arXiv subjects
Publications and source records attributed to Claude de Calan.
The large N analysis of an extreme type II superconductor is revisited. It is found that the phase transition is of second-order in dimensions 4 < d < 6. For the physical dimension d=3 no sign of phase transition is found, contrary to early claims.
An unifying scenario for the critical behavior of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ (BSCCO) is proposed. It is shown that both critical crossovers observed in these materials follow by considering two different scalings in the dual Ginzburg-Landau model. The first scaling leads to the critical exponents $ν\approx 2/3$, $ν'\approx 1/3$ and $α\approx 0$, with $ν$ and $α$ being respectively the correlation lenght and specific heat exponents while $ν'$ is the magnetic field penetration depth exponent. These values for the critical exponents agree with the ones obtained experimentally for YBCO single crystals. For the second scaling we obtain $ν=1$ and $α=-1$ which must be compared with the measured values $ν\approx 1$ and $α\approx-0.7$ for BSCCO. For the penetration depth exponent it is predicted the value $ν'=1$.
The gauge dependence of the renormalization group functions of the Ginzburg-Landau model is investigated. The analysis is done by means of the Ward-Takahashi identities. After defining the local superconducting order parameter, it is shown that its exponent $β$ is in fact gauge independent. This happens because in $d=3$ the Landau gauge is the only gauge having a physical meaning, a property not shared by the four-dimensional model where any gauge choice is possible. The analysis is done in both the context of the $ε$-expansion and in the fixed dimension approach. It is pointed out the differences that arise in both of these approaches concerning the gauge dependence.
The gauge dependence of the renormalization group functions of the Ginzburg-Landau model is investigated. The analysis is done by means of the Ward-Takahashi identities. After defining the superconducting order parameter, it is shown that its exponent $β$ is in fact gauge independent. This happens because in d=3 the Landau gauge is the only gauge having a physical meaning, a property not shared by the four-dimensional model where any gauge choice is possible. The analysis is done in both the context of the $ε$-expansion and in the fixed dimension approach. It is pointed out the differences that arise in both of these approaches concerning the gauge dependence.