We analyze the transport properties of a Cooper pair splitter device composed of two-point electrodes in contact with a ferromagnetic/superconductor (F/S) junction constructed on the surface of a topological insulator (TI). For the pair potential in the S region, we consider $s$- and $d$-wave symmetries, while for the F region, we focus on a magnetization vector normal to the TI surface. Nonlocal transport along the F/S interface is mediated by chiral Majorana edge states, with chirality controlled by the polarization of the magnetization vector. We demonstrate that crossed Andreev reflections slowly decay with the separation of the electrodes in standard clean samples. Our system exhibits a maximum Cooper-pair-splitting efficiency of 80% for a symmetrical voltage configuration, even in high-temperature superconductor devices.

Steady current in metals induces a thermal gradient, a phenomenon known as the Peltier effect. The Peltier effect is one of the fundamental phenomena in the thermoelectric properties of materials and is also used in applications such as refrigerators. In this work, we show that an analogous phenomenon occurs by phonons in a noncentrosymmetric insulator, e.g., ferroelectrics, subject to linearly polarized light. Under light illumination, an energy current of phonons occurs through a nonlinear optical effect similar to the bulk photovoltaic effect. We formulate the nonlinear Peltier coefficient of the energy current carried by phonon photocurrent using nonlinear response theory. From the general formula, we show that the phonon photocurrent occurs only in a noncentrosymmetric system with two or more optical phonon bands. We demonstrate the generation of the energy current using a one-dimensional ion chain with three ions in a unit cell, which predicts the generation of an experimentally observable energy current using available THz-infrared light sources.

The search for hidden orders in photoexcited lattice systems is an active research field driven by experimental reports of light-induced or light-stabilized phases. In this study, we investigate hidden electronic orders in strongly correlated two-orbital Hubbard models with orbital-dependent bandwidths. In equilibrium, the half-filled systems are antiferromagnetically ordered. Using nonequilibrium dynamical mean field theory we demonstrate the appearance of nonthermal ferromagnetic order in the photodoped state, if the two bandwidths are sufficiently different, and its coexistence with spin-singlet $\eta$ superconductivity in the high photodoping region. Spin-triplet $\eta$-superconducting order appears instead if the two bandwidths are comparable. The rich nonequilibrium phasediagram uncovered in this work shows that Mott insulating multiorbital systems provide an interesting platform for the realization of nonthermal electronic orders.

The newly discovered high-$T_c$ nickelate superconductor ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ has generated significant research interest. To uncover the pairing mechanism, it is essential to investigate the intriguing interplay between the two $e_g$, i.e., $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Here we conduct an infinite projected entangled-pair state (iPEPS) study of the bilayer $t\text{−}J$ model, directly in the thermodynamic limit and with orbitally selective parameters for $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, respectively. The $d_{x^2-y^2}$ electrons exhibit significant intralayer hopping $t_{\parallel }$ (and spin couplings $J_{\parallel }$) as well as strong interlayer $J_{\perp }$ passed from the $d_{z^2}$ electrons. However, the interlayer $t_{\perp }$ is negligible in this case. In contrast, the $d_{z^2}$ orbital demonstrates strong interlayer $t_{\perp }$ and $J_{\perp }$, while the inherent intralayer $t_{\parallel }$ and $J_{\parallel }$ are small. Based on the iPEPS results, we find clear orbital-selective behaviors in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. The $d_{x^2-y^2}$ orbitals exhibit robust superconductive (SC) order driven by the interlayer coupling $J_{\perp }$, while the $d_{z^2}$ band shows relatively weak SC order as a result of small $t_{\parallel }$ (lack of coherence) but large $t_{\perp }$ (strong Pauli blocking). Furthermore, by substituting rare-earth element Pm or Sm with La, we find an enhanced SC order, which opens up a promising avenue for discovering nickelate superconductors with even higher $T_c$.

It is well known that the thermal conductance of Abelian integer and fractional quantum Hall (QH) states is quantized and is determined by the net and total chirality of downstream and upstream modes. We furthermore demonstrate that the finite frequency noise of the heat current of the Abelian particle and holelike states is quantized when the system size is smaller than the thermal equilibration length. It is shown that the finite frequency noise of the heat current is a universal and independent physical quantity, which provides information about the microscopic structure of edge excitations.

This study scrutinizes one-dimensional three-boson systems with on-site interactions, delving into perturbation theory, continuous-time quantum walks, and quantum Fisher information (QFI), among other areas. Notably, two critical on-site interaction strength points emerge. At these specific locations, the QFI reaches its zenith, exhibiting a proportionality to $t^4$. This substantively amplifies the precision in measuring both the Newtonian constant of gravitation and the Eötvös parameter. The improvement surpasses models devoid of on-site interactions by 6 orders of magnitude. The methodology used to measure big $G$ can be adapted to quantify the Casimir energy of a many-particle system.

We use atomistic simulations to examine the sliding dynamics of a skyrmion in a two-dimensional system containing a periodic one-dimensional stripe pattern of variations between low and high values of the perpendicular magnetic anisotropy. The skyrmion changes in size as it crosses the interface between two anisotropy regions. On applying combined dc and ac driving in either parallel or perpendicular directions, we observe a wide variety of Shapiro steps, Shapiro spikes, and phase-locking phenomena. The phase-locked orbits have two-dimensional dynamics due to the gyrotropic or Magnus dynamics of the skyrmions and are distinct from the phase-locked orbits found for strictly overdamped systems. Along a given Shapiro step when the ac drive is perpendicular to the dc drive, the velocity parallel to the ac drive is locked while the velocity in the perpendicular direction increases with increasing drive to form Shapiro spikes. At the transition between adjacent Shapiro steps, the parallel velocity jumps up to the next step value, and the perpendicular velocity drops. The skyrmion Hall angle shows a series of spikes as a function of increasing dc drive, where the jumps correspond to the transition between different phase-locked steps. At high drives, the Shapiro steps and Shapiro spikes are lost. When both the ac and dc drives are parallel to the stripe periodicity direction, Shapiro steps appear, while if the dc drive is parallel to the stripe periodicity direction and the ac drive is perpendicular to the stripe periodicity, then there are only two locked phases, and the skyrmion motion consists of a combination of sliding along the interfaces between the two anisotropy values and jumping across the interfaces.

Magnonic topological phases realize chiral edge spin waves that are protected against backscattering, potentially enabling highly efficient spin transport. Here we show that the spin transport through these magnonic chiral edge states can be electrically manipulated by non-Hermitian control. We consider the paradigmatic magnon Haldane model and show that it is transformed into an effective non-Hermitian magnon Chern insulator by including a sublattice-dependent spin-orbit torque. In linear spin-wave theory, this electrically induced torque reduces the damping of the chiral edge magnons along certain edge directions, leading to an enhancement of the spin-wave amplitude. This prediction is confirmed by numerical simulations based on the Landau-Lifshitz-Gilbert equation. For a spin-wave transport setup, in which magnons are excited by a microwave field and detected with a normal metal conductor, we find that the magnon amplification is remarkably robust against disorder, establishing non-Hermitian control as a promising avenue for topological magnonics.

We study the $N$ fracton problem in classical mechanics, with fractons defined as point particles that conserve multipole moments up to a given order. We find that the nonlinear Machian dynamics of the fractons is characterized by late-time attractors in position-velocity space for all $N$, despite the absence of attractors in phase space dictated by Liouville's theorem. These attractors violate ergodicity and lead to nonequilibrium steady states, which always break translational symmetry, even in spatial dimensions where the Hohenberg-Mermin-Wagner-Coleman theorem for equilibrium systems forbids such breaking. We provide a conceptual understanding of our results using an adiabatic approximation for the late-time trajectories and an analogy with the idea of “order-by-disorder” borrowed from equilibrium statistical mechanics. Altogether, these fracton systems host a paradigm for Hamiltonian dynamics and nonequilibrium many-body physics.

