Kohn anomalies in superconductors.

Energy gaps and Kohn anomalies in elemental superconductors.

The momentum and temperature dependence of the lifetimes of acoustic phonons in the elemental superconductors lead and niobium were determined by resonant spin-echo spectroscopy with neutrons. In both elements, the superconducting energy gap extracted from these measurements was found to converge with sharp anomalies originating from Fermi-surface nesting (Kohn anomalies) at low temperatures. T...

Kohn Anomalies in Graphite and Nanotubes

Atomic vibrations are partially screened by electrons. In a metal this screening can change rapidly for vibrations associated to certain points of the Brillouin zone, entirely determined by the shape of the Fermi surface. The consequent anomalous behaviour of the phonon dispersion is called Kohn anomaly. Graphite is a semimetal. Nanotubes can be metals or semiconductors. We demonstrate that two...

Superconducting vortices in ac fields: does the Kohn theorem work?

Electrodynamics of clean pinning-free type II superconductors in the mixed state is derived using the Boltzmann kinetic equations for excitations. The condition of the vortex cyclotron resonance is found. The reason why this resonance does not comply with the Kohn theorem is discussed.

Orbital magnetism in the density functional theory of superconductors

Phonon anomalies predict superconducting T(c) for AlB2-type structures.

We show that the well-known Kohn anomaly predicts Tc for ordered AlB2-type structures. We use ab initio density functional theory to calculate phonon dispersions for Mg1-xAlxB2 compositions and identify a phonon anomaly with magnitude that predicts experimental values of Tc for all x. Key features of these anomalies correlate with the electronic structure of Mg1-xAlxB2. This approach predicts T...