Pressure effects on out-of-plane resistivity in La2-xSrxCuO4

We have investigated pressure and temperature dependence of out-of-plane resistivity ρc for La2-xSrxCuO4. By applying pressure, we found a drastic decrease in ρc which reaches 50% at 8 GPa. If the out-of-plane conduction is caused by the tunneling or hopping between adjacent CuO2 layers, then the strong pressure dependence of ρc is understood in terms of a small variation of the interlayer spacing. In comparison with a change of ρc(T) estimated from the thermal contraction of interlayer spacing, the well-known T-linear term in ρc does not mean the coherent band conduction. Therefore, the nonmetallic ρc(T) is a key feature for understanding the exotic electronic states of high-Tc cuprates. We propose one of the possible functional forms of ρc(T) which reasonably include both the high-temperature T-linear term AT+B and the semiconductor-like upturn at low temperatures. (orig.)