The central issue for practical applications of the anomalous valley Hall effect (AVHE) is the tunable and nonvolatile nature of the valley splitting. We predict a type of ferrovalley material, Janus $1T-\mathrm{CrO}X (X=\mathrm{F},\mathrm{Cl},\mathrm{Br},\mathrm{I})$, in which the switching effect of the AVHE can be achieved by adjusting the biaxial strain or building a multiferroic heterostructure $\mathrm{CrO}X/{\mathrm{In}}_2{\mathrm{Se}}_3$. Stable out of plane magnetization in $\mathrm{CrO}X$ induces the valley splitting which can reach to 112 meV in the CrOBr monolayer. Interestingly, we find that the valley splitting of CrOCl is robust against the biaxial strain both in the conduction band and the valence band. In contrast, the valley splitting of the CrOBr at the conduction band can be linearly modulated, while it has a switching response at the valence band due to the strong orbital hybridization induced by compressive strain, so a reversible switch of the AVHE can be achieved. Furthermore, the electric reversible valley splitting switch is also obtained in multiferroic van der Waals heterostructure $\mathrm{CrOCl}/{\mathrm{In}}_2{\mathrm{Se}}_3$, and the reversible switch of the AVHE can also be manipulated by controlling the polarization states of the ferroelectric layer. The AVHE in $\mathrm{CrO}X$ can be readily switched on or off by either applying biaxial strain or reversing the ferroelectric polarization of the substrate ${\mathrm{In}}_2{\mathrm{Se}}_3$, which may be a promising application in the field of valleytronics.

Measurements of the energy relaxation in the integer quantum Hall edge at filling factor $\nu =2$ suggest the breakdown of heat current quantization [H. le Sueur et al., Phys. Rev. Lett. 105, 056803 (2010)]. It was shown in a hydrodynamic model that dissipative neutral modes contributing apparently less than a quantum of heat can be an explanation for the missing heat flux [A. Goremykina et al., arXiv:1908.01213]. This hydrodynamic model relies on the introduction of an artificial high-energy cutoff and lacks a way of a priori obtaining the correct definition of the heat flux. In this work we overcome these limitations and present a formalism, effectively modeling dissipation in the quantum Hall edge, proving the quantization of heat flux for all modes. We mapped the quantum Hall edge to a transmission line by analogy and used the Langevin equations and scattering theory to extract the heat current in the presence of dissipation.

In the metal/degenerately doped silicon bilayer structure, the interfacial flexoelectric effect due to strain gradient leads to charge carrier transfer from metal layer to the silicon layer. This excess charge carrier concentration is called flexoelectronic doping or flexoelectronic charge transfer, which gives rise to an electronically polarized (order of magnitude larger than ferroelectric materials) silicon layer. In the transport measurements, the charge carrier concentration in silicon is found to increase by two orders of magnitude due to flexoelectronic doping, which changes the Fermi level and the Hall response. The flexoelectronic charge accumulation modifies the electron-electron and the electron-phonon coupling, which gives rise to Mott metal-insulator transition and magnetism of phonons, respectively. The coexistence of flexoelectronic polarization and magnetism gives rise to a class of materials called electronic multiferroics or magnetoelectronics. By controlling the flexoelectronic doping, material behavior can potentially be engineered for quantum, spintronics, and electronics applications in semiconductor materials.

Spin-1/2 chains with alternating antiferromagnetic (AFM) and ferromagnetic (FM) couplings have attracted considerable interest due to the topological character of their spin excitations. Here, using density functional theory and density-matrix renormalization-group (DMRG) methods, we have systematically studied the dimerized chain system ${\mathrm{Na}}_2{\mathrm{Cu}}_2{\mathrm{TeO}}_6$ with a $d^9$ electronic configuration. Near the Fermi level, in the nonmagnetic phase the dominant states are mainly contributed by the Cu $3d_{x^2-y^2}$ orbitals highly hybridized with the O $2p$ orbitals, leading to an “effective” single-orbital low-energy model. By calculating the relevant hoping amplitudes, we explain the size and sign of the exchange interactions in ${\mathrm{Na}}_2{\mathrm{Cu}}_2{\mathrm{TeO}}_6$. In addition, a single-orbital Hubbard model is constructed for this dimerized chain system where the quantum fluctuations are taken into account. Both AFM and FM couplings (leading to an $\uparrow \text{−}\downarrow \text{−}\downarrow \text{−}\uparrow$ state) along the chain were found in our DMRG and Lanczos calculations, in agreement with density functional theory and neutron-scattering results. The hole pairing binding energy $\mathrm{\Delta }E$ is predicted to be negative at Hubbard $U\sim 11\mathrm{eV}$, suggesting incipient pairing tendencies.

