Ian D Lawrie | Searcharxiv

arXiv1998

Nonequilibrium quantum dynamics of phase transitions in an expanding universe

I summarize the derivation of a set of Feynman rules appropriate for the perturbative description of the nonequilibrium dynamics of the symmetry-breaking phase transition in $λϕ^4$ theory in a Robertson-Walker universe. The approximation scheme I develop provides for a treatment of dissipative effects which are essential to an adequate description of the nonequilibrium state. It also provides for the emergence from an initially symmetric state of a final state exhibiting the properties of spontaneous symmetry breaking without the introduction by hand of any explicit symmetry breaking.

hep-ph↗

arXiv1994

Scaling in high-temperature superconductors

A Hartree approximation is used to study the interplay of two kinds of scaling which arise in high-temperature superconductors, namely critical-point scaling and that due to the confinement of electron pairs to their lowest Landau level in the presence of an applied magnetic field. In the neighbourhood of the zero-field critical point, thermodynamic functions scale with the scaling variable $(T-T_{c2}(B))/B^{1/2ν}$, which differs from the variable $(T - T_c(0))/B^{1/2ν}$ suggested by the gaussian approximation. Lowest-Landau-level (LLL) scaling occurs in a region of high field surrounding the upper critical field line but not in the vicinity of the zero-field transition. For YBaCuO in particular, a field of at least 10 T is needed to observe LLL scaling. These results are consistent with a range of recent experimental measurements of the magnetization, transport properties and, especially, the specific heat of high-$T_c$ materials.

cond-mat↗