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Register a new userFilling-Factor-Dependent Magnetophonon Resonance in Graphene
التأثير المغناطيسي-الفونوني بحسب عامل التعبئة في الغرافين
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نحن نصف البنية الخاصة التي تم الحصول عليها من قبل الصوت البصري في المستوى الداخلي في الجرافين عندما يتم إحداث التوازن مع واحد من الانتقالات بين مستويات لاندو في هذا المادة. يتم تأثير هذا بشكل أكبر عندما يكون هذا الوضع اللازم (المرتبط بالطيف G في طيف رامان الجرافين) في التوازن مع الانتقالات بين مستويات لاندو 0 -> (+,1) و (-,1) -> 0 عند مجال المغناطيسي B_0 ~ 30 T. يمكن استخدامه لقياس قوة الارتباط الإلكتروني-الصوتي مباشرة، ويمكن استخدام تباينه حسب العامل التعبئة للكشف عن الأوضاع الصوتية مدورة تدويريا.
We describe a peculiar fine structure acquired by the in-plane optical phonon at the Gamma-point in graphene when it is brought into resonance with one of the inter-Landau-level transitions in this material. The effect is most pronounced when this lattice mode (associated with the G-band in graphene Raman spectrum) is in resonance with inter-Landau-level transitions 0 -> (+,1) and (-,1) -> 0, at a magnetic field B_0 ~ 30 T. It can be used to measure the strength of the electron-phonon coupling directly, and its filling-factor dependence can be used experimentally to detect circularly polarized lattice modes.
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Van der Waals materials and their heterostructures offer a versatile platform for studying a variety of quantum transport phenomena due to their unique crystalline properties and the exceptional ability in tuning their electronic spectrum. However, most experiments are limited to devices that have lateral dimensions of only a few micrometres. Here, we perform magnetotransport measurements on graphene/hexagonal boron-nitride Hall bars and show that wider devices reveal additional quantum effects. In devices wider than ten micrometres we observe distinct magnetoresistance oscillations that are caused by resonant scattering of Landau-quantised Dirac electrons by acoustic phonons in graphene. The study allows us to accurately determine graphenes low energy phonon dispersion curves and shows that transverse acoustic modes cause most of phonon scattering. Our work highlights the crucial importance of device width when probing quantum effects and also demonstrates a precise, spectroscopic method for studying electron-phonon interactions in van der Waals heterostructures.
We have investigated the magnetophonon resonance (MPR) effect in a series of single GaAs quantum well samples which are symmetrically modulation doped in the adjacent short period AlAs/GaAs superlattices. Two distinct MPR series are observed originating from the $Gamma$ and X electrons interacting with the GaAs and AlAs longitudinal optic (LO) phonons respectively. This confirms unequivocally the presence of X electrons in the AlAs quantum well of the superlattice previously invoked to explain the high electron mobility in these structures (Friedland et al. Phys. Rev. Lett. 77,4616 (1996).
Microwave pinning-mode resonances found around integer quantum Hall effects, are a signature of crystallized quasiparticles or holes. Application of in-plane magnetic field to these crystals, increasing the Zeeman energy, has negligible effect on the resonances just below Landau level filling $ u=2$, but increases the pinning frequencies near $ u=1$, particularly for smaller quasiparticle/hole densities. The charge dynamics near $ u=1$, characteristic of a crystal order, are affected by spin, in a manner consistent with a Skyrme crystal.
Emergence of half-integer filling factor states, such as nu=5/2 and 7/2, is found in quantum dots by using numerical many-electron methods. These states have interesting similarities and differences with their counterstates found in the two-dimensional electron gas. The nu=1/2 states in quantum dots are shown to have high overlaps with the composite fermion states. The lower overlap of the Pfaffian state indicates that electrons might not be paired in quantum dot geometry. The predicted nu=5/2 state has high spin polarization which may have impact on the spin transport through quantum dot devices.
The integer quantum Hall (QH) effects characterized by topologically quantized and nondissipative transport are caused by an electrically insulating incompressible phase that prevents backscattering between chiral metallic channels. We probed the incompressible area susceptible to the breakdown of topological protection using a scanning gate technique incorporating nonequilibrium transport. The obtained pattern revealed the filling-factor ($ u$)-dependent evolution of the microscopic incompressible structures located along the edge and in the bulk region. We found that these specific structures, respectively attributed to the incompressible edge strip and bulk localization, show good agreement in terms of $ u$-dependent evolution with a calculation of the equilibrium QH incompressible phases, indicating the robustness of the QH incompressible phases under the nonequilibrium condition. Further, we found that the $ u$ dependency of the incompressible patterns is, in turn, destroyed by a large imposed current during the deep QH effect breakdown. These results demonstrate the ability of our method to image the microscopic transport properties of a topological two-dimensional system.
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