ISIS Neutron and Muon Source Data Journal

Spin excitations approaching the Mott transition in NiS2-xSex

Abstract: NiS2-xSex provides a prototypical bandwidth-controlled Mott system where isovalent Se substitution drives an insulator-metal transition (IMT) near x = 0.42~0.5. The parent compound NiS hosts a geometrically frustrated fcc lattice with two successive AFM phases: M1 (k1 = (1,0,0), TN1 = 39 K) and M2 (k = (0.5,0.5,0.5), TN2 = 30 K). Inelastic neutron studies have revealed well-defined spin waves below TN1, and an energy gap of ~12 meV emerging at (0,1,1) after a first-order transition at TN2, linked to a small lattice distortion that relieves frustration. With increasing Se doping, the M2 phase vanishes near x ~0.4 and the M1 phase is eventually quenched at x ~1. This evolution raises the questions of how the spin dynamics in NiS2-xSex evolve with Se doping approaching the IMT, and whether geometric frustration plays a role in the IMT. We propose TOF inelastic neutron scattering on NiS2 and NiS2-xSex (x = 0.42) single crystals to map how the excitations evolve upon Se-doping. Using Ei = 40 meV on MERLIN, we will resolve the ~12 meV magnon gap, and clarify how spin dynamics evolve with bandwidth tuning and geometric frustration, providing new insight into the coupling between magnetism and electron correlations in a Mott system.

Principal Investigator: Dr Yu Song
Local Contact: Dr Devashi Adroja
Experimenter: Mr Yu Tang
Experimenter: Mr Saizheng Cao

DOI: 10.5286/ISIS.E.RB2610517

ISIS Experiment Number: RB2610517

Publisher: STFC ISIS Neutron and Muon Source

Data format: RAW/Nexus
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Data Citation

The recommended format for citing this dataset in a research publication is as:
[author], [date], [title], [publisher], [doi]

For Example:
Dr Yu Song et al; (2026): Spin excitations approaching the Mott transition in NiS2-xSex, STFC ISIS Neutron and Muon Source, https://doi.org/10.5286/ISIS.E.RB2610517

Data is released under the CC-BY-4.0 license.