Abstract
We investigate the tunneling conductance of superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS) heterostructures with one superconducting side of the junction that is electrically driven and can exhibit $\pi$-pairing through a modification of the surface inversion asymmetric couplings. In SIN tunneling we find that the variation of the electrically driven interactions generally brings an increase of quasi-particles in the gap due to orbitally polarized depaired states, irrespective of the inter-band phase rearrangement. The peak of SIN conductance at the gap edge varies with a trend that depends both on the strength of the surface interactions as well as on the character of the gate-induced superconducting state. While this shift can be also associated with thermal effects in the SIN configuration, for the SIS geometry at low temperature the electric field does not yield the characteristic matching peak at voltages related with the difference between the gaps of the superconducting electrodes. This observation sets out a distinctive mark for spectroscopically distinguishing the thermal population effects from the quantum gate-driven signatures. In SIS the electrostatic gating yields a variety of features with asymmetric peaks and broadening of the conductance spectral weight. These findings indicate general qualitative trends for both SIN and SIS tunneling spectroscopy which could serve to evaluate the impact of gate-control on superconductors and the occurrence of non-centrosymmetric orbital antiphase pairing.
Highlights
Understanding the interplay of electricity and superconductivity is a fundamental problem that stands out for its general relevance, the great impact it can have for accessing, controlling, or driving new phases of quantum matter, and the enticing perspectives for the development of future quantum technologies
This observation sets out a distinctive mark for spectroscopically distinguishing thermal population effects from signatures that are mainly related to a variation of the electric field
Since the amplitude of the microscopic parameters directly affected by the electric field is generally proportional to Es with a factor that depends on materials characteristics, we have taken different trajectories in the phase space spanned by αOR and λ
Summary
Understanding the interplay of electricity and superconductivity is a fundamental problem that stands out for its general relevance, the great impact it can have for accessing, controlling, or driving new phases of quantum matter, and the enticing perspectives for the development of future quantum technologies. They can provide insight into the tunneling spectroscopy of superconducting thin films where the interband phase reconstruction already manifests in the absence of an applied electric field and the application of other drives can affect the orbital polarization of the electronic state on the surface and further reconstruct the superconducting phase Starting from this physical outlook it is relevant to consider whether spectroscopically one can assess the nature of the gate-driven superconducting phases and search for fingerprints which can be employed to understand the way the electric field affects the superconductivity. The key target is to track the evolution of the tunneling conductance in all phases that are obtained within the scenario of an electrostatically triggered orbital polarization at the surface [Fig. 1(b)] and extract the main spectral signatures In this way one can get a significant insight into the spectroscopic response that can result when considering the gate-driven superconducting transitions. We present the basic elements for the derivation of the tight-binding model in the presence of an electrostatic potential at the surface and the temperature dependence of orbital-dependent superconducting order parameters obtained by self-consistently solving the gap equations
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