Flux melting in Bi2Sr2CaCu2O8+δ: Incorporating both electromagnetic and Josephson couplings

Abstract

Multilevel Monte Carlo simulations of a Bi2Sr2CaCu2O8+δ (BSCCO) system are carried out including both Josephson and electromagnetic couplings for a range of anisotropies. A first-order melting transition of the flux lattice is seen on increasing the temperature and/or the magnetic field. The phase diagram for BSCCO is obtained for different values of the anisotropy parameter γ. The best fit to the experimental results of Majer et al. [Phys. Rev. Lett. 75, 1166 (1995)] is obtained for γ≈250 provided one assumes a temperature dependence λ2(0)∕λ2(T)=1−t of the penetration depth with t=T∕Tc. Assuming a dependence λ2(0)∕λ2(T)=1−t2 the best fit is obtained for γ≈450. For finite anisotropy the data are shown to collapse on a straight line when plotted in dimensionless units which shows that the melting transition can be satisfied with a single Lindemann parameter whose value is about 0.3. A different scaling applies to the γ=∞ case. The energy jump is measured across the transition and for large values of γ it is found to increase with increasing anisotropy and to decrease with increasing magnetic field. For infinite anisotropy we see a two-dimensional behavior of flux droplets with a transition taking place at a temperature independent of the magnetic field. We also show that for smaller values of anisotropy it is reasonable to replace the electromagnetic coupling with an in-plane interaction represented by a Bessel function of the second kind (K0), thus justifying our claim in a previous paper.

Source-reported materials — not catalogue approval

Similar papers