High-resolution real-space evaluation of the self-energy operator of disordered lattices: Gade singularity, spin–orbit effects and p-wave superconductivity

Abstract

Disorder is a key factor influencing the behavior of condensed states of matter, however the true extent of its impact is generally difficult to determine due to the prominent roles played by quantum interference, entanglement between spin and orbital degrees of freedom and proximity to quantum critical points. Here we show that the one-particle disorder self-energy—a direct probe of the renormalization of low-energy excitations due to defects and impurities distributed randomly in a crystal—can be obtained by means of unbiased spectral expansions of lattice Green’s functions in a computationally expedient manner. Our scheme provides a powerful framework to map out the frequency and wavevector dependence of electronic excitations in unprecedented large tight-binding systems, up to 109 orbitals, with energy resolution only limited by the mean level spacing. We demonstrate the versatility of our approach in three distinct problems: (i) the Gade singularity in honeycomb layers with dilute topological defects; (ii) the rich landscape of impurity resonances in a spin–orbit-coupled ferromagnet; and (iii) the tailoring of emergent s-wave and p-wave superconducting phases in graphene via atomic defects. These examples reveal rich features in the disorder self-energy that are absent from the self-consistent T-matrix approach and other common approximation schemes, which include regimes of nontrivial wavevector dependence and anomalous dependence upon the impurity concentration. Our study unravels puzzling, and so far largely inaccessible, manifestations of strong nonperturbative quantum interference effects in quantum materials and disordered phases of matter.