Superconductivity at 32 K and anisotropy in Tl _0.58 Rb _0.42 Fe _1.72 Se ₂ crystals

Abstract

We successfully grew the high-quality single crystal of Rb0.78Fe2Se1.78, which shows sharp super-conducting transition in magnetic susceptibility and electrical resistivity. Resistivity measurements show the onset superconducting transition (Tc) at 32.1 K and zero resistivity at 30 K. From the low-temperature iso-magnetic-field magnetoresistance, large upper critical field Hc2(0) has been estimated as high as 180 T for in-plane field and 59 T for out-of-plane field. The anisotropy H ab c2 (0)/H c c2 (0) is around 3.0, right lying between those observed in KxFe2Se2 and CsxFe2Se2.

Optical conductivity of superconducting K0.8Fe2−ySe2

“…Just above T c we note that σ dc = σ 1 (ω → 0) ≃ 44 Ω −1 cm −1 , or ρ dc ≃ 23 mΩ cm. The highly-anisotropic nature of these materials [34] suggests that the transport be described in terms of a sheet resistance R = ρ dc /d, where d is the separation between the iron-chalcogenide sheets. Using d ≃ 7Å [24][25][26] yields R ≃ 320 kΩ.…”

Structure, magnetic order and excitations in the 245 family of Fe-based superconductors

“…After the initial report [5] and confirmation [12] of superconductivity in the nominal K x Fe 2 Se 2 , Cs and Rb compounds of the similar nominal composition [13,14] as well as Tl containing compounds of a different nominal composition (Tl,A)Fe 2−x Se 2 (A=K,Rb) [15,16] were reported to superconduct also at T C ≈ 30 K. The former composition formula indicates an intact FeSe plane as in the 11 compounds as well as "heavy electron doping" [17]. The latter suggests Fe vacancy in the FeSe plane since two different kinds of Fe vacancy orders have been reported previously in chalcogenide TlFe 2−x S 2 and TlFe 2−x P 2 [18,19].…”

Structure and composition of the superconducting phase in alkali iron selenideKyFe1.6+xSe2

“…Of all the iron-based superconductors [1][2][3] , alkali iron selenides A y Fe 1.6+x Se 2 (A = K, Rb, Cs, Tl) [4][5][6][7][8][9] are unique in that superconductivity in this class of materials always coexists with a static long-range antiferromagnetic (AF) order with a large moment and high Néel temperature [10][11][12][13][14] . This is in contrast to iron pnictide superconductors [1][2][3] where optimal superconductivity arises from the suppression of the static AF order in their nonsuperconducting parent compounds 15,16 .…”