9 research outputs found
Influence of Fermi surface topology on the quasiparticle spectrum in the vortex state
We study the influence of Fermi surface topology on the quasiparticle density
of states in the vortex state of type II superconductors. We observe that the
field dependence and the shape of the momentum and spatially averaged density
of states is affected significantly by the topology of the Fermi surface. We
show that this behavior can be understood in terms of characteristic Fermi
surface functions and that an important role is played by the number of points
on the Fermi surface at which the Fermi velocity is directed parallel to the
magnetic field. A critical comparison is made with a broadened BCS type density
of states, that has been used frequently in analysis of tunneling data. We
suggest a new formula as a replacement for the broadened BCS model for the
special case of a cylindrical Fermi surface. We apply our results to the two
gap superconductor MgB and show that in this particular case the field
dependence of the partial densities of states of the two gaps behaves very
differently due to the different topologies of the corresponding Fermi
surfaces, in qualitative agreement with recent tunneling experiments.Comment: 12 pages 12 figure
Lattice dynamics and electron-phonon coupling in transition metal diborides
The phonon density-of-states of transition metal diborides TMB2 with TM = Ti,
V, Ta, Nb and Y has been measured using the technique of inelastic neutron
scattering. The experimental data are compared with ab initio density
functional calculations whereby an excellent agreement is registered. The
calculations thus can be used to obtain electron-phonon spectral functions
within the isotropic limit. A comparison to similar data for MgB2 and AlB2
which were subject of prior publications as well as parameters important for
the superconducting properties are part of the discussion.Comment: 4 pages, 3 figure
Theoretical Study of Electron-Phonon Interaction in ZrB2 and TaB2
Using full-potential, density-functional-based methods we have studied
electron-phonon interaction in ZrB2 and TaB2 in P6/mmm crystal structure. Our
results for phonon density of states and Eliashberg function show that the
electron-phonon coupling in ZrB2 is much weaker than in TaB2. In particular, we
find that the average electron-phonon coupling constant \lambda is equal to
0.14 for ZrB2 and 0.72 for TaB2. The solutions of the isotropic Eliashberg gap
equation indicate no superconductivity for ZrB2 but a superconducting
transition temperature Tc of around 12 K for TaB2 with \mu* ~0.16.Comment: Increased q points from 12 to 28, added 3 figs and a section on
convergence analysi