Method for Measuring the Momentum-Dependent Relative Phase of the Superconducting Gap of High-Temperature Superconductors

摘要

The phase variation of the superconducting gap over the (normal) Fermisurface of the high-temperature superconductors remains a significantunresolved question. Is the phase of the gap constant, does it change sign, oris it perhaps complex? A detailed answer to this question would provideimportant constraints on various pairing mechanisms. Here we propose a newmethod for measuring the relative gap PHASE on the Fermi surface which isdirect, is angle-resolved, and probes the bulk. The required experimentsinvolve measuring phonon linewidths in the normal and superconducting state,with resolution available in current facilities. We primarily address theLa_1.85Sr_.15CuO_4 material, but also propose a more detailed study of aspecific phonon in Bi_2Sr_2CaCu_2O_8.