arXiv subjects

A. Aharony

Publications and source records attributed to A. Aharony.

At least 19 recordsLinked to original sources

arXiv2026

Wannier-Stark localization, confinement and edge states

The boundary between a system's bulk and the vacuum can be modeled by a potential which confines the electrons to the bulk. Here we present the example of the Wannier-Stark linear potential, generated by an electric field along one axis of a two-dimensional lattice. Along that axis, the potential generates electronic states which are localized around each lattice site, with eigenenergies which form the Wannier-Stark ladder. In the transverse direction, the states are governed by a tight binding model with free Bloch states. In the ground state, filling these states under the Pauli principle generates an insulating bulk and an edge which can be metallic in the transverse direction. This paper explains the concepts of localization, localization length, filling and confinement. The paper also acquaints the readers with the use of Bessel functions in the solution of a simple physical model. These topics can be easily included in courses on solid state physics, and only require prior knowledge of quantum mechanics.

cond-mat.mes-hall↗

arXiv2025

Magnetizing weak links by time-dependent spin-orbit interactions: momentum conserving and non-conserving processes

Rashba spin-orbit interactions generated by time-dependent electric fields acting on weak links (that couple together non-magnetic macroscopic leads) can magnetize the junction. The Rashba spin-orbit interaction that affects the spins of electrons tunneling through the weak links changes their momentum concomitantly. We establish the connection between the magnetization flux induced by processes that conserve the momentum and the magnetization created by tunneling events that do not. Control of the induced magnetization can be achieved by tuning the polarization of the AC electric field responsible for the spin-orbit Rashba interaction (e.g., from being circular to linear), by changing the applied bias voltage, and by varying the degree of a gate voltage-induced asymmetry of the device.

cond-mat.mes-hall↗

arXiv2024

Enhanced Non-linear Response by Manipulating the Dirac Point in the (111) LaTiO$_3$/SrTiO$_3$ Interface

Tunable spin-orbit interaction (SOI) is an important feature for future spin-based devices. In the presence of a magnetic field, SOI induces an asymmetry in the energy bands, which can produce non-linear transport effects ($V\sim I^2$). Here, we focus on such effects to study the role of SOI in the (111) LaTiO$_3$/SrTiO$_3$ interface. This system is a convenient platform for understanding the role of SOI since it exhibits a single-band Hall-response through the entire gate-voltage range studied. We report a pronounced rise in the non-linear resistance at a critical in-plane field $H_{cr}$. This rise disappears with a small out-of-plane field. We explain these results by considering the location of the Dirac point formed at the crossing of the spin-split energy bands. An in-plane magnetic field pushes this point outside of the Fermi surface, and consequently changes the symmetry of the Fermi contours and intensifies the non-linear transport. An out-of-plane magnetic field opens a gap at the Dirac point, thereby significantly diminishing the non-linear effects. We propose that magnetoresistance effects previously reported in interfaces with SOI could be comprehended within our suggested scenario.

cond-mat.str-el↗

arXiv2024

Thermoelectric performance of nano junctions subjected to microwave driven spin-orbit coupling

Coherent charge and heat transport through periodically driven nanodevices provide a platform for studying thermoelectric effects on the nanoscale. Here we study a junction comprising a quantum dot connected to two fermionic terminals by two weak links. An AC electric field induces time-dependent spin-orbit interaction in the weak links. We show that this setup supports DC charge and heat currents and that thermoelectric performance can be improved, as reflected by the effect of the spin-orbit coupling on the Seebeck coefficient and the electronic thermal conductance. Our analysis is based on the nonequilibrium Keldysh Green's function formalism in the time domain and reveals an interesting distribution of the power supply from the AC source among the various components of the device, apparently not realized before.

