查看更多>>摘要：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 0.2µrad.As a demonstration,we investigate TbMn6Sn6,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.
查看更多>>摘要：Ba6Cr2S10 is a recently discovered magnetic material,in which the spins are aligned ferromagnetically in the ab-plane and anti-parallelly in a paired form along the c-axis.It is characterized as a quasi-one dimensional(1D)dimerized structure with a ferrotoroidic order,forming the simplest candidate toroidal magnetic(TM)order and exhibiting an anti-ferromagnetic-like transition at around 10 K.Time-resolved ultrafast dynamics investigation of the novel A-Cr-S(A:metal elements)family of quantum materials has rarely been reported.Here,we investigate the time-resolved pump-probe ultrafast dynamics of a Ba.6Cr2S10 single crystal.A prominent change in the photo-excited carrier dynamics is observed at Tc=10 K,corresponding to the reported TM-paramagnetic phase transition.A potential unknown magnetic transition is also found at T*=29 K.Our results provide new evidence for the TM magnetic transition in Ba6Cr2S10,and shed light on phase transitions in TM quantum materials.
查看更多>>摘要：Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressure-driven changes in electronic structures and insulator-to-metal transitions under high pressure.The λ-N2 formed by cold compression is known to be the most stable one in all solid nitrogen phases observed so far.By optimizing the optical system,we successfully measured the high-pressure absorption spectra of λ-N2 covering the polymeric-nitrogen synthetic pressures(124 GPa-165 GPa).The measured optical band gap decreases with increasing pres-sure,from 2.23eV at 124GPa to 1.55eV at 165GPa,with a negative pressure coefficient of-18.4meV/GPa,which is consistent with the result from our ab initio total-energy calculations(-22.6meV/GPa).The extrap-olative metallization pressure for the λ-N2 is around 288(18)GPa,which is close to the metallization pressure(280 GPa)for the 7-N2 expected by previous absorption edge and direct electrical measurements.Our results provide a direct spectroscopic evidence for the pressure-driven band gap narrowing of solid nitrogen.
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