Quantum impurity spin in Majorana edge modes

We show that Majorana edge modes of two-dimensional spin-triplet topological superconductors (superfluids) have Ising-like spin density whose direction is determined by the d-vector characterizing the spin-triplet pairing symmetry in the bulk. Thus, when a quantum impurity spin is introduced at the edge of the spin-triplet topological superconductors (superfluids), the exchange coupling between this impurity spin and the Majorana modes becomes Ising-type. Observing this, we argue that, under the external magnetic fields, this quantum impurity spin exhibits anisotropic dissipative quantum dynamics due to the `background' massless Majorana edge modes. We also discuss how the magnetic response of this impurity spin can serve as a local probe for spin-triplet superconducting order parameter in the bulk.