Graphene spin circuits and spin-orbit phenomena in van der Waals heterostructures with topological insulators
Doktorsavhandling, 2021

Spintronics offers an alternative approach to conventional charge-based information processing by using the electron spin for next-generation non-volatile memory and logic technologies. To realize such technologies, it is necessary to develop spin-polarized current sources, spin interconnects, charge-to-spin conversion processes, and gate-tunable spintronic functionalities. The recently emerged two-dimensional (2D) and topological materials represent a promising platform to realize such spin-based phenomena. Due to its small spin-orbit coupling (SOC), graphene was predicted to preserve electron spin coherence for a long time, making it an ideal material for spin communication. In contrast, topological insulators (TIs) have high SOC and develop a nontrivial band structure with insulating bulk but conducting spin-polarized surface states. Combining these materials in van der Waals heterostructures has been predicted to give rise to unique proximity-induced spin-orbit phenomena that may be used for electrical control of spin polarization.

In this thesis, we experimentally prove that the large-area chemical vapor deposited (CVD) graphene is an excellent material choice for the realization of robust spin interconnects, which are capable of spin communication over channel lengths exceeding 34 μm. Utilizing such graphene, we realize a spin summation operation in multiterminal devices and employ it to construct a prototype spin majority logic gate operating with pure spin currents. In topological insulators, we electrically detect the spin-momentum locking and reveal how the bulk and surface conducting channels affect the charge-to-spin conversion efficiency. Finally, by combining graphene and TIs in hybrid devices, we confirm the emergence of a strong proximity-induced SOC with a Rashba spin texture in graphene. We further show that in such heterostructures a spin-charge conversion capability is induced in graphene via the spin-galvanic effect at room temperature and reveal its strong tunability in magnitude and sign by the gate voltage. These findings demonstrate the robust performance of graphene as a spin interconnect for emerging spin-logic architectures and present all-electrical and gate-tunable spintronic devices based on graphene-TI heterostructures, paving the way for next-generation spin-based computing.

Spin-charge conversion

Van der Waals heterostructures

Graphene

Spintronics

Topological insulator

Proximity effect

Kollektorn, Kemivägen 9, Chalmers
Opponent: Research Professor Felix Casanova, CIC NanoGUNE, Spain

Författare

Dmitrii Khokhriakov

Chalmers, Mikroteknologi och nanovetenskap (MC2), Kvantkomponentfysik

Two-dimensional spintronic circuit architectures on large scale graphene

Carbon,; Vol. 161(2020)p. 892-899

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Origin and evolution of surface spin current in topological insulators

Physical Review B,; Vol. 97(2018)

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Tailoring emergent spin phenomena in Dirac material heterostructures

Science advances,; Vol. 4(2018)

Artikel i vetenskaplig tidskrift

Electronics has become ubiquitous in many aspects of our society, where microcontrollers, computers, and artificial intelligence are widely used for automation, home appliances, medicine, transportation, navigation, communications, and entertainment. The remarkable pace of the technological advancement in the electronics industry over the last 70 years, driven by the ever-increasing demands for faster processing rates, improved power efficiency, and larger information storage capacity, was made possible by the developments in condensed matter physics and the progress in semiconductor manufacturing technology. It was noticed that the number of transistors per unit area on a chip doubles approximately every 2 years, an empirical trend known as Moore's law. This exponential growth was maintained by a continuous shrinking of the transistor dimensions over the past decades. However, it is believed that in the near future this trend could no longer be sustained as the minimum feature size of nanoelectronic components approaches the fundamental atomic limit. In addition, in such small devices, quantum mechanical effects lead to increased leakage currents that pose heat dissipation and power consumption issues. To cope with these issues and continue the development of electronics beyond Moore's law, alternative routes and prospective architectures for future computing electronic devices are being investigated.

Spintronics offers an alternative approach to conventional charge-based information processing by using the electron spin, i.e. its magnetic properties, to record, store, transfer and manipulate information. Due to the smaller amount of energy needed to control electron spin in comparison with the energy required to move electrical charges in common transistors, spin-based devices may offer decreased power consumption and increased operation speed.

In this thesis, we investigate spin-based phenomena in the recently emerged family of two-dimensional (2D) materials. We demonstrate the large-area graphene as a robust spin interconnect capable of preserving and transporting spin polarization over long distances. Furthermore, a spin summation operation in multiterminal graphene devices is realized and employed to construct a prototype spin majority logic gate operating with pure spin currents. A great advantage of 2D materials is the possibility to stack various layers on top of each other to form van der Waals heterostructures, in which the interactions between constituent materials can change their properties and induce novel physical effects. In this thesis, we study the emerging proximity-induced spin-orbit phenomena in the van der Waals heterostructures of graphene and topological insulators (TIs). We show that the strong spin interactions in such heterostructures allow to perform tunable spin-charge conversion directly in graphene, which is not possible in pristine material. The obtained findings demonstrate the robust performance of graphene as a spin interconnect for emerging spin-logic architectures and present all-electrical and gate-tunable spintronic devices based on graphene-TI heterostructures, paving the way for next-generation spin-based computing.

Styrkeområden

Nanovetenskap och nanoteknik (SO 2010-2017, EI 2018-)

Ämneskategorier

Nanoteknik

Den kondenserade materiens fysik

Infrastruktur

Nanotekniklaboratoriet

ISBN

978-91-7905-470-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4937

Utgivare

Chalmers tekniska högskola

Kollektorn, Kemivägen 9, Chalmers

Online

Opponent: Research Professor Felix Casanova, CIC NanoGUNE, Spain

Mer information

Senast uppdaterat

2021-06-01