ABSTRACT
Motivated by the recent activities on the Ni-based diamond lattice antiferromagnet NiRhO4, we theoretically explore on a general ground the unique spin and orbital physics for the Ni ions with a d^8 electron configuration in the tetrahedral crystal field environment and on a diamond lattice Mott insulator. The superexchange interaction between the local moments usually favors magnetic orders. Due to the particular electron configuration of the Ni ion with a partially filled upper eg level and a fully filled lower t2g level, the atomic spin-orbit coupling becomes active at the linear order and would favor a spin-orbital-entangled singlet with quenched local moments in the single-ion limit. Thus, the spin-orbital entanglement competes with the superexchange and could drive the system to a quantum critical point that separates the spin-orbital singlet and the magnetic order. We further explore the effects of magnetic field and uniaxial pressure. The non-trivial response to the magnetic field is intimately tied to the underlying spin-orbital structure of the local moments. We discuss the future experiments such as doping and pressure, and point out the correspondence between different electron configurations.
BIOGRAPHY
Prof Gang Chen received his bachelor's degree from USTC in 2004 and graduated with the University's highest honor. He received his PhD in 2010 from Univ of California, Santa Barbara, working with Prof Leon Balents from the Kavli Institute for Theoretical Physics. He was appointed the professor position in 2015 at Fudan University, and elected into the 1000-youth-talent program. In 2017, he was awarded the Daniel Tsui Fellowship from The University of Hong Kong, and in 2018 he was awarded Qiushi Junior Fellowship by the Hong Kong Qiushi Foundation. Prof Chen has a broad interest in condensed matter theory, and most of his works are experimentally motivated.