⁷⁵As Nuclear Magnetic Resonance Studies on Ba(Fe_1−xNi_x)₂As₂ Single Crystals under High Pressure

⁷⁵As nuclear magnetic resonance (NMR) was measured for Ba(Fe_1−xNi_x)₂As₂ single crystals with x=0.05 and x=0.1 under 0 and 1.5 GPa, respectively. For the optimal doped sample with x=0.05, the superconducting transition temperature, T_c, is strongly suppressed from 18 to 5 K, while for the over−doped sample with x=0.1, it is turned from a superconducting ground state to a disordered paramagnetic state under 1.5 GPa. Our experimental results show that the antiferromagnetic spin fluctuations, as well as T_c, are suppressed. The experimental results can be explained with the two-band model. As a result, the electronic band is shifted downwards with an increase in pressure, and the electrons become the dominant carriers in the system.