We present detailed high-resolution angle-resolved photoemission experiments on $\mathrm{V}{\mathrm{Se}}_2$ grown under various conditions. The surface electronic structure optimally grown samples can host high-temperature spectral kink, quasiparticle peak, and the Fermi gap. Collective observation of these electronic features refers to the strong electronic correlation and is usually attributed to the characteristics of superconductors. Temperature evolution of the quasiparticle peak and the Fermi gap also follow the trend observed in high-$T_c$ superconductors as progressive quenching of the quasiparticle peak at a lower temperature than the complete Fermi gap closing. As a result, the quasiparticle peak can be observed up to 100 $\pm$5 K while the Fermi gap persists up to $\sim$150 K. These realizations can guide future studies to induce high-temperature superconductivity in transition metal dichalcogenides as well as understand the physics behind high-$T_c$ superconductors.

Motivated by the intriguing physics of quasi-two-dimensional fermionic systems, such as high-temperature superconducting oxides, layered transition metal chalcogenides, or surface or interface systems, the development of many-body computational methods geared at including both local and nonlocal electronic correlations has become a rapidly evolving field. It has been realized, however, that the success of such methods can be hampered by the emergence of noncausal features in the effective or observable quantities involved. Here, we present an approach wherein local many-body techniques such as dynamical mean-field theory (DMFT) are extended to nonlocal correlations and interactions, which preserves causality and has a physically intuitive interpretation. Our strategy has implications for the general class of DMFT-inspired many-body methods and can be adapted to cluster, dual boson, or dual fermion techniques with minimal effort.

We develop a theory of cavity quantum electrodynamics for a two-dimensional electron gas in the presence of Rashba spin-orbit and Zeeman couplings and perpendicular magnetic field, coupled to a spatially nonuniform quantum photon field. We show that the superradiant quantum phase transition (SQPT), also known as photon condensation, can, in principle, occur through a pure in-plane Zeeman coupling, but it requires extremely small (unrealistic) quantum well widths or extremely fine tuning of the effective Landé factor which makes two Landau levels coincide. Landau-level crossings can also be induced by the Rashba spin-orbit coupling and they promote the SQPT, which can be obtained for certain values of the effective Landé factor and filling factors.

To study excitonic effects on high-harmonic generation (HHG) in Mott insulators, we investigate pumped nonequilibrium dynamics in the one-dimensional extended Hubbard model. By employing time-dependent calculations based on the exact diagonalization and infinite time-evolving block decimation methods, we find the strong enhancement of the HHG intensity around the exciton energy. The subcycle analysis in the sub-Mott-gap regime shows that the intensity region of the time-resolved spectrum around the exciton energy splits into two levels and oscillates following the driving electric field. This excitonic dynamics is qualitatively different from the dynamics of free doublon and holon but favorably contributes to HHG in the Mott insulator.

The pursuit for clearly identifiable signatures of viscous electron flow in the solid state systems has been a paramount task in the search of the hydrodynamic electron transport behavior. In this work, we investigate theoretically the nonlocal electric and thermal resistances for the generic non-Galilean-invariant electron liquids in the multiterminal Hall-bar devices in the hydrodynamic regime. The role of the device inhomogeneity is carefully addressed in the model of the disorder potential with the long-range correlation radius. We obtain analytic expressions for the thermoelectric resistances that are applicable in the full crossover regime from charge neutrality to high electron density. We show that the vortical component of the electron flow manifests in the thermal transport mode close to the charge neutrality where vorticity is already suppressed by the intrinsic conductivity in the electric current. This behavior can be tested by the high-resolution thermal imaging probes.

We study the influence of the inverse proximity effect on the nucleation of superconductivity in planar hybrid structures consisting of a thin superconducting film proximity coupled to a material with a strong exchange or Zeeman field and the Rashba spin-orbit interaction. Based on numerical simulations and analytical estimates within the framework of the Gor'kov equations, we find the superconducting transition temperature of the system and determine the spatial structure of the gap function. It is shown that the spin-orbit interaction partially compensates the pair-breaking effect of the exchange or Zeeman field and stabilizes modulated superconducting states, which can be traced to the Lifshitz invariant in the Ginzburg-Landau free-energy density. The suggested approach provides a microscopic justification of this invariant for a large class of superconducting hybrid systems and clarifies the validity range of the corresponding phenomenological models with terms linear in the spatial gradients of the superconducting order parameter.