cond-mat.mes-hall↗

arXiv2023

Scattering description of edge states in Aharonov-Bohm triangle chains

Scattering theory has been suggested as a convenient method to identify topological phases of matter, in particular of disordered systems for which the Bloch band-theory approach is inapplicable. Here we examine this idea, employing as a benchmark a one-dimensional triangle chain whose versatility yields a scattering matrix that ``flows" in parameter space among several members of the topology classification scheme. Our results show that the reflection amplitudes (from both ends of a sufficiently long chain) do indicate the appearance of edge states in {\it all} (topological and non-topological) cases. For the topological cases, the transmission has a peak at the topological phase transition, which happens at the Fermi energy. A peak still exists as one moves into the non-topological `trivial' regions, in which another transmission peak may occur at nonzero energy, at which a relevant edge state appears in the isolated chain. For finite chains, the peak in the transmission strongly depends on their coupling of the leads, and {\it not} on the phase transition of the isolated chain. In any case, {\it the appearance of a peak in the transmission is not sufficient to conclude that the system undergoes a topological phase transition.}

cond-mat.mes-hall↗

arXiv2023

Magnetization near a constriction between BCS superconductors by spin-dependent tunneling

Spin-dependent electron tunneling through a voltage-biased micro-constriction between two bulk superconductors is shown to create a static magnetization near the constriction and an ac Josephson-like spin current. Although spin-dependent tunneling generates quantum spin fluctuations even in the absence of a bias, the formation of spin-triplet Cooper pairs necessary for the creation of magnetization is blocked by destructive interference between different quasi-electron and quasi-hole tunneling channels, unless there is an asymmetry between the tunneling densities of states for electrons and holes. Breaking the symmetry in the electron-hole tunnel density of states and creating electron-hole tunneling imbalance by biasing the device destroys the destructive interference and enables triplet Cooper-pair formation. As a result, magnetizing the superconductor becomes possible. The role of the voltage in lifting the blockade hindering the spin-triplet Cooper pair formation is an example of an electrically-controlled dissipation-less spintronic phenomenon.

cond-mat.supr-con↗

arXiv2023

Coexistence of insulating phases in confined fermionic chains with a Wannier-Stark potential

We study fermions on a finite chain, interacting repulsively when residing on the same and on nearest-neighbor sites, and subjected to a Wannier-Stark linearly-varying potential. Using the density matrix renormalization-group numerical technique to solve this generalized extended Hubbard model, the ground state exhibits a staircase of (quasi) plateaus in the average local site density along the chain, decreasing from being doubly-filled to empty as the potential increases. These `plateaus' represent locked-in commensurate phases of charge density waves together with band and Mott insulators. These phases are separated by incompressible regions with incommensurate fillings. It is suggested that experimental variations of the slope of the potential and of the range of the repulsive interactions will produce such a coexistence of phases which have been individually expected theoretically and observed experimentally for uniform systems.

cond-mat.str-el↗

arXiv2023

Effective exponents near bicritical points

The phase diagram of a system with two order parameters, with ${\it n_1}$ and $n_2$ components, respectively, contains two phases, in which these order parameters are non-zero. Experimentally and numerically, these phases are often separated by a first-order "flop" line, which ends at a bicritical point. For $n=n_1+n_2=3$ and $d=3$ dimensions (relevant e.g. to the uniaxial antiferromagnet in a uniform magnetic field), this bicritical point is found to exhibit a crossover from the isotropic $n$-component universal critical behavior to a fluctuation-driven first-order transition, asymptotically turning into a triple point. Using a novel expansion of the renormalization group recursion relations near the isotropic fixed point, combined with a resummation of the sixth-order diagrammatic expansions of the coefficients in this expansion, we show that the above crossover is slow, explaining the apparently observed second-order transition. However, the effective critical exponents near that transition, which are calculated here, vary strongly as the triple point is approached.

cond-mat.stat-mech↗

arXiv2022

Magnetoconductance Anisotropies and Aharonov-Casher Phases

The spin-orbit interaction is a key tool for manipulating and functionalizing spin-dependent electron transport. However, the precise value of the spin-orbit coupling constant is hard to determine and control. Here we propose a measurement of the geometric (Aharonov-Casher) phase of the electron wavefunction generated by the spin-orbit coupling as a means to deduce the spin-orbit coupling strength in weak links. Unlike other proposed measurements of geometric phases, which rely on interference, we show that the anisotropy of the magnetoconductance, measured at different directions of an external magnetic field,is determined by the geometric phase. Specifically we consider weak links in which the Rashba interaction is caused by an external electric field, but our method is expected to apply also for other forms of the spin-orbit coupling. Measuring this magnetoconductance anisotropy thus allows calibrating Rashba spintronic devices by an external electric field that tunes the spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2022

