paper

Multigap nodeless superconductivity in CsCa2Fe4As4F2 probed by heat transport

arXiv:1811.06379 · doi:10.1103/PhysRevB.99.020502

Abstract

Recently, a new family of iron-based superconductors called 12442 was discovered and the muon spin relaxation ( $I^¼$ SR) measurements on KCa $_{2}$ Fe $_{4}$ As $_{4}$ F $_{2}$ and CsCa $_{2}$ Fe $_{4}$ As $_{4}$ F $_{2}$ polycrystals, two members of the family, indicated that both have a nodal superconducting gap structure with $s + d$ pairing symmetry. Here we report the ultralow-temperature thermal conductivity measurements on CsCa $_{2}$ Fe $_{4}$ As $_{4}$ F $_{2}$ single crystals ( $T_{c}$ = 29.3 K). A negligible residual linear term $I^º_{0} / T$ in zero field and the field dependence of $I^º_{0} / T$ suggest multiple nodeless superconducting gaps in CsCa $_{2}$ Fe $_{4}$ As $_{4}$ F $_{2}$ . This gap structure is similar to CaKFe $_{4}$ As $_{4}$ and moderately doped Ba $_{1 - x}$ K $_{x}$ Fe $_{2}$ As $_{2}$ , but contrasts to the nodal gap structure indicated by the $I^¼$ SR measurements on CsCa $_{2}$ Fe $_{4}$ As $_{4}$ F $_{2}$ polycrystals.

6 pages, 4 figures