Spin-singlet state of electrons in filled skutterudites

¹ National Research Center “ Kurchatov Institute” - Kurchatov Square 1, Moscow 123182, Russia
² Physik-Institut der Universität Zürich - CH-8057 Zürich, Switzerland
³ Department of Physics and Astronomy, University of British Columbia - Vancouver, British Columbia, Canada V6T 1Z1
⁴ Max-Planck-Institut für Chemische Physik fester Stoffe - Nöthnitzer Str. 40, 01187 Dresden, Germany, EU
⁵ Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory Upton, NY 11973, USA

^a mussr@triumf.ca

Received: 11 July 2011
Accepted: 17 October 2011

Abstract

Muon spin rotation experiments have been performed on filled skutterudites PrOs₄Sb₁₂ and REPt₄Ge₁₂ (RE = La, Pr, Nd, Eu) over a temperature range 0.025–300 K in magnetic fields up to 7 T. An electron bound state is detected spectroscopically in filled skutterudites containing magnetic ions, both below and above the superconducting transition temperature T_c and both below and above the corresponding upper critical magnetic field H_c2, including the pseudogap region. This state is proposed to be a spin-singlet —an electron pair confined around the positive muon.