Emergence of Superconductivity on the Border of Antiferromagnetic Order in RbMn_6Bi_5 under High Pressure: A New Family of Mn-Based Superconductors

We report the discovery of superconductivity on the border of antiferromagnetic order in a quasi-one-dimensional material RbMn_6Bi_5 via measurements of resistivity and magnetic susceptibility under high pressures. Its phase diagram of temperature versus pressure resembles those of many magnetism-mediated superconducting systems. With increasing pressure, its antiferromagnetic ordering transition with T_\rm N = 83 K at ambient pressure is first enhanced moderately and then suppressed completely at a critical pressure of P_\rm c \approx 13 GPa, around which bulk superconductivity emerges and exhibits a dome-like T_\rm c(P) with a maximal T_\rm c^\rm onset \approx 9.5 K at about 15 GPa. In addition, the superconducting state around P_\rm c is characterized by a large upper critical field \mu_0H_\rm c2(0) exceeding the Pauli paramagnetic limit, implying a possible unconventional paring mechanism. The present study, together with our recent work on KMn_6Bi_5 (the maximum T_\rm c^\rm onset \approx 9.3 K), makes AMn_6Bi_5 (A = alkali metal) a new family of Mn-based superconductors with relatively high T_\rm c.