Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 39: Transport: Graphene 1 (jointly with MA, HL, DY, DS, O)

TT 39.3: Talk

Thursday, March 29, 2012, 10:00–10:15, BH 334

Single-parameter pumping in graphene — •Sigmund Kohler¹, Pablo San-Jose², Elsa Prada¹, and Henning Schomerus³ — ¹Instituto de Ciencia de Materiales de Madrid, CSIC, 28049 Madrid, Spain — ²Instituto de la Estructura de la Materia, CSIC, 28006 Madrid, Spain — ³Department of Physics, Lancaster University, Lancaster, LA1 4YB, United Kingdom

The ratchet or pump effect, which is the induction of a dc current by an ac force in the absence of any net bias, represents one of the most intriguing phenomena in non-equilibrium transport. For graphene, one expects that its gapless and chiral nature negatively affects pumping, because it hinders the confinement of electrons. Despite this expectation, a pump mechanism that is particularly efficient in graphene exists [1]: It is based on barriers in which the, say, left half is modulated by an ac gate voltage. Then electrons entering the barrier in evanescent modes from that side may be excited to propagating modes. Evanescent mode entering from the right, by contrast, decay before reaching the driving region. This mechanism is rather efficient in graphene, because all evanescent modes within a certain energy range contribute. The corresponding mechanism in a two-dimensional electron gas works only with modes that fulfill certain resonance conditions, which leads to a much smaller pump current.

[1] P. San-Jose, E. Prada, S. Kohler, and H. Schomerus, Phys. Rev. B 80, 155408 (2011)