paper

Relationship between critical current and flux-flow resistivity in the mixed state of Ba(Fe $_{1 - x}$ Co $_{x}$ ) $_{2}$ As $_{2}$

arXiv:1706.00543 · doi:10.1103/PhysRevB.96.094509

Abstract

We studied the temperature and magnetic field dependence of vortex dissipation and critical current in the mixed-state of unconventional superconducting alloys Ba(Fe $_{1 - x}$ Co $_{x}$ ) $_{2}$ As $_{2}$ ( $0.044 \leq x \leq 0.100$ ) through current-voltage measurements. Our results reveal that all the electric field $E$ vs current density $j$ curves in the Ohmic regime merge to one point ( $j_{0}, E_{0}$ ) and that there is a simple relationship between the critical current density $j_{c}$ and flux-flow resistivity $I ¨ _{ff}$ : $I ¨ _{ff} / I ¨ _{n} = (1 - j_{c} / j_{0})^{- 1}$ , where $I ¨ _{n} = E_{0} / j_{0}$ is the normal-state resistivity just above the superconducting transition. In addition, $E_{0}$ is positive for all five dopings, reflecting the abnormal behavior of the flux-flow resistivity $I ¨ _{ff}$ : it increases with decreasing magnetic field. In contrast, $E_{0}$ is negative for the conventional superconductor Nb since, as expected, $I ¨ _{ff}$ decreases with decreasing magnetic field. Furthermore, in the under-doped and over-doped single crystals of Ba(Fe $_{1 - x}$ Co $_{x}$ ) $_{2}$ As $_{2}$ , the parameter $E_{0}$ remains temperature independent, while it decreases with increasing temperature for the single crystals around optimal doping ( $0.060 \leq x \leq 0.072$ ). This result points to the co-existence of superconductivity with some other phase around optimal doping.

6 pages, 6 figures

Relationship between critical current and flux-flow resistivity in the mixed state of Ba(Fe1−x​Cox​)2​As2​

Abstract

Relationship between critical current and flux-flow resistivity in the mixed state of Ba(Fe $_{1 - x}$ Co $_{x}$ ) $_{2}$ As $_{2}$