Emergent spacetime supersymmetry at fractionalized quantum criticality in 2D

Spacetime supersymmetry (SUSY) was introduced as a novel symmetry interchanging fermions and bosons. However, finding evidences of spacetime SUSY in particle physics remains elusive so far. Here we explore the honeycomb lattice spin-1/2 Kitaev model with spin-phonon coupling and show that emergent spacetime SUSY can appear at the fractionalized quantum critical point between the gapless quantum spin liquid (QSL) and a gapped QSL with valence-bond ordering. Moreover, such fractionalized quantum critical point can be reached by turning only a single parameter.