Achieving the depairing limit along the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>c</mml:mi></mml:math> axis in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>Fe</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>+</mml:mo><mml:mi>y</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>Te</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>Se</mml:mi></mml:mrow><mml:mi>x</mml:mi></mml:msub></mml:math> single crystals
Yue Sun, Haruka Ohnuma, Shin-ya Ayukawa, Takashi Noji, Yōji Koike, T. Tamegai, Haruhisa Kitano
Abstract
We report achievement of a depairing current limit along the $c$ axis in ${\mathrm{Fe}}_{1+y}{\mathrm{Te}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x}$ single crystals. A series of crystals with ${T}_{\mathrm{c}}$ ranging from 8.6 K to 13.7 K (different amounts of excess Fe, $y$) were fabricated into $c$-axis bridges with a square-micrometer cross-section. The critical current density, ${J}_{\mathrm{c}}$, was directly estimated from the transport current-voltage measurements. The transport ${J}_{\mathrm{c}}$ reaches a very large value, which is about one order of magnitude larger than the depinning ${J}_{\mathrm{c}}$, but comparable to the calculated depairing ${J}_{\mathrm{c}}\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}\phantom{\rule{4pt}{0ex}}{10}^{6}$ $\mathrm{A}/{\mathrm{cm}}^{2}$ at 0 K, based on the Ginzburg-Landau (GL) theory. The temperature dependence of the depairing ${J}_{\mathrm{c}}$ follows the GL theory [$\ensuremath{\propto}$(1-$T/{T}_{\mathrm{c}}{)}^{3/2}$] down to $\ensuremath{\sim}0.83\phantom{\rule{4pt}{0ex}}{T}_{\mathrm{c}}$, then increases with a reduced slope at low temperatures, which can be qualitatively described by the Kupriyanov-Lukichev theory. Our study provides a route to understand the behavior of depairing ${J}_{\mathrm{c}}$ in iron-based superconductors in a wide temperature range.