Vortex state study of superconducting Fe(Te, Se) thin films deposited on SrTiO3 substrate by pulsed laser deposition technique

Rohit Kumar,A Mitra,G D Varma

doi:10.1063/1.5129605

Abstract

Superconducting thin films of two thicknesses have been fabricated on (100) oriented SrTiO3 (STO) substrates using the target of composition Fe1.05Te0.50Se0.50 by pulsed laser deposition technique. The structural and transport properties of the fabricated thin films have been investigated and the results indicate the enhancement in the superconducting properties with increasing thickness of the thin films. The onset of the superconducting transition temperature of the grown thin films of thicknesses ∼78 nm and ∼177 nm are ∼12.10 and 12.62 K at 0 T magnetic field, respectively. To estimate the upper critical fields HC2(0), thermally activated energy (TAE) and vortex phase diagram, the magnetoresistance measurements have been performed in the magnetic field range of 0 - 8 T. HC2(0) have been calculated by Ginzburg Landau (GL) theory and Werthamer-Helfand-Hohenberg model by taking the criterion of 90%, 50% and 10% of normal state resistivity and the corresponding GL coherence lengths have also been calculated. In the present work, the TAE has been estimated by conventional Arrhenius relation and modified thermally activated flux flow (TAFF) theory. The power law dependence of TAE, shows prominently the possible planer defects in the system. From the modified TAFF model, the values of fitting parameter ‘q’ suggests the 3 dimensional behaviour of the vortices for both the grown thin films. The vortex phase diagram study reveals the transition from the vortex liquid to vortex glass state.

Highlights

Since the discovery of superconductivity in bulk Fe-based compounds, great efforts have been devoted to the preparation of thin films of different classes of iron (Fe) based superconductors (IBS) on various substrates.[1,2,3,4,5,6] The thin films are useful to understand the basic intrinsic properties of IBS which are comparatively difficult to study in bulk single crystalline samples due to the small size of grown crystals of some of the IBSs, such as LnFeAs(O, F).[1]
The high quality epitaxial thin films of IBS are suitable for the production of Fe based superconducting devices such as superconducting quantum interface devices (SQUIDs), coated conductors and Josephson junctions.[7]
The broadening and shifting of the resistive transitions in external magnetic fields, are subject of great interest in high TC superconductors.[8–12]. Such behaviour of resistive transition is due to the thermal fluctuations developed via short coherence length, large anisotropy and high TC.[11,12]. These thermal fluctuations are responsible for the thermally activated flux flow (TAFF) which leads to the tail in resistive transition induced via the motion of vortices

Summary

INTRODUCTION

Since the discovery of superconductivity in bulk Fe-based compounds, great efforts have been devoted to the preparation of thin films of different classes of iron (Fe) based superconductors (IBS) on various substrates.[1,2,3,4,5,6] The thin films are useful to understand the basic intrinsic properties of IBS which are comparatively difficult to study in bulk single crystalline samples due to the small size of grown crystals of some of the IBSs, such as LnFeAs(O, F).[1]. The broadening and shifting of the resistive transitions in external magnetic fields, are subject of great interest in high TC superconductors.[8–12]. Such behaviour of resistive transition is due to the thermal fluctuations developed via short coherence length, large anisotropy and high TC.[11,12]. These thermal fluctuations are responsible for the thermally activated flux flow (TAFF) which leads to the tail in resistive transition induced via the motion of vortices. Structural and superconducting properties of the Fe(Te, Se) thin films, grown on STO with different thicknesses, have been described

MATERIAL AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS