Nesting Induced Peierls-Type Instability for Compressed Li-cI16

Abstract

Alkalies are considered to be simple metals at ambient conditions. However, recently reported theoretical and experimental results have shown an unexpected and intriguing correlation between complex structures and an enhanced superconducting transition temperature in lithium under pressure. In this article we analyze the pressure induced Fermi surface deformation in bcc lithium, and its relation to the observed cI16 structure. According to our calculations, the Fermi surface becomes increasingly anisotropic with pressure and develops an extended nesting along the bcc [121] direction. This nesting induces a phonon instability of both transverse modes at N , so that a Peierls-type mechanism is proposed to explain the stability of Li-cI16.

Structure stability in the simple element sodium under pressure

“…This qualitative picture is in tune with the first-principle calculation of electronic density of states for Li-cI16 [5]. Calculations of the Fermi surface of bcc Li in the cI16 stability field show that it becomes increasingly anisotropic with pressure and develops an extended nesting along the bcc [211] direction [45], which goes along with our model shown in Fig. 3b.…”

Lifshitz Transition and Superconductivity Enhancement in High Pressure $cI$16 Li

“…Our results also visually decode the effects of three-dimensional charge density waves on the Fermi surface. We find the cI 16 nesting vectors [200] 2π a cI16 and [110] 2π a cI16 to be as relevant as the previously reported [211] 2π a cI16 [18]. These intriguing and direct observations demonstrate the general value of Fermi surface unfolding in the study of topological features associated with symmetry breaking phase transitions in materials.…”

“…The most prominent FS depletion takes place on the 24 large holes along the [211] direction had been previously been assigned to the G = [211] 2π a cI16 nesting vector [18]. Indeed V 211 CDW partially contributes to those substantial gaps.…”

“…3(b), the FS of the fictitious CDW-free bcc system with a bcc = a cI16 /2. For example the necks at the high symmetry points N resembling the FS of copper [11,18] are still clearly recognizable in the unfolded FS. The grey balls in Fig.…”

Kohn anomalies and enhanced superconductivity in simple systems under pressure: Insights from the nearly free electron model

“…In most of these systems, these anomalies have been linked to the large deformations sustained by their Fermi surfaces, going from the NFE sphere at low density to non-spherical surfaces exhibiting nesting in the pressure range of interest. The wave vectors of the anomalous phonons have been positively correlated to the nesting wave vectors of the Fermi surfaces [2,3], suggesting that the anomalous phonons are in fact caused by the singularities in the density response function of the electron gas induced by the nesting [4,5]. Sodium is a notable exception: although computations show that it does exhibit phonon softening like the other alkalies, its Fermi surface remains exquisitely spherical in the pressure range of interest [2].…”