Unconventional Transport Properties of Reduced Tungsten Oxide WO2.9

Alexander Shengelaya,Kazimierz Conder,Fabio La Mattina

doi:10.3390/condmat5040063

Abstract

The temperature and magnetic field dependence of resistivity in WO2.9 was investigated. The variation of resistivity with temperature displayed unusual features, such as a broad maximum around 230 K and a logarithmic increase of resistivity below 16 K. In the temperature range 16–230 K, we observed metallic-like behavior with a positive temperature coefficient. The combined analysis of resistivity and magnetoresistance (MR) data shows that these unusual transport properties of WO2.9 can be understood by considering the (bi)polaronic nature of charge carriers. In contrast to magnetization data, superconducting transition below Tc = 80 K was not detected in resistivity measurements, indicating that the superconductivity is localized in small regions that do not percolate. We found a strong increase in positive MR below 80 K. This effect is similar to that observed in underdoped cuprates, where the substantial increase of MR is attributed to superconducting fluctuations in small clusters. Therefore, the temperature dependence of MR indicates the presence of non-percolating superconducting clusters in WO2.9 below 80 K in agreement with magnetization data.

Highlights

It is remarkable that reduced SrTiO3−x was the first oxide in which superconductivity was found in 1964 [1]
The Tc was further increased to 94 K. These results indicate that there is a potential for high-Tc superconductivity in oxygen-reduced tungsten oxide, which has not been sufficiently explored
The DC magnetization measurements were performed on a Quantum Design magnetic property measurement system (MPMS) magnetometer

Summary

Introduction

It is remarkable that reduced SrTiO3−x was the first oxide in which superconductivity was found in 1964 [1]. The composition of the superconducting regions could not be determined due to their small size Another possible method to dope charge carriers in a tungsten oxide is to reduce the oxygen content. Despite the filamentary characteristics of superconductivity and low Tc, an unusually large upper critical field μ0Hc2(0) above 15 T was found in WO3−x This large μ0Hc2(0) violates the Pauli paramagnetic limit by a factor of three. The Tc was further increased to 94 K These results indicate that there is a potential for high-Tc superconductivity in oxygen-reduced tungsten oxide, which has not been sufficiently explored. We report results of combined magnetic, transport, and magnetotransport measurements of oxygen reduced tungsten oxide WO2.9 in a broad temperature range, including the previously unexplored low temperature (T < 80 K) region

Experimental Details

Results and Discussion

Summary and Conclusions