Achieving the depairing limit along $c$ axis in Fe$_{1+y}$Te$_{1-x}$Se$_x$ single crystals

TL;DR

This study demonstrates that the critical current density along the c-axis in Fe$_{1+y}$Te$_{1-x}$Se$_x$ single crystals reaches the theoretical depairing limit, providing insights into the fundamental current-carrying capacity of iron-based superconductors.

Contribution

The paper reports the first experimental achievement of depairing current limit along the c-axis in Fe-based superconductor crystals, aligning with Ginzburg-Landau theory predictions.

Findings

Transport critical current density approaches the depairing limit.

Temperature dependence follows GL theory down to ~0.83 T_c.

Depairing J_c estimated at ~2 x 10^6 A/cm^2 at 0 K.

Abstract

We report the achieving of depairing current limit along $c$-axis in Fe$_{1+y}$Te$_{1-x}$Se$_x$ single crystals. A series of crystals with $T_{\rm{c}}$ ranging from 8.6 K to 13.7 K (different amount of excess Fe, $y$) were fabricated into $c$-axis bridges with a square-micrometer cross-section. The critical current density, $J_{\rm{c}}$, was directly estimated from the transport current-voltage measurements. The transport $J_{\rm{c}}$ reaches a very large value, which is about one order of magnitude larger than the depinning $J_{\rm{c}}$, but comparable to the calculated depairing $J_{\rm{c}}$ $\sim$ 2 $\times$ 10$^6$ A/cm$^2$ at 0 K, based on the Ginzburg-Landau (GL) theory. The temperature dependence of the depairing $J_{\rm{c}}$ follows the GL-theory ($\propto$ (1-$T/T_{\rm{c}}$)$^{3/2}$) down to $\sim$ 0.83 $T_{\rm{c}}$, then increases with a reduced slope at low temperatures, which can be qualitatively described by the Kupriyanov-Lukichev theory. Our study provides a new route to understand the behavior of depairing $J_{\rm{c}}$ in iron-based superconductors in a wide temperature range.