External factors acting on low-temperature conductivity of superconductor–insulator–normal metal–insulator–superconductor tunnel structures

We review the most notable experiments conducted at the Institute for Physical Problems, Russian Academy of Sciences, in cooperation with the Kotelnikov Institute of Radioengineering and Electronics, Russian Academy of Sciences, on the effect that millimeter-wave irradiation, temperature $T$, and magnetic field $B$ have on the conductivity of superconductor–insulator–normal metal–insulator–superconductor (SINIS) tunnel structures at temperatures $T\ll T_{\rm c}$ and at low voltages, such that the single-electron current is comparable to or smaller than the subgap two-electron Andreev current. We find that, under irradiation with energy of quanta $\hbar \omega \gg kT$, the normal-metal electron subsystem does not reach equilibrium. Under pulsed irradiation, the time constant of SINIS structures regarded as radiation detectors is estimated at the level of a few microseconds. The effect of a magnetic field on the single-electron and Andreev conductivity of SINIS structures is studied.