Current-carrying States Research Articles

Single-Defect-Induced Peculiarities in Inverse Faraday-Based Switching of Superconducting Current-Carrying States near a Critical Temperature

The Inverse Faraday Effect (IFE) is a phenomenon that enables non-thermal magnetization in various types of materials through the interaction with circularly polarized light. This study investigates the impact of single defects on the ability of circularly polarized radiation to switch between distinct superconducting current states, when the magnetic flux through a superconducting ring equals half the quantum flux, Φ0/2. Using both analytical methods within the standard Ginzburg–Landau theory and numerical simulations based on the stochastic time-dependent Ginzburg–Landau approach, we demonstrate that while circularly polarized light can effectively switch between current-carrying superconducting states, the presence of a single defect significantly affects this switching mechanism. We establish critical temperature conditions above which the switching effect completely disappears, offering insights into the limitations imposed by a single defect on the dynamics of light-induced IFE-based magnetization in superconductors.

Generalized hydrodynamics and approach to generalized Gibbs equilibrium for a classical harmonic chain

Abstract We study the evolution of a classical harmonic chain with nearest-neighbor interactions starting from domain wall initial conditions. The initial state is taken to be either a product of two Gibbs ensembles (GEs) with unequal temperatures on the two halves of the chain or a product of two generalized Gibbs ensembles (GGEs) with different parameters in the two halves. For this system, we construct the Wigner function and demonstrate that its evolution defines the generalized hydrodynamics (GHD) describing the evolution of the conserved quantities. We solve the GHD for both finite and infinite chains and compute the evolution of conserved densities and currents. For a finite chain with fixed boundaries, we show that these quantities relax as ∼ 1 / t to their respective steady-state values given by the final expected GE or GGE state, depending on the initial conditions. Exact expressions for the Lagrange multipliers of the final expected GGE state are obtained in terms of the steady-state densities. In the case of an infinite chain, we find that the conserved densities and currents at any finite time exhibit ballistic scaling while, at infinite time, any finite segment of the system can be described by a current-carrying non-equilibrium steady state (NESS). We compute the scaling functions analytically and show that the relaxation to the NESS occurs as ∼ 1 / t for the densities and as ∼ 1 / t 2 for the currents. We compare the analytical results from hydrodynamics with those from exact microscopic numerics and find excellent agreement.

Near-circularly polarized isolated attosecond pulse generation from a current-carrying state of Ar atom by two-color cross-linearly-polarized laser fields

Abstract We theoretically propose an efficient method to generate near-circularly polarized isolated attosecond (as) pulses (NCP-IAPs) from a current-carrying state of Ar atom driven by two-color cross-linearly-polarized laser fields. We find that the ellipticity of high harmonics can be controlled by adjusting the crossing angle of two linearly polarized lasers and the near-circularly polarized supercontinuum harmonics are obtained when the crossing angle is around 140°. Furthermore, we can produce the NCP-IAPs with the ellipticity up to 0.94 and the shortest one achieves 196 as. This work demonstrates the possibility for generating the NCP-IAPs using a current-carrying state of atoms driven by two-color cross-linearly-polarized laser fields.

Electronic Vector Potential from the Exact Factorization of a Complex Wavefunction.

We generalize the definitions of local scalar potentials named and , which are relevant to properly describe phenomena such as molecular dissociation with density-functional theory, to the case in which the electronic wavefunction corresponds to a complex current-carrying state. In such a case, an extra term in the form of a vector potential appears which cannot be gauged away. Both scalar and vector potentials are introduced via the exact factorization formalism which allows us to express the given Schrödinger equation as two coupled equations, one for the marginal and one for the conditional amplitude. The electronic vector potential is directly related to the paramagnetic current density carried by the total wavefunction and to the diamagnetic current density in the equation for the marginal amplitude. An explicit example of this vector potential in a triplet state of two non-interacting electrons is showcased together with its associated circulation, giving rise to a non-vanishing geometric phase. Some connections with the exact factorization for the full molecular wavefunction beyond the Born-Oppenheimer approximation are also discussed.

