Direct observation of electrically induced Pauli paramagnetism in single-layer graphene using ESR spectroscopy

Abstract

Graphene has been actively investigated as an electronic material owing to many excellent physical properties, such as high charge mobility and quantum Hall effect, due to the characteristics of a linear band structure and an ideal two-dimensional electron system. However, the correlations between the transport characteristics and the spin states of charge carriers or atomic vacancies in graphene have not yet been fully elucidated. Here, we show the spin states of single-layer graphene to clarify the correlations using electron spin resonance (ESR) spectroscopy as a function of accumulated charge density using transistor structures. Two different electrically induced ESR signals were observed. One is originated from a Fermi-degenerate two-dimensional electron system, demonstrating the first observation of electrically induced Pauli paramagnetism from a microscopic viewpoint, showing a clear contrast to no ESR observation of Pauli paramagnetism in carbon nanotubes (CNTs) due to a one-dimensional electron system. The other is originated from the electrically induced ambipolar spin vanishments due to atomic vacancies in graphene, showing a universal phenomenon for carbon materials including CNTs. The degenerate electron system with the ambipolar spin vanishments would contribute to high charge mobility due to the decrease in spin scatterings in graphene.

Microwave Energy Drives “On–Off–On” Spin‐Switch Behavior in Nitrogen‐Doped Graphene

“…This effect must originate from a more efficient quantum admixture of the S I domains with part of the S L sites in p‐ 14 NG, forming S I · S L , a Fermi‐degenerate 2D electron system. Electronic fingerprints of this type are typical of conducting electrons with Pauli character (Fermi‐degenerate electron systems) . The presence of such electrons is consistent with our theoretical calculations, which correlated the S I spin population with the valence band derived primarily from the delocalized C p z (and Np z ) electrons (Figure D).…”

Spin-states in MoS2 thin-film transistors distinguished by operando electron spin resonance

“…For the electron doping, as described above, the spin density never vanishes and is believed to make an effect on the spin scattering of charge carriers, lowering the mobility. Contrary to MoS 2 , in graphene, the ambipolar spin vanishing under applied V G has been demonstrated and discussed to cause an improvement of the charge mobility by a suppression of the spin scattering of charge carriers 25 . That is, the spin species of a vacancy has magnetic dipolar interaction with the spin of a charge carrier, which disturbs the charge transport, while nonmagnetic vacancy does not have such interaction with a charge carrier that usually has a spin in semiconductor materials, which preserves the intrinsic mobility.…”

“…Thus we have confirmed no impact of device fabrication on our conclusions. The parts of the above-mentioned fabrication method have been described in the previous work 25 .…”

“…Electron spin resonance (ESR) spectroscopy is useful for the spin-states study of the organic electronic devices, such as transistors, solar cells, and light-emitting diodes [22][23][24] . From the ESR study of graphene transistors, we have found a correlation between atomic vacancies and their conducting mechanisms 25 . That is, spins exist in the charge-neutral graphene due to atomic vacancies; however, when positive or negative gate voltage is applied, spins vanish and then the spin scattering of charge carriers decreases.…”

“…That is, spins exist in the charge-neutral graphene due to atomic vacancies; however, when positive or negative gate voltage is applied, spins vanish and then the spin scattering of charge carriers decreases. Thus the electrically induced ambipolar spin vanishment is believed to contribute to the high carrier mobility in graphene 25 . Previous reports for MoS 2 materials include the ESR and DFT studies of the atomic vacancies, antisites, impurities, etc.…”