The puzzle of bicriticality in the XXZ antiferromagnet

Renormalization-group theory predicts that the XXZ antiferromagnet in a magnetic field along the easy Z-axis has asymptotically either a tetracritical phase-diagram or a triple point in the field-temperature plane. Neither experiments nor Monte Carlo simulations procure such phase diagrams. Instead, they find a bicritical phase-diagram. Here this discrepancy is resolved: after generalizing a ubiquitous condition identifying the tetracritical point, we employ new renormalization-group recursion relations near the isotropic fixed point, exploiting group-theoretical considerations and using accurate exponents at three dimensions. These show that the experiments and simulations results can only be understood if their trajectories flow towards the fluctuation-driven first order transition (and the associated triple point), but reach this limit only for prohibitively large system sizes or correlation lengths. In the crossover region one expects a bicritical phase diagram, as indeed is observed. A similar scenario may explain puzzling discrepancies between simulations and renormalization-group predictions for a variety of other phase diagrams with competing order parameters.

cond-mat.stat-mech↗

arXiv2022

Bi- and tetracritical phase diagrams in three dimensions

The critical behavior of many physical systems involves two competing $n^{}_1-$ and $n^{}_2-$component order-parameters, ${\bf S}^{}_1$ and ${\bf S}^{}_2$, respectively, with $n=n^{}_1+n^{}_2$. Varying an external control parameter $g$, %(e.g. uniaxial stress or magnetic field), one encounters ordering of ${\bf S}^{}_1$ below a critical (second-order) line for $g<0$ and of ${\bf S}^{}_2$ below another critical line for $g>0$. These two ordered phases are separated by a first-order line, which meets the above critical lines at a bicritical point, or by an intermediate (mixed) phase, bounded by two critical lines, which meet the above critical lines at a tetracritical point. For $n=1+2=3$, the critical behavior around the (bi- or tetra-) multicritical point either belongs to the universality class of a non-rotationally invariant (cubic or biconical) fixed point, or it has a fluctuation driven first-order transition. These asymptotic behaviors arise only very close to the transitions. We present accurate renormalization-group flow trajectories yielding the effective crossover exponents near multicriticality.

cond-mat.stat-mech↗

arXiv2022

Different critical behaviors in cubic to trigonal and tetragonal perovskites

Perovskites like LaAlO3 (or SrTiO3) undergo displacive structural phase transitions from a cubic crystal to a trigonal (or tetragonal) structure. For many years, the critical exponents in both these types of transitions have been fitted to those of the isotropic three-components Heisenberg model. However, field theoretical calculations showed that the isotropic fixed point of the renormalization group is unstable, and renormalization group iterations flow either to a cubic fixed point or to a fluctuation-driven first-order transition. Here we show that these two scenarios correspond to the cubic to trigonal and to the cubic to tetragonal transitions, respectively. In both cases, the critical behavior is described by slowly varying effective critical exponents, which exhibit universal features. For the trigonal case, we predict a crossover of the effective exponents from their Ising values to their cubic values (which are close to the isotropic ones). For the tetragonal case, the effective exponents can have the isotropic values over a wide temperature range, before exhibiting large changes en route to the first-order transition. New renormalization group calculations near the isotropic fixed point in three dimensions are presented and used to estimate the effective exponents, and dedicated experiments to test these predictions are proposed. Similar predictions apply to cubic magnetic and ferroelectric systems.

cond-mat.stat-mech↗

arXiv2021

Topological states and interplay between spin-orbit and Zeeman interactions in a spinful Su-Schrieffer-Heeger nanowire

The interplay between the spin-orbit and Zeeman interactions acting on a spinful Su-Schrieffer-Heeger model is studied based on an InAs nanowire subjected to a periodic gate potential along the axial direction. It is shown that a nontrivial topological phase can be achieved by regulating the confining-potential configuration. In the absence of the Zeeman field, we prove that the topology of the chain is not affected by the Rashba spin-orbit interaction due to the persisting chiral symmetry. The energies of the edge modes can be manipulated by varying the magnitude and direction of the external magnetic field. Remarkably, the joint effect of the two spin-related interactions leads to novel edge states that appear in the gap formed by the anti-crossing of the bands of a finite spinful dimerized chain, and can be merged into the bulk states by tilting the magnetic-field direction.

