Tunable pseudogaps due to nonlocal coherent transport in voltage-biased three-terminal Josephson junctions

Abstract

We investigate the proximity effect in junctions between N = 3 superconductors under commensurate voltage bias. The bias is chosen to highlight the role of transport processes that exchange multiple Cooper pairs coherently between more than two superconductors. Such nonlocal processes can be studied in the dc response, where local transport processes do not contribute. We focus on the proximity-induced normal density of states that we investigate in a wide parameter space. We reveal the presence of deep and highly tunable pseudogaps and other rich structures. These are due to a static proximity effect that is absent for N = 2 and is sensitive to an emergent superconducting phase associated to nonlocal coherent transport. In comparison with results for N = 2, we find similarities in the signature peaks of multiple Andreev reflections. We discuss the effect of electron-hole decoherence and of various types of junction asymmetries. Our predictions can be investigated experimentally using tunneling spectroscopy.

Quartet currents in a biased three-terminal diffusive Josephson junction

“…The dependence of currents with voltage and quartet phase is studied in detail, both for a symmetric and a strongly asymmetric TTJ. This paper follows previous ones where the spectral normal density of states NDOS was calculated, first at equilibrium [40], then at nonzero voltages [32] at which BCS-like resonances appear at MAR voltages. Moreover, the low-voltage behavior of the NDOS of a symmetric TTJ displays a phase-dependent pseudogap behavior, allowing to make the link with an adiabatic regime when V → 0.…”

“…where σz acts in Nambu space while 1 acts in Keldysh space, and Ǧi (t 1 − t 2 ) corresponds to the equilibrium Green's function given by Eqs. ( 1), (4), and (5) (upon Fourier transforming back from energy to time variable), Due to the time dependence in the Hamiltonian, and periodicity with a single Josephson frequency ω 0 = 2eV h , one can use double-time Fourier transform and represent the Green's functions in terms of a single energy variable (within the interval [32]. Notice that this definition is redundant, as Ǧ(E , n, m) = Ǧ(E − pω 0 , n + p, m + p) for any integer p, such that calculations can be performed in the energy interval [− ω 0 2 , ω 0 2 ] [42].…”

“…Another striking signature of the voltage commensurability is the presence of phase-dependent "phase-MAR" currents, where quasiparticle transport is accompanied by quartets instead of single pairs like in the two-terminal case [16,31,32].…”

Local tuning of the order parameter in superconducting weak links: A zero-inductance nanodevice

“…For instance, our results suggest that gated devices with tunable complex order parameter are useful for realizing local tunability of the superconducting-to-insulating transition in nanostructures. Lastly, our work offers another angle to the increasing interest in the study of multi-terminal Josephson junctions (see the recent work by Padurariu et al 34 and references therein). Specifically, our demonstrated method for tuning electrically the local quantum, or mesoscopic state of a nano three-terminal device may pave the way to novel quantum and energy-efficient switching technologies.…”

Theory of nonequilibrium noise in general multiterminal superconducting hybrid devices: Application to multiple Cooper pair resonances

“…(vii) The investigation of electron-hole decoherence effects on the zero frequency noise, using methods borrowed from quasiclassical circuit theory [61][62][63].…”