Speaker
Description
Intuition suggests that, given its simple electronic configuration, the physical characteristics of metallic lithium should not be riddled with many surprises. This intuition, however, does not belie the lesser-known fact that it's low-temperature crystal structure has, to this day, eluded determination, despite decades of active study.
The various crystal structures (fcc, hcp, 9R, etc.) which have been proposed for lithium are all examples of close-packed solids. Previously, we have traced the indeterminacy in its crystal structure to a hidden gauge symmetry in the electronic Hamiltonian, which forces all close-packed structures to have the exact same band structure. Small perturbations, such as the admixture of p-orbitals, or phononic contributions to the free energy, destroy the symmetry and lead to the phenomenon of `state selection', as in the field of frustrated magnetism.
In this presentation, we will investigate whether or not this gauge symmetry is respected in transport measurements. Starting from the Bloch Hamiltonian, we derive an analytic formula for the surface Green's function (GF) of a semi-infinite, close-packed stacking. With electronic hoppings cut off beyond the second nearest-neighbour, we combine the GF with the Landauer-Buttiker formalism to show that all close-packed solids are indeed characterised by exactly the same conductance. The inclusion of the third nearest-neighbour hopping, which gives rise to an hcp-like "stacking fault", renders the conductance sensitive to the stacking sequence and disrupts the symmetry. When many such stacking faults are present, wavefunction localization suppresses the transmission altogether. Our results may be pertinent to metallic lithium under pressure, which is known to adopt a clean fcc structure. Transport measurements may then reflect signs of stacking faults.
| Keyword-1 | quantum_transport |
|---|---|
| Keyword-2 | tight_binding |
| Keyword-3 | transmission |