The recently discovered ramp reversal memory (RRM) is a nonvolatile memory effect observed in correlated oxides with temperature-driven insulator–metal transitions (IMT). It appears as a resistance increase at predefined temperatures that are set or erased by simple heating–cooling (i.e., ramp reversal) protocols. Until now RRM was measured for two materials: ${\mathrm{VO}}_2$ and ${\mathrm{NdNiO}}_3$. A heuristic model suggests that the RRM is caused by a local transition temperature increase at boundaries of spatially separated metallic and insulating domains during ramp reversal. However, there is no experimental measure of the magnitude of the effect, which is crucial for the development of a theoretical account of the RRM. Here we show that ${\mathrm{V}}_2{\mathrm{O}}_3$ also shows RRM, including all related features, highlighting the generality of the effect. Moreover, an analysis of the RRM as an effective (average) increase of the critical temperature provides a quantitative measure of its magnitude as a function of temperature and ramp reversal protocols. We provide clear evidence that the RRM is the outcome of a local increase in transition temperature of the microscopic-scale phase boundaries that are created during temperature ramp reversal (from heating to cooling) within the insulator–metal phase coexistence regime.

Hermitian bipartite models are characterized by the presence of chiral symmetry and by Lieb's theorem, which derives the number of zero-energy flat bands of the model from the imbalance of sites between its two sublattices. Here, we introduce a class of non-Hermitian models with an arbitrary number of sublattices connected in a unidirectional and cyclical way and show that the number of zero-energy flat bands of these models can be found from a generalized version of Lieb's theorem, in what regards its application to noninteracting tight-binding models, involving the imbalance between each sublattice and the sublattice of lowest dimension. Furthermore, these models are also shown to obey a generalized chiral symmetry, of the type found in the context of certain clock or parafermionic systems. The main results are illustrated with a simple toy model and possible realizations in different platforms of the models introduced here are discussed.

In spite of extensive works on non-Hermitian topology, interaction effects remain crucial questions. We analyze correlated non-Hermitian systems with special emphasis on the one-dimensional point-gap topology. Specifically, our analysis elucidates that interactions result in a reduction of the topological classification $\mathbb{Z}\times \mathbb{Z}\to \mathbb{Z}$ for systems of one synthetic dimension with charge $\mathrm{U}\left(1\right)$ symmetry and spin-parity symmetry. Furthermore, we analyze an extended Hatano-Nelson chain which exhibits striking interaction effects; interactions destroy the non-Hermitian skin effect at the noninteracting level. This fragility of the non-Hermitian skin effect against interactions is consistent with the reduction of the point-gap topology in the one spatial dimension. The above discoveries shed light on the topology of correlated systems and open up different directions for research on non-Hermitian topological physics.

We study the effect of the formation and screening of local magnetic moments on the temperature and interaction dependences of spectral functions and resistivity in the vicinity of the metal-insulator transition. We use dynamical mean-field theory for the strongly correlated Hubbard model and associate the peculiarities of the above-mentioned properties with those found for the local charge ${\chi }_c$ and spin ${\chi }_s$ susceptibilities. We show that at half filling the maximum of resistivity at a certain temperature $T^{*}$ corresponds to the appearance of a central quasiparticle peak of the spectral function and entering the metallic regime with well-defined fermionic quasiparticles. At the same time, the temperature of the crossover to the regime with screening of local magnetic moments, determined by the minimum of double occupation, is smaller than the temperature scale $T^{*}$ and coincides at half filling with the boundary $T_{\beta =1}\left(U\right)$ corresponding to the exponent of resistivity $\beta \equiv dln\rho /dlnT=1$. Away from half filling we find a weak increase of the temperature of the beginning and completion of the screening (i.e., Kondo temperature) of local magnetic moments, while the unscreened local magnetic moments exist only up to a few percent of doping. In the low-temperature regime $T<T_{\beta =1}$ the simultaneous presence of itinerant and localized degrees of freedom yields an almost linear temperature dependence of the scattering rate and resistivity.

Using the determinant quantum Monte Carlo method, we investigate the metal-insulator transition in the interacting disordered Hubbard model of a Lieb lattice in which the system characterizes the flat band centered at the Fermi level. By choosing suitable electron densities, we ensure the weak interaction sign problem to improve the reliability of our results. It is found that disorder and on-site Coulomb repulsive interaction produce interesting effects that induce the metal-insulator transition which is impossible in the half-filled case. The density of states at the Fermi energy is still finite in the thermodynamic limit, suggesting that the system is an Anderson insulator rather than a Mott insulator. Moreover, this doping system is paramagnetic, unlike the half-filled system which is ferrimagnetic.