Lifshitz transitions and Weyl semimetals from a topological superconductor with supercurrent flow

A current flowing through a superconductor induces a spatial modulation in its superconducting order parameter, characterized by a wave vector Q related to the total momentum of a Cooper pair. Here we investigate this phenomenon in a p-wave topological superconductor, described by a one-dimensional Kitaev model. We demonstrate that, by treating Q as an extra synthetic dimension, the current-carrying nonequilibrium steady state can be mapped into the ground state of a half-filled two-dimensional Weyl semimetal, whose Fermi surface exhibits Lifshitz transitions when varying the model parameters. Specifically, the transition from type-I to type-II Weyl phases corresponds to the emergence of a gapless p-wave superconductor, where Cooper pairs coexist with unpaired electrons and holes. Such a transition is signaled by the appearance of a sharp cusp in the Q-dependence of the supercurrent, at a critical value Q* that is robust to variations of the chemical potential μ. We determine the maximal current that the system can sustain in the topological phase, and we discuss possible implementations. Published by the American Physical Society 2024

Free energy of a two-liquid system of charge carriers in strongly coupled electron and phonon fields and common nature of three phases in hole-doped cuprates

Hole-doped cuprates exhibit partially coexisting pseudogap (PG), charge ordering (CO) and superconductivity; we show that there exists a class of systems in which they have a single nature as it has recently been supposed. Since the charge-ordered phase exhibits large frozen deformation of the lattice, we develop a method for calculating the phase diagram of a system with strong long-range (Fröhlich) electron–phonon interaction. Using a variational approach, we calculate the free energy of a two-liquid system of carriers with cuprate-like dispersion comprising a liquid of autolocalized carriers (large polarons and bipolarons) and Fermi liquid of delocalized carriers. Comparing it with the free energy of pure Fermi liquid and calculating (with standard methods of Bose liquid theory) a temperature of the superfluid transition in the large-bipolaron liquid we identify regions in the phase diagram with the presence of PG (caused by the impact of the (bi)polarons potential on delocalized quasiparticles), CO and superconductivity. They are located in the same places in the diagram as in hole-doped cuprates, and, as in the latter, the shape of the calculated phase diagram is resistant to wide-range changes in the characteristics of the system. As in cuprates, the calculated temperature of the superconducting transition increases with the number of conducting planes in the unit cell, the superfluid density decreases with doping at overdoping, the bipolaron density (and bipolaronic plasmon energy) saturates at optimal doping. Thus, the similarity of the considered system with hole-doped cuprates is not limited to the phase diagram. The results obtained allow us to discuss ways of increasing the temperature of the superfluid transition in the large-bipolaron liquid and open up the possibility of studying the current-carrying state and properties of the bipolaron condensate.

In-field electro-magnetic-force characteristics of high-temperature superconducting films containing cracks

Superconducting materials have so far been applied in the fields of superconducting motors, flux pumps and nuclear magnetic resonance, but they are prone to mechanical damage due to their material properties. In this paper, the influences of different crack types (including position, angle, size, quantity and spacing) on the characteristics of current-carrying and excited superconducting thin films are analyzed by numerical simulations, as well as their electromagnetic and mechanical characteristics. Several novel and important conclusions are found. In both states, the boundary crack presents the largest current density concentration, while the central crack produces the largest stress concentration. With the increase of crack spacing, the current density on the multi-crack film decreases and eventually tends to be stable. In the current-carrying state, compared with 3 mm cracked film, the current density of 1 mm cracked film is reduced by up to 62.5 %. The von Mises stress of high-temperature superconducting film with 0.1 mm single-spacing cracks is 22.5 % higher than that for 0.3 mm double-spacing cracks, which indicates that close spacing and a high number of crack types are most detrimental to the mechanical properties of high-temperature superconducting films. In the excited state, when the crack angle θ is 90°, the current density streamlines cannot be segmented effectively, which results in the current distribution trend closer to the defect-free film. A large amount of induced current flows into the low-flux region at the 3 mm crack, leading to an increased risk of film quench. The films with 1 mm single-spacing and double-spacing cracks form a low-flux region between the cracks, which makes the magnetic field more difficult to penetrate.

