Quantum criticality and dynamical scaling in a Mn-based kagome metal*

Geometric frustration in magnetic materials occurs when the magnetic interactions and the lattice geometry together result in a system with a very large ground state degeneracy. Such a degeneracy results in a wide range of ever-interesting phenomena. Notable examples are compounds with antiferromagnetic Heisenberg spin-$\frac{1}{2}$ moments on a kagome lattice, a system theorized to be a quantum spin liquid. Indeed herbertsmithite is a close realization of this model and shows no magnetic order to sub kelvin temperatures despite superexchange on the order of 200 K. We present our results on the material Sc$_3$Mn$_3$Al$_7$Si$_5$, a compound with Mn atoms on a kagome lattice. This material has a combination entirely unique for magnetic kagome lattice materials: no chemical disorder, no magnetic ordering and metallic conduction. This combination of properties makes it the only suitable known candidate to study the magnetically frustrated kagome lattice in a metallic material. We present results on this material from heat capacity, magnetic susceptibility measurements, and inelastic neutron scattering measurements. Heat capacity measurements confirm the lack of any zero-field phase transitions down to $T = 50$ mK. Both heat capacity and magnetic susceptibility measurements show critical scaling in field and two orders of magnitude in temperature. Measurements of the dynamical susceptibility through inelastic neutron scattering also show signs of criticality through $\omega / T$ scaling.