Changes in the in- and out-of-plane magnetic susceptibility of YBCO crystals with temperature and hole content

¹ Cavendish Laboratory, University of Cambridge - Cambridge CB3 OHE, UK, EU
² IFW Dresden - Helmholtzstrasse 20, 01069 Dresden, Germany, EU
³ Department of Physics, Faculty of Science, University of Zagreb - P.O. Box 331, Zagreb, Croatia

^a kivan@phy.hr

Received: 2 February 2012
Accepted: 21 May 2012

Abstract

We report new magnetic susceptibility and anisotropy data for single crystals of YBa₂Cu₃O_6+x from x=0.38 to 0.95. We argue that the temperature (T) dependence of the magnetic anisotropy in the normal state well above T_c arises from a combination of the pseudogap and substantial g-factor anisotropy. With this interpretation we obtain onset temperatures for superconducting fluctuations over a wide range of x. For hole concentrations p<0.14 there are two extra contributions to the magnetic susceptibility and its anisotropy. We analyse these in terms of changes in the Van Vleck paramagnetism plus a significant paramagnetic contribution from an electron pocket at low fields in the region 0.084<p<0.135. This is where the superconducting transition temperature T_c(p) deviates from the usual parabolic law and where quantum oscillations and a negative Hall coefficient are observed.