Exploring the low energy excitations of the S=1 quasi-1D molecular system Mo3Se7(dmit)3

The molecular magnetic system Mo3S7(dmit)3 is a semiconductor with a charge gap of around 100 K and no magnetic transition or spin freezing down to 50 mK. In the crystal structure the molecules form closely coupled triangles and these triangular units are arranged in hexagonal layers. Theoretical studies indicate that each of the triangles has spin 1 and that the in-plane coupling between triangles is very weak compared to the inter-plane coupling of the triangles. The system can thus be viewed as a strong-rung three-leg spin ladder which is expected to behave as a symmetry-protected topological phase with a Haldane spin gap on the order of 1 K. Temperature dependent muSR studies in longitudinal fields up to 2 T have observed a gap feature that closes with field, becoming zero at around 1.2 T. This is consistent with the expectation for such a Haldane spin chain. This study will explore the properties of the isostructural system Mo3Se7(dmit)3 which is also expected to have a Haldane-gapped state at low field, with gap closure at a quantum critical point reached by a field that will be comfortably within the range of the HiFi instrument.