Phonon properties of realistic materials are routinely calculated within the density functional perturbation theory (DFPT). This is a semiclassical approach where the atoms are assumed to oscillate along classical trajectories immersed in the electronic Kohn–Sham system. In this paper, we demonstrate that, in metals, nonadiabatic effects induce a deviation of the DFTP phonon frequencies from the quantistic solution of the Dyson equation—a deviation that increases with the phonon energy width, reflecting the breakdown of the semiclassical DFPT description. The final message is that nonadiabatic phonon effects can be described only by using a fully quantistic approach.

A recent experiment on the bulk compound $4Hb\text{−}{\mathrm{TaS}}_2$ reveals an unusual time-reversal symmetry-breaking superconducting state that possesses a magnetic memory not manifest in the normal state. Here we provide a mechanism for this observation by studying the magnetic and electronic properties of $4Hb\text{−}{\mathrm{TaS}}_2$. We discuss the criterion for a small magnetization in the normal state in terms of spin and orbital magnetizations. Based on an analysis of lattice symmetry and Fermi surface structure, we propose that $4Hb\text{−}{\mathrm{TaS}}_2$ realizes superconductivity in the interlayer, equal-spin channel with a gap function whose phase winds along the Fermi surface by an integer multiple of $6\pi$. The enhancement of the magnetization in the superconducting state compared to the normal state can be explained if the state with a gap winding of $6\pi$ is realized, accounting for the observed magnetic memory. We discuss how this superconducting state can be probed experimentally by spin-polarized scanning tunneling microscopy.

We investigate the formation of magnetic polarons in the Kondo lattice model. Calculations are done in the framework of the bond particle formalism. We show that the quasiparticles correspond to spin polarons with a $\mathbf{k}$-dependent spatial extent. Polaron formation leads to a significant enhancement of the effective mass in the heavy parts of the band structure.

A quantum many-body system subject to unitary evolution and repeated local measurements with an increasing rate undergoes a measurement-induced entanglement transition from extensive (or subextensive) to area law entropy scaling. We find that certain open boundary systems under “generalized monitoring,” consisting of “projective monitoring” and conditional feedback, display an anomalous late-time particle concentration on the edge, reminiscent of the “skin effect” in non-Hermitian systems. Such feedback-induced skin effect will suppress the entanglement generation, rendering the system short-range entangled without measurement-induced entanglement transition. While initially emerged in noninteracting models, such skin effect can also occur in chaotic interacting systems and Floquet quantum circuits subjected to random generalized measurements. Since the dynamics of the skin effect do not require postselection and can be observed at the particle number level, the phenomenon is experimentally relevant and accessible in noisy intermediate-scale quantum platforms, such as trapped ions.

A one-parameter family of invertible states gives a topological transport phenomenon, similar to the Thouless pumping. As a natural generalization of this, we can consider a family of invertible states parametrized by some topological space $X$. This is called a higher pump. It is conjectured that a $(1+1)$-dimensional bosonic invertible state parametrized by $X$ is classified by ${\mathrm{H}}^3(X;\mathbb{Z})$. In this paper, we construct two higher pumping models parametrized by $X=\mathbb{R}{P}^2\times S^1$ and $X=\mathrm{L}(3,1)\times S^1$ that corresponds to the torsion part of ${\mathrm{H}}^3(X;\mathbb{Z})$. As a consequence of the nontriviality as a family, we find that a quantum mechanical system with a nontrivial discrete Berry phase is pumped to the boundary of the $(1+1)$-dimensional system. We also study higher pump phenomena by using matrix product states, and construct a higher pump invariant which takes value in a torsion part of ${\mathrm{H}}^3(X;\mathbb{Z})$. This is a higher analog of the ordinary discrete Berry phase that takes value in the torsion part of ${\mathrm{H}}^2(X;\mathbb{Z})$. In order to define the higher pump invariant, we utilize the smooth Deligne cohomology and its integration theory. We confirm that the higher pump invariant of the model has a nontrivial value.

