Tuning the transport properties of graphene through ac fields

599 views

Published on

Luis Foa Torres' talk at the Graphene 2012 Conference in Brussels (April, 2012).
More info and updated references at:
http://nanocarbon.famaf.unc.edu.ar/

Published in: Education
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
599
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
0
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Tuning the transport properties of graphene through ac fields

  1. 1. http://nanocarbon.famaf.unc.edu.ar/ Tuning the transport properties of grapheneHernán L. Calvo (RWTH – Aachen)Claudia G. Rocha (University of Jyväskylä, Finland) through AC fieldsLucas Ingaramo (UNC - Córdoba)Pablo Pérez Piskunow (UNC – Córdoba) Luis E. F. FOA TORRESG. Cuniberti (TU Dresden)Horacio M. Pastawski (UNC - Córdoba) Graphene 2012, BrusselsStephan Roche (ICN - Barcelona) April 2012
  2. 2. Our vision : AC fields for novel, low dissipation, active nanodevices ~ ~ Why ac fields? control novel phenomena applications conductance quantum pumping noise laser-induced gaps Floquet topological insulators LFT, PRB 72, 245339 (2005). ... LFT and Cuniberti, APL 94, 222103 (2009). Rocha, LFT and Cuniberti, PRB 81, 115435 (2010); Calvo, Pastawski, Roche and LFT, APL 98, 232103 Rocha, Pacheco et al. EPL (2011) (2011). LFT, Calvo, Rocha, and Cuniberti, APL 99, 092102 (2011). Calvo, Pastawski, Roche and LFT, to appear (2012). Ingaramo and LFT, to be published. Suárez-Morell and LFT, to be published.Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  3. 3. S. V. Syzranov, M. V. Fistul, and K. B. Efetov, PRB 78, 045407 (2008). microwavesT. Oka and H. Aoki, PRB 79, 081406(R) (2009) “Photovoltaic Hall effect in graphene” visible light Could a laser induce a measurable gap in graphene? How and for which frequencies / intensities / polarization? Idea: Exploit the low dimensionality and the peculiar electronic structure of graphene.
  4. 4. Overview of the simulation scheme z y x Hernán Calvo A(t) kph Semi-classical propagation of monochromatic plane waves: E A 0= ( 1, e iφ ) Intensity and polarization Ω Hamiltonian model for the electronic structure: k.p, tight-binding Floquet theory for the solutionsLuis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  5. 5. Contents not available for the online version. For more info please check http://nanocarbon.famaf.unc.edu.ar/Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  6. 6. Brief Summary of Floquet Theory Floquet Hamiltonian Floquet (Sambe) space Usual Hilbert space R T Space of T-periodic functions 2Ω Then use Floquet theory approach for driven transport: ΩS. Camalet et al., PRB 70, 155326 (2004);S. Kohler, J. Lehmann and P. Hänggi, Phys. Rep. 406, 379 (2005). 0L. Foa Torres, PRB 72 245339 (2005) -Ω -2Ω
  7. 7. Laser-induced gaps in the Floquet spectra For visible light: effects are too small, the required gate voltages as too large... Mid-infrared laser, λ = 8 µmLuis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  8. 8. Laser-induced gaps Gaps evolve with polarization They appear at ± ħΩ/2 and at the Dirac point (pseudogap)Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  9. 9. Simple picture for laser-induced gaps n=1 n=0 n=−1 Inelastic Bragg reflection /Lifting of degeneracies in Floquet spaceLuis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  10. 10. Simple picture for laser-induced gaps n=1 n=0 n=−1 Inelastic Bragg reflection /Lifting of degeneracies in Floquet space Similar to mechanism in : LFT and S. Roche, PRL 97, 076804 (2006); LFT, R. Avriller, S. Roche, PRB 2008Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  11. 11. Laser-induced gaps Dynamical Gap Dirac Gap Circ. Pol. Oka and Aoki PRB 2009 H. L . Calvo, H. M. Pastawski, S. Roche and L. E. F. Foa Torres, Appl. Phys. Lett. 98, 232103 (2011)Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  12. 12. What about the influence on transport?Observable effects of these gaps in the Floquet spectra ? 04/20/12
  13. 13. Tight-binding model and Floquet space (R x T) 2Ω The ac field is included through the Peierls substitution Ω We use the Anger-Jacobi 0 expansion • m – Absorbed or emitted photons -Ω -2Ω We choose Ax = A0 y Ay = 0, in order to decompose HF in the transversal momentum basisLuis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  14. 14. Radiation effects on the dc Conductance Linear polarization http://nanocarbon.famaf.unc.edu.ar/– armchair– 1µm x 1µm size (!)– no dissipation in the sample– no radiation in the leadsMid-infrared laser (λ=8µm) Depletion areas mimic what we showed for the DOS. H. L . Calvo, H. M. Pastawski, S. Roche and L. E. F. Foa Torres, Appl. Phys. Lett. 98, 232103 (2011)Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  15. 15. What about nanoribbons? Contents not available for the online version. For more info please check http://nanocarbon.famaf.unc.edu.ar/Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  16. 16. Power and Temperature dependence Contents not available for the online version. For more info please check http://nanocarbon.famaf.unc.edu.ar/Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  17. 17. A laser-induced Topological Insulator?“Floquet topological insulator in semiconductor quantum Evanescent transmission in irradiated system.wells”Netanel H. Lindner, Gil Refael and Victor GalitskiNature Physics 7, 490 (June 2011).“Transport properties of nonequilibrium systems under the radiation onapplication of light: Photoinduced quantum Hall insulators Ballistic transportwithout Landau levels” due to edge states transportT. Kitagawa, T. Oka, A. Brataas, L. Fu, E. Demler,PRB 84 235108 (Dec. 2011). radiation off Can be verified as well by: - Calculation of effective Hamiltonian. + - Calculation of the associated Chern number, which gives 1 for circular polarization. Zhenghao Gu, H.A. Fertig, Daniel P. Arovas, Assa Auerbach PRL 107, 216601 (Nov. 2011) Eric Suárez Morell and LFT, to be published.Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  18. 18. Contents not available for the online version. For more info please check http://nanocarbon.famaf.unc.edu.ar/Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  19. 19. Conclusions Our simulations show that laser fields in the mid-infrared can be used to induce tunable gaps in the electrical response of graphene. First atomistic simulations of the transport response. Key ingredients: low dimensionality, peculiar electronic structure, » non adiabaticity Possibility of inducing a topological insulator. Related publications available at : http://nanocarbon.famaf.unc.edu.ar/ http://nanocarbon.famaf.unc.edu.ar/Luis Foa Torres http://nanocarbon.famaf.unc.edu.ar/
  20. 20. Thank you! Gracias! | Hernán Calvo Horacio Pastawski Stephan RocheG. Cuniberti Claudia Rocha Lucas Ingaramo Pablo Pérez Piskunow http://nanocarbon.famaf.unc.edu.ar/

×