Instabilities in the flux-line lattice of anisotropic superconductors

Abstract

The stability of the flux-line lattice has been investigated within anisotropic London theory. This is a full-scale investigation of instabilities in the ''chain'' state, the equilibrium lattice that is similar to the Abrikosov lattice at large fields but crosses over smoothly to a pinstripe structure at low fields. By calculating the normal modes of the elasticity matrix, it has been found the lattice is stable at large fields, but that instabilities occur as the field is reduced. The field at which these instabilities first arise, b*(⑀,), depends on the anisotropy ⑀ and the angle at which the lattice is tilted away from the c axis. These instabilities initially occur at wave vector k*(⑀,). The dependence of k* on ⑀ and is complicated, but the component of k* along the average direction of the flux lines, k z , is always finite. For rigid straight flux lines, the cutoff necessary for London theory has been ''derived'' from Landau-Ginzburg theory, where the shape of the vortex core is known. However, for investigating instability at finite k z it is necessary to know the dependence of the cutoff on k z , and we have used a cutoff suggested by Sudbo " and Brandt. The instabilities only occur for values of the anisotropy ⑀ appropriate to a material like BSCCO, and not for anisotropies more appropriate to YBCO. The lower critical field H c 1 () is calculated as a function of the angle at which the applied field is tilted away from the crystal axis. The presence of kinks in H c 1 () is seen to be related to instabilities in the equilibrium flux-line structure.

Vortex matter transition inBi2Sr2CaCu2Ooi1, Shibauchi2, Itaka3 et al. 2000Phys. Rev. B372100View full textAdd to dashboardCite

“…teristic features that H p *() reaches maximum at about 80°a nd decreases at higher angles are consistent with the expectation of the instability field for ␥ϭ60 and ϭ50 by Thompson and Moore. 25 The angle where the instability field has a maximum is predicted to shift to lower angle at smaller anisotropy ␥. This is actually observed in our experiments.…”

“…Besides Koshelev's theory, the instability of uniformly tilted vortex lattice has been predicted by several theories. [23][24][25] Particularly, Thompson and Moore 25 have suggested that uniformly tilted vortex lattice state including vortex chain state observed in YBCO is not stable in low and tilted fields, when the superconductor has larger anisotropy ratio than a threshold. According to their calculation, the threshold is ␥ ϳ12 for ϭ50, which is much smaller than ␥ of BSCCO.…”

Stripe Domains and First-Order Phase Transition in the Vortex Matter of Anisotropic High-Temperature Superconductors

“…Experimentally, stripes of vortices intermittent with Meissner phase were observed in M gB 2 single crystals [13,14] and were treated as a possible consequence of the two different SC condensates in the 2-band magnesium diborate.In this work we discovered a new vortex structure of regular stipe domains with alternating flux density, B z , generated by magnetic fields tilted from the ab-plane in a nearly twin-free YBCO platelet crystal. Unlike vortex/Meissner domains and vortex chain structures, our vortex domains are created via an instability in the vortex state [15][16][17][18][19][20][21][22] due to a first order phase transition characterized by an abrupt jump in the vortex tilt angle [23]. A possibility of such first order transition in the vortex orientation was first noticed by Buzdin and Simonov in [24].…”

Flux-line lattices in artificially layered superconductors

“…The cutoff function S(k) = exp(−ξ 2 k 2 ) removes the divergences within London Theory due to the absence of the flux line cores. The use of different cutoffs within London Theory has been discussed previously 12 .…”