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Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and Heterostructures

Xu, Jinsong
http://rave.ohiolink.edu/etdc/view?acc_num=osu1531925662989238

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Physics.
Graphene has remarkable opportunities for spintronics due to its high mobility and long spin diffusion length, especially when encapsulated in hexagonal boron nitride (h-BN). Beyond the three basic processes of spin injection, spin transport, and spin detection, it is crucial to explore new methods of spin manipulation in order to develop novel architectures for spin-based logic. In the first chapter of this thesis, I briefly introduce the field of spintronics and graphene related research. In the second chapter, I present the spin diffusion model used in this thesis to analyze spin transport in graphene and heterostructures spintronics. In the third chapter, I present my work on gate-tunable spin transport in h-BN encapsulated graphene-based spin valves with one-dimensional ferromagnetic contacts. The non-local spin signal can be tuned by gate voltage and even change polarity. The gate-controlled spin polarity via magnetic proximity effect may overcome the usual need for an applied magnetic field and a magnetization reversal to implement the graphene-based spin logic. Beyond magnetic proximity effect, another route for graphene spintronics is to combine with other two-dimensional (2D) materials, such as transition metal dichalcogenide (TMDC). In the fourth chapter, I demonstrate spin injection from monolayer MoS2 to few-layer graphene following optical valley/spin exciation in MoS2 with circularly polarized light up to room temperature. The magnitude and direction of spin polarization is controlled by both helicity and photon energy. These results demonstrate a 2D spintronic/valleytronic system that achieves optical spin injection and lateral spin transport at room temperature in a single device, which paves the way for multifunctional 2D spintronic devices for memory and logic applications. While graphene/TMDC heterostructures hold great promise for the electrical and optical control of spins in graphene, the observed spin lifetimes in these heterostructures are short (< 50 ps). In the fifth chapter, I discuss the remarkable manipulation of spin anisotropy in bilayer graphene by electric field with excellent spin lifetimes up to 7.8 ns. We find that near the charge neutrality point, the application of a perpendicular electric field opens a band gap and generates an out-of-plane spin-orbit field that stabilizes out-of-plane spins against spin relaxation, leading to a large spin lifetime anisotropy. This intriguing behavior occurs because of the unique spin-valley coupled band structure of bilayer graphene. Our results demonstrate the potential for highly tunable spintronic devices based on dual-gated 2D materials. In addition to graphene, layered Zintl phase materials are another class of 2D van der Waals material that can be metallic, semiconducting, magnetic, or superconducting and are predicted to possess topological states. At the end, I present the successful growth of large area CaGe2 films, as a model of layered Zintl phase materials, on atomically flat Ge(111) substrates by molecular beam epitaxy using alternating layer growth protocol. This result demonstrates a novel method of deposition of CaGe2 that could be also applied to other layered Zintl phase van der Waals materials. Furthermore, the high quality of the CaGe2 film is promising for the exploration of novel properties of germanane.
Roland Kawakami (Advisor)
Jonathan Pelz (Advisor)
Richard Kass (Committee Member)
Yuan-Ming Lu (Committee Member)
179 p.
Condensed Matter Physics; Experiments; Physics
2D materials, heterostructures, graphene, spintronics, opto-valleytronics, magnetic proximity effect, spin lifetime anisotropy, gate-tunable

Recommended Citations

Citations

  • Xu, J. (2018). Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and Heterostructures [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531925662989238

    APA Style (7th edition)

  • Xu, Jinsong. Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and Heterostructures. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1531925662989238.

    MLA Style (8th edition)

  • Xu, Jinsong. "Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and Heterostructures." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531925662989238

    Chicago Manual of Style (17th edition)

osu1531925662989238
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This open access ETD is published by The Ohio State University and OhioLINK.