26/06/2009 : Searching for fractional quantum hall effect in graphite
by Yakov Kopelevich Instituto de Física Gleb Wataghin, UNICAMP, Brasil
Measurements of basal plane longitudinal r_b (B) and Hall r_H (B) resistivities were performed on highly oriented pyrolytic graphite (HOPG) samples in pulsed magnetic field up to B = 50 T applied perpendicular to graphene planes, and temperatures 1.5 K £ T £ 4.2 K. At B > 30 T and for all studied samples, we observed a sign change in r_H (B) from electron- to hole-like. For our best quality sample, the measurements revealed the enhancement in r_b (B) for B > 34 T (T = 1.8 K), presumably associated with the field-driven charge density wave or Wigner crystallization transition. Besides, well defined plateaus in r_H (B) were detected in the ultra-quantum limit revealing the signatures of fractional quantum Hall effect in graphite.