Superconductor–insulator transitions in three-dimensional indium-oxide at high pressures

Bar Hen,Victor Shelukhin,Gregory Kh Rozenberg,Eran Greenberg,Aharon Kapitulnik,Alexander Palevski

doi:10.1088/1361-648x/ac48bf

Abstract

Experiments investigating magnetic-field-tuned superconductor–insulator transition (HSIT) mostly focus on two-dimensional material systems where the transition and its proximate ground-state phases, often exhibit features that are seemingly at odds with the expected behavior. Here we present a complementary study of a three-dimensional pressure-packed amorphous indium-oxide (InOx) powder where granularity controls the HSIT. Above a low threshold pressure of ∼0.2 GPa, vestiges of superconductivity are detected, although neither a true superconducting transition nor insulating behavior are observed. Instead, a saturation at very high resistivity at low pressure is followed by saturation at very low resistivity at higher pressure. We identify both as different manifestations of anomalous metallic phases dominated by superconducting fluctuations. By analogy with previous identification of the low resistance saturation as a ‘failed superconductor’, our data suggests that the very high resistance saturation is a manifestation of a ‘failed insulator’. Above a threshold pressure of ∼6 GPa, the sample becomes fully packed, and superconductivity is robust, with T C tunable with pressure. A quantum critical point at P C ∼ 25 GPa marks the complete suppression of superconductivity. For a finite pressure below P C, a magnetic field is shown to induce a HSIT from a true zero-resistance superconducting state to a weakly insulating behavior. Determining the critical field, H C, we show that similar to the 2D behavior, the insulating-like state maintains a superconducting character, which is quenched at higher field, above which the magnetoresistance decreases to its fermionic normal state value.

Highlights

In spite of extensive experimental and theoretical studies, the subject of superconductor to insulator quantum phase transitions (SIT) [1,2,3] remains controversial and new experimental findings in this subject are still in great demand
Since the thickness of the films was at most 2000 Å, the authors could not approach the quantum critical point of the disordered driven phase transition while remaining in 3D since the hopping or localization lengths exceeded the thickness of the samples
The resistance does not vanish at very low temperatures, but rather starts to increase upon continuation of cooling to lower temperatures and eventually saturates at ultra-low temperatures attaining a value which is higher than the normal state resistance

Summary

Introduction

In spite of extensive experimental and theoretical studies, the subject of superconductor to insulator quantum phase transitions (SIT) [1,2,3] remains controversial and new experimental findings in this subject are still in great demand. Since the SIT is observed at low temperatures, the tuning parameter cannot be changed using annealing in-situ and, preparation and low temperature measurements of different samples is required For this reason, the most reliable experimental method for studying critical phenomena is achieved a Present address: Applied Physics Division, Soreq Nuclear Research Center (SNRC), Yavne 81800, Israel by bringing the system close to the critical point in a discrete manner using annealing, and applying a continuous control parameter such as magnetic field at low temperatures to drive the system from the superconducting phase to the insulating phase continuously. Magnetic-field-tuned phase transitions in 2D films of InOx were reported in numerous studies [5, 6, 911]. No magnetic-field-tuned phase transition was reported in 3D InOx as well as no saturation of resistivity at low temperatures. The first, to tune the transition without the necessity of annealing, and the second, to enable measurements of much thicker InOx samples up to tens of microns which, for all practical purposes, are 3D

Results

Discussion

Conclusion