Yen-Lin Chen edited introduction.tex  over 8 years ago

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\section{Introduction}   The idea of charge density waves was first proposed by Frohlich \cite{Frohlich_1954} in 1954. It was not until the late 1970s that CDW phenomenon was investigated and physical models were constructed \cite{Bardeen_1979}. Later on, the CDW material was found to have interesting non-linear current response and frequency dependence when applied dc or ac electric fields \cite{Thorne_1996}. The electric properties of CDW could be engineered by applying gate voltage to build field-effect CDW electronic devices, which can function as gate-controlled switch \cite{Adelman_1995} and current oscillator \cite{Thorne_1986}.  Some quasi-one-dimensional materials such as niobium triselenide (NbSe_3) will undergo phase transition of the electron states in the conduction band due to the electron-phonon interaction. Pointed out by Peierls in 1955 in This phase transition will produce band gaps near \cite{Peierls_2001}, the conduction electron state is unstable below certain temperature \textit{T_P}, also known as Peierls temperature. The ground state is  the Fermi surface, transforming CDW state which reduces  the material from conductor total electric energy at the cost of small amount of deformation energy of the quasi-one-dimensional lattice. The charge density varies periodically according  to semiconductor or insulator. the deformation. The non-uniform charge density transport and its interaction with the lattice plays a key role in current characteristics.