Magnetic penetration depth measurements of the heavy-fermion superconductor [formula omitted

Abstract

Previous studies of the magnetic penetration depth in the heavy-fermion superconductor PrOs 4 Sb 12 reported contradictory results about its pairing state. While muon spin rotation measurements report a fully gapped quasiparticle spectrum, inductive measurements at radio frequencies suggest the existence of point nodes in the energy gap. Here, we report on new measurements of the in-plane magnetic penetration depth of PrOs 4 Sb 12 . The measurements were performed using a tunnel diode oscillator that exhibits excellent frequency stability and low-power dissipation. We report the first ever measurements of the penetration depth of this material at temperatures as low as 20 mK. At about 450 mK, we observe the onset of a superconducting-transition-like drop in the magnetic penetration depth.