Local Orbital Degeneracy Lifting as a Precursor to Orbital-Selective Peierls Transitions

Fundamental electronic principles underlying all transition metal compounds are the symmetry and filling of the d-electron orbitals and the influence of this filling on structural configurations and responses. Here we use a sensitive local structural technique, x-ray atomic pair distribution function analysis, to reveal the presence of fluctuating local-structural distortions at high temperature of several transition metal based quantum materials exhibiting orbital-selective groud states. We show that this hitherto overlooked fluctuating symmetry-lowering is electronic in origin and will modify the energy-level spectrum and electronic and magnetic properties. The explanation is a local, spatio-temporally fluctuating, orbital degeneracy lifted state, a precur to electronic phenomena observed at low temperature. We demonstrate that such local orbital states come in many flavors (e.g. engaging single [1,2] or multiple d orbitals [3]), and that they are likely to exist both in the proximity to itinerant-to-localized crossover [1,3] and deep in the Mott insulating regime where charge fluctuations are suppressed [4]. These observations suggest that such precursor states are likely to be widespread amongst diverse classes of partially filled nominally degenerate d-electron systems, with potentially broad implications for our understanding of their properties.

[1] E.S. Bozin et al., Nature Comms. 10, 3638 (2019).
[2] R.J. Koch et al., Phys. Rev. B 100, 020501(R) (2019).
[3] L. Yang et al., arXiv:2009.08923 (2020).
[4] R.J. Koch et al., arXiv:2009.14288 (2020).