Transport Anomalies and the Role of Pseudogap in the 60-K Phase ofYBa2Cu3O7−δ

We report the result of our accurate measurements of the $a$- and $b$-axis resistivity, Hall coefficient, and the $a$-axis thermopower in untwinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ single crystals in a wide range of doping. It is found that both the $a$-axis resistivity and the Hall conductivity show anomalous dependences on the oxygen content $y$ in the 60-K phase below the pseudogap temperature $T^{*}$. The complete data set enables us to narrow down the possible pictures of the 60-K phase, with which we discuss a peculiar role of the pseudogap in the charge transport.