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arXiv · 2507.16619

A long-range model for the electron-nuclear coupling and two-stage order in TmVO$_4$

Sayan Ghosh·Anirudha Menon·Manoranjan Kumar·Rajiv R. P. Singh
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Abstract

We study an infinite-range coupled electronic-quadrupole and nuclear-spin model for ferro-quadrupolar and nuclear-spin ordering in TmVO$_4$ in external magnetic and strain fields. This material is an experimental realization of a Transverse-Field Ising Model, where the Ising degree of freedom is quadrupolar and non-magnetic, but a transverse component is magnetic and couples both to external magnetic fields and to the nuclear spins via a hyperfine coupling. In zero external magnetic-field, there is a well-separated two-step order of the electronic and nuclear degrees of freedom and the release of their respective entropies. A transverse magnetic-field polarizes the electronic orbital moments and also the nuclear spins via the hyperfine coupling. The quadrupolar ordering temperature is gradually reduced to zero. But, there is no longer a nuclear transition in non-zero fields. Quantum fluctuations are magnified near the phase transitions and lead to peaks in the magnetic susceptibility. The spectral functions reveal a softening of a low-energy mode near the quantum critical point, consistent with the closing of the excitation gap and its reopening in the disordered phase, providing direct dynamical signatures of the field-driven quantum critical phenomena.

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Sayan Ghosh, Anirudha Menon, Manoranjan Kumar, Rajiv R. P. Singh. 2025-07-22. A long-range model for the electron-nuclear coupling and two-stage order in TmVO$_4$. https://arxiv.org/abs/2507.16619

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