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Vacancy-Induced Tunable Kondo Effect in Twisted Bilayer Graphene
Yueqing Chang1,2, Jinjing Yi1,2, Ang-Kun Wu1,2
1Department of Physics and Astronomy, <a href="https://ror.org/05vt9qd57">Rutgers University</a>, Piscataway, New Jersey 08854, USA.
Physical Review Letters
|October 7, 2024
Summary
Vacancy-induced states in twisted bilayer graphene (TBG) host a tunable Kondo effect. Researchers explored these impurity states, revealing a dichotomy in their behavior and their potential as probes for quantum phenomena in magic-angle TBG.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Mechanics
Background:
- Single-layer graphene vacancies exhibit Kondo screening of spin-1/2 holes.
- Twisted bilayer graphene (TBG) offers a tunable platform for studying quantum phenomena.
Purpose of the Study:
- Investigate the survival and behavior of vacancy-induced impurity states in TBG near the magic angle.
- Probe the critical destruction of the Kondo effect in pseudogap hosts within TBG.
- Explore TBG as a tunable system for quantum impurity studies.
Main Methods:
- Ab initio calculations and atomic-scale modeling to characterize vacancy states.
- Construction and solution of an Anderson impurity model using numerical renormalization group and kernel polynomial method.
- Determination of the phase diagram for vacancy states in TBG.
Main Results:
- Vacancy states in TBG behave as quantum impurities.
- A strict dichotomy exists between vacancy states in AA/BB and AB/BA tunneling regions.
- In AB/BA vacancies, Kondo temperature exhibits a broad distribution with a tail to vanishing temperatures at the magic angle due to multifractal wave functions.
Conclusions:
- Vacancy-induced states persist in TBG, offering a tunable platform for Kondo effect research.
- The behavior of these states depends critically on their location within the TBG lattice.
- Scanning tunneling microscopy can probe both single-particle states and many-body ground states in magic-angle TBG vacancies.
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