Possible Indications of Electronic Inhomogeneities in Superconducting Nanowire Detectors

Abstract

The voltage-carrying state of superconducting NbTiN nanowires, used for single-photon detectors, is analyzed. Upon lowering the current, the wire returns to the superconducting state in a steplike pattern, which differs from sample to sample. Elimination of geometrical inhomogeneities, such as sharp corners, does not remove these steplike features. They appear to be intrinsic to the material. Since the material is strongly disordered, electronic inhomogeneities are considered as a possible cause. A thermal model, taking into account random variations of the electronic properties along the wire, is used as an interpretative framework.

Superconducting Nanowires for Single‐Photon Detection: Progress, Challenges, and Opportunities

“…The effects of geometry on timing jitter became clearer when devices that involve SNSPDs connected in parallel (superconducting nanowire avalanche photodetectors, SNAPs) and other large‐area devices demonstrated high SNR but high timing jitter . Similar to DE and DCR, constrictions in the wires (narrower areas due to inhomogeneity in fabrication, due to substrates effects, due to granular structure or due to current crowding) deteriorate also timing performance . Pictorial illustration of the effects of constrictions and inhomogeneities on timing jitter is given in Figure .…”

Optical Single-Photon Detection in Micrometer-Scale NbN Bridges

“…The commonly used material for single photon-detection is NbN with a thickness of about 5 nanometer, chosen because of its fast electronphonon relaxation including phonon-escape to the substrate. However, such films have a fairly high resistivity, a low diffusion constant, and a high resistance per square in the order of 800 Ω, which implies that they have an intrinsic tendency to become electronically inhomogeneous with a spatially fluctuating superconducting energy gap [10,11], which may worsen due to material imperfections. Therefore, it is to be expected that the critical current for a long superconducting wire is determined by the weakest spot, which statistically will be the lowest value of the energy gap along the wire.…”

Characterization of superconducting nanowire single-photon detector with artificial constrictions

“…A series of articles have proven that current-crowding effect appears in the bend or the turn in a superconducting nanowire which happens to exist in artificial constrictions. [10][11][12][13] As a result, J sw should be smaller than the intrinsic critical current density of the film.…”