Scar states are special many-body eigenstates that weakly violate the eigenstate thermalization hypothesis (ETH). Using the explicit formalism of the Lanczos algorithm, usually known as the forward scattering approximation in this context, we compute the Krylov state (spread) complexity of typical states generated by the time evolution of the PXP Hamiltonian, hosting such states. We show that the complexity for the Néel state revives in an approximate sense, while complexity for the generic ETH-obeying state always increases. This can be attributed to the approximate SU(2) structure of the corresponding generators of the Hamiltonian. We quantify such “closeness” by the $q$-deformed SU(2) algebra and provide an analytic expression of Lanczos coefficients for the Néel state within the approximate Krylov subspace. We intuitively explain the results in terms of a tight-binding model. We further consider a deformation of the PXP Hamiltonian and compute the corresponding Lanczos coefficients and the complexity. We find that complexity for the Néel state shows nearly perfect revival while the same does not hold for a generic ETH-obeying state.

We show theoretically that electromagnetic waves propagating in the transparency region of a noncentrosymmetric medium can induce a DC electric current. The origin of the effect is the Raman scattering of light by free carriers in the system. Due to the photon scattering, electrons undergo real quantum transitions resulting in the formation of their anisotropic momentum distribution and in shifts of electronic wave packets giving rise to a steady-state photocurrent. We present the microscopic theory of the Raman photogalvanic effect (RPGE) focusing on two specific situations: (i) generic case of a bulk gyrotropic semiconductor and (ii) a quantum well structure where the light is scattered by intersubband excitations. We uncover the relation of the predicted RPGE and the traditional photogalvanic effect at the light absorption.

We develop in this work a qualitative quantum electron transport model, in the strong light-matter coupling regime under dipole approximation, able to capture polaritonic signatures in the time-dependent electrical current. The effect of the quantized electromagnetic field in the displacement current of a resonant tunneling diode inside an optical cavity is analyzed. The original peaks of the bare electron transmission coefficient split into two new peaks due to the resonant electron-photon interaction, leading to coherent Rabi oscillations among the polaritonic states that are developed in the system in the strong coupling regime. This mimics known effects predicted by a Jaynes-Cummings model in closed systems and shows how a full quantum treatment of electrons and electromagnetic fields may open interesting paths for engineering new THz electron devices. The computational burden involved in the multi-time measurements of THz currents is tackled by invoking a Bohmian description of the light-matter interaction. We also show that the traditional static transmission coefficient used to characterize DC quantum electron devices has to be substituted by a new displacement current coefficient in high-frequency AC scenarios.

Coupling nontrivial topological physics to ferroelectricity in two-dimensional lattice is highly desirable in both fundamental research and devices applications. Here, using first-principles calculations, we report that in a multiferroic heterobilayer consisting of a antiferromagnetic layer MnSe and a ferroelectric layer ${\mathrm{In}}_2{\mathrm{S}}_3$, the typical type-III band alignment can be realized. Upon introduction of spin-orbit coupling, a band gap is created, giving rise to a nontrivial antiferromagnetic topological phase. By reversing ferroelectric polarization, the nontrivial antiferromagnetic topology of $\mathrm{MnSe}/{\mathrm{In}}_2{\mathrm{S}}_3$ can be annihilated, yielding a wide-gap antiferromagnetic semiconductor with trivial physics. It thus proves to be a feasible approach to realize purely electric-field control of antiferromagnetic topological physics in this heterobilayer. The physical mechanism of such phenomenon is further unveiled to be related to the interlayer charge transfer between the two layers. These findings shed light on the design and control of antiferromagnetic topological physics in two dimensions.

Transition-metal dichalcogenide (TMD) nanotubes with small band gap exhibit higher photocurrent than their layered counterparts [J. H. Smet and Y. Iwasa, Nature (London) 570, 349 (2019); X. Zhou et al., Small 15, 1902528 (2019)], but the mechanism remains unclear. Herein, using ${\mathrm{WS}}_2$ as an example, we revealed that the higher photovoltaic effect of the nanotubes originates from the quantum coherence between the band edges in the perspective of photogenerated carrier recombination. By using first-principles calculations and nonadiabatic molecular dynamics simulations, we revealed that small nonadiabatic coupling and short pure-dephasing time improve the photogenerated carrier lifetime and increase the photocurrent of ${\mathrm{WS}}_2$ nanotubes. Moreover, an extremum of carrier lifetime in ${\mathrm{WS}}_2$ nanotubes is found at a certain diameter, where the nanotube exhibits the longest carrier lifetime. The insights into the high photocurrent of TMD nanotubes may provide ideas for the design of advanced optoelectronic devices.

