Condensed Matter Physics Seminar

2 p.m., Thursday, March 15, 2007
Room 1201, Physics Building

 Coherent charge and spin transport phenomena in graphene

Barbaros zyilmaz

(Columbia University)

Abstract:  Recently it has become possible to fabricate atomically thin sheets of graphite, which are referred to as graphene. Graphene is a strictly 2D crystal and can be viewed as an unrolled single wall Carbon nanotube. Its unique band structure leads to remarkable electronic transport properties, which are fundamentally different from that of two 2D systems realized in semiconducting heterostructures. Perhaps the most intriguing example is the unusual quantization of the Quantum Hall effect. Furthermore, graphene is likely to become an important material system in the fields of nanotechnology and spintronics. For example, its mean free path and both its phase and spin coherence length are expected to be very long.

After describing the fabrication and patterning of graphene, I will present experiments, which address the phase coherence length and spin coherence length in this novel 2 dimensional electron gas. I will start with the discussion of electronic transport in graphenen ribbons patterned down to a width of ~ 20 nm. I will show that the finite size of such ribbons leads to the formation of a band-gap. Low temperature experiments show that the phase-coherence length in such samples is in the order of 1 μm. Such a long phase coherence length allows the direct observation of quantum interference phenomena in ring shaped graphene nanoribbons. I will conclude my talk with experiments addressing the spin coherence length in graphene. For these studies I have fabricated graphene based lateral spin valves. The spin injection has been achieved by means of ferromagnetic Co/Cu/Co multilayer electrodes. I will discuss the magnetoresistance of such devices in both the local and non-local geometry.

Host:  Fuhrer
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