Unlike the conventional BCS superconductor, spin triplet superconductor is a special quantum state integrating ferromagnetism and superconductivity. It is an interesting but challenging research topic in the fields of condensed matter physics and material science. One of the characteristics of spin triplet superconductor is the spin alignment of paired electrons, which allows spin to transmit over a long distance realize non-dissipative spin current. In addition, spin triplet superconductor is theoretically proposed to hold topologically non-trivial Majorana fermion excitations, which has important application prospects for topological quantum computing. The intrinsic spin triplet superconductor materials are very rare; therefore, the artificial construction of spin triplet superconductors has attracted extensive attention.

Recently, ICQM Prof. Wei Han group collaborated with Prof. Xincheng Xie, Prof. Qingfeng Sun, Prof. Shuang Jia of ICQM, and Prof. Igor Zutic of university at Buffalo made an important breakthrough by the artificially constructing spin triplet superconductivity at the two-dimensional ferromagnet/superconductor interface. The spin triplet superconductivity is induced by Rashba spin orbit coupling at the interface and detected by the spin-polarized current (Fig. a). The research team successfully observed the magnetoresistance behavior (Fig. c) induced by anisotropic spin triplet Andreev reflection at the interface between a two-dimensional Fe_xTaS₂ and an s-wave superconductor NbN (Fig. b). Systematic investigation of the temperature, voltage, and interface barrier dependences of the MR strongly supports the interfacial spin triplet superconductor.

This work is an important breakthrough in the field of superconductor spintroincs. These results provide a new experimental strategy for the artificial construction of spin triplet superconductivity, thus, could pave the way for the development of quantum devices based on spin triplet superconductivity.

These results are published online in Nature Communications tilted “Evidence for anisotropic spin-triplet Andreev reflection at the 2D van der Waals ferromagnet/superconductor interface” on November 18, 2021. This work was done by two PhD students Ranran Cai and Yunyan Yao in ICQM, who serves as the co-first authors and Prof. Wei Han is the corresponding author of the paper. This work has been supported by the National Science Foundation of China, the Ministry of science and technology, the Chinese Academy of Sciences, and Beijing National Science Foundation.

Paper Link: https://www.nature.com/articles/s41467-021-27041-w

Fig. a: Schematic of the spin-triplet Andreev reflection resulting from Rashba SOC at the interface between a FM and a conventional s-wave SC. Fig. b: Illustration of the 2D vdW Fe_xTaS₂/NbN MR device and the measurement geometry. Fig. c: MR behavior at the 2D vdW Fe_xTaS₂/NbN interface caused by anisotropic spin triplet Andreev reflection.