Making a Quantum Hall Interferometer Based on Marginally Rotated Graphene
The Quantum Hall Effect (QH) enables the exploitation of the quantum coherence of electrons for a wide range of applications from metrology to quantum computing. QH interferometry is a handy tool that provides an archetypal platform for achieving interwoven statistics of fractional QH states. However, the phase coherence along the interferometer and the suppression of the Coulomb filling energy are required to observe the fractional statistics.
Study: Quantum Hall interferometry in the triangular domain of a marginally twisted bilayer graphene. Image Credit: Neon_dust/Shutterstock.com
In an article recently published in the journal nano letter, The QH interferometer is based on a slightly twisted bilayer graphene with a twist angle (θ) of 0.16 degrees. Operation of the device in the QH regime results in unique magneto-thermopower features, including Aharonov–Bohm (AhB) and Fabry–Pérot (FP) oscillations in the magnetic-density field phase, where the Landau level fill factor (ν) is 4.8.
The QH interference effect is limited to the triangular domains AB/BA in a slightly bent bilayer graphene and exhibits a lower Coulomb filling effect. The overall results demonstrate the QH edge mode phase-coherent interference without the need for additional complex architectures, which are dictated by logic gates in twisted bilayer graphene materials.
QH Interferometry in Triangular Domains and Rotating Bilayer Graphene
The quasiparticle excitation hierarchy can be investigated using the interference between the fractional QH mode and the integer edge mode. This method can help observe the statistics of non-Abelian interweaving of quasiparticles in the fractional QH regime. However, it is difficult to achieve this phenomenon experimentally due to the unavoidable Coulomb repulsion of the quasiparticles, which are spatially constrained, consequently changing the effective area of the interferometer.
The additional charging effect of the interferometer hinders the statistical robustness of the link. However, increasing device dimensions can prevent additional cost impacts on the interferometer at the expense of the phase coherence that unifies the interfering path. As a result, various device architectures were designed, and the material was engineered to suppress Coulomb repulsion without affecting the phase coherence of the quasiparticles.
The physical properties of bent bilayer graphene depend on the angle of twisting between these two layers of two-dimensional (2D) material. Bent bilayer graphene has a torsion angle close to 1.1 degrees. This bent bilayer 2D graphene material exhibits phase transitions from a conductor system to a correlated insulator phase, a ferromagnetic phase, and a superconductivity phase.
This study discusses the operation of a new QH interferometer based on slightly twisted bilayer graphene. The moiré lattice band structure of the bilayer graphene bends around a magic angle (θm) of 1.1 degrees can facilitate a variety of new phases such as superconductivity, magnetism and correlated insulators.
However, at the bent angle of the bent bilayer graphene underm, the atomic registers in the moiré lattice are altered due to the relaxation effect, leading to a mosaic structure of triangular regions with alternating AB and BA arrays, separated by domain walls. However, the gaps from the AB or BA regions in the bent bilayer graphene due to the vertical displacement planes result in a one-dimensional (1D) network conducting channels hosted by the domain walls.
Triangular Domain of Marginal Twisted Bilayer Graphene
Here, the thermoelectric and electrical measurements are carried out in a bilayer graphene that is marginally twisted by 1.6 degrees in the integer QH regime and in a negligible displacement plane. Here, the thermoelectric coefficient provides a basic characterization of the electronic state due to the sensitivity of the charge carriers to the scattering dynamics.
Moreover, the excitation of the quasiparticles carries entropy in the QH regime. In this regime, magneto-thermopower provides insight into the quasiparticle spectrum. Moreover, under suitable conditions, thermoelectric measurements help to explore the statistical properties of non-Abelian quasiparticles due to their higher entropy than Abelian ones. In the QH regime, various characteristics of the interference effect were investigated using the correlation between thermal stress and magnetic field (B) along with the gate-induced density (n).
Conclusion
In summary, the magneto-thermopower transport of marginally twisted bilayer graphene was measured using about 0.16 degrees. The thermovoltage periodic oscillations at B and n are in line with the electronic FP and AhB interference between the charge carrier paths that include a limited magnetic flux at a lower temperature of 3 kelvin in twisted bilayer graphene.
Thermovoltage measurements show periodic oscillations, which are absent in conventional resistance measurements. The resonance pattern appears in the QH regime at 4 and 8. The loop obtained from the AhB oscillation periodicity is like the size of the moiré lattice.
The overall results show that the local Landau-level charge carriers are in the triangular domain AB/BA. Additionally, QH mode interferes through the AA stacked region. The original QH interference effect in slightly twisted bilayer graphene can serve as a new platform to achieve any statistic in the QH regime.
Reference
Mahapatra, PS, Garg, M., Ghawri, B., Jayaraman, A., Watanabe, K., Taniguchi, T., Ghosh, A et al. (2022). Quantum Hall interferometry in the triangular domain of a marginally twisted bilayer graphene. Nano letter. https://pubs.acs.org/doi/10.1021/acs.nanolett.2c00627
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