LiVO2 is a model system of the valence bond solid (VBS) in 3d2 triangular lattice. The origin of the VBS formation has remained controversial. We investigate the microscopic mechanism by elucidating the d orbital character via on-site 51V NMR measurements in a single crystal up to 550 K across a structural transition temperature Tc. The Knight shift, K, and nuclear quadrupole frequency, δν, show that the 3d orbital with local trigonal symmetry are reconstructed into a dyzdzx orbital order below Tc. Together with the NMR spectra with three-fold rotational symmetry, we confirm a vanadium trimerization with d-dσ bonds. The Knight shift extracts the large Van-Vleck orbital susceptibility, χVV=3.6×10−4, in a paramagnetic state above Tc, which is comparable to the spin susceptibility. The results suggest that orbitally induced Peierls transition in the proximity of the frustrated itinerant state is the dominant driving force of the trimerization transition.
@article{arxiv.1302.3662,
title = {Orbital reformation with vanadium trimerization in $d^2$ triangular lattice LiVO$_2$ revealed by $^{51}$V NMR},
author = {Takaaki Jin-no and Yasuhiro Shimizu and Masayuki Itoh and Seiji Niitaka and Hidenori Takagi},
journal= {arXiv preprint arXiv:1302.3662},
year = {2015}
}