Superconductivity from quasiparticle pairing of intervalley coherent state in rhombohedral trilayer graphene.
basic_science · Level V
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- Record sourced from PubMed, PMID 42209489.
- Also identified by DOI 10.1038/s41467-026-72135-y.
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Abstract
Superconductivity is observed in rhombohedral trilayer graphene in a narrow regime between the flavour-symmetric state and the symmetry breaking phase, which cannot be described by the conventional Bardeen-Cooper-Schrieffer theory. The measured coherence length, for instance, is roughly two orders of magnitude shorter than the value predicted by the Bardeen-Cooper-Schrieffer relation based on the large fermi velocity and an extremely low charge carrier density of the flavour-symmetric phase. To resolve the discrepancies, we propose that the rhombohedral trilayer graphene superconducting phase arises from the pairing of quasiparticles of the adjacent inter-valley coherent state. We illustrate the superconducting phenomenology using gapped Dirac cones with the chemical potential μ close to the valence band's edge. Our findings indicate that the transition temperature T<sub>c</sub> obeys <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>∝</mo><msub><mrow><mi>ϵ</mi></mrow><mrow><mi>D</mi></mrow></msub><mi>exp</mi><mrow><mo>(</mo><mrow><mo>-</mo><mn>2</mn><mo>/</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mi>qp</mi></mrow></msub><mi>U</mi></mrow><mo>)</mo></mrow></math> with the density of states ρ<sub>qp</sub> of intervalley coherent state quasiparticles, which is much suppressed compared to predictions from the Bardeen-Cooper-Schrieffer theory. The coherence length ξ we predict behaves according to <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ξ</mi><mo>~</mo><mi>v</mi><mo>/</mo><msqrt><mrow><mi>μ</mi><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub></mrow></msqrt></math> with v being the velocity of Dirac cone. Applying our assumption to a microscopic model, our predictions align well with experimental data and effectively capture key measurable quantities such as the transition temperature T<sub>c</sub> and the coherence length ξ `without parameter fine-tuning.