Perfect Transmission

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Science  24 Aug 2012:
Vol. 337, Issue 6097, pp. 893
DOI: 10.1126/science.337.6097.893-b

In quantum mechanics, when a particle encounters a potential energy barrier that it cannot classically overcome, most of the time that particle will be reflected, but some of the time it will be able to make it through to the other side. The probability of tunneling is generally less than 1; however, in the special case where there is dissipation in the system and instead of a single barrier there is a double barrier supporting a resonant state, perfect transmission has been predicted to occur under certain circumstances. Mebrahtu et al. used a carbon nanotube coupled to two resistive (dissipative) leads to realize this system; two side gates controlled the coupling between the nanotube and the two leads. When the couplings were asymmetrical, there was the usual decreasing dependence of resonance conductance with lowering temperature. For exactly even couplings, the behavior was the opposite of that, and the conductance at the lowest measured temperature showed perfect transmission. The authors interpreted their results as a quantum phase transition of the unusual “boundary” type, where only a local part of the system undergoes the transition.

Nature 488, 61 (2012).

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