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B. L. Gyorffy

Publications and source records attributed to B. L. Gyorffy.

43 records · Page 3Linked to original sources
arXiv2000

A First-Principles Theory of Bloch Walls in Ferromagnets

We present a first principles account of Bloch Walls on the basis of relativistic Spin-Density Functional Theory in the Local Density Approximation (LDA). We argue that calculations based on this description will provide useful and novel informations about the physics of this important element of micro-magnetics. To illustrate the points we wish to make we implement the proposed calculations for Fe and determine the Bloch Wall thickness $\ell_{BW}$. Moreover we study features of the electronic structure which arise due to the presence of the Bloch Wall.

cond-mat.mtrl-sci↗
arXiv1999

Oscillatory Exchange Coupling across Cr$_{(1-x)}$V$_x$ Alloy spacers

We have identified the pieces of the Fermi surface responsible for the long period oscillations of magnetic coupling across Cr and Cr$_{(1-x)}$V$_x$ alloy spacers in metallic multilayers. Analysing experiments and results of KKR-CPA calculations we find that the periods are determined by the extremal wave~vectors of the hole pockets centered on the N-point in the Brillouin zone.

cond-mat.mtrl-sci↗
arXiv1999

Van Hove Singularity and Superconductivity in Disordered Sr2RuO4

On the basis of a simple model we analyse the influence of disorder on critical temperature T_C in p-wave superconductors. The disorder is treated by means of the Coherent Potential Approximation (CPA) and we focus our attention on the effect of a van Hove singularity near Fermi energy E_F. For the appropriate values of its parameters our model reproduces the experimentally found behaviour of Sr2RuO4.

cond-mat↗
arXiv1999

Percolation of Superconductivity

In case of superconductors whose electrons attract each other only if they are near certain centers, the question arises 'How many such centers are needed to make the ground state superconducting?' We shall examine it in the context of a random U Hubbard model. In short we study the case where U_i is -|U| and 0 with probability c and 1-c respectively on a lattice whose sites are labelled i using the Gorkov decoupling and the Coherent Potential Approximation (CPA). We argue that for this model there is a critical concentration c_0 below which the system is not a superconductor.

cond-mat.supr-con↗
arXiv1999

Coherent Potential Approximation for `d - wave' Superconductivity in Disordered Systems

A Coherent Potential Approximation is developed for s-wave and d-wave superconductivity in disordered systems. We show that the CPA formalism reproduces the standard pair-breaking formula, the self-consistent Born Approximation and the self-consistent T-matrix approximation in the appropriate limits. We implement the theory and compute T_c for s-wave and d-wave pairing using an attractive nearest neighbor Hubbard model featuring both binary alloy disorder and a uniform distribution of scattering site potentials. We determine the density of states and examine its consequences for low temperature heat capacity. We find that our results are in qualitative agreement with measurements on Zn doped YBCO superconductors.

cond-mat.supr-con↗
arXiv1998

Van Hove Singularity and D-Wave Pairing in Disordered Superconductors

We apply the coherent potential approximation (CPA) to a simple model for disordered superconductors with d-wave pairing. We demonstrate that whilst the effectiveness of an electronic Van Hove singularity to enhance the transition temperature T$_c$ is reduced by disorder it is not eliminated. In fact we give a qualitative account of changes in the T$_c$ vs. doping curve with increasing disorder and compare our results with experiments on the Y_{0.8}Ca_{0.2}Ba_2(Cu_{1-c}Zn_c)_{3}O_{7-δ} alloys.

cond-mat.supr-con↗