Electronic topological transition in zinc metal at high external pressure

Abstract

We report investigations of Zn metal under quasi-hydrostatic pressures up to 16 GPa by 67 Zn Mössbauer spectroscopy and scalar-relativistic linearized augmented plane wave (LAPW) calculations. Our studies show that at 4.2 K an electronic topological transition (ETT) occurs at about 6.6 GPa, corresponding to a volume change of (1−V /V • ) ≈ 0.085. At the ETT conduction electron states in the third Brillouin zone at the symmetry point L ('butterflies') move below the Fermi surface and start being occupied. At the ETT the electric field gradient tensor and the s electron density ρ(0) at the 67 Zn nucleus remain virtually unchanged, but the lattice dynamics is drastically affected. The Lamb-Mössbauer factor (LMF) abruptly drops by a factor of two between 6.5 and 6.7 GPa and the curvature of the pressure dependence of the second-order Doppler shift (S SOD ) changes markedly. The results on LMF and S SOD are described by a sudden destruction of a giant Kohn anomaly which accompanies the ETT.

Electronic structure of materials under pressure

“…On the other hand, if an anomaly in c/a does exist, it is very likely to induce a corresponding anomaly in V zz . This simply follows from the results of the same authors [77], which show that the main contribution to the decrease of the EFG in hcp Zn under external pressure is essentially determined by the decrease of c/a. To resolve this controversy, we calculated the pressure dependence of EFG using our optimized c/a values for all volumes considered and for both metals.…”

“…Takemura [75] has shown that the volume dependence of c/a in Zn changes its slope at V/V 0 = 0.893 (P = 9.1 GPa), while Potzel et al [76] found a drastic drop (by a factor of 2) of the Lamb-Mössbauer factor, indicating a drastic softening of low-frequency acoustic and optical phonons at V/V 0 ≈ 0.915 (P = 6.6 GPa). A change in the curvature of the electric field gradient (EFG) dependence on pressure was also observed [76,77].…”

“…The giant Kohn anomaly in Cd was observed in inelastic neutron scattering experiment by Chernyshov et al [82]. Recent LAPW calculations [76,77], performed at several experimental lattice parameters without complete structure optimization, suggest that a collapse of the giant Kohn anomaly induced by pressure is responsible for phonon softening at V/V 0 ≈ 0.915 and possibly also for the anomalous behavior of the c/a ratio. Unfortunately, no complete theoretical analysis of the lattice behavior of Zn under pressure exists so far.…”

“…Large c/a ratios make many of their solid-state properties highly anisotropic and so they have been extensively studied both experimentally [64 -69] and theoretically [70 -74]. Although the electronic and lattice properties of Zn and Cd have been studied for many years, recent publications by Takemura [75] on Zn in high-pressure powder Xray diffraction experiments (at room temperature) and by Potzel et al [76,77] on 67 Zn Mössbauer studies (at 4.2 K) have renewed interest in these metals, and seem to resolve the question of the anomalous lattice properties of Zn under hydrostatic pressure. The earlier studies by Lynch and Drickamer [78], which found a nonmonotonic pressure dependence of the c/a ratio in Zn and Cd, are contradicted by more recent results by Schlute et al [79], where c/a did not show such a behavior.…”

“…The dependence of the electric field gradient on hydrostatic pressure in hcp Zn was first measured by Potzel et al [76] and calculated [77] using the FP-LAPW method. Although the experimental data show a change in the slope of the pressure dependence of the main component, V zz , of the EFG tensor at a pressure corresponding to the c/a anomaly, the calculations were not able to detect any such anomaly.…”