In superconductors, the inversion symmetry of the crystal structure plays a central role in the formation of the Cooper pairs. Systems lacking a center of inversion exhibit a nonuniform lattice potential, giving rise to a Rashba-type antisymmetric spin-orbit coupling. This can lead to exotic physics, such as time-reversal symmetry (TRS) breaking, below the superconducting transition temperature T_c. Until recently, only two NCS compounds, Re₆Zr and LaNiC₂, have been shown to break TRS below T_c [1,2]. The nature of the pairing states in these superconductors continues to be a puzzling and challenging question. Now we have discovered a third NCS material, polycrystalline La₇Ir₃, that shows broken TRS below T_c [3]. Here, we report the first growth of single crystals of La₇Ir₃. We present experimental data on these single crystals that shed light on to the unconventional superconducting state of La₇Ir₃. We compare our results with other members of the La₇T₃ (T = transition metal) family of superconductors and discuss the unconventional superconductivity in this exciting new family of materials.

[1] A. D. Hillier et al., Phys. Rev. Lett. 102, 117007 (2009).
[2] R. P. Singh et al., Phys. Rev. Lett. 112, 107002 (2014).
[3] J. A. T. Barker et al., Phys. Rev. Lett. 115, 267001 (2015).