Quasiparticle Excitation Spectrum of an Isolated Vortex in a High--Temperature Superconduct.pdf

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Quasiparticle Excitation Spectrum of an Isolated Vortex in a High--Temperature Superconduct.pdf

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Quasiparticle Excitation Spectrum of an Isolated Vortex in a High--Temperature Superconduct

a r X i v : c o n d - m a t / 9 8 1 2 1 3 2 v 1 [ c o n d - m a t .s u p r - c o n ] 8 D e c 1 9 9 8 Quasiparticle Excitation Spectrum of an Isolated Vortex in a High–Temperature Superconductor Irena Knez?evic? and Zoran Radovic? Department of Physics, University of Belgrade, P. O. Box 368, 11001 Belgrade, Yugoslavia Abstract The quasiparticle energy spectrum of an isolated vortex in a clean layered d-wave su- perconductor is calculated. The Bogoliubov–de Gennes equations are solved perturbatively, within the model of step-variation of the gap function, adjusting the Caroli, de Gennes and Matricon approach for low-lying excitations in cuprates. A large peak in the density of states in a ”pancake” vortex is found, as a consequence of two-dimensionality and strong coupling. PACS numbers: 74.60.-w, 74.20.Fg Keywords: vortex core, localized states, d–wave superconductor 1 1 Introduction Enhancing interest has been focused on quasiparticle spectra properties around vortices. Density of localized states near the Fermi surface in the vortex core in conventional super- conductors (s–wave pairing, weak coupling, isotropic) is equivalent to the electron density of states of a normal-metal area with radius of the order of the coherence length ξ ～ 10 nm.[1- 3] High-temperature superconductors (HTS) are layered, having a cylindrical Fermi surface, the superconductivity is of d-wave and strong coupling type, the coherence length being much smaller, ξ ～ 1nm. This implies a crucial difference in the quasiparticle spectra in the vortex core between conventional superconductors and HTS. Numerous computations of the quasiparticle spectra around two-dimensional (2D) vor- tices have been performed recently.[4-10] The common feature of layered superconductors is the appearance of a large peak in the quasiparticle density of states (DOS) in the vortex core, in agreement with the scanning tunneling microscopy (STM) observations on NbSe2[11] and YBCO.[12] However, in BSCCO the gap s