Large magnetoresistance of insulating silicon films with superconducting nanoprecipitates

V Heera,J Fiedler,W Skorupa

doi:10.1063/1.4964931

Abstract

We report on large negative and positive magnetoresistance in inhomogeneous, insulating Si:Ga films below a critical temperature of about 7 K. The magnetoresistance effect exceeds 300 % at temperatures below 3 K and fields of 8 T. The comparison of the transport properties of superconducting samples with that of insulating ones reveals that the large magnetoresistance is associated with the appearance of local superconductivity. A simple phenomenological model based on localized Cooper pairs and hopping quasiparticles is able to describe the temperature and magnetic field dependence of the sheet resistance of such films.

Highlights

The magnetoresistance MR is the relative change of the resistance R of a material in a magnetic field B
We report on large negative and positive MR in Ga-rich, p-type Si films and demonstrate that a simple phenomenological model based on local superconductivity and hopping transport can describe the complex temperature and field dependence of the resistance
The critical temperature T c Cooper pairs are formed in the Garich nanoprecipitates which remain localized if the distance between neighboring superconducting regions is too large or the Coulomb barrier too high for tunneling

Summary

INTRODUCTION

The magnetoresistance MR is the relative change of the resistance R of a material in a magnetic field B. MR as well as the related Hall effect are caused by the Lorentz force acting on the charge carriers in a magnetic field perpendicular to the current direction. Large MR has been observed in several inhomogeneous or disordered materials that exhibit a superconductor-insulator transition[21,22] as e.g. thin amorphous or granular metallic films on insulators,[23,24,25,26] fractal Pb films on silicon,[27] Pb-Si hetorojunctions,[28] amorphous metal-metalloid films,[29,30,31,32,33] cuprate superconductors[34,35,36,37,38] and heavily doped semiconductors.[39,40,41,42,43] There has been an academic debate about the nature of this phase transition and the origin of the large negative MR.[12,44,45,46] Some theories consider a global quantum phase transition[21,33,47,48] or quantum corrections to the classical magnetotransport.[12,24,49,50] Here we report on large negative and positive MR in Ga-rich, p-type Si films and demonstrate that a simple phenomenological model based on local superconductivity and hopping transport can describe the complex temperature and field dependence of the resistance

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS