We discover a new superconductor, TiIrSi at Tc = 1.4 K, and reveal a superconducting state of TrIrSi (Tr = Ti, Zr, and Hf) by using dc magnetic susceptibility , electrical resistivity , and specific heat C(T) measurements. Superconductivity of TrIrSi is confirmed in at Tc = 1.4, 1.85, and 3.4 K, respectively. The electronic specific heat of TrIrSi can be fitted with the theoretical BCS curve of the weak-coupling limit with / = 1.43. Measurements in several magnetic fields suggest that TrIrSi is a type-II superconducting material with upper critical fields of (0) = 0.751, 0.618, and 2.23 T, respectively. The electron–phonon coupling constants are calculated to be 0.441, 0.464, and 0.545, which are consistent with the weak-coupling limit inferred from the specific jump. The Tc of TrIrSi depends on and is inversely proportional to .

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Among exotic pairing states of interacting fermions, the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, characterized by Cooper pairs condensed at finite momentum, has been a long-sought state that remains unresolved in many classes of systems, including superconductors and ultracold atoms. A fascinating aspect of the FFLO state is the emergence of periodic nodal planes in real space, but its observation is still lacking. Here we investigate the order parameter structure for c-axis fields on a high purity single crystal of FeSe. The heat capacity and magnetic torque provide thermodynamic evidence for a distinct superconducting phase at the low-temperature/high-field corner of the phase diagram. Despite the bulk superconductivity, spectroscopic-imaging scanning tunneling microscopy (SI-STM) performed on the same crystal demonstrates that the superconducting order parameter vanishes at the surface upon entering the high-field phase. These results imply that the planar node induced perpendicular to H is pinned at the surface, providing evidence of the FFLO pairing state with zeroth Landau level.