Proximity effect, Andreev reflections, and charge transport in mesoscopic superconducting/semiconducting heterostructures

Abstract

Received ( )In the quasi-twodimensional (Q2D) electron gas of an InAs channel between an AlSb substrate and superconducting Niobium layers the proximity effect induces a pair potential so that a Q2D mesoscopic superconducting-normal-superconducting (SNS) junction forms in the channel. The pair potential is calculated with quasiclassical Green's functions in the clean limit. For such a junction alternating Josephson currents and current-voltage characteristics (CVCs) are computed, using the non-equilibrium quasiparticle wavefunctions which solve the time-dependent Bogoliubov-de Gennes Equations. The CVCs exhibit features found experimentally by the Kroemer group: A steep rise of the current at small voltages ("foot") changes at a "corner current" to a much slower increase of current with higher voltages, and the zero-bias differential resistance increases with temperature. Phase-coherent multiple Andreev reflections and the associated Cooper pair transfers are the physical mechanisms responsible for the oscillating Josephson currents and the CVCs. Additional experimental findings not reproduced by the theory require model improvements, especially a consideration of the external current leads which should give rise to hybrid quasiparticle/collective-mode excitations.

Coherent multiple Andreev reflections and current resonances in SNS quantum point contacts

“…[33][34][35] However, these studies were restricted to fully transparent junctions where the bound states are strongly washed out and the resonances are not pronounced ͑in fact, as we will show, at zero temperature the current in such junctions does not show any structures͒. We will study junctions with arbitrary transmissivity, 0ϽDϽ1, and pay special attention to the lowtransparency limit, DӶ1, where the resonance effects are most pronounced.…”

Amplitudes of minima in dynamic conductance spectra of the SNS Andreev contact

“…6 the solutions evolving from the scattering states play the dominant role) and quasiparticle start their motion in the electric field from energy |E| < ∆ after each Andreev reflection. 15 Since, the SNS junction is connected by normal conducting external current leads to the voltage source almost all quasiparticle excitations have energies |E| < ∆ and they are completely Andreev reflected at the external interfaces between the leads and the junction.…”

Dynamics of conversion of supercurrents into normal currents and vice versa

“…The Tomasch effect in tunnel junctions [2], Josephson currents [3][4][5][6][7][8], excess currents, and subharmonic gap structures [9][10][11][12] in superconducting (S)-normal conducting (N )-superconducting junctions, as well as the transfer of half of the Magnus force to the core electrons of a moving vortex line [13] are due to AS. It is involved in the persistent currents around the AharonovBohm flux in an N/S metal loop [14], and there is AS in He 3 , too [15].…”

“…Andreev scattering (AS) of electrons into holes and vice versa by spatial variations of the superconducting pair potential [1], in competition and cooperation with conventional scattering, determines the electronic structure and transport properties of inhomogeneous superconductors. The Tomasch effect in tunnel junctions [2], Josephson currents [3][4][5][6][7][8], excess currents, and subharmonic gap structures [9][10][11][12] in superconducting (S)normal conducting (N )-superconducting junctions, as well as the transfer of half of the Magnus force to the core electrons of a moving vortex line [13] are due to AS. It is involved in the persistent currents around the Aharonov-Bohm flux in an N/S metal loop [14], and there is AS in He 3 , too [15].…”