Non-Maxwell–Boltzmann dependence of channel carrier concentration in a quasi one dimensional charge density wave channel in the ballistic transport regime

Abstract

With the aid of a coherent transport model utilizing the Non-Equilibrium Green Function (NEGF) approach, a three terminal device with metallic gate, source and drain and a quasi one dimensional Charge Density Wave (CDW) channel is simulated focussing on the transistor behaviour brought about by a sweep of the channel potential or equivalently the chemical potential in the channel. The channel is strongly insulating only at half-filling and moving to lower and higher carrier concentrations both incur a mean field phase transition to a conducting state. With the aid of conductance calculations for a pinned CDW condensate, we present calculations for the sub-threshold slope in terms of the hopping parameter or equivalently the width of the tight-binding chain. The effects of source to drain bias and length are examined. The conductance profiles are analyed in relation to transmission profiles. The observed CDW profiles are explained in terms of filling and Fermi Surface Nesting (FSN). Boundary conditions, gap equations and response functions are shown to reveal the commensurability conditions and size of the transport gap. The channel carrier concentration is modulated in an athermal (non-Maxwellian-Boltzmann) fashion, thereby making it an interesting prospect for steep transistors.

Charge filling induced quasi-two dimensional charge/spin density wave channel in a ballistic transport device

“…Conductance profiles reveal information on the nature of MIT in the channel of the three terminal device formed out of source, drain, and gate. As previously found in [8], density waves supported by hard-wall boundary conditions and commensurability are only observed in the atomistic model. Non-Equilibrium Green Function (NEGF) approach is adopted for the simulation of the finite atom device.…”

“…We adopt this method of simulating the electron-phonon interaction with a purely electronic model with U < 0. Mean field decomposed negative-U Hubbard models emulate the nesting instabilities most reliably depending on geometry and commensurability [8]. In materials where changing wave-vectors of CDW can appear with changes in the band filling, mean field decomposed negative-U Hubbard can emulate the material behaviour.…”

“…Away from halffilling incommensurate CDWs are expected to become more important than (π/a, π/a) commensurate order [23][24][25]. Since in a finite geometry incommensurate CDWs will be broken up into domains separated by domain wall/phase slips [8], the conductance of the channel can change drastically.…”

“…Abrupt change in magnetic order in response to doping is also known [5]. Phase transition empowered steep sub-threshold slope transistors have been realized experimentally [6,7] and investigated theoretically [8] in recent times to sustain the longstanding research in device industry to propose novel ideas to overcome the 1 Previously at Department of Electrical Engineering, University of California, Riverside, CA 92521-0204, United States of America 60 meV dec −1 physical limit of traditional switching devices [9]. Design of materials for switching device based on metalinsulator transitions in Peierls insulators have come to the fore recently [10].…”

“…The NEGF framework can facilitate a study of transport through an interacting systems at the mean field level [11,12]. The details of the implementation and the transport calculations for a quasi-1D CDW/SDW was presented in [8]. Here, in the quasi-2D CDW/SDW case, a CDW/SDW phase can be incurred as a result of FSN or vHS in the Density of States supporting the singular response functions [13][14][15][16].…”