Effective Disappearance of the Meissner Signal in the Cuprate Superconductor YBa2Cu4O8 under Uniaxial Strain

The effects of uniaxial strain and hydrostatic pressure on YBa2Cu4O8 were investigated through magnetic measurements under stresses of up to 25 GPa. The out-of-plane (along the c-axis), in-plane (along the c-plane), and hydrostatic contractions all initially bring about an increase in the superconducting transition temperature (Tc). In the case of the out-of-plane and in-plane contractions, the Meissner signal disappears at a stress corresponding to about 10 GPa. However, under the hydrostatic contraction, the maximum Tc was about 100 K at 9–12 GPa, and the Meissner effect was observed at pressures of at least 16 GPa.