Magneto-optical evidence for a gapped Fermi surface in underdoped YBa 2Cu3O6+x

Abstract

The infrared (900–1100 cm−1) Faraday rotation and circular dichroism are measured in the normal state of underdoped High Tc superconductors and used to study the magnetotransport. YBa2Cu3O6+x thin films are investigated in the temperature range 10–300 K in magnetic fields up to 8 T and as a function of oxygen concentration. A dramatic increase of the Hall frequency is observed for underdoped samples, which is not consistent with the approach to a Mott transition but is consistent with a partial gapping of the Fermi surface as predicted in density wave models.