Publications

1. Destroying superconductivity in thin films with an electric field
   Amoretti, Andrea; Brattan, Daniel K.; Magnoli, Nicodemo; Martinoia, Luca; Matthaiakakis, Ioannis; Solinas, Paolo
   
   In this paper, we use a Ginzburg-Landau approach to show that a suitably strong electric field can drive a phase transition from a superconductor to a normal metal. The transition is induced by taking into account corrections to the permittivity due to the superconductive gap and persists even when screening effects are considered. We test the model against recent experimental observations in which a strong electric field has been observed to control the supercurrent in superconducting thin films. We find excellent agreement with the experimental data and are able to explain several observed features. We additionally suggest a way to test our theoretical proposal via superconductor-superconductor electron tunneling.
   
   Physical Review Research, Volume 4, Issue 3, article id.033211 (September 2022).
   
   

2. Superconductors in strong electric fields: Quantum Electrodynamics meets Superconductivity
   Amoretti, Andrea
   
   A static electric field has always been thought to play little role in the physics of ideal conductors, since the screening effects of mobile carriers prevent it from penetrating deep into the bulk of a metal. Very recently however, experimental evidence has been obtained which indicates that static electric fields can be used to manipulate the superconductive properties of metallic BCS superconducting thin films, weakening the critical current. In this paper I will show how possible explanations to this striking effect can be found relying on the analogy between Superconductivity and Quantum Electrodynamics noticed by Nambu and Iona-Lasinio in the sixties. I will show that, following this parallelism, it is possible to predict a new phenomenon: the superconducting Schwinger effect. Secondly I will explain how this new microscopic effect can be connected to a modified Gizburg-Landau theory where additional couplings between electric field and the superconductive condensate are taken into account. Eventually I will connect these theoretical predictions to the experiments, proposing them as a possible explanation of the weakening of superconductivity due to an external electric field.
   
   J. Phys. Conf. Ser. 2531 1, 012001 (September 2022).
   
   

3. Sauter-Schwinger effect in a Bardeen-Cooper-Schrieffer superconductor
   Amoretti, Andrea;  Solinas, Paolo;  Giazotto, Francesco
   
   Since the 1960s a deep and surprising connection has followed the development of superconductivity and quantum field theory. The Anderson-Higgs mechanism and the similarities between the Dirac and Bogoliubov–de Gennes equations are the most intriguing examples. In this last analogy, the massive Dirac particle is identified with a quasiparticle excitation and the fermion mass energy with the superconducting gap energy. Here we follow further this parallelism and show that it predicts an outstanding phenomenon: the superconducting Sauter-Schwinger effect. As in the quantum electrodynamics Schwinger effect, where an electron-positron couple is created from the vacuum by an intense electric field, we show that an electrostatic field can generate two coherent excitations from the superconducting ground-state condensate. Differently from the dissipative thermal excitation, these form a new macroscopically coherent and dissipationless state. We discuss how the superconducting state is weakened by the creation of this kind of excitations. In addition to shedding a different light and suggesting a method for the experimental verification of the Sauter-Schwinger effect, our results pave the way to the understanding and exploitation of the interaction between superconductors and electric fields.
   
   Phys. Rev. Lett. 126 11, 117001 (July 2020).