Key Findings
The study reports the realization of a nodal nematic superconducting state in mirror-symmetric magic-angle twisted trilayer graphene (MATTG). The researchers observed a pronounced two-fold anisotropy in the zero-bias tunneling conductance under an in-plane magnetic field deep within the superconducting state. This anisotropy is strongly suppressed as temperature or perpendicular magnetic fields increase, coinciding with the suppression of superconductivity. Notably, the major axis of this anisotropy rotates by up to 90° across the superconducting dome, indicating that the symmetry of low-energy excitations is intrinsic and tunable via field and density.
Technical Details
To identify these properties, the team developed a platform integrating transport measurements and tunneling spectroscopy within a single device. This allowed for the direct characterization of the density of states (DOS) and rotational symmetry while independently tracking the onset of superconductivity. The observed behaviors imply a superconducting state that spontaneously breaks the six-fold rotational symmetry of the moiré superlattice, confirming a multi-component pairing symmetry.
Background and Context
Nematic superconductivity occurs when the rotational symmetry of a lattice is broken in the superconducting state. While some materials exhibit nematicity emerging from a preexisting nematic normal state, intrinsic nematic superconductors—which break symmetry on their own—are exceedingly rare. Previous evidence for unconventional superconductivity in MATTG included a double V-shaped gap structure and a linear dependence of zero-bias tunneling conductance on temperature, as well as a square-root dependence on out-of-plane magnetic fields (the Volovik effect).
Significance and Outlook
The identification of a multi-component nodal nematic superconductor is significant because the interplay between nodal quasiparticles and nematicity is theoretically linked to unique topological behavior and quantum critical phenomena. By utilizing the gate voltage and twist angle tunability of moiré graphene, this research provides a method to overcome ambiguities found in bulk materials, opening new avenues for investigating unconventional symmetry-breaking in two-dimensional systems.
Source: https://arxiv.org/html/2610.20605v1
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