Bulk quantum Hall effect: Evidence that surface states play a key role

Abstract

It has been suggested recently that the \ensuremath{\alpha}-(BEDT-TTF${)}_{2}$MHg(SCN${)}_{4}$ salts (M=K and Tl) exhibit a bulk quantum Hall effect at high fields [Harrison et al., Phys. Rev. Lett. 77, 1576 (1996)]. We have examined experimentally predictions concerning the transport of current under such conditions. We find that the high field Shubnikov--de Haas oscillations exhibit a complicated temperature dependence, which is not evident in de Haas--van Alphen measurements on the same samples. These differences may be explained in terms of the competition between transport via the bulk and via the surface of the sample.