Fermi Surface of Lithium by Positron Annihilation

Abstract

The angular correlation of radiation from positrons annihilating in lithium single crystals has been measured. The crystals were oriented in the [100], [110], and [111] directions, and the measurements yield information closely related to the areas of slices through the Fermi surface normal to these directions. The measurements show that the Fermi surface of lithium is anisotropic, the length of the radius vector &no being about 5% greater than km. The measurements also yield estimates of the energy gap at the boundary of the first Brillouin zone, and the amplitudes of the most important higher-momentum components of the electron wave function.

New Approach to Energy-Band Calculations with Results for Lithium Metal

“…However, the Fermi surface overlaps the first two GI bands and intersects the sc BZ at about 0.734 of the distance from k= (2ir/ a)(i,0,0) to k = (2?r/a)(ii0), at which point (k ¥ = 0.59a 0~1 ) the energy gap should be about 0.08 to 0.16 eV. 17 This gap size should cause little distortion from sphericity for the Fermi surface, which is in agreement with de Haas-van Alpen, 18 cyclotron-resonance, 19 and positron-annihilation experiments, 20 and with the x-ray determination of electron moments. 21 But optical transitions are now allowed between occupied states of the first band and empty states of the second band, and thus the threshold for optical transitions should be very small.…”

Investigation of Some Ground State Properties of Lithium with the All Electron MAPW Method

“…Some experimental studies [3][4][5] also favour a Fermi surface of less distortion e.g. ð2:6 AE 0:9Þ%, ð2:8 AE 0:6Þ% and ð3:6 AE 1:1Þ% whereas other investigations gave the anisotropy value ð4:6 AE 1:0Þ% [10], ð4:7 AE 0:2Þ% [9] and ð4:8 AE 0:3Þ% [52] closer to the results first estimated by Donaghy and Stewart [8] by analysing measurements of the angular correlation of the positron annihilation in the bcc phase at T ¼ 100 K.…”

“…Open triangles and crosses represent measurements of the two-dimensional angular correlation positron-electron annihilation radiation (2D-ACAR) by Oberli et al [4] and by Basinski et al [51], respectively. The dashed lines are the uncorrected Compton scattering data of Schü lke et al [5] experiments in the long-slit geometry done by Donaghy and Stewart [8] at 100 K allow to extrapolate the correlation curve of positron annihilation to zero angle yielding values which are proportional to the extremal areas of the slices through the Fermi surface. In this way they obtained the values ðA ½111 À A ½110 Þ=A ½110 ¼ 0:045 AE 0:012 and ðA ½100 À A ½110 Þ=A ½110 ¼ 0:020 AE 0:012.…”

Lithium nanocluster formation in Li+ - ion implanted MgO

“…Similarly, the results for the implanted layer show four relatively intense peaks, now closer to the center of the plot. The peak positions are found just inside the Fermi-radius of lithium [12]. The fourfold symmetry indicates again a cubic symmetry.…”