Penetration depth measurements of K 2 Cr 3 As 3 and Rb 2 Cr 3 As 3

作者：G. Pang, M. Smidman, W. B. Jiang, Y. Shi, J. Bao, Z. T. Tang, Z. Weng, Yinzhou Wang, L. Jiao, Jingjing Zhang, J. Luo, Guanghan Cao, H. Yuan · 年份：2015 · DOI：10.1016/j.jmmm.2015.08.093 · 被引用次数：18 · 研究领域：Physics、Materials Science

Abstract The newly discovered superconductors A 2 Cr 3 As 3 ( A =K, Rb, Cs), with a quasi-one-dimensional crystal structure have attracted considerable interest. The crystal structure consists of double-walled tubes of [Cr 3 As 3 ] 2− that extend along the c -axis. Previously we reported measurements of the change in London penetration depth of polycrystalline samples of K 2 Cr 3 As 3 using a tunnel diode oscillator based technique, which show a linear temperature dependence at low temperatures, giving evidence for line nodes in the superconducting gap. Here we report similar measurements of the penetration depth for polycrystalline Rb 2 Cr 3 As 3 and several single crystals of K 2 Cr 3 As 3 , prepared by two different research groups. The single crystal measurements show similar behavior to polycrystalline samples down to 0.9–1.2 K, where a downturn is observed in the frequency shift for all single crystal samples. These results give further evidence for nodal superconductivity in K 2 Cr 3 As 3 , which indicates that the superconducting pairing state is unconventional. The different low temperature behavior, observed in samples which have deteriorated after being exposed to air, emphasizes that it is necessary to properly handle the samples prior to being measured because the A 2 Cr 3 As 3 compounds are extremely air sensitive and evidence for nodal superconductivity from penetration depth measurements is only observed in the samples which display a sharp superconducting tra...