cond-mat.mes-hall↗

arXiv2020

Effects of magnetic fields on the Datta-Das spin field-effect transistor

A Datta-Das spin field-effect transistor is built of a heterostructure with a Rashba spin-orbit interaction (SOI) at the interface (or quantum well) separating two possibly magnetized reservoirs. The particle and spin currents between the two reservoirs are driven by chemical potentials that are (possibly) different for each spin direction. These currents are also tuned by varying the strength of the SOI, which changes the amount of the rotation of the spins of electrons crossing the heterostructure. Here we investigate the dependence of these currents on additional Zeeman fields on the heterostructure and on variations of the reservoir magnetizations. In contrast to the particle current, the spin currents are not necessarily conserved; an additional spin polarization is injected into the reservoirs. If a reservoir has a finite (equilibrium) magnetization, then we surprisingly find that the spin current into that reservoir can only have spins which are parallel to the reservoir magnetization, independent of all the other fields. This spin current can be enhanced by increasing the magnetization of the other reservoir, and can also be tuned by the SOI and the various magnetic fields. When only one reservoir is magnetized then the spin current into the other reservoir has arbitrary tunable size and direction. In particular, this spin current changes as the magnetization of the other reservoir is rotated. The optimal conditions for accumulating spin polarization on an unpolarized reservoir are to either apply a Zeeman field in addition to the SOI, or to polarize the other reservoir.

cond-mat.mes-hall↗

arXiv2020

Magnetization generated by microwave-induced Rashba interaction

We show that a controllable dc magnetization is accumulated in a junction comprising a quantum dot coupled to non-magnetic reservoirs if the junction is subjected to a time-dependent spin-orbit interaction. The latter is induced by an ac electric field generated by microwave irradiation of the gated junction. The magnetization is caused by inelastic spin-flip scattering of electrons that tunnel through the junction, and depends on the polarization of the electric field: a circularly polarized field leads to the maximal effect, while there is no effect in a linearly polarized field. Furthermore, the magnetization increases as a step function (smoothened by temperature) as the microwave photon energy becomes larger than the absolute value of the difference between the single energy level on the quantum dot and the common chemical potential in the leads.

cond-mat.mes-hall↗

arXiv2020

Photovoltaic effect generated by spin-orbit interactions

An AC electric field applied to a junction comprising two spin-orbit coupled weak links connecting a quantum dot to two electronic terminals is proposed to induce a DC current and to generate a voltage drop over the junction if it is a part of an open circuit. This photovoltaic effect requires a junction in which mirror reflection-symmetry is broken. Its origin lies in the different fashion inelastic processes modify the reflection of electrons from the junction back into the two terminals, which leads to uncompensated DC transport. The effect can be detected by measuring the voltage drop that is built up due to that DC current. This voltage is an even function of the frequency of the AC electric field and is {\em not} related to quantum pumping.

cond-mat.mes-hall↗

arXiv2019

Spin geometric-phases in hopping magnetoconductance

We identify theoretically the geometric phases of the electrons' spin that can be detected in measurements of charge and spin transport through Aharonov-Bohm interferometers threaded by a magnetic flux $Φ$ (in units of the flux quantum) in which both the Rashba spin-orbit and Zeeman interactions are active. We show that the combined effect of these two interactions is to produce a $\sin(Φ)$ [in addition to the usual $\cos(Φ)$] dependence of the magnetoconductance, whose amplitude is proportional to the Zeeman field. Therefore the magnetoconductance, though an even function of the magnetic field is not a periodic function of it, and the widely-used concept of a phase shift in the Aharonov-Bohm oscillations, as indicated in previous work, is not applicable. We find the directions of the spin-polarizations in the system, and show that in general the spin currents are not conserved, implying the generation of magnetization in the terminals attached to the interferometer.

cond-mat.mes-hall↗

arXiv2019

DC spin generation by junctions with AC driven spin-orbit interaction

An unbiased one-dimensional weak link between two terminals, subjected to the Rashba spin-orbit interaction caused by an AC electric field which rotates periodically in the plane perpendicular to the link, is shown to inject spin-polarized electrons into the terminals. The injected spin-polarization has a DC component along the link and a rotating transverse component in the perpendicular plane. In the adiabatic, low rotation-frequency regime, these polarization components are proportional to the frequency. The DC component of the polarization vanishes for a linearly-polarized electric field.

cond-mat.mes-hall↗