Extensive long-range entanglement in a nonequilibrium steady state

Entanglement measures constitute powerful tools in the quantitative description of quantum many-body systems out of equilibrium. We study entanglement in the current-carrying steady state of a paradigmatic one-dimensional model of noninteracting fermions at zero temperature in the presence of a scatterer. We show that disjoint intervals located on opposite sides of the scatterer, and within similar distances from it, maintain volume-law entanglement regardless of their separation, as measured by their fermionic negativity and coherent information. The mutual information of the intervals, which quantifies the total correlations between them, follows a similar scaling. Interestingly, this scaling entails in particular that if the position of one of the intervals is kept fixed, then the correlation measures depend non-monotonically on the distance between the intervals. By deriving exact expressions for the extensive terms of these quantities, we prove their simple functional dependence on the scattering probabilities, and demonstrate that the strong long-range entanglement is generated by the coherence between the transmitted and reflected parts of propagating particles within the bias-voltage window. The generality and simplicity of the model suggest that this behavior should characterize a large class of nonequilibrium steady states.

Helicity-controlled switching of superconducting states by radiation pulse

We provide a theoretical analysis of the possibility of using circularly polarized radiation to switch between two different quantum states of a superconducting nanoring subjected to the half quantum flux. Numerical modeling, performed in the framework of the time-dependent Ginzburg–Landau equation, reveals the condition for on-demand switching between current-carrying states with different helicities with 100% probability. An experimental demonstration of this effect will be unambiguous evidence of the inverse Faraday effect in superconductors and pave the way for the design of light-operated superconducting devices.

Elliptical high-order harmonic generation from current-carrying orbitals of prealigned molecules

The polarization of high harmonics generated from current-carrying state of nitric oxide molecules irradiated by linear laser fields is investigated by numerically solving the three-dimensional time-dependent Schrödinger equation. It is found that the ellipticity of high harmonics is obviously dependent on the polar angle between the driving laser polarization and molecular axis which is interpreted by the strong field approximation model. Moreover, our results also show that the helicity of near-threshold harmonics is opposite to that of plateau harmonics when the molecule is at any polar angle. To analyze this phenomenon, we simulate the dipole matrix element numerically. Finally, the attosecond pulses with opposite helicities can be obtained by synthesizing near-threshold and plateau harmonics. The ellipticity can be tuned by the alignment angle of molecules. Our work may provide a theoretical guiding and detection tool for the electron dynamics of molecular current-carrying states.

Cable current-carrying status analysis and early fault warning method based on temperature information

Long-term operation of cables and equipment under abnormal currents can cause insulation aging and reduce the service life of the equipment. Identifying the current-carrying status accurately and early detection of potential failures of power cables is particularly significant for ensuring the operation of power equipment safely and economically. This paper proposed a method for detecting the current-carrying status of power cables and an early fault warning based on temperature information. Based on the theoretical basis of the relationship between temperature and current. According to IEC 61000-3-7 and IEC 60038 standards, the current-carrying state evaluation method is analyzed and given, and the early fault warning model is established. Finally, the paper takes the cable connector and the lightning arrester in the power ring network cabinet as an example to verify the method’s feasibility. It shows that the characteristic information of the relative temperature variation curves under different current carrying states significantly differs. Includes the slope of hour 9, the slope of hour 2, and the maximum. Then the total duration under abnormal current operation is calculated, and the early warning of faults can realize.

