Inelastic light scattering signatures of magnetic ordering and topological properties in strongly-correlated electron systems

[摘要] We investigate strongly-correlated electron systems where magnetically frustrated and Kondo insulating states show significant sensitivity to disorder and defects. Inelastic light scattering provides an effective tool for probing magnetic and electronic structures of novel states that arise from correlations through their excitation spectra along with characterizing weak distortions and disorder within crystal lattices. We explore triangular-lattice Heisenberg antiferromagnets where ground-state properties are altered from an isotropic triangular-lattice model by weak disorder present in the compounds. In the anisotropic triangular-lattice Heisenberg antiferromagnet SrCr2O4, a coupling of the lattice to magnetic degrees of freedom is observed through a redistribution of phonon intensities that onsets with the formation of peaks within the magnetic spectrum. The triangular-lattice compound NiGa2S4 with competing interactions shows spin freezing where theoretical modeling suggests a magnetically ordered ground state. We demonstrate evidence for structural disorder within this compound that would modify the Heisenberg Hamiltonian through the loss of superexchange pathways and a breaking of crystal inversion symmetry. Heavy fermion systems combine localized magnetism with itinerant electron bands that can drive Kondo insulating behavior in certain materials. Renewed interest in Kondo insulator SmB6 has arisen as a result of the proposal of a strongly correlated topological insulating state in this material which is dependent on the formation of a hybridization gap at low temperatures. Inelastic scattering shows a 10 meV symmetry forbidden mode appearing in the spectrum in samples known to have off-stoichiometries assigned to scattering from acoustic modes away from the Brillouin zone center that results from crystal defects. The intensity of this band is used as a measure of Sm vacancies to identify their effect on the low temperature electronic properties of the system. A suppression of the bulk hybridization gap is found in samples with as little as 1% Sm vacancies demonstrating the sensitivity of the topological insulating state to weak structural disorder.

[发布机构] Johns Hopkins University

[效力级别] strongly-correlated electrons

[关键词] Raman spectroscopy;strongly-correlated electrons;frustrated magnetism;Kondo insulator;topological insulator;Physics