Pseudogap in a thin film of a conventional superconductor

TL;DR

This paper demonstrates the existence of a pseudogap in ultrathin titanium nitride films, induced by superconducting fluctuations, challenging the notion that pseudogaps are exclusive to high-temperature superconductors.

Contribution

It provides evidence of a pseudogap in a conventional superconductor, showing it arises from fluctuations and two-dimensional effects, not solely from unconventional mechanisms.

Findings

Pseudogap observed in ultrathin titanium nitride films above Tc.

Pseudogap is induced by superconducting fluctuations.

Two-dimensionality and proximity to insulating transition favor pseudogap formation.

Abstract

A superconducting state is characterized by the gap in the electronic density of states which vanishes at the superconducting transition temperature Tc. It was discovered that in high temperature superconductors a noticeable depression in the density of states still remains even at temperatures above Tc; this feature being called pseudogap. Here we show that a pseudogap exists in a conventional superconductor: ultrathin titanium nitride films over a wide range of temperatures above Tc. Our study reveals that this pseudogap state is induced by superconducting fluctuations and favored by two-dimensionality and by the proximity to the transition to the insulating state. A general character of the observed phenomenon provides a powerful tool to discriminate between fluctuations as the origin of the pseudogap state, and other contributions in the layered high temperature superconductor compounds.