Spectroscopic investigation on inter-valley coherence and superconductivity in twisted trilayer graphene*

Experimental identification of the symmetry-broken ground state at partial filling of the flat band in twisted graphene systems is an important goal to shed light on the origin of the superconductivity. Here, we utilize scanning tunneling microscopy (STM) on magic-angle twisted trilayer graphene (MATTG) to measure atomic resolution tunneling conductance maps. We observe the restructuring of the graphene lattices into Kekule supercells, which is evidence of an inter-valley coherent ground state. Expanding the range of 2D maps to cover multiple moire AAA sites reveals the gradual evolution of the Kekule pattern on the moire scale, consistent with the incommensurate Kekule spiral (IKS). We developed a Fourier transformation analysis to extract the IKS wavevector for each conductance map. The magnetic field and temperature at which the Kekule pattern is observed coincide with the appearance of the pseudogap. High-resolution spectroscopic maps show the complicated evolution of the Kekule pattern across the pseudogap. Our measurement highlights the interplay between the superconductivity and the inter-valley coherent parent state.