Phys Seminar - A. Avşar Electronic Spin Transport in Graphene

"Electronic Spin Transport in Graphene"

Ahmet Avsar

Graphene Research Center in National University of Singapore

High charge mobility, small spin orbit coupling (SOC) and negligible hyperfine interaction allow micrometer long spin relaxation lengths in graphene even at room temperature, making this layer of carbon atoms an exceptional material for potential spintronics applications [1]. Unfortunately, these excellent properties were demonstrated just in proof of principle with exfoliated graphene which has scalability problem for the real applications. In the first part of the  presentation, after describing the patterning and fabrication of large arrays of spin valves based on mono and bi-layer graphene grown by chemical vapour deposition (CVD), I will present that spin relaxation lengths in such CVD graphene-based devices are higher than 1 mm and spin relaxation times are higher than 100 ps, both comparable with the results obtained on exfoliated graphene [2]. It will be discussed that CVD graphene specific scattering sources such as residual catalysts, wrinkles, ripples, grain boundaries and organic residues do not limit the spin transport. These results represent a real demonstration that graphene could be used in realistic applications. I will conclude the first half of the presentation by discussing the dominant spin scattering mechanisms in CVD mono and bi-layer graphene-based devices.

While the observation of long spin relaxation lengths make graphene a compelling spintronics material, its negligibly small SOC makes the realization of both the spin Hall effect (SHE) and spin based field effect transistor practically impossible. In the second part of the presentation, I will show that by creating an artificial interface between monolayer graphene and few-layers semiconducting WS2, the SOC of graphene is enhanced as high as 17meV, three orders of magnitude higher than its intrinsic value, without modifying any of the structural properties of graphene [3]. This SOC enhancement gives rise to the SHE even at room temperature. Our detailed theoretical and experimental analyses show that this proximity induced SOC enhancement is originated from the intrinsic defects in the WS2 substrate. I will also discuss how the charge transport property of graphene is affected in such heterostructure devices [4].

[1] N. Tombros, C. Jozsa, M. Popinciuc, H. T. Jonkman, and B. J. Van Wees, Nature, 448, 571-574 (2007).

[2] A. Avsar, T. Y. Yang, S. K. Bae, J. Balakrishnan, F. Volmer, M. Jaiswal, Z. Yi, S. R. Ali, G. Güntherodth, B. H. Hong, B. Beschoten, and B. Özyilmaz, Nano Lett. 11, 2363-2368 (2011).

[3] A. Avsar, J. Y. Tan, J. Balakrishnan, G. K. W. Koon, J. Lahiri, A. Carvalho, A. S. Rodin, T. Taychatanapat, E. C. T. O’Farrell, G. Eda, A. H. Castro Neto, and B. Özyilmaz, submitted (2013).

[4] J. Y. Tan, A. Avsar, J. Balakrishnan, G. K. W. Koon, T. Taychatanapat, E. C. T. O’Farrell, K. Watanabe, T. Taniguchi, E. Goki, A. H. Castro Neto, and B. Özyilmaz, submitted (2014).

Bio: Ahmet Avşar obtained his B.Sc degree from Physics Department of Middle East Technical University. During his graduate studies at the Graphene Research Center in National University of Singapore (NUS), he focused on the charge and spin transport phenomena in graphene-based devices. He is currently a postdoc researcher in Özyılmaz group at NUS.

Place: SUNUM

Time: 15 April 2014, 13:40