Pressure-Induced Superconductivity up to 9 K in the Quasi-One-Dimensional KMn_{6}Bi_{5}

The Mn-based superconductor is rare owing to the strong magnetic pair-breaking effect. Here we report on the discovery of pressure-induced superconductivity in KMn_{6}Bi_{5}, which becomes the first ternary Mn-based superconductor. At ambient pressure, the quasi-one-dimensional KMn_{6}Bi_{5} is an antiferromagnetic metal with T_{N}≈75  K. By measuring resistance and ac magnetic susceptibility under hydrostatic pressures up to 14.2 GPa in a cubic anvil cell apparatus, we find that its antiferromagnetic transition can be suppressed completely at a critical pressure of P_{c}≈13  GPa, around which bulk superconductivity emerges and displays a superconducting dome with the maximal T_{c}^{onset}=9.3  K achieved at about 14 GPa. The close proximity of superconductivity to a magnetic instability in the temperature-pressure phase diagram of KMn_{6}Bi_{5} and an unusually large μ_{0}H_{c2}(0) exceeding the Pauli paramagnetic limit suggests an unconventional magnetism-mediated paring mechanism. In contrast to the binary MnP, the flexibility of the crystal structure and chemical compositions in the ternary AMn_{6}Bi_{5} (A=alkali metal) can open a new avenue for finding more Mn-based superconductors.