Anisotropic optical band structure of van der Waals antiferromagnet NiPS3

Abstract

The Zhang-Rice exciton state in NiPS3, closely connected to the underlying zigzag antiferromagnetic order, is a representative case of intricate interaction among quasiparticles in van der Waals magnets. NiPS3 is usually described by a XXZ-type Hamiltonian below its N & eacute;el temperature of 155 K. The spin-orbit entangled Zhang-Rice exciton state of 1A1g symmetry emerges at 1.4756 eV below TN and becomes exceptionally prominent below about 50 K where the full width at half maximum reaches 0.4 meV, narrower than the thermal fluctuation kBT. Here, we report a second Zhang-Rice exciton state in NiPS3 observed at 1.0975 eV by conducting temperature-dependent high-resolution transmittance measurements on bulk NiPS3 single crystals over the frequency range 0.62-2 eV. We identify the second Zhang-Rice exciton state to result from the initial Zhang-Rice triplet ground state 3A2g to the excited Zhang-Rice singlet state 1Eg. In addition, the 3T2g state, which overlapped with the 1Eg state, split to 3Eg and 3A1g states as the temperature decreased, and the temperature dependence of their parameters changed below TN. Our results offer valuable information on the intricate electronic structure of NiPS3, where charge transfer and spin-orbit entanglement bring in an exciting arena to study many-body interactions.