Multiband Superconductivity in KFe2As2 : Evidence for one Isotropic and several Liliputian Energy Gaps

Frédéric Hardy (1) , Robert Eder (1) , Martin Jackson (2) , Dai Aoki (3) , Carley Paulsen (2) , Thomas Wolf (1) , Philipp Burger (1) , Anna Böhmer (1) , Peter Schweiss (1) , Peter Adelmann (1) , Robert A. Fisher (4) , Christoph Meingast (1)

1 KIT - Karlsruher Institut für Technologie
2 NEEL - MagSup - Magnétisme et Supraconductivité
3 IMAPEC - Instrumentation, Material and Correlated Electrons Physics
4 LBNL - Lawrence Berkeley National Laboratory [Berkeley]

We report a detailed low-temperature thermodynamic investigation (heat capacity and magnetization) of the superconducting state of KFe 2 As 2 for H || c axis. Our measurements reveal that the properties of KFe 2 As 2 are dominated by a relatively large nodeless energy gap (∆ 0 = 1.9 k B T c) which excludes d x 2 −y 2 symmetry. We prove the existence of several additional extremely small gaps (∆ 0 < 1.0 k B T c) that have a profound impact on the low-temperature and low-field behavior, similar to MgB 2 , CeCoIn 5 and PrOs 4 Sb 12. The zero-field heat capacity is analyzed in a realistic self-consistent 4-band BCS model which qualitatively reproduces the recent laser ARPES results of Okazaki et al. (Science 337 (2012) 1314). Our results show that extremely low-temperature measurements, i.e. T < 0.1 K,will be required in order to resolve the question of the existence of line nodes in this compound.

Mots clés: iron pnictide; magnetization; KFe 2 As 2; multiband superconductivity; heat capacity

Domaines: Physique [physics]

Frédéric Hardy, Robert Eder, Martin Jackson, Dai Aoki, Carley Paulsen, et al.. Multiband Superconductivity in KFe2As2 : Evidence for one Isotropic and several Liliputian Energy Gaps. Journal of the Physical Society of Japan, 2014, 83 (1), pp.014711. ⟨10.7566/JPSJ.83.014711⟩. ⟨hal-01328088⟩