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Overcoming Anderson localization in chiral-disordered graphene

Speaker: 
Aires Ferreira (University of York, UK)
Date: 
Wed, 02/12/2015 - 11:00am to 12:00pm
Location: 
Physics Conference Room (S11-02-07)
Host: 
Vitor Pereira
Event Type: 
Seminars

Abstract

Graphene subjected to chiral disorder is believed to host zero energy modes resilient to localization, as dictated by the renormalization group analysis of the underlying field theory [1]. For disorder in the BDI chiral orthogonal class – such as vacancies and bond disorder – a line of fixed points with conductivity ~e^2/h is predicted. Such an unconventional quantum transport regime is found at variance with recent numerical works, however, which report the localization of all states, including the zero energy modes [2]. In this talk, I introduce an exact polynomial expansion of quantum-mechanical lattice response functions, whose implementation in large-memory machines allows tackling disordered systems with multi-billion (>10^9) atoms and fine meV resolutions. Its application to the honeycomb lattice with random vacancy defects reveals an unprecedentedly robust metallic state in two dimensions. The Kubo conductivity of zero energy modes is found to match graphene’s universal ballistic conductivity - 4e^2/(pi h) - within 1% accuracy, over a wide range of energy level broadenings and vacancy concentrations [3]. These results testify to the power of the novel polynomial expansion, and shed new light on the nature of electronic transport at the Dirac point of graphene. 

[1] P.M. Ostrovsky, I.V. Gornyi & A.D. Mirlin, PRB 74, 235443 (2006). P.M. Ostrovsky, et al., PRL 105, 266803 (2010). 
[2] G.T. de Laissardiere & D. Mayou, PRL 111, 146601 (2013). A. Cresti, F. Ortmann, T. Louvet, D.V. Tuan & S. Roche, PRL 110, 196601 (2013). Z. Fan, A. Uppstu & A. Harju, PRB 89, 245422 (2014).
[3] A. Ferreira & E. Mucciolo, PRL 115, 106601 (2015). 

 

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