Upper critical field of high-quality single crystals of KFe2As2

Abstract

Measurements of temperature-dependent in-plane resistivity ρ(T) were used to determine the upper critical field and its anisotropy in high-quality single crystals of the stoichiometric iron arsenide superconductor KFe 2 As 2 . The crystals were characterized by the residual resistivity ratio ρ(300 K)/ρ(0) up to 3000 and the resistive transition midpoint temperature T c =3.8 K, significantly higher than in previous studies on the same material. We find increased H c2 (T) for both directions of the magnetic field, which scale with the increased T c . This unusual linear H c2 (T c ) scaling is not expected for an orbital-limiting mechanism of the upper critical field in clean materials. Keywords Physics and Astronomy Disciplines Condensed Matter Physics | Materials Science and Engineering | Metallurgy CommentsThis article is from Physical Review B 87 (2013) Measurements of temperature-dependent in-plane resistivity ρ(T ) were used to determine the upper critical field and its anisotropy in high-quality single crystals of the stoichiometric iron arsenide superconductor KFe 2 As 2 . The crystals were characterized by the residual resistivity ratio ρ(300 K)/ρ(0) up to 3000 and the resistive transition midpoint temperature T c = 3.8 K, significantly higher than in previous studies on the same material. We find increased H c2 (T ) for both directions of the magnetic field, which scale with the increased T c . This unusual linear H c2 (T c ) scaling is not expected for an orbital-limiting mechanism of the upper critical field in clean materials.

Comprehensive scenario for single-crystal growth and doping dependence of resistivity and anisotropic upper critical fields in (Ba1−xKx)FeLiu1, Tanatar2, Straszheim3 et al. 2014Phys. Rev. BSelf Cite6415722View full textAdd to dashboardCite

“…In KFe 2 As 2 , the orbital H c2 found in H c configuration, is close to T linear [40]. The slope of the dependence does not depend on T c suppression with impurities [43]. In configuration with magnetic field parallel to the plane, H ab, the upper critical field is Pauli limited, as suggested both by the difference in the shape of the phase diagram and quite sharp changes at H c2 [48].…”

“…Broad crossover in the temperature-dependent resistivity is observed in in-plane transport in single crystals of BaK122 at doping close to optimal [38], similar to pure stoichiometric KFe 2 As 2 (K122) [39][40][41][42][43]. Explanation of the crossover was suggested as arising from multi-band effects [38], with contribution of two conductivity channels, as found in optical studies [44] with nearly temperature-independent and strongly temperature dependent resistivities, respectively.…”

“…In Fig. 14 of the H c2 line and T c is grossly violated in KFe 2 As 2 when T c is controlled by disorder: here the slope was found to be independent of T c [43], despite the sample being clearly in the clean limit. For H ab, the H c2,0 (x) curve is also close to linear, but does not extrapolate to zero on T c → 0.…”

“…This technique allowed us to avoid use of quartz tubes in direct contact with K vapor and use of expensive sealed tantalum tubes. Analysis of the growth morphology in the case of KFe 2 As 2 [43] lead us to conclude that the crystals nucleate on the surface of the melt and grow by the reaction on the top surface of the crystal with K and As in the vapor phase. We were able to promote this reaction by developing an inverted-temperature-gradient method with the colder zone at the top of the crucible, as shown in Fig.…”

“…We have previously described successful growth of highquality single crystals of stoichiometric KFe 2 As 2 at T = 1157 K using KAs flux [43]. One of the key elements of the growth technique was using a liquid-Sn sealing of alumina crucibles to suppress the evaporation of K and As.…”