Spin excitation in d-wave superconductors: a Fermi liquid picture

Abstract

A detailed study of the inelastic neutron scattering (INS) spectra of the high- T c cuprates based on the Fermi liquid (FL) picture is given. We focus on the issue of the transformation between the commensurate and incommensurate (IC) excitation driven by frequency or temperature. For La 2− x Sr x CuO 4 (LSCO), the condition of small Δ(0)/ v F can simultaneously reproduce the always existing IC peaks in the superconducting (SC) and normal states, and the always fixed location at temperature or frequency change. For YBa 2Cu 3O 6+ x (YBCO), a moderate Δ(0)/ v F and proximity of the van Hove singularity (vHS) at M=(0,π) to the Fermi level can reproduce the frequency- and temperature-driven shifting IC peaks in the SC state, and the vanishing of the IC peak in the normal state. We address the conditional peak shifting behavior to a refined consideration on the nesting effect which is previously overlook. As a result, both the well documented data on LSCO and the recent data on YBCO (on YBa 2Cu 3O 6.7 by [Phys. Rev. Lett 83 (1999) 608] and YBa 2Cu 3O 6.85 by [Science 288 (2000) 1234]) can be reasonably reconciled within a FL picture. We also point out that the one-dimensional-like data by [Condmat/9811100; Nature 404 (2000) 729] on a detwinned and more underdoped sample YBa 2Cu 3O 6.6 could be due to a gap anisotropy effect originally discussed by [Phys. Rev. B 53 (1996) 5889], and we proceed to suggest a way of clarifying it.