Density of states of narrow superconducting channels in the regime of quantum fluctuations of the order parameter

The current–voltage characteristics of superconductor–insulator–semiconductor (S$_1$–I–S$_2$) tunnel junctions, where superconducting electrode S$_2$ is a thin nanowire, are studied experimentally. The observed blurring of the gap singularities is interpreted as a manifestation of the order parameter quantum fluctuations. We propose a model taking into account the broadening of the density of states due to the interaction of electrons with the Mooij–Schön plasmon mode emerging in a quasi-one-dimensional superconducting channel in the regime of quantum fluctuations of the order parameter. The model gives results that are in a reasonable qualitative agreement with the experimental data.