Secondary charge-density waves

We propose a new type of charge-density wave which occurs in a two-band model rather than the conventional one-conduction-band type Peierls wave. In our case distortions are associated with the magnetic valence band as well as with the metallic conduction band. A numerical solution demonstrates multiple gaps in the dispersion.     

Chiral charge-density waves

We discovered the chirality of charge-density waves (CDW) in 1T-TiSe? by using STM and time-domain optical polarimetry. We found that the CDW intensity becomes Ia?∶Ia?∶Ia? = 1∶0.7 ± 0.1∶0.5 ± 0.1, where Ia(i) (i=1,2,3) is the amplitude of the tunneling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease clockwise and anticlockwise. The chirality in CDW results in the threefold symmetry breaking. Macroscopically, twofold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H(CDW) ≡ q?·(q?×q?), where q(i) are the CDW q vectors, which is independent of the symmetry of components. The nonzero H(CDW)-the triple-q vectors do not exist in an identical plane in the reciprocal space-should induce a real-space chirality in CDW system.     

Competition of charge-density waves and superconductivity in sulfur

A one-dimensional charge-density wave (CDW) instability is shown to be responsible for the formation of the incommensurate modulation of the atomic lattice in the high-pressure phase of sulfur. The coexistence of, and competition between, the CDW and the superconducting state leads to the previously observed increase of T{c} up to 17 K, which we attribute to the suppression of the CDW instability, the same phenomenology found in doped layered dichalcogenides.     

Commensurable charge-density waves in a random potential

We study commensurable charge-density wave systems in the presence of random impurities. The results of the microscopic theory, especially the contributions of second order in the impurity fields, are briefly discussed. The lifetime of the excitations is calculated, as well as the response of a soliton to an external field.     

Convective terms and transversely driven charge-density waves

We derive the convective terms in the damping which determine the structure of the moving charge-density wave (CDW), and study the effect of a current flowing transverse to conducting chains on the CDW dynamics along the chains. In contrast to a recent prediction we find that the effect is orders of magnitude smaller, and that contributions from transverse currents of electron- and holelike quasiparticles to the force exerted on the CDW along the chains act in the opposite directions. We discuss recent experimental verification of the effect and demonstrate experimentally that geometry effects might mimic the transverse current effect.     

Non-local conduction by charge-density waves in niobium triselenide

The threshold field E_T for the onset of nonlinear conduction in NbSe₃ has been measured using both the normal 4-terminal arrangement, and a transposed version with current flow between the inner pair and voltage measured between the outer. When the distance between the inner terminals is small, and the temperature between 60 and 110 K, E_T is significantly greater for the transposed than for the normal arrangement. The phenomenon is thought to demonstrate that the nonlinear conduction, which arises from motion of the charge-density wave (CDW) forming at 144 K, is non-local over distances of the order of 100μm.Further experiments indicate that E_T is greater with the transposed arrangement because the CDW then has to be broken near the inner terminals, in order that its central section might move independently. Evidence is presented that the breaking process at an inner terminal depends on whether current flows from or towards it, and that above 110 K breaking occurs even when the normal configuration is used, apparently because the CDW is then too weak to overcome the pinning introduced by the contact material.No corresponding effects have been observed in nonlinear conduction by the CDW which forms at 59 K.