B. Mitrović

Monte Carlo study of the XY-model on Penrose lattices

We have carried out a Monte Carlo study of the nearest-neighbour ferromagnetic XY-model on the two-dimensional (2D) Penrose lattice and on periodically stacked (three-dimensional) 2D Penrose lattices. For the 2D case we have examined the magnetization, specific heat, linear susceptibility, helicity modulus and the derivative of the helicity modulus with respect to inverse temperature. The behaviour of all of these quantities points to a Kosterlitz-Thouless transition occurring in the temperature range , with critical exponents that are consistent with those obtained for crystalline (e.g., square) lattices. For the 3D stacking of the 2D Penrose lattices, examination of the magnetization, specific heat and linear susceptibility reveals a conventional second-order phase transition. Through cumulant analysis and finite-size scaling we obtain a critical temperature and critical exponents and , in agreement with previous studies of the XY-model on the 3D cubic lattice.

Functional derivatives of T\(\mathsf{_c}\) for a two-band superconductor: application to MgB\(\mathsf{_{2}}\)

We address the question of how phonons of various frequencies contribute to the superconducting transition temperature

NMR relaxation time in a clean two-band superconductor

T_c

Why do the self-energy effects appear in the elastic tunneling conductance?

of a multi-band superconductor by considering the functional derivatives of

Effect of disorder on the far-infrared conductivity and on the microwave conductivity of two-band superconductors

T_c

Effect of disorder on the NMR relaxation rate in two-band superconductors

with respect to various intraband and interband electron-phonon coupling functions. A general scheme for computing such functional derivatives is developed. The proofs are given that the functional derivatives which are diagonal in band indices are linear in phonon energy

Superconducting and normal state properties of Sr0.15La1.85CuO4 determined from magnetization measurements

Omega

The absence of phase transition for the classical XY-model on Sierpiński pyramid with fractal dimension D=2

at small

Possible two-dimensional XY spin/gauge glasses on periodic and quasiperiodic lattices

Omega

Divergence of the orbital nuclear magnetic relaxation rate in metals

, while the functional derivatives which are off-diagonal in band indices diverge at