Temperature Dependent Zero-Field Splittings in Graphene

Abstract

Graphene is a quantum spin Hall insulator with a 45 $\mu$eV wide non-trivial topological gap induced by the intrinsic spin-orbit coupling. Even though this zero-field spin splitting is weak, it makes graphene an attractive candidate for applications in quantum technologies, given the resulting long spin relaxation time. On the other side, the staggered sub-lattice potential, resulting from the coupling of graphene with its boron nitride substrate, compensates intrinsic spin-orbit coupling and decreases the non-trivial topological gap, which may lead to the phase transition into trivial band insulator state. In this work, we present extensive experimental studies of the zero-field splittings in monolayer and bilayer graphene in a temperature range 2K-12K by means of sub-Terahertz photoconductivity-based electron spin resonance technique. Surprisingly, we observe a decrease of the spin splittings with increasing temperature. We discuss the origin of this phenomenon by considering possible physical mechanisms likely to induce a temperature dependence of the spin-orbit coupling. These include the difference in the expansion coefficients between the graphene and the boron nitride substrate or the metal contacts, the electron-phonon interactions, and the presence of a magnetic order at low temperature. Our experimental observation expands knowledge about the non-trivial topological gap in graphene.

Main text with figures (20 pages) and Supplementary Information (14 pages) Accepted in Phys. Rev. B

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Cited by in corpus (5)

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• Terahertz Spin-Light Coupling in Proximitized Dirac Materials
• Terahertz and gigahertz magneto-ratchets in graphene-based 2D metamaterials
• Temperature and magnetic field dependent $g$-factors in electron spin resonance spectroscopy
• Spin-dependent photovoltage in graphene/MoS2-based field-effect transistors