Pressure effects on anisotropic resistivity in detwinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }:$ Unconventional carrier doping

We investigated pressure dependence of the in-plane, chain, and out-of-plane resistivity of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ under hydrostatic pressure P of up to 2 GPa using detwinned crystals. A dramatic decrease in all the resistive components and the disappearance of ${\rho }_c\mathrm{}\left(T\right)\mathrm{}$ upturn with P can be explained by assuming that applied pressure induces additional carriers in both the ${\mathrm{CuO}}_2$ planes and the CuO chains, as is similar to the chemical doping. Therefore, the conventional model of the carrier transfer from the chains to the planes is to be reexamined.