Quantum transport of topological spin solitons in a one-dimensional organic ferroelectric

We report the dielectric, magnetic, and ultrasonic properties of a one-dimensional organic salt TTF-QBr3I. These indicate that TTF-QBr3I shows a ferroelectric spin-Peierls (FSP) state in a quantum critical regime. In the FSP state, coupling of charge, spin, and lattice leads to emergent excitation of spin solitons as topological defects. Amazingly, the solitons are highly mobile even at low temperatures, although they are normally stationary because of pinning. Our results suggest that strong quantum fluctuations enhanced near a quantum critical point enable soliton motion governed by athermal relaxation. This indicates the realization of quantum topological transport at ambient pressure.