Strong pinning and vortex energy distributions in single crystalline Ba(Fe1-xCox)2As2

S. DEMIRDIS; C. J. VAN DER BEEK ; Y. FASANO; N. R. CEJAS BOLECEK; H. PASTORIZA; D. COLSON ; F. RULLIER-ALBENQUE

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Año: 2011 vol. 84 p. 94517 - 94524

1098-0121

The interrelation between heterogeneity and flux pinning is studied in Ba(Fe1−xCox )2As2 single crystals with widely varying Co content x.Magnetic Bitter decoration of the superconducting vortex ensemble in crystals with x = 0.075 and x = 0.1 reveals highly disordered vortex structures. The width of the Meissner belt observed at the edges of the crystals, and above the surface steps formed by cleaving, as well as the width of the intervortex distance distribution, indicate that the observed vortex ensemble is established at a temperature just below the critical temperature Tc. The vortex interaction energy and pinning force distributions extracted from the imagesstrongly suggest that the vortex lattice disorder is attributable to strong pinning due to spatial fluctuations of Tc and of the superfluid density. Correlating the results with the critical current density yields a typical length scale of the relevant disorder of 40–60 nm.