Collective charge density wave

Plasmons exist in bulk metal, metal surfaces as well as in metal nanoparticles and are based on the coherent oscillations of (i)-electrons under the influence of an external photon field. In fhe case of a bulk metal a collective charge density wave in the electron gas is built up and its plasmon frequency lies in the range of UV light. Above this plasma frequency the radiation is partly absorbed or transmitted, since the electrons in the field cannof follow fhe incidenf field. Its frequency is simply to fast for the electrons to respond. Below the plasma frequency, the incoming field is screened by the electrons and oscillates. As a consequence, the incoming radiation is... 

Peierls pointed out in 1955 that a one-dimensional metallic chain is not stable at T = 0 K, against a periodic lattice distortion of wave vector 2kF, as the result of electron-phonon coupling, opening a gap 2A at the Fermi level. From this fact a collective electronic state results called a charge density wave (CDW). In the limit where U, the intrasite Coulomb repulsion, is infinite, since a given k state cannot be occupied by more than one... 

The divergence of the density-response function x q) occurs only in a 1-d metal [M4, M2, Chap. 17]. It gives rise to the collective state of the electrons (the charge-density wave) and the static lattice distortion with the same period q = 2kp, as well as the opening of an energy gap at the Fermi energy Ep (Fig. 9.8c). 

A very important feature of the Frohlich model is that the lattice distortion and the charge density wave need not be fixed to the frame of reference of the lattice (i.e., the phase of the distortion need not be fixed). The electrons which make up the charge density wave may then move as a unit (collective charge transport) with a large effective charge and large effective mass leading to enhanced conductivity. 

The collective behavior of condensed modulated structures like charge or spin density waves (CDWs/SDWs) [23, 22, 4], flux line lattices [2, 36] and Wigner crystals [4] in random environments has been the subject of detailed investigations since the early 1970s. These were motivated by the drastic influence... 

Further possibilities for long-range effects of chemical carcinogens are provided by the change or occurrence of different collective states in these complex polymers. These collective states can be vibrational or conformational solitons, Mott insulator states, Peierls instabilities, plasmon-type states, charge and spin density waves, excitonic insulator states, etc. Here only one example (which has been worked out in some detail), namely a conformational soliton caused by carcinogen binding, will be discussed. 

First, let us consider the measurement of CVR When the density of the particles Pp differs from that of the medium Pjjj, the particles move relative to the medium under the influence of an acoustic wave. This motion causes a displacement of the internal and external parts of the double layer (DL). The phenomenon is usually referred to as a polarization of the DL (6). This displacement of opposite charges gives rise to a dipole moment. The superposition of the electric fields of these induced dipole moments over the collection of particles gives rise to a macroscopical electric field which is referred to as the colloid vibration potential (CVP). Thus, the fourth mechanism of particles interaction with sound leads to the transformation of part of the acoustic energy to electrical energy. This electrical energy may then be dissipated if die opportunity for electric current flow exists. 

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