Organic molecular materials are potential high-performance thermoelectric materials. Theoretical understanding of thermoelectric conversion in organic materials is essential for rational molecular design for efficient energy conversion materials. In organic materials, nonlocal electron-phonon coupling plays a vital role in charge transport and leads to complex transport mechanisms, including hopping, phonon assisted, band, and transient localization. In this work, based on the time-dependent density matrix renormalization group method, we look at the role of nonlocal electron-phonon coupling on the thermoelectric conversion in organic systems described by the Holstein-Peierls model. We calculate the current-current correlation and the heat current-current correlation functions. We find that (i) nonlocal electron-phonon coupling has a very weak influence on the Seebeck coefficient because of the cancellation between the heat current-current correlation function and the current-current correlation function, but it has a strong influence on the conductivity through dynamic disorders; and (ii) doping concentration has a strong influence on both the conductivity and Seebeck coefficient, and the optimal doping ratio to reach the highest power factor is 3%–10% fillings when the Holstein-Peierls model is valid. These findings suggest that we can design organic materials with higher power factors by first enhancing mobility through rational design, and then searching for the optimal doping ratio.

Using the tight-binding model, we report a gap opening in the energy spectrum of a twisted bilayer graphene under the application of pressure, that can be further amplified by the presence of a perpendicular bias voltage. The valley edges are located along the $K\text{−}\mathrm{\Gamma }$ path of the superlattice Brillouin zone, with the band gap reaching values up to 200 meV in the single-particle picture. Employing the formalism of the semiconductor Bloch equations, we observe an enhancement of the band gap due to the electron-electron interaction, with a renormalization of the band gap of about 160 meV. From the solution of the corresponding Bethe-Salpeter equation, we show that this system supports highly anisotropic bright excitons whose electrons and holes are strongly hybridized between the adjacent layers.

Domain boundaries often play a pivotal role in surface dynamics and surface phase transitions. In this study we scrutinize the dynamics of domain boundaries on the $\mathrm{Ge}\left(111\right)\text{−}c(2\times 8)$ surface using scanning tunneling microscopy. The dynamics of these domain boundaries, which are aligned along the $\langle 1\text{−}10\rangle$ directions, is governed by the diffusion of vacancies. The hop rate of a vacancy at a domain boundary is more than one order of magnitude larger than the hop rate of a vacancy in a pristine $c(2\times 8)$ domain. The diffusion pathway of a single vacancy along the domain boundary involves the formation of two, more mobile, semivacancies. The probability that these two semivacancies rejoin is very likely, but there is also a chance that the two semivacancies diffuse away from each other. This scenario provides a logical explanation of why single vacancies occasionally exhibit unusually long displacements along the domain boundary.

We present an infinite Grassmann time-evolving matrix product operator method for quantum impurity problems, which directly works in the steady state. The method embraces the well-established infinite matrix product state algorithms with the recently developed GTEMPO method, and benefits from both sides: it obtains real-time Green's functions without sampling noises and bath discretization error, it is applicable for any temperature without the sign problem, and its computational cost is independent of the transient dynamics and does not scale with the number of baths. We benchmark the method on the finite-temperature equilibrium Green's function in the noninteracting limit against exact solutions and in the single-orbital Anderson impurity model against GTEMPO calculations. We also study the zero-temperature nonequilibrium steady state of an impurity coupled to two baths with a voltage bias, obtaining consistent particle currents with existing calculations. The method is ideal for studying steady-state quantum transport, and can be readily used as an efficient real-time impurity solver in the dynamical mean-field theory and its nonequilibrium extension.