Instability Peierls

The smectic A phase is a liquid in two dimensions, i.e. in tire layer planes, but behaves elastically as a solid in the remaining direction. However, tme long-range order in tliis one-dimensional solid is suppressed by logaritlimic growth of tliennal layer fluctuations, an effect known as tire Landau-Peierls instability [H, 12 and 13]... 

Monte Carlo simulations [17, 18], the valence bond approach [19, 20], and g-ology [21-24] indicate that the Peierls instability in half-filled chains survives the presence of electron-electron interactions (at least, for some range of interaction parameters). This holds for a variety of different models, such as the Peierls-Hubbard model with the onsite Coulomb repulsion, or the Pariser-Parr-Pople model, where also long-range Coulomb interactions are taken into account ]2]. As the dimerization persists in the presence of electron-electron interactions, also the soliton concept survives. An important difference with the SSH model is that neu-... 

The most striking implication of the electron lattice coupling in ID chains is the appearance of the semiconducting state the equal bond ID lattice (metallic state) is unstable (33) with respect to a lattice distorsion and this so called static Peierls instability is the origin of the opening of the intrinsic band gap at the edge of the B.Z. with an infinite density of states there and the presence of band alternation. 

In several separate or joint recent (1981-85) communications from these groups,164-113 the structural, conductive and magnetic aspects of these complexes, including the nature of the Peierls instability,168 173 were described. 

Although the anisotropy of the complexes electrical conductivity was not mentioned, the three-dimensional nature of the complex facilitates a metal-like temperature dependence of its conductivity down to 4K where a = 105 2 lcm l (room-temperature a is a respectable 300 2 1cm 1). The absence of a metal-insulator transition down to 4K shows that the Peierls instability has been successfully avoided by increasing the interstack coupling. 

The highly conductive class of solids based on TTF—TCNQ have less than complete charge transfer ( 0.6 electrons/unit for TTF—TCNQ) and display metallic behavior above a certain temperature. However, these solids undergo a metal-to-insulator transition and behave as organic semiconductors at lower temperatures. The change from a metallic to semiconducting state in these chain-like one-dimensional (ID) systems is a result of a Peierls instability. Although for tme one-dimensional systems this transition should take place at 0 Kelvin, interchain interactions lead to effective non-ID behavior and inhibit the onset of the transition (6). 

On the basis of these extensive studies, LiPt(mnt) behaves as a simple quasi-one-dimensional conductor with a mean-field-like metal—semiconductor transition due to the Peierls instability. 

One can describe this as the presence of a charge-density wave in the electronic system. In this case the charge-density wave follows from displacement of the atoms. One can ask the question whether in a rigid lattice the electron system itself can distort spontaneously to lower its symmetry, producing an effect that would then attempt to force the nuclei to follow suit. The driving force in this case would not be the movement of the atoms as in the Peierls instability but rather the inherent instability of the electron system itself. The answer to this question is yes. The study of these types of instabilities and associated instabilities in the spin system of the electrons has become an important part of the physics of limited dimensionality. 

---