Scanning SQUID microscopy of sparsely twinnedYBa2Cu3

Abstract

Magnetic images of two sparsely twinned YBa 2 Cu 3 O 7Ϫ␦ single crystals were taken in low applied magnetic fields (H a Ͻ100 mG͒ with a scanning SQUID microscope. The SQUID sensors have 4 or 8 m pickup loops and a magnetic flux resolution of 10 Ϫ3 hc/2e under normal operating conditions. The images showed Meissner screening with a large demagnetization factor and isolated trapped vortices. The trapped vortices carried integral (hc/2e) magnetic flux and were much smaller than the spatial resolution of the sensor. At this level of resolution, there was no evidence for unusual magnetic features, such as fractional vortices, associated with the twin boundaries.

Low temperature specific heat of the hole-dopedBa0.6K0.4Fe2As2Mu1, Luo2, Wang3 et al. 2009Phys. Rev. B181311803View full textAdd to dashboardCite

“…This linear behavior is actually anticipated by the theoretical prediction for superconductors with a full gap [29], in which γ(H) is mainly contributed by the localized quasiparticle DOS within vortex cores. This is in sharp contrast with the results in cuprates [30,31] and the LaFeAsO 0.9 F 0.1−δ system [4] where a γ(H) ∝ √ H relation was observed and attributed to the Doppler shift of the nodal quasiparticle spectrum. The curve plotted using the relation γ(H) = A √ H is also presented in Fig.…”

Electronic specific heat and low-energy quasiparticle excitations in the superconducting state ofLa2−xSrxCuO4Wen1, Liu2, Zhou3 et al. 2004Phys. Rev. B613440View full textAdd to dashboardCite

“…It was shown that the contribution from the delocalized part (outside the core) will prevail over the core part and the specific heat is predicted to behave as 15,16 C vol = kγ n T H/H c2 with k in the order of unity. This prediction has been verified by many measurements which were taken as the evidence for d-wave symmetry 8,9,10,11,12,13,14,17 . In the finite temperature and field region a scaling law is proposed 18 as…”

“…This scaling law can be further converted into the form of C vol /H = g(T / √ H) or C vol /T 2 = y(T / √ H), here f (x), or g(x) or y(x) are unknown scaling functions. This scaling law has been proved in Y BCO 8,9,10 and in LSCO 11,12,13,14 . It remains however unclear whether this scaling law is still valid in the very overdoped region since the vortex core size ξ grows up.…”

“…This has been supported by tremendous experiments 1 both from surface detection 2,3,4,5,6 and bulk measurements 7,8,9,10,11,12,13,14 . In a d-wave superconductor with line nodes in the gap function, the quasiparticle density of states (DOS) N (E) rises linearly with energy at the Fermi level in zero field, i.e., N (E) ∝ |E − E F |, resulting in 15 an electronic specific heat C e = αT 2 , where α ∝ γ n /T c and γ n is the specific heat which is proportional to the DOS at the Fermi level of the normal state.…”

“…In addition, as observed in other cuprate superconductors, the curve at zero field extrapolates to a finite value (γ 0 ) at 0 K instead of zero. This was interpreted as potential scattering effect due to small amount impurities or disorders 8,30 . We will argue that this residual linear term may also reflect physics beyond the simple argument of impurity scattering (see later).…”