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Lee, SungBin,Lee, Eric Kin-Ho,Paramekanti, Arun,Kim, Yong Baek American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.1
We study the finite-temperature phase diagram of the Heisenberg-Kitaev model on a three-dimensional hyperhoneycomb lattice. Using semiclassical analysis and classical Monte Carlo simulations, we investigate quantum and thermal order-by-disorder, as well as the magnetic-ordering temperature. We find the parameter regime where quantum and thermal fluctuations favor different magnetic orders, which leads to an additional finite-temperature phase transition within the ordered phase. This transition, however, occurs at a relatively low temperature and the entropic effects may dominate most of the finite-temperature region below the ordering temperature. In addition, we explore the magnetization process in the presence of a magnetic field and discover spin-flop transitions which are sensitive to the applied-field direction. We discuss implications of our results for future experiments on a hyperhoneycomb lattice system such as the recently discovered beta-Li2IrO3.
Determination of Hund's coupling in 5d oxides using resonant inelastic x-ray scattering
Yuan, Bo,Clancy, J. P.,Cook, A. M.,Thompson, C. M.,Greedan, J.,Cao, G.,Jeon, B. C.,Noh, T. W.,Upton, M. H.,Casa, D.,Gog, T.,Paramekanti, A.,Kim, Young-June American Physical Society 2017 Physical Review B Vol.95 No.23
<P>We report resonant inelastic x-ray scattering (RIXS) measurements on ordered double-perovskite samples containing Re5+ and Ir5+ with 5d(2) and 5d(4) electronic configurations, respectively. In particular, the observedRIXS spectra of Ba2YReO6 and Sr2MIrO6 (M = Y, Gd) show sharp intra-t(2g) transitions, which can be quantitatively understood using a minimal 'atomic' Hamiltonian incorporating spin-orbit coupling. and Hund's coupling J(H). Our analysis yields lambda = 0.38(2) eV with J(H) = 0.26(2) eV for Re5+ and lambda = 0.42(2) eV with J(H) = 0.25(4) eV for Ir5+. Our results provide sharp estimates for Hund's coupling in 5d oxides and suggest that it should be treated on equal footing with spin-orbit interaction in multiorbital 5d transition-metal compounds.</P>