The application of voltage pulse in a scanning tunneling microscope has been demonstrated to induce dehydrogenation on hydrogenated silicene/Ag(111), recovering intact silicene phases. This manipulation provides us a method to build a relationship between various silicene phases and their hydrogenated structures. Combining with density-functional theory calculations, hydrogenation of silicene-$\left(\surd 13\times \surd 13\right)R13.9^{\circ }$ is found to produce the same half silicane as hydrogenated silicene-$\left(2\surd 3\times 2\surd 3\right)R{30}^{\circ }$. These two silicene phases are suggested to be the same monolayer silicene on Ag(111), albeit with different Si buckling configurations and lattice strains. Our study not only reveals the hydrogenated structure of silicene-$\left(\surd 13\times \surd 13\right)R13.9^{\circ }$, but also offers significant potential for lithography and modification of hydrogenated silicene at atomic scale for future design of silicene-based electronic devices.

Excited states of spin chains play an important role in condensed matter physics. We present a method of calculating the single magnon excited states of the Heisenberg spin chain that can be efficiently implemented on a quantum processor for small spin chains. Our method involves finding the stationary points of the energy vs wave-number curve. We implement our method for four-site and eight-site Heisenberg Hamiltonians using numerical techniques as well as using an IBM quantum processor. Finally, we give insight into the circuit complexity and scaling of our proposed method.

$M\mathrm{P}{X}_3$ ($M=\mathrm{metals}$; $X=\mathrm{S}\mathrm{or}\mathrm{Se}$) represents a large family of van der Waals (vdW) materials featuring P-P dimers of $\sim 2.3\AA$ separation. A dramatic alteration of its electrical transport properties, such as metal-insulator transition, has not been realized by intentional chemical doping and ionic intercalation. Here, we employ an entropy-enhancement strategy to successfully obtain a series of medium-entropy $M\mathrm{P}{\mathrm{Se}}_3$ $(M=\mathrm{Fe},\mathrm{Mn},\mathrm{Cd},\mathrm{and}\mathrm{In})$, in which the electrical and magnetic properties change simultaneously. Lone-pair electrons of P emerge due to the dissociation of the dimers as evidenced by a 35% elongation in the P-P interatomic distance. The band gap widens from 0.1 to 0.7 eV by this dissociation. Under external physical pressure up to $\sim 50$ GPa, a giant collapse of up to 15% in the $c$ axis happens, which is in contrast to the in-plane shrinkage of their counterparts $\mathrm{Fe}/\mathrm{MnP}{\mathrm{Se}}_3$. It leads to the recombination of ${\mathrm{P}}^{3-}$ with lone-pair electrons into a P-P dimer and the smallest bulk modulus of 28 GPa in $M\mathrm{P}{X}_3$. The medium-entropy $M\mathrm{P}{\mathrm{Se}}_3$ transitions from a spin-glass insulator to metal, and to superconductor, which is rarely observed in $M\mathrm{P}{X}_3$. Our findings highlight the P-P dimer as an indicator to probe diverse electronic structure and the effectiveness of entropy enhancement in materials science.

Kagome metals $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A$ = K, Rb, and Cs) are recently discovered platforms featuring an unusual charge-density-wave (CDW) order and superconductivity. The electronic band structure of a kagome lattice can host both flat bands as well as Dirac-like bands, offering the possibility to stabilize various quantum states. Here, we probe the band structure of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ via Shubnikov–de Haas quantum oscillations on both bulk single crystals and thin flakes. Although our frequency spectra are broadly consistent with the published data, we unambiguously reveal the existence of new frequencies with large frequencies ranging from $\sim 2085$ to $\sim 2717$ T in thin flakes when the magnetic field is along the $c$ axis. These quasi-two-dimensional frequencies correspond to $\sim 52\%$ to 67% of the CDW-distorted Brillouin-zone volume. The Lifshitz-Kosevich analysis further uncovers surprisingly small cyclotron effective masses, of the order of $\sim 0.1m_e$ for these frequencies. Consequently, a large number of high-velocity carriers exists in the thin flake of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. Comparing with our band-structure calculations, we argue that an orbital-selective modification of the band structure is active. Our results provide indispensable information for understanding the fermiology of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, paving a way for understanding how an orbital-selective mechanism can become an effective means to tune its electronic properties.

