c-axis pressure effects on isovalent doped BaFe2(As1-xPx)2 superconductor

Superconductivity in BaFe2(As1−xPx)2 iron pnictides emerges when its nematic phase and stripe AF order at TN (Ts = TN) are gradually suppressed with increasing x, reaching optimal superconductivity around x = 0.30 with Tc ≈ 30 K. We show that a moderate uniaxial pressure along the c-axis in BaFe2(As0.70P0.30)2 spontaneously induces a 3D collinear antiferromagnetic order with TN = Ts > 30 K, while only slightly suppresses Tc. Furthermore, c-axis pressure pushes the underdoped BaFe2(As0.72P0.28)2 to optimal superconductivity with Tc = 30K without AF order firstly, then AF order emergencies at higher pressure region. We find that a c-axis 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 BaFe2(As0.70P0.30)2. Therefore, the pressure-induced antiferromagnetic order must arise from a strong in-plane magnetoelastic coupling, suggesting the universal phase diagram under c-axis pressure in BaFe2(As1−xPx)2.