NMR and ab initio study of gallium metal under pressure

Gallium metal possesses a complex phase diagram and it has been the subject of many experimental and theoretical studies. Nevertheless, hyperfine properties of its phases requiring higher pressure beyond the liquid-I-II triple point were seldom examined. In this work, hyperfine parameters of liquid and solid gallium metal under pressure are investigated by nuclear magnetic resonance (NMR) measurements and ab initio calculations. The electric field gradient and NMR shift of the Ga-III phase are both measured and calculated and their relation to electronic structure is interpreted. Further, calculations of pressure dependencies of the hyperfine parameters of several other solid gallium phases are presented.

Figure 1

The NMR spectra of both isotopes of gallium recorded at room temperature for three different pressures. The insets show details of central parts of the spectra.

Figure 2

The dependence of ${}^{71}\mathrm{Ga}$ NMR spectra on the orientation of the sample with respect to the magnetic field direction measured at 2.15(5) GPa pressure. The rotation axis was perpendicular to the field direction.

Figure 3

The fit of the dependence of ${}^{71}\mathrm{Ga}$ NMR resonance frequencies of the central (solid line) and satellite (dashed lines) transitions on the orientation of the sample with respect to the magnetic field direction measured at 2.15(5) GPa pressure. The rotation axes were perpendicular to the field direction $\mathit{B}$.

Figure 4

Calculated pressure dependencies of EFG $V_{\mathrm{zz}}$ at Ga sites in the four considered Ga structures. Asymmetry parameter in the case of Ga-III and cubic Ga-II is $\eta =0$, while it is $\eta =0.37$ for $\beta \text{−}\mathrm{Ga}$ in the whole calculated range. For comparison, the square symbols denote the values measured on the investigated solid Ga phase. (The lines serve just as eye guides.)

Figure 5

Calculated pressure dependencies of isotropic and anisotropic parts of NMR shift in Ga-III structure; the total values corrected with respect to the GaAs reference, as well as uncorrected paramagnetic and diamagnetic contributions are shown. (The lines serve just as eye guides.)

Figure 6

Calculated total and partial densities of states in Ga-III structure at several pressures.