in bulk nickelates*

The recent discovery of superconductivity with a high transition temperature (T_c) of ~ 80 K in nickel-based single crystals by M. Wang’s group marks a milestone in the quest for high-temperature superconductors. This discovery bridges the gap between other nickelates and the cuprate superconductors, although the former still requires pressure to reach T_c above 77 K. We have carried out systematic studies on different nickel-based materials at ambient and under high pressure to investigate both superconducting and non-superconducting states, as well as the intertwined orders in this system, which helped to reveal the roles that the different orders, the spin, the orbitals, and the lattice play in the mechanism that produces its high-T_c superconductivity. Approaches to retaining the pressure-induced high T_c in this system at lower or even ambient pressure will also be discussed.