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The Tang-Dresselhaus Theory is a theory of materials developed by Shuang Tang and Mildred Dresselhaus from Massachusetts Institute of Technology (MIT). They have developed the iterative-two-dimensional-two-band model and iterative-low-dimensional-multi-band model to study the bismuth antimony thin films system . They have found that by control the stoichiometry, film thickness, film grow orientation, temperature, pressure etc., different Dirac cone materials can be constructed in the bismuth antimony thin films system . Tang and Dresselhaus became the cover figure of MIT homepage on April 24, 2012.
Materials with two-dimensional (2D) Dirac cones in their electronic band structures have attracted considerable attention. Work on Graphene was awarded the 2010 Nobel Prize in Physics, because of its special properties based on the two Dirac cones at the K point and the K' point. Many important novel physical studies have been carried out on both massless and massive 2D Dirac fermions, including studies of the half-integer quantum Hall effect, the anomalous absence of back scattering, the Klein paradox effect, high temperature superconductivity, and unusual microwave response effects. The ultrahigh carrier mobility of the Dirac fermions offers new opportunities for a variety of electronics applications. 2D Dirac cones observed in topological insulators have identified this class of materials as candidates for quantum computation, spintronics, novel superconductors, and promising thermoelectrics. Anisotropic 2D single-Dirac-cone materials, could potentially be developed for use in nanoelectronic-circuits without cutting processes, and in desktop experiments on relativistic particles propagating in anisotropic space.
Tang and Dresselhaus have given a systematic clue on how to control the mini-band-gap at the L points of single crystal (mosaic single crystal) bismuth antimony thin films, so that it is able to construct different single crystal (mosaic single crystal) bismuth antimony thin films for different research and application purposes, e.g. thermoelectronics, refrigeration, super-speed electronic devices and desktop relativistic particle researches. Tang and Dresselhaus have also shown how to construct single crystal (mosaic single crystal) bismuth antimony thin films in different phases, including semi-metal phases, direct-band-gap semiconductor phases and indirect-band-gap semiconductor phases as a function of the parameters.
The iterative-two-dimensional-two-band model Tang and Dresselhaus have developed can be extended to iterative-low-dimensional-multi-band model to study other narrow-band low-dimensional systems. There are many other narrow-band materials systems that have strongly coupled bands at the band edges where the dispersion relations are non-parabolic or even linear, for example the X-point dispersion relation of silicon germanium and the L-point dispersion relation of lead telluride, as well as bismuth selenide and bismuth telluride under certain conditions. When these narrow-band materials are synthesized as 2D thin films, the problem to describe the 2D non-parabolic dispersion relations are in many ways similar to the problem in bismuth antimony thin films. Furthermore, based on this methodology, the model can be extended to a general iterative-low-dimensional-multi-band model to describe other low-dimensional systems, such as nanowires etc.
The Dirac-cone bismuth-antimony films could be the basis materials for the next generation of electronic devices. Electronic devices based on this materials system have hundreds of times higher electron transport speed than current silicon based devices because of the ultrahigh mobility. Meanwhile, different anisotropies implies different devices out of the same class of material without film cutting processing, which will save quite a lot manufacturing costs. The system of bismuth antimony is one of the traditional best low temperature thermoelectric materials. The Tang-Dresselhaus materials system might also be interesting for cryogenic temperature thermoleectrics and cooling. This is especially interesting for energy generation of space-stations and satellites, where it can make electricity from the temperature difference between the sun-facing side and the shaded side. Because of the highly controllable anisotropy, this Tang-Dresselhaus materials system could also be interesting for anisotropic relativistic particles.
- ↑ Thin films of bismuth-antimony have potential for new semiconductor chips, thermoelectric devices. MIT News Office.
- ↑ Shuang Tang and Institute Professor Mildred Dresselhaus. MIT News Office.
- ↑ Phase diagrams of Bi1−xSbx thin films with different growth orientations. American Physical Society.
- ↑ Constructing Anisotropic Single-Dirac-Cones in Bi1–xSbx Thin Films. American Chemistry Society.
- ↑ Anisotropic Dirac cones for next-generation electronics. Nanotech, Institute of Physics, UK.
- ↑ Dirac cones could exist in bismuth–antimony films. Physics World, Institute of Physics, UK.