Electronic ring current and magnetic field generation induced by current-carrying states of ring molecules in intense fields

The generation of electronic currents and magnetic fields by and molecules with current-carrying states under circularly polarized (CP) and linearly polarized (LP) laser pulses is investigated. Results show that the electronic currents and magnetic fields induced by CP pulses are higher than those by LP pulses for both molecules in the resonance excitation scheme. This can be attributed to the switchable dipole moment of the laser pulses, inducing selective state-to-state electronic transitions. Moreover, it was found that magnetic fields are sensitive to different initial states of the molecules in the ionization scheme. In particular, the magnetic fields induced by the current-carrying states are much higher than that induced by the ground state, which is because the current-carrying states have a stable electronic ring current and the induced magnetic field is contributed by the current-carrying state itself and the laser field. These findings provide a scheme for generating ring-shaped currents and magnetic fields in molecular systems for future research in ultrafast magneto-optics.

Strong quantization of current-carrying electron states in [formula omitted]-layer systems

We present an open-system quantum-mechanical real-space study of the conductive properties and size quantization in phosphorus δ-layers systems, interesting for their beyond-Moore and quantum computing applications. Recently it has been demonstrated that an open-system quantum mechanical treatment provides a much more accurate match to ARPES measurements in highly-conductive, highly-confined systems than the traditional approaches (i.e. periodic or Dirichlet boundary conditions) and, furthermore, it allows accurate predictions of conductive properties of such systems from the first principles. Here we reveal that quantization effects are strong for device widths W<10nm, and we show, for the first time, that the number of propagating modes determines not only the conductivity, but the distinctive spatial distribution of the current-carrying electron states. For W>10nm, the quantization effects practically vanish and the conductivity tends to the infinitely-wide device’s values.

Landau levels and snake states of pseudo-spin-1 Dirac-like electrons in gapped Lieb lattices

This work reports the three-band structure associated with a Lieb lattice with arbitrary nearest and next-nearest neighbors hopping interactions. For specific configurations, the system admits a flat band located between two dispersion bands, where three inequivalent Dirac valleys are identified. Furthermore, quasi-particles are effectively described by a spin-1 Dirac-type equation. Under external homogeneous magnetic fields, the Landau levels are exactly determined as the third-order polynomial equation for the energy can be solved using Cardano’s formula. It is also shown that an external anti-symmetric field promotes the existence of current-carrying states, so-called snake states, confined at the interface where the external field changes its sign.

Conductivity and size quantization effects in semiconductor delta-layer systems

We present an open-system quantum-mechanical 3D real-space study of the conduction band structure and conductive properties of two semiconductor systems, interesting for their beyond-Moore and quantum computing applications: phosphorus delta-layers and P delta-layer tunnel junctions in silicon. In order to evaluate size quantization effects on the conductivity, we consider two principal cases: nanoscale finite-width structures, used in transistors, and infinitely-wide structures, electrical properties of which are typically known experimentally. For devices widths W<10 nm, quantization effects are strong and it is shown that the number of propagating modes determines not only the conductivity, but the distinctive spatial distribution of the current-carrying electron states. For W>10 nm, the quantization effects practically vanish and the conductivity tends to the infinitely-wide device values. For tunnel junctions, two distinct conductivity regimes are predicted due to the strong conduction band quantization.

Enhanced entanglement negativity in boundary-driven monitored fermionic chains

We investigate entanglement dynamics in continuously monitored open quantum systems featuring current-carrying nonequilibrium states. We focus on a prototypical one-dimensional model of boundary-driven noninteracting fermions with monitoring of the local density, whose average Lindblad dynamics features a well-studied ballistic to diffusive crossover in transport. Here we analyze the dynamics of the fermionic negativity, mutual information, and purity along different quantum trajectories. We show that monitoring this boundary-driven system enhances its entanglement negativity at long times, which otherwise decays to zero in the absence of measurements. This result is in contrast with the case of unitary evolution where monitoring suppresses entanglement production. For small values of $\ensuremath{\gamma}$, the stationary-state negativity shows a logarithmic scaling with system size, transitioning to an area-law scaling as $\ensuremath{\gamma}$ is increased beyond a critical value. Similar critical behavior is found in the mutual information, while the late-time purity shows no apparent signature of a transition, being $O(1)$ for all values of $\ensuremath{\gamma}$. Our work unveils the double role of weak monitoring in current-driven open quantum systems, simultaneously damping transport and enhancing entanglement.

