Experimental evidence for nodal superconducting gap in moiré graphene.

Understanding the nature of superconductivity in magic-angle graphene remains challenging. A key difficulty lies in discerning the different energy scales in this strongly interacting system, particularly the superconducting gap. In this work, we report simultaneous tunneling spectroscopy and transport measurements of magic-angle twisted trilayer graphene. This approach allows us to identify two coexisting V-shaped tunneling gaps with different energy scales: a distinct low-energy superconducting gap that vanishes at the superconducting critical temperature and magnetic field and a higher-energy pseudogap. The superconducting tunneling spectra display a linear gap-filling behavior with temperature and magnetic field and exhibit the Volovik effect, consistent with a nodal order parameter. Our work suggests an unconventional nature of the superconducting gap and establishes an experimental framework for multidimensional investigation of tunable quantum materials. Editor's summary: Magic angle twisted trilayer graphene, which features top and bottom graphene layers that are rotated by the same angle with respect to the middle layer, is known to host a robust superconducting phase. However, the nature of this superconductivity remains poorly understood. To distinguish the superconducting gap in this two-dimensional (2D) material, Park et al. simultaneously investigated tunneling spectroscopy and transport phenomena. The tunneling spectra revealed two distinct V-shaped gaps, the lower one of which was identified as the superconducting gap. The response of the superconducting gap to temperature and magnetic fields suggests the presence of a nodal superconducting order parameter. —Jelena Stajic [ABSTRACT FROM AUTHOR]