Anisotropy reversal of the upper critical field at low temperatures and spin-locked superconductivity in K2Cr3As3

作者：Balakirev F F; Kong T; Jaime M; McDonald R D; Mielke C H; Gurevich A; Canfield P C; Bud' ko S L

来源：Physical Review B, 2015, 91(22): 220505.

DOI：10.1103/PhysRevB.91.220505

We report the first measurements of the anisotropic upper critical field H-c2(T) for K2Cr3As3 single crystals up to 60 T and T > 0.6 K. Our results show that the upper critical field parallel to the Cr chains, H-c2(parallel to) (T), exhibits a paramagnetically-limited behavior, whereas the shape of the H-c2(perpendicular to)(T) curve (perpendicular to the Cr chains) has no evidence of paramagnetic effects. As a result, the curves H-c2(perpendicular to)(T) and H-c2(parallel to)(T) cross at T\approx 4 K, so that the anisotropy parameter gamma(H)(T)=(Hc2Hc2 parallel to)-H-perpendicular to (T) increases from gamma(H)(T-c) approximate to 0.35 near T-c to gamma(H)(0)approximate to 1.7 at 0.6 K. This behavior of H-c2(parallel to)(T) is inconsistent with triplet superconductivity but suggests a form of singlet superconductivity with the electron spins locked onto the direction of Cr chains.

• 出版日期2015-6-23