In this paper, we consider analytically the density evolution of a spinless Fermi liquid with a nonlinear dispersion relation into which one particle is injected. The interaction is pointlike and the temperature is zero. We obtain a formula for the evolution of the density and discuss the picture it gives as well as the physics behind it. Compared to the case of a linear spectrum, we find further and more complex fractionalization of the initial density hump: it splits into three humps instead of two; moreover, all three change their shapes in a complicated manner. We analyze the mechanisms of these phenomena and calculate their main characteristics. We also show that the fractionalization can be illustrated from a semiclassical point of view.

In this paper, we use the thermodynamically consistent and conserving self-energy embedding theory (SEET) to study the spectra of the prototypical undistorted cubic perovskites ${\mathrm{SrVO}}_3$ and ${\mathrm{SrMnO}}_3$. In the strongly correlated metallic ${\mathrm{SrVO}}_3$ we find that the usual attribution of the satellite peaks at –1.8 eV to Hund or Hubbard physics in the $t_{2g}$ orbitals is inconsistent with our calculations. In the strongly correlated insulator ${\mathrm{SrMnO}}_3$ we recover insulating behavior due to a feedback effect between the strongly correlated orbitals and the weakly correlated environment. Our calculation shows a systematic convergence of spectral features as the space of strongly correlated orbitals is enlarged, paving the way to a systematic parameter-free study of correlated perovskites.

The close similarity of silicon and germanium, isoelectronic group-IV elements, makes the integration of Ge layers on Si substrates suitable for technology development, but the atomic and electronic structures of ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ surfaces are still an open issue, in particular, for the alloy systems where Si is deposited on the Ge substrate. In this study, utilizing low-energy electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy using synchrotron radiation, we demonstrate that the formation mechanisms of the Si-on-Ge structures are controlled by two interface phenomena, namely Si indiffusion and Ge segregation on top of this surface. Employing these phenomena and controlling the Si quantity, one can synthesize the well-defined crystalline Ge-(2 × 1)/${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$/Ge(100) stacks where the number of Si atoms at the host Ge lattice sites can be tuned. Using the obtained data on the atomic and electronic structures of such systems, we also propose a method for interface engineering of Ge/Si/Ge stacks with tailored properties as promising templates for growing the device junctions.

We theoretically analyze dominant plasma modes in a two-dimensional disk of electron gas by calculating the absorption of an incident electromagnetic wave. The problem is solved in a self-consistent approximation, taking into account electromagnetic retardation effects. We use the Drude model to describe the conductivity of the system. The absorption spectrum exhibits a series of peaks corresponding to the excitation of plasma waves. The position and linewidth of the peaks designating, respectively, the frequency and damping rate of the plasma modes. We estimate the influence of retardation effects on the frequency and linewidth of the fundamental (dipole) and axisymmetric (quadrupole) plasma modes both numerically and analytically. We find the net damping rate of the modes to be dependent on not only the sum of the radiative and collisional decays but also their intermixture, even for small retardation. We show that the net damping rate can be noticeably less than that determined by collisions alone.

We construct an effective Floquet lattice model for the triangular network that emerges in interlayer-biased minimally twisted bilayer graphene and which supports two chiral channels per link for a given valley and spin. We introduce the Floquet scheme with the one-channel triangular network and subsequently extend it to the two-channel case. From the bulk topological index (winding number) and finite system calculations, we find that both cases host anomalous Floquet insulators (AFIs) with a different gap-opening mechanism. In the one-channel network, either time-reversal or in-plane inversion symmetry has to be broken to open a gap. In contrast, in the two-channel network, interchannel coupling can open a gap without breaking these symmetries yielding a valley AFI with counterpropagating edge states. This phase is topologically trivial with respect to the total winding number but robust in the absence of intervalley scattering. Finally, we demonstrate the applicability of the Floquet model with magnetotransport calculations.

Due to the presence of many-body interactions, strong enhancement effects of heat flux and rich thermophysical phenomena are possible. In this work, we build a many-particle radiative heat transfer model inside a cavity consisting of two graphene sheets. By introducing an additional particle and the graphene cavity in the near field, the heat transfer between two particles is discussed. We show that the mutual interactions greatly enhance the heat exchange and observe an interference fringe pattern. Moreover, the nonreciprocal plasmons on the drift-biased graphene provide a rotational degree of freedom to control the heat transfer and can be used to effectively rectify the thermal energy. Our findings extend recent progress in understanding and tailoring energy exchange in the many-body systems.