We have studied the electronic structure of $\mathrm{Cs}{\mathrm{W}}_2{\mathrm{O}}_6$ across its metal-insulator transition by means of hard/soft x-ray photoelectron spectroscopy. In the high-temperature metallic phase, the W $5d$ band exhibits a clear Fermi edge. The W $4f_{7/2}$ and $4f_{5/2}$ core-level peaks are accompanied by shoulders on their lower binding energy side. The shoulder and main peaks, respectively, are attributed to the well- and poorly screened final states where the screening is due to the W $5d$ electronic states in the vicinity of the chemical potential. In going from 300 to 180 K (across the metal-insulator transition), a band gap of about 0.2 eV is created at the Fermi level. The origin of the band gap can be assigned to the trimerization of the W sites. The W $4f$ and $5d$ spectra exclude the possibility of charge disproportionation and suggest moderate electronic correlation effects.

The Hubbard model is a longstanding problem in the theory of strongly correlated electrons and a very active one in the experiments with ultracold fermionic atoms. Motivated by current and prospective quantum simulations, we apply a two-dimensional tensor network—an infinite projected entangled pair state—evolved in imaginary time by the neighborhood tensor update algorithm working directly in the thermodynamic limit. With $\mathrm{U}\left(1\right)\times \mathrm{U}\left(1\right)$ symmetry and the bond dimensions up to 29, we generate thermal states down to the temperature of 0.17 times the hopping rate. We obtain results for spin and charge correlators, unaffected by boundary effects. The spin correlators—measurable in prospective ultracold atoms experiments attempting to approach the thermodynamic limit—provide evidence of disruption of the antiferromagnetic background with mobile holes in a slightly doped Hubbard model. The charge correlators reveal the presence of hole-doublon pairs near half filling and signatures of hole-hole repulsion on doping. We also obtain specific heat in the slightly doped regime.

Disorder in a proximitizing bulk superconductor can scatter quasiparticles in a putative topological superconductor and eventually destroy the topological superconducting state. We use a scattering approach and a random-matrix calculation to estimate the disorder scattering time in a topological Josephson junction. We find that the disorder scattering rate from the bulk of the superconductor, even in the strong-coupling limit, is suppressed in the ratio of Fermi momenta between the semiconductor and superconductor. This suppression of disorder scattering is accompanied by near-perfect Andreev reflection at such semiconductor-superconductor interfaces, which can be used as a signature of such clean proximity effect. We also find that these results can be understood by a semiclassical estimate of scattering. We discuss limits in other systems such as the semiconductor nanowire where disorder scattering is suppressed according to similar classical estimates.

Based on the Bogoliubov–de Gennes equations, we investigate the transport of the Josephson current in a $\mathrm{S}/f_L-{\mathrm{F}}_1-f_C-{\mathrm{F}}_2-f_R/\mathrm{S}$ junction, where S and ${\mathrm{F}}_{1,2}$ are superconductors and ferromagnets, and $f_{L,C,R}$ are the left, central, and right spin-active interfaces. These interfaces have noncollinear magnetizations, and the azimuthal angles of the magnetizations at the $f_{L,C,R}$ interfaces are ${\chi }_{L,C,R}$. We demonstrate that, if both the ferromagnets have antiparallel magnetizations, the critical current oscillates as a function of the exchange field and the thickness of the ferromagnets for particular ${\chi }_L$ or ${\chi }_R$. By contrast, when the magnetization at the $f_C$ interface is perpendicular to that at the $f_L$ and $f_R$ interfaces, the critical current reaches a larger value and is hardly affected by the exchange field and the thickness. Interestingly, if both the ferromagnets are converted to antiparallel half-metals, the critical current maintains a constant value and rarely changes with the ferromagnetic thicknesses and the azimuthal angles. At this time, an anomalous supercurrent can appear in the system, in which case the Josephson current still exists even if the superconducting phase difference $\varphi$ is zero. This supercurrent satisfies the current-phase relation $I=I_{c}sin(\varphi +{\varphi }_0)$ with $I_c$ being the critical current and ${\varphi }_0=2{\chi }_C-{\chi }_L-{\chi }_R$. We deduce that the additional phase ${\varphi }_0$ arises from phase superposition, where the phase is captured by the spin-triplet pairs when they pass through each spin-active interface. In addition, when both the ferromagnets are transformed into parallel half-metals, the $f_C$ interface never contributes any phase to the supercurrent and ${\varphi }_0={\chi }_R-{\chi }_L+\pi$. In such a case, the current-phase relation is similar to that in a $\mathrm{S}/f_L-\mathrm{F}-f_R/\mathrm{S}$ junction.

