P ve n katkılı grafen elektrotlara asimetrik bağlı güçlü korelasyonlu bir kuantum noktacığında gerçek zamanlı elektron dinamikleri

Öz

Kesişmeme yaklaşımını kullanarak p ve n katkılı grafen elektrotlara asimetrik olarak bağlanmış güçlü korelasyonlu bir kuantum noktacığı boyunca kuantum taşınmasını araştırdık. Kuantum noktacığı bir kapı voltajı yoluyla aniden elektrotların Fermi düzeyine yakın bir noktaya getirildiğinde meydana gelen iletkenliğin karmaşık dalgalanmalar gösterdiğini bulduk. Bu dalgalanmaların ortam sıcaklığı Kondo sıcaklığının üstüne çıktığında ve asimetri faktörü azaldığında giderek sönümlendiğini tespit ettik. Gözlemlenen dalgalanmaların Fourier dönüşümü yoluyla analizi sonucunda, titreşimlerin n katkılı grafende Dirac noktası ve bant kenarının Fermi düzeyine uzaklığıyla orantılı iki farklı frekansta gerçekleşirken p katkılı grafende bant kenarının Fermi düzeyine uzaklığıyla orantılı sadece tek bir titreşim frekansı olduğunu bulduk. Bu durumu Fermi düzeyindeki gelişen Kondo rezonansının elektrotların durumlar yoğunluğundaki van Hove tekillikleriyle dinamik girişimini öneren bir mikroskopik teoriye bağladık. 

Anahtar Kelimeler

• Grafen,Kondo etkisi,kuantum noktacığı

Real time electron dynamics in a strongly correlated quantum dot asymmetrically coupled to p and n doped graphene electrodes

Öz

We investigated the quantum transport through a strongly correlated quantum dot asymmetrically coupled to p and n doped graphene electrodes invoking the non-crossing approximation. We found that the conductance exhibits complex fluctuations when the dot level is abruptly moved to a position close to the Fermi level of the electrodes via a gate voltage. We determined that these fluctuations get gradually suppressed when the ambient temperature starts to exceed the Kondo temperature and the asymmetry factor decreases. As a result of the analysis of these fluctuations via the Fourier transform, we found that while the oscillations take place in two distinct frequencies which are proportional to the distance of the Dirac point and the band edge to the Fermi level for the n doped graphene, there exists only one oscillation frequency proportional to the distance of the band edge to the Fermi level. We attributed this situation to a microscopic theory which suggests the dynamical interference of the developing  Kondo resonance at the Fermi level with the van Hove singularities at the density of states of the electrodes.

Anahtar Kelimeler

• Graphene,Kondo effect,quantum dot

Kaynakça

1. Nordlander, P., Pustilnik, M., Meir, Y., Wingreen, N.S. ve Langreth, D.C., How long does it take for the Kondo effect to develop?, Physical Review Letters, 83, 4, 808-811, (1999).
2. Plihal, M., Langreth, D.C. ve Nordlander, P., Kondo time scales for quantum dots: Response to pulsed bias potentials, Physical Review B, 61, 20, R13341-R13344, (2000).
3. Schiller, A. ve Hershfield, S., Out-of-equilibrium Kondo effect: Response to pulsed fields, Physical Review B, 62, 24, R16271-R16274, (2000).
4. Plihal, M., Langreth, D.C. ve Nordlander, P., Transient currents and universal timescales for a fully time-dependent quantum dot in the Kondo regime, Physical Review B, 71, 16, 165321, (2005).
5. Anders, F.B. ve Schiller, A., Real time dynamics in quantum-impurity systems: A time-dependent numerical renormalization-group approach, Physical Review Letters, 95, 19, 196801, (2005).
6. Goker, A., Friedman, B.A. ve Nordlander P., Transient current in a quantum dot asymmetrically coupled to metallic leads, Journal of Physics: Condensed Matter, 19, 37, 376206, (2007).
7. Novoselov, K.S., Geim, A.K. , Morozov, S.V. , Jiang, D., Zhang, Y., Dubonos, S.V., Grigorieva, I.V. ve Firsov, A.A., Electric field effect in atomically thin carbon films, Science, 306, 5696, 666-669, (2004).
8. Nair, R. R., Blake, P., Grigorenko, A. N., Novoselov, K. S., Booth, T. J., Stauber, T., Peres, N.M.R. ve Geim, A.K., Fine structure constant defines visual transparency of graphene, Science, 320, 5881, 1308, (2008).

9. Lee, C., Wei, X., Kysar, J.W. ve Hone, J., Measurement of the elastic properties and intrinsic strength of monolayer graphene, Science, 321, 5887, 385-388, (2008).
10. Balandin, A.A., Thermal properties of graphene and nanostructured carbon materials, Nature Materials, 10, 8, 569-581, (2011).
11. Anderson, P.W., Localized magnetic states in metals, Physical Review, 124, 41-53, (1961).
12. Kadanoff, L.P. ve Baym, G., Quantum statistical mechanics, New York, W.A. Benjamin, (1976).
13. Langreth, D.C., Linear and nonlinear response theory with applications in J.T. Devreese and V.E. van Doren, Linear and nonlinear electron transport in solids, Plenum Press, 3-32, New York NY, (1976).
14. Coleman, P., New approach to the mixed valence problem, Physical Review B, 29, 6, 3035-3044, (1984).
15. Langreth, D.C. ve Nordlander, P. , Derivation of a master equation for charge-transfer processes in atom-surface collisions, Physical Review B, 43, 4, 2541-2557, (1991).
16. Shao, H.X., Langreth, D.C. ve Nordlander, P., Many-body theory for charge-transfer in atom-surface collisions, Physical Review B, 49, 19, 13929-13947, (1994).
17. Langreth, D.C. ve Nordlander, P., Derivation of a master equation for charge-transfer processes in atom-surface collisions, Physical Review B, 43, 4, 2541-2557, (1991).
18. Kondo, J., Resistance minimum in dilute magnetic alloys, Progress in Theoretical Physics, 32, 1, 37-49, (1964). Izmaylov, A.F., Goker, A., Friedman, B.A. ve Nordlander, P., Transient current in a quantum dot subject to a change in coupling to its leads, Journal of Physics: Condensed Matter, 18, 39, 8995–9006, (2006).