We compute scattering rates for electrons in the two-dimensional Hubbard model for a one-orbital metal and Mott insulator and a two-orbital band insulator by means of dynamical mean-field theory (DMFT) and the Boltzmann scattering equation (BSE), which for the considered equilibrium scattering rates is equivalent to second order perturbation theory. As an intermediate method between both, we also consider the BSE without momentum conservation. In the weak interaction regime and for the band insulator, the last two agree to very good accuracy. The BSE with momentum conservation, on the other hand, shows slightly larger scattering rates, and a momentum differentiation of these on the Fermi surface. For the Mott insulator at strong interaction, the DMFT electron scattering rates are much larger and defy a BSE description. Noteworthy, the scattering rates for the band insulator are exceedingly small because—in contrast to the Mott insulator—impact ionization is not mediated by strong (density-density) Coulomb matrix elements.

Non-Hermitian skin effects and exceptional points are topological phenomena characterized by integer winding numbers. In this study, we give methods to theoretically detect skin effects and exceptional points by generalizing inversion symmetry. The generalization of inversion symmetry is unique to non-Hermitian systems. We show that parities of the winding numbers can be determined from energy eigenvalues on the inversion-invariant momenta when generalized inversion symmetry is present. The simple expressions for the winding numbers allow us to easily analyze skin effects and exceptional points in non-Hermitian bands. We also demonstrate the methods for (second-order) skin effects and exceptional points by using lattice models.

We have carried out quantum Monte Carlo (QMC) calculations of silicon crystal focusing on the accuracy and systematic biases that affect the electronic structure characteristics. The results show that 64 and 216 atom supercells provide an excellent consistency for extrapolated energies per atom in the thermodynamic limit for ground, excited, and ionized states. We have calculated the ground state cohesion energy with both systematic and statistical errors below $\approx 0.05$ eV. The ground state exhibits a fixed-node error of only 1.3(2)% of the correlation energy, suggesting an unusually high accuracy of the corresponding single-reference trial wave function. We obtain a very good agreement between optical and quasiparticle gaps that affirms the marginal impact of excitonic effects. Our most accurate results for band gaps differ from the experiments by about 0.2 eV. This difference is assigned to a combination of residual finite-size and fixed-node errors. We have estimated the crystal Fermi level referenced to vacuum that enabled us to calculate the edges of valence and conduction bands in agreement with experiments.

Theoretical descriptions of Yu-Shiba-Rusinov (YSR) states induced by magnetic impurities inside the gap of a superconductor typically rely on a classical spin model or are restricted to spin-$\frac{1}{2}$ quantum spins. These models fail to account for important aspects of YSR states induced by transition-metal impurities, including the effects of higher quantum spins coupled to several conduction-electron channels, crystal or ligand-field effects, and magnetic anisotropy. We introduce and explore a zero-bandwidth model, which incorporates these aspects, is readily solved numerically, and analytically tractable in several limiting cases. The principal simplification of the model is to neglect Kondo renormalizations of the exchange couplings between impurity spin and conduction electrons. Nevertheless, we find excellent correspondence in those cases, in which we can compare our results to existing numerical-renormalization-group calculations. We apply the model to obtain and understand phase diagrams as a function of pairing strength and magnetic anisotropy as well as subgap excitation spectra. The single-channel case is most relevant for transition-metal impurities embedded into metallic coordination complexes on superconducting substrates, while the multichannel case models transition-metal adatoms.

A microscopic calculation is presented for the spin-transfer torques (STTs) and damping torques in metallic antiferromagnets (AFs). It is found that the sign of the STT is opposite to that in ferromagnets (FMs) because of the AF transport character, and the current-to-STT conversion factor is enhanced near the AF gap edge. The dissipative torque parameter ${\beta }_n$ and the damping parameter ${\alpha }_n$ for the Néel vector arise from spin relaxation of electrons. Physical consequences are demonstrated for the AF domain wall motion using collective coordinates, and some similarities to the FM case are pointed out such as intrinsic pinning and the specialty of ${\alpha }_n={\beta }_n$. A recent experiment on a ferrimagnetic GdFeCo near its angular-momentum compensation temperature is discussed.

We characterize non-Hermitian band structures by symmetry indicator topological invariants. Enabled by crystalline inversion symmetry, these indicators allow us to short-cut the calculation of conventional non-Hermitian topological invariants. In particular, we express the three-dimensional winding number of point-gapped non-Hermitian systems, which is defined as an integral over the whole Brillouin zone, in terms of symmetry eigenvalues at high-symmetry momenta. Furthermore, for time-reversal symmetric non-Hermitian topological insulators, we find that symmetry indicators characterize the associated Chern-Simons form, whose evaluation usually requires a computationally expensive choice of smooth gauge. In each case, we discuss the non-Hermitian surface states associated with nontrivial symmetry indicators.

Interaction induced topological states remain one of the most fascinating phenomena in condensed matter physics. The exciton condensate has recently sparked renewed interest due to the discovery of new candidate materials and its driving force to realize exotic topological states. In this work, we explore the exciton order induced high-order topology in the bilayer quantum spin Hall insulators and find that the topological excitonic corner states can be realized by tuning the gate and magnetic field. When an in-plane Zeeman field is applied to the system, two or four excitonic boundary-obstructed corner states emerge in the bilayer system for distinct possible $s$-wave excitonic pairings. Besides, we also find a two-dimensional excitonic Weyl nodal phase, which supports flat band edge states connecting the bulk Weyl nodes.

