ has marginal, if any, effects on the ortho-para conversion rate of molecular hydrogen in silicon.

We investigate a spinful double quantum dot coupled to leads in a pseudospin valve configuration. The interplay of interaction and interference produces, in the stability diagram, a rich variety of current resonances modulated by the system parameters. In the presence of ferromagnetic leads and pseudospin anisotropy, those resonances split, turn into dips, and acquire a Fano shape, thus revealing a synthetic spin-orbit interaction induced on the double quantum dot. A set of rate equations derived for a minimal model captures those features. The model accurately matches the numerical results obtained for the full system in the framework of a generalized master equation and calculated within the next to leading order approximation.

The design of applications, especially those based on heterogeneous integration, must rely on detailed knowledge of material properties, such as thermal conductivity (TC). To this end, multiple methods have been developed to study TC as a function of vibrational frequency. Here, we compare three spectral TC methods based on velocity decomposition in homogenous molecular dynamics simulations: Green-Kubo modal analysis (GKMA), the spectral heat current (SHC) method, and a method we propose called homogeneous nonequilibrium modal analysis (HNEMA). First, we derive a convenient per-atom virial expression for systems described by general many-body potentials, enabling compact representations of the heat current, each velocity decomposition method, and other related quantities. Next, we evaluate each method by calculating the spectral TC for carbon nanotubes, graphene, and silicon. We show that each method qualitatively agrees except at optical phonon frequencies, where a combination of mismatched eigenvectors and a large density of states produces artificial TC peaks for modal analysis (MA) methods. Our calculations also show that the HNEMA and SHC methods converge much faster than the GKMA method, with the SHC method being the most computationally efficient. Finally, we demonstrate that our MA implementation in the Graphics Processing Units Molecular Dynamics code on a single graphics processing unit is over 1000 times faster than the existing implementation in the Large-scale Atomic/Molecular Massively Parallel Simulator code on one central processing unit.

From both a fundamental viewpoint and the perspective of wave-function engineering of an electron pumped by single-electron sources, it is important to understand how an electron gains energy while propagating along a time-dependent region in a quantum Hall channel. In our previous work, we experimentally observed that, when the electron travels through the time-dependent region before entering the pump, the pump current becomes substantially larger than the quantized value. We here present the results of a theoretical and experimental investigation of the mechanism underlying the heating of electrons traveling through a region of time-dependent potential induced by an rf signal. Using the Floquet scattering theory, we describe the energy distribution of the heated electrons, whose effective temperature can be substantially larger than the cryostat temperature. The behavior of the measured currents when the barrier height and the radio-frequency power are varied is in good qualitative agreement with the theoretical predictions.

A well-known property of aromatic molecules is their highly anisotropic response to an external magnetic field: the magnetic susceptibility parallel to the field is generally much larger than the in-plane components. This intriguing phenomenon is rationalized as a consequence of the delocalization of the itinerant electrons that populate the aromatic ring. In this work, we revisit the magnetism of aromatic molecules and show that if the interaction between the itinerant and bonding electrons is taken into account, a large enhancement of the molecule magnetic response takes place. The itinerant electrons are described by an extended Hubbard Hamiltonian with an effective momentum-momentum interaction between them which is mediated by the bonding electrons. For the particular case of a benzene molecule, our model reproduces the experimentally observed magnetic anisotropy.

We study analytically a current-biased topological Josephson junction supporting ${\mathbb{Z}}_n$ parafermions. First, we show that in an infinite-size system a pair of parafermions on the junction can be in $n$ different states; the $2\pi n$ periodicity of the phase potential of the junction results in a significant suppression of the maximum current $I_m$ for an insulating regime of the underdamped junction. Second, we study the behavior of a realistic finite-size system with avoided level crossings characterized by splitting $\delta$. We consider two limiting cases: when the phase evolution may be considered adiabatic, which results in the $2\pi$ periodicity of the effective potential, and the opposite case, when Landau-Zener transitions restore the $2\pi n$ periodicity of the phase potential. We also study the case with time-reversal symmetry and show that breaking this symmetry gives different phase periodicity reductions. resulting current $I_m$ is exponentially different in the opposite limits, which allows us to propose another detection method to establish the appearance of parafermions in the system experimentally, based on measuring $I_m$ at different values of the splitting $\delta$.

Carrier doping to the Mott insulator is essential to produce highly correlated metals with emergent properties. The pyrochlore ruthenates ${\mathrm{Pr}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ (Ru $4d$ electron number $n=4$) and ${\mathrm{Ca}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ ($n=3$) are a Mott insulator and a magnetic bad metal, respectively, due to the strong electron correlation. We investigate magnetotransport properties of ${\left({\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x\right)}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ in a whole band-filling range, $0\le x\le 1$. With increasing hole doping $x$, the system undergoes an insulator-metal transition. When ${\mathrm{Ca}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ is doped with electrons ($0.5<x<0.9$), the enhanced coupling among Ru $4d$ spins produces a ferromagnetic-metal phase with a large anomalous-Hall angle up to 2%. We discuss the electronic phase transitions in ${\left({\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x\right)}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ in view of Hund's metal.

A quantum spin-$\frac{1}{2}$ antiferromagnetic Heisenberg trimerized chain with strong intradimer and weak monomer-dimer coupling constants is studied using the many-body perturbation expansion, which is developed from the exactly solved spin-$\frac{1}{2}$ Ising-Heisenberg diamond chain preserving correlations between all interacting spins of the trimerized chain. It is evidenced that this perturbation approach is superior with respect to the standard perturbation scheme developed from a set of noninteracting spin monomers and dimers, and its accuracy even coincides, up to a moderate ratio of the coupling constants, with state-of-the-art numerical techniques. The Heisenberg trimerized chain shows the intermediate one-third plateau, which was also observed in the magnetization curve of the polymeric compound ${\mathrm{Cu}}_3{\left({\mathrm{P}}_2{\mathrm{O}}_6\mathrm{OH}\right)}_2$ affording its experimental realization. Within the modified strong-coupling method we have obtained the effective Hamiltonians for the magnetic field range from zero to the one-third plateau, and from the one-third plateau to the saturation magnetization. The unconventional second-order perturbation theory provides extremely accurate results for both critical fields of the intermediate one-third plateau up to a moderate ratio of the coupling constants as convincingly evidenced through a comparison with numerical density-matrix renormalization group data. It is shown that the derived effective Hamiltonian also provides at low enough temperatures sufficiently accurate results for magnetization curves and thermodynamic properties as corroborated through a comparison with quantum Monte Carlo simulations. Using the results for the effective Hamiltonian, we additionally suggest a straightforward procedure for finding the microscopic parameters of one-dimensional trimerized magnetic compounds with strong intradimer and weak monomer-dimer couplings. We found the refined values for the coupling constants of ${\mathrm{Cu}}_3{\left({\mathrm{P}}_2{\mathrm{O}}_6\mathrm{OH}\right)}_2$ by matching the theoretical results with the available experimental data for the magnetization and magnetic susceptibility in a wide range of temperatures and magnetic fields.