On the relative stability of the metallic and the insulating states of a half‐filled band

Interband Electron Pairing for Superconductivity from the Breakdown of the Born-Oppenheimer Approximation

The origin of interband electron pairing, responsible for enhancing superconductivity, and the factors controlling its strength were examined. We show that interband electron pairing is a natural consequence of breaking down the Born-Oppenheimer approximation during electron-phonon interactions. Its strength is determined by the pair-state excitations around the Fermi surfaces that take place to form a superconducting state. Fermi surfaces favorable for the pairing were found, and the implications of this observation are discussed.

Hidden fermi surface nesting and charge density wave instability in low-dimensional metals

The concept of hidden Fermi surface nesting was introduced to explain the general observation that certain low-dimensional metals with several partially filled bands exhibit charge density wave (CDW) instabilities, although their individual Fermi surfaces do not reveal the observed nesting vectors. This concept was explored by considering the Fermi surfaces of the purple bronze AMo(6)O(17) (A = sodium or potassium) and then observing the CDW spatial fluctuations expected from its hidden nesting on the basis of diffuse x-ray scattering experiments. The concept of hidden Fermi surface nesting is essential for understanding the electronic instabilities of low-dimensional metals.

A vibronic approach to the band-filling and temperature-dependent metal-insulator transition

A model of vibronic origin is used to investigate the important issue of metal-insulator transition in low-dimensional materials. For zero temperature, the stability of the single-band model chain is controlled by the competition between the internal electron-phonon coupling and the nearest-neighbor hopping integral. Assuming one particular deformation mode, one can analytically derive an instability criterion in which the band filling is explicitly included. The carrier doping directly controls the stability of a one-dimensional chain. For a half-filled band, the Peierls instability is recovered. For finite temperatures, a similar criterion is derived and can be used to investigate the metal-insulator transition temperatures.

Relative importance of local and collective effects in the distortivity of one-dimensional chains

On the basis of an original coupled-cluster type formalism developed previously [J.-P. Malrieu and V. Robert, J. Chem. Phys. 120, 7374 (2004)], the cohesive energies and the occurrence of Peierls instability are investigated in half-filled one-dimensional systems. Starting from various parametrizations of the Huckel Hamiltonian, this approach allows one to evaluate the relative contribution of local and collective interactions by comparison to exact tight-binding crystal calculations. For an alternating (AA('))(n) chain, quantitative agreement with the exact solution is obtained starting from either an atom-centered or a bond-centered reference function. The distortion takes place beyond a critical value of the electron-phonon/elastic strength ratio which is correctly predicted. Its amplitude and the corresponding stabilization energy are also accurately reproduced, suggesting that the driving force of the second-order Peierls distortion is essentially local. For homogeneous (A)(n) systems and the first-order Peierls distortion traditionally presented as resulting from a band gap opening (i.e., collective effects), our localized approaches are deficient only in the domain of weak electron-phonon/elastic ratio where the distortion amplitude is almost negligible. These results confirm that the short-range delocalization effects are the leading phenomenon responsible for the bond alternation in conjugated hydrocarbons.

Evidence for an enhanced flow of virtual energy in the progression from inanimate matter and its role in behaviour proper to the animate state

There are reasons for cleaving a virtual or phase space component from electromagnetic radiation and for reposing in this component properties of specific value for the functioning biosystem. Putative mechanisms are derived by which a stream or streams of virtual energy dissipates biomatter, providing global control of component chemical reactions. Characteristics include a variety of wavelengths whose interactions can change rapidly producing a collapse-restoration cycle of values, an exquisite sensitivity to external fields of magnetic, gravity and heat origin plus a property for electron transport from lesser to more dense streams. Disturbances in the virtual control stream over chemical events become available as resonances to macroscopic measuring tools including those of clinical use.