Magnetic field effects on superconductivity near frustrated Mott insulator.

Quasi-2D organic charge transfer salts are considered model systems for understanding unconventional superconductivity (SC) in cuprates and other correlated electron systems.  However, studies of SC in quasi-2D organics have been limited because the SC phase is typically reached by applying pressure.  In contrast, we perform experiments under ambient pressure on κ-[(BEDT-TTF)_0.88(BEDT-STF)_0.12]₂Cu₂(CN)₃, which is formed by partial chemical substitution of a quantum spin liquid candidate κ-(BEDT-TTF)₂Cu₂(CN)₃.  We measure linear and nonlinear dc transport over a wide range of perpendicular magnetic fields (H) and temperatures (T) down to ~0.25 K.  The results indicate the onset of SC at ~ 3 K for H=0.  The suppression of SC with H reveals, surprisingly, an insulatinglike normal state.  The underlying field-tuned superconducting quantum phase transition and the nature of the high-field normal state will be discussed and compared to those in cuprates.