Abstract
We study the current-voltage characteristics of Fe(Se,Te) thin films deposited on CaF2 substrates in form of nanostrips (width w ~ λ, λ the London penetration length). In view of a possible application of these materials to superconductive electronics and micro-electronics we focus on transport properties in small magnetic field, the one generated by the bias current. From the characteristics taken at different temperatures we derive estimates for the pinning potential U and the pinning potential range δ for the magnetic flux lines (vortices). Since the sample lines are very narrow, the classical creep flow model provides a sufficiently accurate interpretation of the data only when the attractive interaction between magnetic flux lines of opposite sign is taken into account. The observed voltages and the induced depression of the critical current of the nanostrips are compatible with the presence of a low number (lesssim 10) magnetic field lines at the equilibrium, a strongly inhomogeneous current density distribution at the two ends of the strips and a reduced Bean Livingston barrier. In particular, we argue that the sharp corners defining the bridge geometry represent points of easy magnetic flux lines injection. The results are relevant for creep flow analysis in superconducting Fe(Se,Te) nanostrips.
Highlights
Iron based superconductors are object of intense investigations as concerns their fundamental properties[1,2,3,4,5,6,7,8,9,10]
The resistive state of current-voltage characteristics (CVCs) emerges at finite temperatures, well below Tc, at small bias current densities, revealing the occurrence of creep flow, i.e. the vortex thermal depinning process
We have studied the resistive state induced by the current in Fe(Se0.5,Te0.5) superconducting nanostrips, in view of a potential application of iron based superconductors in the field of electronics and nano-electronics
Summary
Iron based superconductors are object of intense investigations as concerns their fundamental properties[1,2,3,4,5,6,7,8,9,10]. In the case of micro-electronics and nano-electronics applications based on the new superconducting materials, like iron based pnictides and chalcogenides, the study of the pinning energy and of the current transport under condition of weak magnetic fields is of fundamental interest In these kind of applications the magnetic field experienced by the films, typically patterned in the form of submicron strip-lines, is as low as few tens of gauss. With conventional flux creep models in zero external field[21, 22] qualitatively accounts for the observed features, a corrective term, proportional to film thickness d normalized to the width w of the strip (d/w) had to be introduced for improving the accuracy of the pinning energy estimate This correction stems from the very narrow width, of nano-metric order, of the samples considered in the tests. In the Discussion section we: (i) review the mechanism underlying the onset of resistance in a superconducting strip driven by the bias current; (ii) identify several possible issues related to the scaling from micro to nano-scale of the samples and focus on the vortex anti-vortex interaction effect on creep; (iii) calculate the pinning potential U(T) with and without the effect of this interaction;(iv) try to identify the type of defects; (v) draw the conclusions
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