The concept of higher-order topology has prompted the development of topological insulators, and a series of theoretical and experimental schemes have been proposed and realized to demonstrate higher-order hinge or corner states. While these ideas thrive in topological semimetals such as higher-order Dirac or Weyl semimetals, other degeneracy types such as nodal lines or nodal loop semimetals still remain to be fully exploited. In this work we consider a setup that hosts an acoustic springlike higher-order nodal-line semimetal protected by a screw-rotational symmetry. The underlying sandwich architecture is engineered with different coupling modes between different layers to construct a specific space group configuration, which enables the emergence of higher-order nodal lines in momentum space. Numerical calculations of the band dispersion show that nodal lines in opposite directions result in linked double hinge arcs. A corresponding topological invariant index is introduced to characterize the different topological phases. Furthermore, a propagation simulation of hinge and surface waves in a multilayer sample is performed that matches well with theoretical computations. Our work thus presents a higher-order nodal-line semimetal in an acoustic crystal and may receive practical applications in manufacturing sonic devices.

We carried out systematic magnetotransport measurements to study the magnetic phase diagram of ${\mathrm{PrMn}}_{1-x}{\mathrm{Sb}}_2$, where two antiferromagnetic orders associated with the moments of Pr and Mn coexist. When the magnetic field ($H$) was applied parallel to the crystallographic $c$ axis, we found a tricritical point where a first-to-second order changeover takes place as in ordinary metamagnets. On the other hand, the metamagnetic transition field decreased unexpectedly with decreasing the temperature at low temperatures for $H\parallel \left[110\right]$. Further, the transition line associated with the metamagnetic transition terminated at low temperature, where a multicritical point was formed. Starting from a three-dimensional phase diagram predicted from a simple model and modifying it to fit our experimental results, we argue that the magnetic interaction between the two magnetic elements is responsible for forming the new critical point and influences the shape of the phase boundaries.

We develop a stochastic path-integral approach for predicting the superconducting transition temperatures of anharmonic solids. By defining generalized Bloch basis, we generalize the formalism of the stochastic path-integral approach, which is originally developed for liquid systems. We implement the formalism for ab initio calculations using the projector augmented-wave method, and apply the implementation to estimate the superconducting transition temperatures of metallic deuterium and hydrogen sulfide. For metallic deuterium, which is approximately harmonic, our result coincides well with that obtained from the standard approach based on the harmonic approximation and the density functional perturbation theory. For hydrogen sulfide, we find that anharmonicity strongly suppresses the predicted superconducting transition temperature. Compared to the self-consistent harmonic approximation approach, our approach yields a transition temperature closer to the experimentally observed one.

We have applied ${}^{27}\mathrm{Al}$ nuclear magnetic resonance (NMR) spectroscopy to investigate the iron-based aluminide of $\mathrm{Ba}{\mathrm{Fe}}_2{\mathrm{Al}}_9$. This material has been a subject of current interest due to indications of charge density wave behavior below the transition temperature $T_C\simeq 100$ K. Two sets of the ${}^{27}\mathrm{Al}$ NMR resonance lines that are associated with two nonequivalent crystallographic aluminum sites have been well resolved. We have discussed the obtained electric field gradient and anisotropic Knight shift for each individual aluminum site, revealing the strong $ab$ plane bonding configuration for the structural properties of $\mathrm{Ba}{\mathrm{Fe}}_2{\mathrm{Al}}_9$. Pronounced features in the isotropic Knight shift and nuclear spin-lattice relaxation rate have been observed in the vicinity of $T_C$. Furthermore, the detailed ${}^{27}\mathrm{Al}$ NMR analyses have provided evidence for the decrease of the electronic density of states upon lowering temperature below $T_C$.

We study the boundary theory of the ${\mathbb{Z}}_N$ X-cube model using a continuum perspective, from which the exchange statistics of a subset of bulk excitations can be recovered. We discuss various gapped boundary conditions that either preserve or break the translation and rotation symmetries on the boundary, and further present the corresponding ground-state degeneracies on $T^2\times I$. The low-energy physics is highly sensitive to the boundary conditions: even the extensive part of the ground-state degeneracy can vary when different sets of boundary conditions are chosen on the two boundaries. We also examine the anomaly inflow of the boundary theory and find that the X-cube model is not the unique $(3+1)$-dimensional theory that cancels the 't Hooft anomaly of the boundary.

We present here a theoretical method to determine the phononic contribution to the thermal conductance of nanoscale systems in the phase-coherent regime. Our approach makes use of classical molecular dynamics (MD) simulations to calculate the temperature-dependent dynamical matrix, and the phononic heat conductance is subsequently computed within the Landauer-Büttiker formalism with the help of nonequilibrium Green's function techniques. Tailored to nanostructures, crucial steps of force constant and heat transport calculations are performed directly in real space. As compared to conventional density functional theory (DFT) approaches, the advantage of our method is twofold. First, interatomic interactions can be described with the method of choice. Semiempirical potentials may lead to large computational speedups, enabling the study of much larger systems. Second, the method naturally takes into account the temperature dependence of atomic force constants, an aspect that is ignored in typical static DFT-based calculations. We illustrate our method by analyzing the temperature dependence of the phononic thermal conductance of gold (Au) chains with lengths ranging from 1 to 12 atoms. Moreover, in order to evaluate the importance of anharmonic effects in these atomic-scale wires, we compare the phase-coherent approach with nonequilibrium MD (NEMD) simulations. We find that the predictions of the phase-coherent method and the classical NEMD approach largely agree above the Debye temperature for all studied chain lengths, which shows that heat transport is coherent and that our phase-coherent approach is well suited for such nanostructures.

In the last decades, dynamical mean-field theory (DMFT) and its diagrammatic extensions have been successfully applied to describe local and nonlocal correlation effects in correlated electron systems. Unfortunately, except for the exact solution, it is impossible to fulfill both the Pauli principle and conservation laws at the same time. Consequently, fundamental observables such as the kinetic and potential energies are ambiguously defined. In this work, we propose an approach to overcome the ambiguity in the calculation of the potential energy within the ladder dynamical vertex approximation ($\mathrm{D}\mathrm{\Gamma }\mathrm{A}$) by introducing an effective mass renormalization parameter in both the charge and the spin susceptibility of the system. We then apply our method to the half-filled single-band Hubbard model on a three-dimensional bipartite cubic lattice. We find (i) at weak-to-intermediate coupling, a reasonable modification of the transition temperature $T_{\mathrm{N}}$ to the antiferromagnetically ordered state with respect to previous ladder $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$ calculations without charge renormalization. This is in good agreement with dual fermion and Monte Carlo results; (ii) the renormalization of charge fluctuations in our new approach leads to a unique value for the potential energy which is substantially lower than corresponding ones from DMFT and non-self-consistent ladder $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$; and (iii) the hierarchy of the kinetic energies between the DMFT and the ladder $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$ in the weak coupling regime is restored by the consideration of charge renormalization.

The optical selection rules of an electron system under a magnetic field play key roles in determining its optical properties, from which the band structures and underlying symmetries can be derived. In this paper, based on a three-dimensional strong topological insulator model describing ${\mathrm{ZrTe}}_5$, we study the Landau levels (LLs) and magneto-optical conductivity under an in-plane magnetic field. We reveal that in the transverse conductivity $\mathrm{Re}\left({\sigma }_{zz}\right)$, the unconventional optical selection rules $n\to n\pm 2$ dominate, with $n$ being the LL index. We attribute the unconventional selection rules to the peculiar distribution of parity carried by the LLs, resulting from the chiral symmetry of the sub-Hamiltonians. Moreover, we predict that, if the strong anisotropic system is tuned to be nearly isotropic, the LLs would redistribute and the conventional selection rules $n\to n\pm 1$ can be recovered.

