Superconducting Tunnel Junction Radiation Detectors

Abstract

Superconducting tunnel junction (STJ) radiation detectors consist of two superconducting electrodes separated by a thin insulating tunnel barrier. Absorption of radiation in one of the electrodes excites excess quasiparticles above the superconducting gap in proportion to the deposited energy, and the subsequent increase in tunneling current can be read out with an amplifier at room temperature. STJ detectors are categorized as quantum detectors that convert incoming radiation into an electrical signal directly. When a photon is absorbed in a superconducting material, it initially transfers its entire energy to a single photoelectron. Since superconductors have zero resistance and therefore cannot sustain a voltage to drift excess quasiparticles to the electrodes, the junction structure is needed to provide a preferential direction of the quasiparticle flow. To combine high spectral and high spatial resolution, an absorber can be read out by two STJs on opposite sides so that the charge from a single photon produces two coincident signals.