1. 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: v2
1Department of Physics, Kyoto University, Sakyo-ku, Kyoto , Japan 2Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki , Japan 3Nanoelectronics Research Institute (NeRI), National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Umezono, Tsukuba, Ibaraki , Japan

2. 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).

3. 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

4. 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: K. Kuroki et al., arXiv: M. M. Parish et al., arXiv:
Our results demonstrate that the finite gap opens up all over the Fermi surface.
Dmin/kBTc~

5. 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.