${\mathrm{Mn}}_3\mathrm{Sn}$ is a fascinating kagome metal exhibiting anomalous Hall effect, spin Hall effect, and anomalous Nernst effect. Using density functional theory plus dynamical mean-field theory ($\mathrm{DFT}+\mathrm{DMFT}$), we investigate the electronic structures of ${\mathrm{Mn}}_3\mathrm{Sn}$ in the paramagnetic and noncollinear antiferromagnetic (NAFM) states. In the paramagnetic state, ${\mathrm{Mn}}_3\mathrm{Sn}$ has intermediate electronic correlation strength and exhibits typical features of kagome metals including flat bands, Dirac points, and saddle points. In the NAFM state, $\mathrm{DFT}+\mathrm{DMFT}$ calculations reproduce well the experimental Mn magnetic moment and angle-resolved photoemission spectroscopy measurements. Electronic correlation shifts the bands around $E_F$ and moves the Weyl point between $K$ and $M$ points from $\sim 40\mathrm{meV}$ above $E_F$ in DFT calculations to $\sim 5\mathrm{meV}$ below $E_F$, which can strongly enhance the anomalous Hall effect and chiral anomaly observed in ${\mathrm{Mn}}_3\mathrm{Sn}$. More importantly, we find that the existence of the Weyl point along the $K\text{−}M$ path depends strongly on the ordering pattern of the Mn moments in the NAFM state, which implies that the exotic properties arising from the Weyl points in ${\mathrm{Mn}}_3\mathrm{Sn}$ can be manipulated by tuning the ordering pattern of the Mn moments in the NAFM state.

A common experimental setup to study light-matter interactions consists of semiconducting crystals placed in a metallic cavity that can support confined photons. In that case, the regime of strong coupling can be achieved provided that the semiconducting crystal supports excitons of large oscillatory strength. Here the coupling between transverse-electric cavity-photons and excitons in crystalline ${\mathrm{C}}_{60}$ films of different thicknesses is studied in the framework of the quantum-electrodynamical Bethe-Salpeter equation. The binding strength is characterized by the Rabi splitting $\mathrm{\Omega }$ of exciton-polaritons as a function of a number of crystal layers $N$ in the van der Waals heterostructures. For the considered nanocavity system a transition from the weak ($\mathrm{\Omega }=50\mathrm{meV}$) to the strong ($\mathrm{\Omega }=350\mathrm{meV}$) coupling with an increasing number of layers N is obtained. This layer-dependent effect seems to be universal, since we also estimate an enhancement of exciton-photon binding energy by a factor of $\sim 4$ in hBN multilayers. With this we show that a few nanometer thick two-dimensional heterostructures can significantly modify the zero-point fluctuation energy of cavity photons, which may have many fundamental and practical consequences within the field of light-matter interactions.

The on-site Coulomb repulsion $U$ is the key ingredient for describing the magnetic properties of Mott insulators, leading to a popular belief that many limitations of the density-functional theory based methods can be cured by artificially incorporating such on-site interactions for localized electrons in the model form. The layered antiferromagnet $\mathrm{Na}\mathrm{Mn}{\mathrm{Cl}}_3$ reveals quite a different story: while the Coulomb $U$ on the Mn sites controls the strength of antiferromagnetic superexchange interactions, an equally important parameter is the Stoner coupling ${\mathcal{I}}_{\mathrm{Cl}}$ on the ligand sites. The latter is responsible for large ferromagnetic contributions to the interatomic exchange interactions, which in $\mathrm{Na}\mathrm{Mn}{\mathrm{Cl}}_3$ nearly cancel the effect of the superexchange interactions. Although such behavior is anticipated from the phenomenological Goodenough-Kamanori-Anderson rules, the quantitative description of the ligand-related contributions remains disputable. Considering $\mathrm{Na}\mathrm{Mn}{\mathrm{Cl}}_3$ as an example, we discuss how they can be generally taken into account in the linear response theory to regain the dependence of the exchange interactions on ${\mathcal{I}}_{\mathrm{Cl}}$. The problem is complicated by the fact that, for the nearly filled Cl $3p$ shell, the parameters ${\mathcal{I}}_{\mathrm{Cl}}$ are sensitive to the model assumptions.