Photodoping of Mott insulators or correlated metals can create an unusual metallic state which simultaneously hosts holelike and electronlike particles. We study the dynamics of this state up to long times, as it passes its kinetic energy to the environment. When the system cools down, it crosses over from a bad metal into a resilient quasiparticle regime, in which quasiparticle bands are formed with separate Fermi levels for electrons and holes, but quasiparticles do not yet satisfy the Fermi-liquid paradigm. Subsequently, the transfer of energy to the environment slows down significantly, and the system does not reach the Fermi-liquid state even on the timescale of picoseconds. The transient photodoped strange metal exhibits unusual properties of relevance for ultrafast charge and heat transport: In particular, there can be an asymmetry in the properties of electrons and holes, and strong correlations between electrons and holes, as seen in the spectral properties.

We report the dielectric, magnetic, and ultrasonic properties of a one-dimensional organic salt $\mathrm{TTF}\text{−}{\mathrm{QBr}}_3\mathrm{I}$. These indicate that $\mathrm{TTF}\text{−}{\mathrm{QBr}}_3\mathrm{I}$ shows a ferroelectric spin-Peierls (FSP) state in a quantum critical regime. In the FSP state, coupling of charge, spin, and lattice leads to emergent excitation of spin solitons as topological defects. Amazingly, the solitons are highly mobile even at low temperatures, although they are normally stationary because of pinning. Our results suggest that strong quantum fluctuations enhanced near a quantum critical point enable soliton motion governed by athermal relaxation. This indicates the realization of quantum topological transport at ambient pressure.

Multicomponent quantum Hall effect, under the interplay between intercomponent and intracomponent correlations, leads us to new emergent topological orders. Here, we report the theoretical discovery of fractional quantum hall effect of strongly correlated Bose-Fermi mixtures classified by the $\mathbf{K}=\left(\begin{array}{cc}m& 1\\ 1& n\end{array}\right)$ matrix (even $m$ for boson and odd $n$ for fermion), using topological flat band models. Utilizing the state-of-the-art exact diagonalization and density-matrix renormalization group methods, we build up the topological characterization based on three inherent aspects: (i) topological $(mn-1)$-fold ground-state degeneracy equivalent to the determinant of the $\mathbf{K}$ matrix; (ii) fractionally quantized topological Chern number matrix equivalent to the inverse of the $\mathbf{K}$ matrix; and (iii) two parallel-propagating chiral edge branches with level counting 1,2,5,10 consistent with the conformal field theory description.

Two-dimensional (2D) semiconducting multiferroics that can effectively couple magnetic and polarization $\left(P\right)$ orders have great interest for both fundamental research and technological applications in nanoscale, which are, however, rare in nature. In this paper, we propose a general mechanism to realize semiconducting 2D multiferroics via van der Waals (vdW) heterojunction engineering, as demonstrated in a typical heterostructure consisting of magnetic bilayer $\mathrm{Cr}{\mathrm{I}}_3\left(bi\text{-Cr}{\mathrm{I}}_3\right)$ and ferroelectric monolayer ${\mathrm{In}}_2{\mathrm{Se}}_3$. Interestingly, the novel indirect orbital coupling between $\mathrm{Se}4p$ and $\mathrm{Cr}3d$ orbitals, intermediated by the interfacial $\mathrm{I}5p$ orbitals, is switchable in the opposite $P$ configurations, resulting in an unexpected mechanism of strong asymmetrical magnetoelectric coupling. Therefore, along with the noticeable ferroelectric energy barrier induced by ${\mathrm{In}}_2{\mathrm{Se}}_3$, the realization of opposite magnetic orders in opposite $P$ configurations can eventually result in the novel multiferroicity in $bi\text{−}{\mathrm{CrI}}_3/{\mathrm{In}}_2{\mathrm{Se}}_3$. Finally, we demonstrate that our mechanism can generally be applied to design other vdW multiferroics even with tunable layer thickness.

We show with a recently devised extended first-principles molecular dynamics method that calculated Hugoniots of poly-$\alpha$-methylstyrene agree well with precision experimental results of Kritcher et al. [Nature (London) 584, 51 (2020)] and Döppner et al. [Phys. Rev. Lett. 121, 025001 (2018)]. The deviation is smaller than 0.8%. This agreement does not sensitively rely on the approximations in the employed first-principles methods as long as underlying physics are well described, as illustrated in the calculation of equation of state for polystyrene covering the warm dense regime. These results may stimulate a broad range of quantitative investigations on warm dense matter that were not thought possible before, and may thus afford a new prospect to the field of inertial confinement fusion and high-energy-density physics.