Evidence for light and heavy conduction electrons at the zone center in KTaO3

The Shubnikov-de Haas oscillation of the magnetoresistance was observed for the $n$-type KTa${\mathrm{O}}_3$ in the magnetic field up to 105 kOe at liquid-helium temperatures. Angular variation of the extremal areas of the Fermi surface supports the zone-center-warped-band model, and rules out the many-valley model. However, contrary to the theoretical expectation, the $〈100〉$ bulges of the warped Fermi surface of the heavy electron are found to be absent or strongly depressed by some unknown mechanism.