Magneto-optic Kerr Effect Measurement of TbMn6Sn6 at mK-Temperature

Novel electron states stabilized by Coulomb interactions attract tremendous interests in condensed matter physics. These states are studied by corresponding phase transitions occurring at extreme conditions such as mK temperatures and high magnetic field. In this work, we introduce a magneto-optical Kerr effect measurement system to comprehensively explore these phases in addition to conventional transport measurement. This system, composed of an all-fiber zero-loop Sagnac interferometer and in situ piezo-scanner inside a dilution refrigerator, operates below 100 mK, with a maximum field of 12 Tesla and has a resolution as small as 0.2 μrad. As a demonstration, we investigate TbMn 6 Sn 6 , where the manganese atoms form Kagome lattice that hosts topological non-trivial Dirac cones. We observed two types of Kerr signals, stemming from its fully polarized ferromagnetic ground state and positive charged carriers within the Dirac-like dispersion.