University of Cambridge > Talks.cam > Semiconductor Physics Group Seminars > Landau level spectroscopy reveals the chirality and Klein tunnelling of electrons in twisted graphene tunnel transistors

Landau level spectroscopy reveals the chirality and Klein tunnelling of electrons in twisted graphene tunnel transistors

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Multilayer transistors based on graphene and other van der Waals crystals exhibit interesting physical properties, high on-off current switching ratios, mechanical flexibility and resonant tunnelling with gate voltage-tuneable negative differential conductance at room temperature [1-3]. In these devices, we have recently demonstrated the strong sensitivity of in-plane momentum conserving tunnel transitions to any small misalignment or twist angle between the crystalline lattices of the two graphene electrodes [4]. Following a brief review of this recent work, we will present new results which investigate the effect of a magnetic field applied perpendicular to the graphene layers on the current-voltage characteristics of devices in which the graphene lattices are carefully aligned to within 1 degree. The magnetic field quantises the electronic states in the conical, gapless conduction and valence bands into a ladder of unequally-spaced Landau levels.

Tunnelling of electrons between the Landau levels of the two graphene electrodes gives rise to a complex pattern of sharp resonant peaks in the differential conductance (dI/dV). To analyse these data, we use a Bardeen transfer Hamiltonian approach which incorporates the two-component spinor-spatial character of the Dirac-Weyl fermions. We demonstrate how the intensity of the energy- and momentum- conserving tunnel transitions reveal the effects of chirality [5], which is a unique feature of electron dynamics in graphene and related materials.

[1] L. Britnell et al., Science 335, 947 (2012). [2] T. Georgiou et al., Nature Nanotechnology 2, 100 (2013). [3] L. Britnell et al., Nature Communications 4, 1794 (2013). [4] A. Mishchenko et al., Nature Nanotechnology 9, 808 (2014). [5] M. Greenaway et al., Nature Physics 11, 1057 (2015).

This talk is part of the Semiconductor Physics Group Seminars series.

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