High-mobility compensated semimetals, orbital magnetization, and umklapp scattering in bilayer graphene moire superlattices

A. L. Shilov, M. A. Kashchenko, P. A. Pantaleón, Yibo Wang, M. Kravtsov, A. Kudriashov, Z. Zhan, T. Taniguchi, K. Watanabe, S. Slizovskiy, K. S. Novoselov, V. I. Fal'ko, F. Guinea, D. A. Bandurin

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Abstract

Twist-controlled moire superlattices (MS) have emerged as a versatile platform in which to realize artificial systems with complex electronic spectra. Bernal-stacked bilayer graphene (BLG) and hexagonal boron nitride (hBN) form an interesting example of the MS that has recently featured a set of unexpected behaviors, such as unconventional ferroelectricity and electronic ratchet effect. Yet, the understanding of the BLG/hBN MS electronic properties has, at present, remained fairly limited. Here we develop a multi-messenger approach that combines standard magnetotransport techniques with low-energy sub-THz excitation to get insights into the properties of this MS. We show that BLG/hBN lattice alignment results in the emergence of compensated semimetals at some integer fillings of the moire bands separated by van Hove singularities where Lifshitz transition occurs. A particularly pronounced semimetal develops when 8 electrons reside in the moire unit cell, where coexisting high-mobility electron and hole systems feature a strong magnetoresistance reaching 2350 % already at B=0.25 T. Next, by measuring the THz-driven Nernst effect in remote bands, we observe valley splitting, pointing to an orbital magnetization characterized by a strongly enhanced effective g-factor of 340. Last, using THz photoresistance measurements, we show that the high-temperature conductivity of the BLG/hBN MS is limited by electron-electron umklapp processes. Our multi-facet analysis introduces THz-driven magnetotransport as a convenient tool to probe the band structure and interaction effects in vdW materials and provides a comprehension of the BLG/hBN MS.
Original languageEnglish
JournalACS Nano
Publication statusAccepted/In press - 26 Mar 2024

Keywords

  • Moir´e superlattices
  • bilayer graphene
  • orbital magnetization
  • compensated semimetals
  • umk-lapp scattering
  • terahertz

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