Unusual upper critical field in the pyrochlore KOs₂O₆

Abstract

We determine the temperature dependence of the upper critical field H c2 in KOs2O6 from resistivity and magnetic measurements in high magnetic fields up to 50 T. By both techniques we find linear temperature dependence all the way below Tc and uncommonly high H c2 (T 0 K) ∼ 33 T. We show that this unusual Hc2 can be understood as a consequence of paramagnetic limit HPremarkably enhanced by the broken spatial inversion symmetry proposed recently, ensuring that the pair-breaking here is executed by orbital degrees, associated with the smaller closed Fermi surfaces. © 2006 IOP Publishing Ltd.