Evidence for fully gapped superconductivity from microwave penetration depth measurements in PrFeAsO1-y single crystals K. Hashimoto1, T. Shibauchi1, T. Kato1, K. Ikada1, R. Okazaki1, H. Shishido1, M. Ishikado2, H. Kito3, A Iyo3, H. Eisaki3, S. Shamoto2, and Y. Matsuda1 arXiv:0806.3149v2 1Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan 2Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan 3Nanoelectronics Research Institute (NeRI), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Central 2, Umezono, Tsukuba, Ibaraki 305-8568, Japan

R. Prozorov and R. W. Giannetta, Supercond. Sci. Tech. 19, R41 (2006). Penetration depth l(T ) a direct probe for low-energy excitations In full gap superconductors, the quasiparticle excitation is of an activated type. In the presence of line nodes, T-linear dependence is expected. l(T ) may be strongly affected by the large paramagnetism arising from the rare earth ions (first pointed out by J. R. Cooper [Phys. Rev. B 54, R3753 (1996)] for (Nd,Ce)2CuO4). R. Prozorov and R. W. Giannetta, Supercond. Sci. Tech. 19, R41 (2006).

PrFeAsO1-y microwave measurements Single crystals l(T ) in Pr-system is free from the rare-earth effect, since Pr3+ (4f 2) ions are in the non-magnetic state. Single crystals microwave measurements High-pressure synthesis method Superconducting cavity f0=27.75 GHz, Q0~106 Electric field Ew Magnetic field Hw Sample Microwave Waveguide Heater Thermometer Cavity Hw // c Jw in the plane #2 Laue pattern of a PrFeAsO1-y crystal (Incident X-ray is along [100]) #1 [100] [010] #2 #3 100 mm Up to 150 mm × 150 mm × 30 mm

Penetration depth l(T ) Theoretical models derive extended s-wave symmetry consistent with our results #1 (Tc=35.4 K) #2 (Tc=36.2 K) #3 (Tc=36.4 K) Nodes (sign changes) hole electron + - Full gap See, for example, I. I. Mazin et al., arXiv:0803.2740. K. Kuroki et al., arXiv:0803.3325. M. M. Parish et al., arXiv:0807.4572. Our results demonstrate that the finite gap opens up all over the Fermi surface. Dmin/kBTc~1.5 +0.3

Reminiscent of superconductors with strong electron correlations. Microwave Surface Impedance Measurements Quasiparticle conductivity Enhancement of s1(T) below Tc s1(T) shows a large enhancement just below Tc much larger than the coherence peak. increase in t(T ) There is strong inelastic electronic scattering in the normal state that is gapped in the superconducting state. Reminiscent of superconductors with strong electron correlations.