c-axis pressure-induced antiferromagnetic order in optimally P-doped BaFe2(As0.70P0.30)2 superconductor

Abstract

Superconductivity in BaFe 2 (As 1−x P x ) 2 iron pnictides emerges when its in-plane two-dimensional (2D) orthorhombic lattice distortion associated with nematic phase at T s and three-dimensional (3D) collinear antiferromagnetic (AF) order at T N (T s = T N ) are gradually suppressed with increasing x, reaching optimal superconductivity around x = 0.30 with T c ≈ 30 K. Here we show that a moderate uniaxial pressure along the c-axis in BaFe 2 (As 0.70 P 0.30 ) 2 spontaneously induces a 3D collinear AF order with T N = T s > 30 K, while only slightly suppresses T c . Although a ∼400 MPa pressure compresses the c-axis lattice while expanding the in-plane lattice and increasing the nearest-neighbor Fe-Fe distance, it barely changes the average iron-pnictogen height in BaFe 2 (As 0.70 P 0.30 ) 2 . Therefore, the pressureinduced AF order must arise from a strong in-plane magnetoelastic coupling, suggesting that the 2D nematic phase is a competing state with superconductivity. arXiv:1808.05153v1 [cond-mat.supr-con]