Impurity-induced resonant spinon zero modes in Dirac quantum spin liquids*

Quantum spin liquids are strongly correlated phases of matter displaying a highly entangled ground state. Quantum spin liquids have attracted much research interest, in particular for their emergent Majorana physics and their long-standing relationship with unconventional superconductivity. Yet, due to their unconventional nature, finding experimental signatures of quantum spin liquids has proven to be a remarkable challenge. Here we show that magnetic S=1/2 impurities create resonant spinon zero modes in Dirac quantum spin liquids at zero energy. We show that the emergence of such zero modes is associated with the low energy Dirac nature of the spinon excitations, and we explore the interference effects between different impurity states. Finally, we show that the spinon zero modes result in a zero frequency divergence in the spin structure factor, that can be probed by inelastic spectroscopy and electrically-driven paramagnetic resonance. Our results highlight the dramatic effect of impurities in a Dirac quantum spin liquid, providing a stepping stone towards identifying Dirac quantum spin liquids through local real space measurement with scanning probe techniques.