Eur. Phys. J. B 19, 5-8 (2001)
https://doi.org/10.1007/s100510170343

Large copper isotope effect on the pseudogap in the high-temperature superconductor HoBa₂Cu₄O₈

¹ Laboratory for Neutron Scattering, ETH Zurich & PSI Villigen, 5232 Villigen PSI, Switzerland
² Petersburg Nuclear Physics Institute, Gatchina 188350, Russia
³ Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland
⁴ Physics Institute, University of Zurich, 8057 Zurich, Switzerland

Corresponding author: ^a albert.furrer@psi.ch

Received: 13 October 2000
Published online: 15 January 2001

Abstract

The copper isotope effect (⁶³Cu vs. ⁶⁵Cu) on the relaxation rate of crystal-field excitations in the slightly underdoped high-temperature superconductor HoBa₂Cu₄O₈ has been investigated by inelastic neutron scattering. For the ⁶³Cu compound there is clear evidence for the opening of an electronic gap in the normal state at 160 K far above K. Upon substitution of ⁶³Cu by ⁶⁵Cu, T_c decreases marginally to 78.6 K, whereas is increased to about 185 K. This large copper isotope shift K -together with the corresponding oxygen isotope shift K found in an earlier investigation -suggests that phonons or lattice fluctuations involving both the copper and the oxygen ions are important for the pairing mechanism in high-T_c materials.