Coherent Lattice Vibrations, Kohn Anomalies, and Pseudogaps in Superconductors

A recent analysis has proposed [1] that the superconducting state is associated with charge density standing waves at k=2k$_{F}$, coupled to coherent lattice vibrations at 2k$_{F}$-G, where G is a reciprocal lattice vector. Independently, Aynajian et al. [2] have recently observed phonon spectral anomalies in Nb and Pb that correspond to Kohn anomalies in the Fermi surface, at energies matching the low T energy gap 2$\Delta $(0). Since Kohn anomalies are also defined by k=2k$_{F}$-G, these observations appear consistent with [1]. This also suggests that Kohn anomalies and an associated pseudogap provide a universal precursor of the superconducting state. Further experiments are proposed that should provide direct evidence of the coherent lattice vibrations in the superconducting state of conventional electron-phonon superconductors, and of alternative coherent oscillations (spin waves, etc.) in unconventional materials. \\[0pt] [1] A.M. Kadin, ``Coherent Lattice Vibrations in Superconductors'', Physica C 468, 255 (2008); http://arxiv.org/abs/0706.0338. \\[0pt] [2] P. Aynajian, et al., ``Energy gaps and Kohn anomalies in elemental superconductors'', Science 319, 1509 (2008); http://arxiv.org/abs/0808.1028.