Article

# Topological quantum phase transition in 5d transition metal oxide Na2IrO3.

Department of Physics and Astronomy and Center for Strongly Correlated Materials Research, Seoul National University, Seoul 151-747, Korea.

Physical Review Letters (Impact Factor: 7.73). 03/2012; 108(10):106401. DOI: 10.1103/PhysRevLett.108.106401 Source: PubMed

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**ABSTRACT:**We studied Sr2IrO4 and Sr3Ir2O7 using angle-resolved photoemission spectroscopy, making direct experimental determinations of intra- and intercell coupling parameters as well as Mott correlations and gap sizes. The results are generally consistent with LDA+U+spin-orbit coupling calculations, though the calculations missed the momentum positions of the dominant electronic states and neglected the importance of intercell coupling on the size of the Mott gap. The calculations also ignore the correlation-induced spectral peak widths, which are critical for making a connection to activation energies determined from transport experiments. The data indicate a dimensionality-controlled Mott transition in these 5d transition-metal oxides.Physical review. B, Condensed matter 06/2013; 87(24). · 3.66 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The stibium-doped iso-structural spinel CuIr2−xSbxS4 system has been thoroughly investigated. With the increase of Sb content, the orbitally induced Peierls phase transition is suppressed gradually. The electro-magnetic behavior display that the hysteresis of the phase transition disappears when x>0.15x>0.15, while the phase transition is entirely suppressed when x>0.2x>0.2. Raman spectroscopy study shows that phonon vibration modes are changed in the Sb-doped samples although the structure remains unchanged. In addition, the disappearance of the hysteresis and entire suppression of the phase transition correspond to the extinction of F2g(2) and F2g(1) modes, respectively. The experimental results indicate that the change of phonon vibration caused by S–S bonds is the dominant factor to drive the phase transition rather than Ir–S bonds.Journal of Magnetism and Magnetic Materials 03/2013; 330:12–15. · 2.00 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We present an effective tight-binding Hamiltonian for Li2IrO3 based on maximally localized Wannier functions for states near the Fermi level as obtained from first-principles electronic structure calculations. The majority of the Wannier orbitals are positioned on the center site with dominant jeff=1/2 character, while relatively small jeff=3/2 tails lie on the three nearest-neighbor sites. Interestingly, the spin quantization axis of the jeff=1/2 components deviates from the local octahedral axis and points toward the nearest-neighbor Ir direction. In our tight-binding model, there are relatively strong next-nearest- and the third-nearest-neighbor hopping terms within the two-dimensional Ir honeycomb lattice in addition to the relatively small but significant interlayer hopping terms. The ratio between the nearest-neighbor and the third-nearest-neighbor hoppings, which can be controlled by the lattice strain, plays a critical role in determinating the Z2-invariant character of Li2IrO3. From our tight-binding model, we also derive an effective Hamiltonian and its parameters for the magnetic exchange interactions. Due to the complex spin-dependent next-nearest-neighbor hopping terms, our pseudospin Hamiltonian includes significant next-nearest-neighbor antiferromagnetic Kitaev terms as well as Dzyaloshinskii-Moriya and Heisenberg interactions. From our model Hamiltonian we estimate classical energies of collinear magnetic configurations as functions of the Hund's coupling of the Ir atom, from which zigzag-type magnetic order gives the lowest energy.Physical review. B, Condensed matter 04/2013; 87(16). · 3.66 Impact Factor

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