Isotope, pressure, and doping effects on the pseudogap in the LSCO-type compounds studied by neutron spectroscopy

Abstract

Isotope, pressure, and doping effects on the pseudogap temperature T ∗ were investigated by neutron spectroscopic experiments of the relaxation rate of crystal-field excitations in La 1.96− x Sr x Ho 0.04CuO 4 ( x=0.11, 0.15, 0.20). With increasing doping, T ∗ is found to decrease from 80 K ( x=0.11) to 60 K ( x=0.15) and 50 K ( x=0.20). The application of hydrostatic pressure ( p=0.8 GPa) results in a downward shift of T ∗ by 5 K for the optimally doped compound. Upon oxygen isotope substitution ( 18O vs 16O), T ∗ is shifted upwards by 20, 10, and 5 K for x=0.11, x=0.15, and x=0.20, respectively. The large isotope and pressure effects indicate that lattice fluctuations are involved in the pseudogap phenomena. Our relaxation data are compatible with the unusual temperature dependence of the gap function in the pseudogap region, namely a breakup of the Fermi surface into disconnected arcs.