DCMPMS Seminars

Analog spin-electronics with Graphene/hBN heterostructures

by Dr. Siddhartha Omar (Postdoc researcher, Physics of Nanodevices, University of Groningen, The Netherlands)

Tuesday, November 5, 2019 from to (Asia/Kolkata)
at AG80
Graphene has proved to be an excellent platform for electron-spin transport due to the presence of low-spin orbit coupling and hyperfine interaction. Along with the charge transport, its spin transport properties can be improved further when it is detached from the external environment and encapsulated with other two-dimensional materials such as insulating boron nitride crystals. In this talk, I will present our experimental findings on using the exfoliated bilayer and trilayer-hBN tunnel barriers for spin-injection and detection in graphene. Spin-injection/detection efficiencies of these contacts can be enhanced using a small dc bias across the contacts and reach unprecedently even up to 100% [1]. This is a nonlinear effect present at the graphene/hBN-tunnel barrier interface and gives rise to the amplification of the spin signal. The amplification is roughly proportional to the magnitude of the applied bias current. The present nonlinearity can be exploited further in two ways. First, we show the analog operations such amplitude and frequency modulation of spin-signals for the first time [2]. Second, due to the specific band-structure of graphene, spin-charge interactions become evident in the presence of such large spin-signals (milli eV) in graphene created by high spin-injection/detection efficiencies and now graphene behaves like a ferromagnet [3]. This effect enables to measure spin-signals in graphene via spin-to-charge conversion even without needing a ferromagnetic detector. The impact and applications of the obtained results can draw its parallel from analog electronics in its early days and would be crucial in developing spintronic circuits.

[1]. M. Gurram, S. Omar, and B.J. van Wees. Bias induced up to 100% spin-injection and detection polarizations in ferromagnet/bilayer-hBN/graphene/hBN heterostructure. Nat. Commun. 8, 248 (2017). 

[2] S. Omar, M. Gurram, M.H.D. Guimaraes, K. Watanabe, T. Taniguchi, and B.J. van Wees, Analog spintronics in trilayer-hBN/ graphene/hBN heterostructures (in preparation)

[3] I.J. Vera Marun, V. Ranjan, and B.J. van Wees Nat. Phys., 8, 313 (2012