The van der Waals interface and interfacial reconstruction between two-dimensional (2D) transition-metal dichalcogenides (TMDCs) and metal electrodes significantly influence their device performance. During the growth of $\mathrm{Mo}{\mathrm{S}}_2$ and $\mathrm{W}{\mathrm{S}}_2$ on metals, the participation of sulfur atoms leads to the Au(100) surface forming a ${\mathrm{Au}}_4{\mathrm{S}}_4@\mathrm{Au}\left(100\right)\text{−}\left(2\sqrt{2}\times 2\sqrt{2}\right)R{45}^{\circ }$ reconstructed phase [Luo et al., Nat. Commun. 11, 1011 (2020)]. To reveal the nature of the reconstructed interface interactions, here we perform a comparative study for Au/TMDCs junctions with and without Au(100) surface reconstruction by density-functional theory calculations. Metal-induced gap states are apparent in the unreconstructed junction, while with reconstruction, significant quasi-bonding-induced gap states (QBIGSs) appear above the valence band maximum of TMDCs, which are antibonding states from the quasi-bonding interaction at the ${\mathrm{Au}}_4{\mathrm{S}}_4$/TMDCs interface. The QBIGS favors the formation of $p$-type contacts and significantly reduce the $p$-type Schottky barrier height (SBH). It is anticipated that QBIGS commonly exist at the chalcogenide-reconstructed metal/TMDCs junctions. This study opens a different route for $p$-type SBH reduction in metal/2D TMDCs junctions.

Achieving effective tuning of glass structures between distinct states is intriguing for fundamental studies and applications, but has previously turned out to be challenging in practice. High-entropy metallic glasses (HEMGs), as an emerging type of metallic glasses (MGs) based on the high-entropy effect, are expected to have more disordered and frustrated chemical short-range structure compared with conventional MGs. Therefore, HEMGs may offer possibilities for structure and properties tuning in glasses. In this work, we employ pressure as a tuning parameter and monitor the atomic structural evolution of a senary HEMG, ${\mathrm{Ti}}_{16.7}{\mathrm{Zr}}_{16.7}{\mathrm{Hf}}_{16.7}{\mathrm{Cu}}_{16.7}{\mathrm{Ni}}_{16.7}{\mathrm{Be}}_{16.7}$, up to ∼40 GPa using in situ synchrotron x-ray diffraction. Analysis of its structure factor in reciprocal space and reduced pair distribution function in real space both reveal a pressure-induced structural crossover at ∼20 GPa with a dramatic change in short-range order (SRO), while no similar phenomenon is observed in a conventional MG, ${\mathrm{Cu}}_{36}{\mathrm{Zr}}_{64}$, as a control sample, suggesting the pressure-induced highly tunable SRO in HEMGs originates from the local chemical complexity, namely, the high-entropy effect. These results confirm that enhanced flexibility and tunability of atomic structures could be achieved by introducing the high-entropy effect into MGs. Therefore, configurational entropy could be another dimension for exploring MGs with highly tunable structures and properties for various potential applications.

While global quantum quench has been extensively used in the literature to understand the localization-delocalization transition for the one-dimensional quantum spin chain, the effect of geometric quench (which corresponds to a sudden change of the geometry of the chain) in the context of such transitions is yet to be well understood. In this work, we investigate the effect of geometric quench in the Aubry-André model, which supports localization-delocalization transition even in one dimension. We study the spreading of the entanglement and the site occupation with time and find many interesting features that can be used to characterize localization-delocalization transition. We observe that geometric quench causes a power-law type growth of the entanglement entropy in the delocalized phase in contrast to the linear growth which is found in the global quench studies. We also find that the saturation values in the many-body localized (MBL) phase obey area law in contrast to the usual volume law, which is a signature feature of the MBL phase in the context of global quench. This area law can also be understood from the long time site-occupation profile in the MBL phase.

The layered crystal structures of cuprates enable collective charge excitations fundamentally different from those of three-dimensional metals. Acoustic plasmons have been observed in electron-doped cuprates by resonant inelastic x-ray scattering (RIXS); in contrast, the characteristics of acoustic plasmons in hole-doped cuprates are under debate, despite extensive measurements. This contrast led us to investigate the charge excitations of hole-doped cuprate ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$. Here we present incident-energy-dependent RIXS measurements and calculations of collective charge response via the loss function to reconcile the issues above. Our results provide evidence for the acoustic plasmons of Zhang-Rice singlet (ZRS), which has a character of the Cu $3d_{x^2-y^2}$ strongly hybridized with the O $2p$ orbitals; the metallic behavior is implied to result from the movement of ZRS rather than the simple hopping of O $2p$ holes.

