Comment on `Electronic Properties of Red P-Type Tl₂S₅ Single Crystals'

Recently, Gamal et al. Chin. Phys. Lett. 22 (2005) 1530 reported the results of electrical conductivity, Hall effect and thermoelectric measurements on p-type Tl₂S₅ single crystals. From the experimental data for the temperature dependence of differential thermoelectric power, Gamal et al. determined the
values of 2.66×10^-41kg and 2.50×10^-41kg, respectively, for the effective masses of electrons and holes in p-type Tl₂S₅, which are about ten orders of magnitude smaller than the free electron mass (9.11×10^-31kg). We argue that the anomalously small values obtained for the effective mass of charge
carriers in Tl₂S₅ have no physical significance.