Optical excitations in systems with frustrated lattice topology
Final Report Abstract
During the course of this project systematic studies of the optical excitation spectra of systems with frustrated lattice topology have been performed. For the frustrated Cr spinels ACr2O4 (A=Cd,Mg,Zn) the exchange-driven phonon splitting has been measured and compared to other antiferromagnetic material classes. A universal correlation of the splitting with the non-dominant exchange coupling suggests a common origin of the phonon splitting. The magnetic excitation spectrum of the model triangular-lattice compounds CuCrO2 and α-CaCr2O4 have been probed optically via magnetic sidebands of Cr crystal-field excitations and compared to the spinel compounds. As a result optical measurements are very sensitive probes of magnon excitation energies in these magnetic systems and can help to identify the complex ground state of frustrated spin systems. A direct measurements of magnons and the comparison with the magnon sidebands was possible for α-CaCr2O4. In addition, an electric-dipole active two-magnon bound state was discovered in α-CaCr2O4 , which may allow to elucidate the role of magnon-magnon interactions in the class of triangular-lattice antiferromagnets. Moreover, the optical data on the semiconducting triangular-lattice compound CuCrS2 reveals a possible spin-density wave formation, suggesting a strong interplay of quasi-free charge carriers and localized magnetic moments in this class of materials.
Publications
- THz spectroscopy in the pseudo-Kagome system Cu3Bi(SeO3)2O2Br. Physical Review B 86, 174411 (2012)
Zhe Wang, M. Schmidt, Y. Goncharov, H.-A. Krug von Nidda, V. Tsurkan, A. Loidl, and J. Deisenhofer
- Universal exchange-driven phonon splitting in antiferromagnets. Physical Review Letters 108, 177203 (2012)
Ch. Kant, M. Schmidt, Zhe Wang, F. Mayr, V. Tsurkan, J. Deisenhofer, and A. Loidl
(See online at https://doi.org/10.1103/PhysRevLett.108.177203) - Exciton-magnon transitions in the frustrated chromium antiferromagnets CuCrO2, α-CaCr2O4, CdCr2O4, and ZnCr2O4. Physical Review B 87, 224424 (2013)
M. Schmidt, Zhe Wang, Ch. Kant, F. Mayr, S. Toth, A. T. M. N. Islam, B. Lake, V. Tsurkan, A. Loidl, and J. Deisenhofer
(See online at https://doi.org/10.1103/PhysRevB.87.224424)
