Reentrant Resistive Behavior and Dimensional Crossover in Disordered Superconducting TiN Films

Svetlana V Postolova,Valerii M Vinokur,Mikhail R Baklanov,Alexey Yu Mironov,Tatyana I Baturina

doi:10.1038/s41598-017-01753-w

Svetlana V Postolova, Valerii M Vinokur + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-01753-w

Copy DOI

Abstract

A reentrant temperature dependence of the normal state resistance often referred to as the N-shaped temperature dependence, is omnipresent in disordered superconductors – ranging from high-temperature cuprates to ultrathin superconducting films – that experience superconductor-to-insulator transition. Yet, despite the ubiquity of this phenomenon its origin still remains a subject of debate. Here we investigate strongly disordered superconducting TiN films and demonstrate universality of the reentrant behavior. We offer a quantitative description of the N-shaped resistance curve. We show that upon cooling down the resistance first decreases linearly with temperature and then passes through the minimum that marks the 3D–2D crossover in the system. In the 2D temperature range the resistance first grows with decreasing temperature due to quantum contributions and eventually drops to zero as the system falls into a superconducting state. Our findings demonstrate the prime importance of disorder in dimensional crossover effects.

Highlights

We undertake a careful study of the strongly disordered ultrathin TiN superconducting film and find that its reentrant behavior occurs due to combined effects of the crossover from the 3D behavior determined by the Bloch-Grüneisen law to the quasi-2D behavior governed by competing quantum contributions to conductivity
As a function of the decreasing temperature, the resistance first decreases linearly at high temperatures, deviates upwards from R ∝ T reaching the minimum at some temperature T*
We construct the phase diagram displaying the effective dimensionality of the TiN films and the corresponding mechanisms of the conductivity

Summary

Introduction

We undertake a careful study of the strongly disordered ultrathin TiN superconducting film and find that its reentrant behavior occurs due to combined effects of the crossover from the 3D behavior determined by the Bloch-Grüneisen law to the quasi-2D behavior governed by competing quantum contributions to conductivity. We summarize our results by phase diagram in the conductance-temperature coordinates. The data are taken on thin, 7 ≤ d ≤ 23 nm, TiN films formed on a Si/SiO2 substrate by the atomic layer deposition. Dashed lines are fits accounting for all the quantum contributions to conductivity (see Fig. 3a and the discussion in the text). The parameters of the sample are calculated in the approximation of the parabolic dispersion law, from the superconducting critical temperature Tc, and carrier density n is found from the measurements of the Hall effect at T = 10 K. Transport measurements are carried out using the low-frequency ac technique in a four-probe configuration

Methods

Results

Discussion

Conclusion