In order to explore the effects of structural geometry on the properties of correlated metals we investigate the magnetic properties of cubic ($3C$) and hexagonal ($4H$) ${\mathrm{BaRuO}}_3$. While the $3C$ variant of ${\mathrm{BaRuO}}_3$ is ferromagnetic below 60 K, the $4H$ phase does not show any long-range magnetic order, though, there is experimental evidence of short-range antiferromagnetic correlations. Employing a combination of computational tools, namely, density-functional theory and dynamical mean-field theory calculations, we probe the origin of contrasting magnetic properties of ${\mathrm{BaRuO}}_3$ in the $3C$ and $4H$ structures. Our study reveals that the difference in connectivity of ${\mathrm{RuO}}_6$ octahedra in the two phases results in different Ru-O covalency, which in turn influences substantially the strengths of screened interaction values for Hubbard $U$ and Hund's rule $J$. With estimated $U$ and $J$ values, the $3C$ phase turns out to be a ferromagnetic metal, while the $4H$ phase shows paramagnetic behavior with vanishing ordered moments. However, this paramagnetic phase bears signatures of antiferromagnetic correlations, as confirmed by a calculation of the magnetic susceptibility. We find that the $4H$ phase is found to be at the verge of antiferromagnetic long-range order, which can be stabilized upon slight changes of screened Coulomb parameters $U$ and $J$, opening up the possibility of achieving a rare example of an antiferromagnetic metal.

This paper explores the behavior of systems of cold fermions as they approach unitary above the critical temperature. Symmetry arguments indicate that at unitarity the Fermi-liquid picture breaks down. As we move away from unitarity, by decreasing the scattering length, the dilaton, the Goldstone boson resulting from the spontaneous breaking of Schrodinger symmetry by the Fermi sea, becomes gapped. At energies below this gap, the interaction between quasiparticles will be dominated by dilaton exchange. The dilaton mass can, in turn, be related via anomaly matching to the scattering length and contact parameter within the confines of a systematic expansion. We use this relation to predict that the quasiparticle width is given by the expression $\mathrm{\Gamma }(E,T)=\frac{8m}{9\pi {\tilde{\mathcal{C}}}^2}(\sqrt{\frac{m}{m^{★}}}\frac{a{\mu }_F^2}{4\hslash E_F^2}{)}^2(E^2+{\pi }^2{k}_B^2{T}^2)$ where $a$ is the the scattering length, $m_{★}$ is the effective mass, and $\tilde{\mathcal{C}}$ is the dimensionless contact parameter. This prediction is valid for ${\left(\frac{E_F}{E}\right)}^2\gg a{k}_f\gg 1$.

We theoretically study the quenching of a charge-density wave phase in a model system of a quasi-two-dimensional material, which includes both electron-hole and electron-phonon interactions leading, respectively, to excitonic and coherent-phonon contributions. We discuss how interaction processes affect anomalous expectation values and present a microscopic dynamical picture of the quenching of the phase. We use projection techniques to illustrate the time-dependent appearance of additional bands and anomalous expectation values. We propose an optical amplification effect with a high modulation frequency in the midinfrared regime.

Magnetized plasma as a topological material has been demonstrated recently. However, a comprehensive description of the bulk-edge correspondence in magnetized plasma is still lacking. In this work, we systematically reveal all types of anomalous bulk-edge correspondence in magnetized plasma. The bulk-edge correspondence can be formally restored by avoiding the unphysical response at the large wave number when the spatial cutoff of magnetized plasma is appropriately considered. Remarkably, a different type of dual-band topologically protected edge states is uncovered when the bulk-edge correspondence is restored. The topology of the dual-band system is verified by the stable propagation of edge waves around defects. The topological wave division of the dual-band edge states is realized by designing a four-channel junction. Our work may provide more flexibility for multiband and multichannel photonic devices.

A quantum thermal transistor controls the flow of thermal energy through two of its terminals in response to an external input signal on its third terminal. In recent years, several realizations of thermal transistors combining individual quantum systems have been proposed using temperatures or optical fields as the control signals. The success of the electronic transistor in modern technology partly lies in its ability to combine and make multi-transistor systems with enhanced flow control capability or even wholly different behaviors. Hence, as the next natural step, we investigate the intricacies of building composite systems combining multiple quantum thermal transistors. We identify that the interconnects of thermal transistors play a critical role in these systems by facilitating energy exchange from one transistor to another. By isolating the exact functionality of these interconnects, we develop a simple model that still captures all its essential characteristics. This model shows that directly coupling transistors allows a substantial energy transfer between them only under highly restrictive conditions. We then develop the energy divider formalism where a single properly tuned quantum harmonic oscillator acts as an intermediary between the transistors. We demonstrate that the oscillator mediates a substantial energy exchange under a considerably relaxed set of conditions and illustrate its operating principles through detailed quantum mechanical state analysis. We compare our energy divider based interconnect against the previously developed intermediate bath method and confirm that both ways achieve similar thermal energy flow rates between the transistors over a broad range of operating temperatures. At the same time, replacing an intermediate bath made up of a large number of harmonic oscillators with a single oscillator avoids many of the theoretical and practical limitations of the earlier method. For instance, time-domain simulations show that the energy divider based interconnect responds far faster to an external excitation than the corresponding intermediate bath based system. We believe the energy divider formalism provides valuable insights into the nature of thermal energy transfer within quantum thermal systems.