Light-Induced Magnetization at the Nanoscale.

Triggering and switching magnetic moments is of key importance for applications ranging from spintronics to quantum information. A noninvasive ultrafast control at the nanoscale is, however, an open challenge. Here, we propose a novel laser-based scheme for generating atomic-scale charge current loops within femtoseconds. The associated orbital magnetic moments remain ferromagnetically aligned after the laser pulses have ceased and are localized within an area that is tunable via laser parameters and can be chosen to be well below the diffraction limit of the driving laser field. The scheme relies on tuning the phase, polarization, and intensities of two copropagating Gaussian and vortex laser pulses, allowing us to control the spatial extent, direction, and strength of the atomic-scale charge current loops induced in the irradiated sample upon photon absorption. In the experiment we used He atoms driven by an ultraviolet and infrared vortex-beam laser pulses to generate current-carrying Rydberg states and test for the generated magnetic moments via dichroic effects in photoemission. Abinitio quantum dynamic simulations and analysis confirm the proposed scenario and provide a quantitative estimate of the generated local moments.

Edge modes and their conductance in narrow nanoribbons of 2D materials in a topological phase

Employing novel 2D materials with topologically protected current-carrying edge states is promising to boost the on-current in electronic devices. Using nanoribbons is essential to reduce the contribution of the 2D bulk states to the current. Making the nanoribbon widths narrower allows one to put more current-carrying edge states under the gate of a fixed width thus increasing the current. However, the edge states from opposite edges may start to interact in narrow nanoribbons. Based on an effective k∙p model, we analyze the topologically protected edge states and their conductance for several 2D materials as a function of the normal electric field. We compare the 2D materials MoS2, MoSe2, WS2, and WSe2 in the topological 1T′ phase and find the largest electric field-induced conductance modulation in MoS2 nanoribbons.

Influence of a nonuniform thermal quench and circular polarized radiation on spontaneous current generation in superconducting rings

We theoretically study the nonequilibrium dynamics of the order parameter of a superconducting ring inhomogeneously quenched through its transition temperature. Numerical simulations based on spectral decomposition of the time-dependent Ginzburg-Landau equation reveal that current-carrying superconducting states can be generated in the ring under certain fast local temperature quench conditions. We also show that illumination of the ring with a circularly polarized electromagnetic radiation during rapid cooling strongly promotes the generation of current-carrying states with rotation directions controlled by the helicity of the radiation field.

Probing long-range current-carrying edge modes by two quantum point contacts

The origin of anomalous current-carrying edge states in quasi-two-dimensional quantum samples with an insulating interior is currently mysterious. We propose to address this issue using a hybrid setup, an interferometric phase-sensitive configuration of two independent scanning probe tips, normal and superconducting, able to realize the quantum interference effect of quasiparticle currents moving in different directions along the metallic-like one-dimensional near-boundary channels. To simulate the dissipationless edge currents, we consider a quantum material with a simple Corbino disk geometry and analyze how the differential conductance spectrum depends on the distance between the two tips, the applied voltage bias, and the presence of a magnetic field. An essential difference between classical and quantum expectations should clarify the enigmatic origin of the long-range conducting modes observed in different materials at low temperatures. Strong dependence on the applied magnetic field can be useful for practical implementation of the quantum effects associated with the phase difference of electron wave functions in the ring geometry.