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Marc Cahay, University of Cincinnati

Nanoelectronics Seminar

Towards the realization of an all electrical spin valve using quantum point contacts

Wednesday, May 9, 1:00pm - 2:00pm
AE107 Paul Allen Center (EE main office)

Host: Anant Anantram

Spin electronics or spintronics is based on the simultaneous manipulation of the spin and charge degrees of freedom in a multitude of systems and aims at developing electronic devices based on control of the electron spin. The controlled creation, detection, and manipulation of spin-polarized currents by purely electrical means are today the challenges facing semiconductor spintronics. Over the last few years we have used Rashba spin-orbit coupling (RSOC) in one-dimensional (1D) ballistic channels made of quantum point contacts to achieve this goal.

We have performed a systematic study of the appearance and evolution of several anomalous (i.e., G < 2e2/h) conductance plateaus in InAs and GaAs based quantum point contacts (QPC). This work was performed at T=4.2K as a function of the bias difference ΔVG between the two in-plane gates of the QPC. These anomalies are believed to be signatures of spin polarization in the QPC, triggered by the imbalance between the lateral spin-orbit coupling on opposite side walls due to the applied bias ΔVG. The number and location of the anomalous plateaus strongly depend on the biases (positive or negative) applied to the two gates. Furthermore, the conductance plots are different when the polarity of the bias difference between the gates is reversed. These results are interpreted as evidence for the sensitivity of the QPC spin polarization to defects (surface roughness and impurity (dangling bond) scattering) generated during the etching process that forms the QPC side walls. The anomalous conductance plateaus appear over a limited range of bias ΔVG of several volts and over a maximum common sweep voltage range of nearly 1 V.

The relevance of these results for the creation of an all-electrical spin valve will be discussed.

In collaboration with R.S. Newrock, P. Debray, K. Chetry (Physics), P.P. Das and N. Bhandari (EECE). This work is supported by NSF Awards ECCS 0725404 and 1028483.


  1. P. Debray, S. M. S. Rahman, J. Wan, R. S. Newrock, M. Cahay, A. T. Ngo, S. E. Ulloa, S. T. Herbert, M. Muhammad, and M. Johnson, Nature Nanotech. 4, 759 (2009).
  2. J. Wan, M. Cahay, P. Debray, and R. S. Newrock, Phys. Rev. B 80, 155440 (2009).
  3. J. Wan, M. Cahay, P. Debray, and R. S. Newrock, Journal of Nanoelectronics and Optoelectronics 6, 95 (2011).
  4. P.P. Das, K. Chetry, N. Bhandari, J. Wan, M.Cahay, R.S. Newrock, and S.Herbert, Applied Physics Letters 6, 95 (2011).
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