Harmonic fingerprint of unconventional superconductivity in twisted bilayer graphene

Abstract

Microscopic details such as interactions and Fermiology determine the structure of superconducting pairing beyond the spatial symmetry classification along irreducible point group representations. From the effective pairing vertex, the pairing wave function related to superconducting order unfolds in its orbital-resolved Fourier profile which we call the harmonic fingerprint (HFP). The HFP allows to formulate a concise connection between microsopic parameter changes and their impact on superconductivity. From a random phase approximation analysis of twisted bilayer graphene (TBG) involving d + id, s±, and f -wave order, we find that nonlocal interactions, which unavoidably enter the low-energy electronic description of TBG, not only increase the weight of higher lattice harmonics but also have a significant effect on the orbital structure of these pairing states. For gapped unconventional superconducting order such as s± and d + id, a change in HPF induces enhanced gap anisotropies. Experimental implications to distinguish the different gaps and HPFs are also discussed.

Correlation-Induced Triplet Pairing Superconductivity in Graphene-Based Moiré Systems

“…Since the result is due to the valley-sublattice structure [32,33] rather than the detail band structure, we anticipate that f -wave is generically the dominating pairing symmetry for spin-triplet superconductivity in the graphene based systems including MATTG, independent of the pairing mechanism. We note that the possibility of realizing f -wave superconductivity was also discussed previously in the context of graphene and MATBG [33,[37][38][39][40][41].…”

Transport and spectral properties of magic angle twisted bilayer graphene junctions based on local orbital models

“…On the one hand, an extension to a Bogoliubov de Gennes formula-tion would allow to study Josephson and Andreev transport in MATBLG junctions including superconducting correlations [60][61][62], in line with recent experiments [9]. This type of calculations could help to identify the symmetry of the order parameter in superconducting MAT-BLG which is at present an open issue attracting great interest [48,[63][64][65][66]. Similar calculations have been implemented in the past by some of the authors for the case of pristine graphene layers in proximity with unconventional and topological superconductors [67].…”

“…This model has been intensively used [46][47][48][49] due to its simplicity but, although it exhibits naturally particle/hole symmetry, due to the Wannier obstruction it lacks the characteristic symmetries of the system and leads to moiré minivalleys with vanishing net chirality.…”

The Fingerprints of Resonant Frequency for Atomic Vacancy Defect Identification in Graphene

“…The position-dependent Fermi velocity fingerprints are figured out based on scanning tunnelling spectra of strained graphene [23]. Furthermore, the harmonic fingerprint of unconventional superconductivity in twisted bilayer graphene is collected [24]. For more physical characteristics of graphene, the spin-orbit interaction fingerprints of a ballistic graphene Josephson junction [25], the enhancing mid-infrared molecular fingerprints by acoustic graphene plasma polarities [26], and the infrared fingerprints of natural 2D talc and plasma phonon coupling in graphene-talc heterostructures [27] are all studied.…”