Search results for "Kosterlitz–Thouless transition"
showing 4 items of 4 documents
Flat-band superconductivity in periodically strained graphene: mean-field and Berezinskii–Kosterlitz–Thouless transition
2019
In the search of high-temperature superconductivity one option is to focus on increasing the density of electronic states. Here we study both the normal and $s$-wave superconducting state properties of periodically strained graphene, which exhibits approximate flat bands with a high density of states, with the flatness tunable by the strain profile. We generalize earlier results regarding a one-dimensional harmonic strain to arbitrary periodic strain fields, and further extend the results by calculating the superfluid weight and the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature $T_\text{BKT}$ to determine the true transition point. By numerically solving the self-consistency …
Phase transition in liquid 4HE by a mean field model
2013
In this work the transition of 4He at the lambda line in presence of a Cattaneo- Maxwell heat flux is studied. A hydrodynamical model is formulated, which chooses as fundamental fields the velocity, the temperature, the heat flux and a phase field function f, for which a time dependent Ginzburg-Landau equation is proposed. Using this model we are able to describe the phase transition and to obtain the pressure-temperature phase diagram which represents the transition, the thermodynamic restrictions and a maximum theorem for the phase field.
Vortex–antivortex unbinding in oxygen-deficient YBa2Cu3O7− films
2007
Abstract In-plane zero-magnetic-field current–voltage ( I – V ) characteristics of oxygen-deficient YBa 2 Cu 3 O 7− δ films (7 − δ ∼6.5, 6.55, and 6.65) were thoroughly investigated. A good agreement with the quasi two-dimensional (2D) vortex–antivortex unbinding scenario was observed, similar to the behaviour of highly anisotropic Bi 2 Sr 2 CaCu 2 O 8+ δ films. The temperature variation of the I – V exponent allows the determination of the Berezinskii–Kosterlitz–Thouless transition temperature T KT at the superconducting Cu–O layer level, and the mean-field critical temperature T c0 . We found that both T KT and T c0 increase with increasing doping, and T c0 remains in the region of the …
Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of twisted bilayer graphene
2019
We study superconductivity of twisted bilayer graphene with local and non-local attractive interactions. We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for microscopic tight-binding and low-energy continuum models. We predict qualitative differences between local and non-local interaction schemes which could be distinguished experimentally. In the flat band limit where the pair potential exceeds the band width we show that the superfluid weight and BKT temperature are determined by multiband processes and quantum geometry of the band.