Temperature and Electric Field Dependence of Spin Relaxation in Graphene on SrTiO₃

Abstract

The theoretically predicted intrinsic spin relaxation time of up to 1 μs in graphene along with extremely high mobilities makes it a promising material in spintronics. Numerous experimental studies, however, find the spin lifetime in graphene to be several orders of magnitude below that theoretically predicted. Additionally, analyses of the spin relaxation mechanisms in graphene using conventional processes such as Elliot-Yaffet and D'yakonov-Perel' show a coexistence of both, with no clear dominance. Central to these experimental discrepancies is the role of the local environment including that of the underlying substrate. In this work, we use the electronically rich platform of SrTiO 3 with broken inversion symmetry and study spin transport in graphene in the presence of surface electric fields. We find spin relaxation time and length as large as 0.96 AE 0.03 ns and 4.1 AE 0.1 μm, respectively at 290 K in graphene, using non-local spin valve studies and find a non monotonous dependence with temperature, unlike that observed in other substrates. Analysis of the temperature dependence indicates the role of surface electric dipoles and electric field driven electronic and structural phase transitions unique to SrTiO 3 for spin transport and spin relaxation in graphene.Charge conduction and spin transport parameters in twodimensional graphene are strongly influenced by extrinsic factors related to their local environment. Extrinsic influences range from the specifics of the underlying substrate (suspended, encapsulated, or high dielectric constant), [1,2] the quality of the contacts [3,4] to spinorbit effects due to adatoms. [5][6][7] Despite significant improvements either on enhancing the graphene quality including encapsulation on an atomically flat two dimensional hexagonal Boron Nitride (hBN) substrate or by resolving extrinsic influences, the experimentally measured spin lifetime in graphene is orders of magnitude smaller than theoretically predicted. [8][9][10][11][12][13] Furthermore, conventional spin relaxation mechanisms such as Elliot-Yaffet and D'yakonov-Perel' fail to unambiguously explain the nature and dominance of the spin dephasing processes in graphene on different substrates. [5][6][7][8]14] Spin dephasing can originate from a multitude of effects such as flexural distortions, ripples, local magnetic moments, to name a few, but understanding of their precise micoroscopic mechanism still remains elusive. [5][6][7] In this context SrTiO 3 (STO) lends itself as an interesting choice of substrate to study spin relaxation mechanisms in graphene. [15] STO has an atomically flat surface, similar to that of hBN, with roughness of 90-150 pm and no dangling bonds. However, unlike hBN, STO is electronically versatile. This stems from the remarkably large dielectric constant (e r ) of 300 at room temperature that increases non-linearly to >20 000 at 4 K. [16] Further, distinct from most other substrates on which charge and spin transport in graphene has been studied, the broken inversion symmetry at the sur...

Photoinduced Dirac semimetal in ZrTe5

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Exciton routing in the heterostructure of TMD and paraelectrics

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“…There is a growing interest in exploring the effect of substrate on the electronic and optical properties of 2D materials. Particularly, the heterostructure of STO substrate with graphene [34][35][36][37][38] and TMD [39,40] is attracting considerable attention. The large dielectric constant of STO substrate strongly screens the long-range Coulomb interactions inside 2D materials.…”

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