We investigate topological phases of monolayer jacutingaite (${\mathrm{Pt}}_2{\mathrm{HgSe}}_3$) that arise when considering the competing effects of spin-orbit coupling (SOC), magnetic exchange interactions, and staggered sublattice potential $V$. The interplay between the staggered potential and exchange field offers the possibility of attaining different topological phases. By analyzing the Berry curvatures and computing the Chern numbers and Hall conductivities, we demonstrate that the system is time-reversal-symmetry-broken quantum spin Hall insulator when $m_b<{\lambda }_{\mathrm{so}}$, where $m_b$ is the exchange field operating on the bottom Hg sublattice and ${\lambda }_{\mathrm{so}}$ is the intrinsic SOC. For $m_b>{\lambda }_{\mathrm{so}}$ and in the presence of Rashba SOC, we find that the band gap at valley $K\left(K^{\prime }\right)$ is topologically trivial (nontrivial) with Chern number $\mathcal{C}=1$ and valley Chern number ${\mathcal{C}}_v=-1$, indicating that the system is valley-polarized quantum anomalous Hall insulator. We show that the topology of each valley is swapped (the Chern number becomes $\mathcal{C}=-1$) by reversing the sign of the exchange field. The system transitions to a valley-polarized metal and quantum valley Hall phase as $V$ increases. Along the phase boundaries, we observe a single Dirac-cone semimetal states. These findings shed more light on the possibility of realizing and controlling topological phases in spintronics and valleytronics devices.

Graphene nanowrinkles (GNWs) are easily formed and manipulated by extrinsic perturbation in a continuous graphene nanosheet, which provides a suitable platform to study strain engineering. The deformation-induced pseudo-Landau levels (PLLs) and the wide bandgap states in GNWs were studied separately in different samples, which makes it hard to distinguish their difference, and the direct switch between them has not been observed yet. Here, using scanning tunneling microscopy (STM) tip manipulation, we realize the transition from PLL states to bandgap states through tuning the structure of the nanowrinkles in the same graphene nanosheet. Taking the close scan method, the GNWs are observed to be flattened with their PLL states turned off. Further applying a STM tip pulse, new nanowrinkles are rebuilt in the same graphene nanosheet. The distance between the ravine region of the newly formed GNWs and the substrate is dramatically shortened by the strong tip force. Therefore, the wide bandgap states are detected in the GNWs because of the resulting strong coupling of the substrate. Our result opens an avenue to engineer the quantum phenomena in strained graphene and provides more possibilities for the application of graphene nanostructures on microelectronic devices in the future.

Acoustic phonon transport is revealed as a potential radiation-to-conduction transition mechanism for single-digit nanometer vacuum gaps. To show this, we measure heat transfer from a feedback-controlled platinum nanoheater to a laterally oscillating silicon tip as the tip-nanoheater vacuum gap distance is precisely controlled from a single-digit nanometer down to bulk contact in a high-vacuum shear force microscope. The measured thermal conductance shows a gap dependence of $d^{-5.7\pm 1.1}$ in the near-contact regime, which is in good agreement with acoustic phonon transport modeling based on the atomistic Green's function framework. The obtained experimental and theoretical results suggest that acoustic phonon transport across a nanoscale vacuum gap can be the dominant heat transfer mechanism in the near- and asperity-contact regimes and can potentially be controlled by an external force stimuli.

We study the backaction of quantum measurements on heat transport through a two-level system by considering the continuous quantum measurement onto an eigenstate of the two-level system. For the nonselective measurement, the backaction appears as a dephasing effect on the two-level system. We formulate the heat current under the selective measurement with a stochastic master equation and show that the cross-correlation between the measurement outcomes and the heat current contains information on the backaction. We expect that our findings can be verified by using a platform of superconducting circuits.

The interaction of magnetic dipole (MD) emitters and common photonic cavities is usually weak, which is partially due to the low magnetic near-field enhancements of the cavities. Here, we show that whispering gallery modes (WGMs) of a subwavelength dielectric cavity can not only greatly boost the emission rate of a MD emitter but also bring efficient couplings between coherent MD emitters. In a WGM cavity, the maximal emission rate (${\gamma }_{\max }$) of a single emitter occurs at an antinode of the field pattern. The emission of the MD emitter can also be greatly affected by another coherent one depending on the magnetic-field response of the WGM. The maximal contribution can also reach ${\gamma }_{\max }$. Notably, the cooperative emission rate of the coherent MD emitters does not decay with distance in the considered range due to the high-quality feature of a WGM. In contrast to the emission, the absorption of an emitter is hardly affected by the coherent couplings between emitters mediated by a WGM. The difference between the performances of emission and absorption is highly related to the excitation behaviors of WGMs. Our results are important for enhanced magnetic light-matter interactions.

