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Onset of Spin Polarization in Four-Gate Quantum Point Contacts

Jones, Alexander M
http://orcid.org/0000-0002-1680-8173
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1485188708345005

Abstract Details

2017, MS, University of Cincinnati, Engineering and Applied Science: Computer Engineering.
A series of simulations which utilize a Non-equilibrium Green’s function (NEGF) formalism is suggested which can provide indirect evidence of the fine and non-local electrostatic tuning of the onset of spin polarization in two closely spaced quantum point contacts (QPCs) that experience a phenomenon known as lateral spin-orbit coupling (LSOC). Each of the QPCs that create the device also has its own pair of side gates (SGs) which are in-plane with the device channel. Numerical simulations of the conductance of the two closely spaced QPCs or four-gate QPC are carried out for different biasing conditions applied to two leftmost and rightmost SGs. Conductance plots are then calculated as a function of the variable, Vsweep, which is the common sweep voltage applied to the QPC. When Vsweep is only applied to two of the four side gates, the plots show several conductance anomalies, i.e., below G0 = 2e2/h, characterized by intrinsic bistability, i.e., hysteresis loops due to a difference in the conductance curves for forward and reverse common voltage sweep simulations. The appearance of hysteresis loops is attributed to the co-existence of multistable spin textures in the narrow channel of the four-gate QPC. The shape, location, and number of hysteresis loops are very sensitive to the biasing conditions on the four SGs. The shape and size of the conductance anomalies and hysteresis loops are shown to change when the biasing conditions on the leftmost and rightmost SGs are swapped, a rectifying behavior providing an additional indirect evidence for the onset of spontaneous spin polarization in nanoscale devices made of QPCs. The results of the simulations reveal that the occurrence and fine tuning of conductance anomalies in QPC structures are highly sensitive to the non-local action of closely spaced SGs. It is therefore imperative to take into account this proximity effect in the design of all electrical spin valves making use of middle gates to fine tune the spin precession between QPC based spin injector and detector contacts.
Marc Cahay, Ph.D. (Committee Chair)
Rashmi Jha, Ph.D. (Committee Member)
Punit Boolchand, Ph.D. (Committee Member)
91 p.
Nanotechnology
Spin Polarization; Quantum Point Contact; NEGF simulation; nanoscale device; spin density; hysteresis

Recommended Citations

Citations

  • Jones, A. M. (2017). Onset of Spin Polarization in Four-Gate Quantum Point Contacts [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1485188708345005

    APA Style (7th edition)

  • Jones, Alexander. Onset of Spin Polarization in Four-Gate Quantum Point Contacts. 2017. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1485188708345005.

    MLA Style (8th edition)

  • Jones, Alexander. "Onset of Spin Polarization in Four-Gate Quantum Point Contacts." Master's thesis, University of Cincinnati, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1485188708345005

    Chicago Manual of Style (17th edition)

ucin1485188708345005
279
© 2017, some rights reserved.Creative Commons License Onset of Spin Polarization in Four-Gate Quantum Point Contacts by Alexander M Jones is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.