STSM of Todor Mishonov at the CNR-SPIN (Consiglio Nazionale delle Ricerche – SuPerconducting and other INnovative materials and devices institute), Rome (Italy)

The STSM to the Institute of Superconductivity and Innovative Materials (CNR-SPIN), Rome, Italy took place in April 2018 and was devoted to theoretical research with Prof. A. Varlamov on fluctuation conductivity in strong electric fields in superconductor nanostructures. Quantum fluctuations in gapless superconductor have also been considered as perspective collaboration and some initial calculations have been done. Explicit analytical expressions for the conductivity and fluctuation conductivity above and below critical temperature have been derived in the framework of time dependent Ginzburg-Landau theory and Boltzmann equation for fluctuation Cooper pairs. It is confirmed that below critical temperature in small electric field the differential conductivity becomes negative. At appropriate coupling with a resonator the negative differential conductivity will generate electric oscillations. The maximal frequency of these oscillations is proportional to the critical temperature and for high temperature superconductors the obtained results can stimulate the development of Terahertz generators based on hybrid superconducting devices.