The detection of Majorana zero modes still remains elusive after extensive searches. The current debates focus on the experimental observation of large zero-bias peaks (ZBPs) near $2e^2/h$ in tunneling conductance. These large ZBPs, induced by Andreev bound states, mimic the Majorana signature and suggest that new diagnostic tools or experimental knobs are highly desired. In this paper, we introduce an interaction effect on these large ZBPs using a weakly dissipative probe. By increasing temperature ($T$), we establish that these large ZBPs can reveal a zero-bias conductance increase, a non-Fermi-liquid behavior due to the environmental Coulomb blockade. This observation forms a sharp contrast to nondissipative devices where ZBPs follow a Fermi-liquid $T$ dependence. Our results open prospects for a better understanding of large ZBPs induced by Andreev bound states and hold relevance for future Majorana detection.

Experimental determinations of the net Berry curvature have been made for the occupied band because they are basically available on the basis of electronic and magnetic responses of carriers occupying the band, for instance, through the measurement of the anomalous Hall effect or the magneto-optical Kerr effect. Here, we investigate the circular dichroism of the high-order harmonic generation (HHG) in undoped monolayer ${\mathrm{MoS}}_2$. Breaking the threefold rotational symmetry of the pristine monolayer ${\mathrm{MoS}}_2$ by applying uniaxial strain and an external bias field, we find that the third-order HHG signals deliver nonvanishing dichroic signatures. These signatures are essentially identical as the net Berry curvatures obtained from the electron-doped monolayer ${\mathrm{MoS}}_2$ with the aforementioned symmetry broken. This finding implies an experimental challenge to observe the net Berry curvature of the unoccupied empty band, which should open another stage toward the advancement of valleytronics.

We study how crystal size influences magnetic ordering in arrays of molecular nanomagnets coupled by dipolar interactions. Compressed fluid techniques have been applied to synthesize crystals of ${\mathrm{Mn}}_6$ molecules (spin $S=12$) with sizes ranging from $28\mu \mathrm{m}$ down to 220 nm. The onset of ferromagnetic order and the spin thermalization rates have been studied by means of ac susceptibility measurements. We find that the ordered phase remains ferromagnetic, as in the bulk, but the critical temperature $T_{\mathrm{c}}$ decreases with crystal size. Simple magnetostatic energy calculations, supported by Monte Carlo simulations, account for the observed drop in $T_{\mathrm{c}}$ in terms of the minimum attainable energy for finite-sized magnetic domains limited by the crystal boundaries. Frequency-dependent susceptibility measurements give access to the spin dynamics. Although magnetic relaxation remains dominated by individual spin flips, the onset of magnetic order leads to very long spin thermalization time scales. The results show that size influences the magnetism of dipolar systems with as many as ${10}^{11}$ spins and are relevant for the interpretation of quantum simulations performed on finite lattices.

Supercurrent transport is experimentally studied in a Josephson junction hosting a double quantum dot (DQD) with tunable symmetries. The QDs are parallel coupled to two superconducting contacts and can be tuned between strong interdot hybridization and a ring geometry where hybridization is suppressed. In both cases, we observe supercurrents when the two interacting orbitals are either empty or filled with spins, or a combination. However, when each QD hosts an unpaired spin, the supercurrent depends on the spin ground state. It is strongly suppressed for the ring geometry with a spin-triplet ground state at zero external magnetic field. By increasing the QD hybridization, we find that a supercurrent appears when the ground state changes to spin singlet. In general, supercurrents are suppressed in cases of spin-doublet ground state, but an exception occurs at orbital degeneracy when the system hosts one additional spin, as opposed to three, pointing to a broken particle-hole symmetry.

We study hydrodynamic electron magnetotransport in graphene devices. We show that in these systems a distinct mechanism of magnetoresistance appears which is absent in systems with Galilean-invariant electron liquid. The resulting magnetoresistance depends on the intrinsic conductivity and viscosity of the electron liquid, and becomes especially pronounced near charge neutrality. We obtain analytic expressions for magnetotransport coefficients of Corbino devices and obtain estimates for the electrical and thermal magnetoresistances for monolayer and bilayer systems at charge neutrality. Magnetoresistance becomes strong (of order $100\%$) at relatively weak fields, at which the kinetic coefficients of the electron liquid are practically unaffected by the magnetic field.