P. Gegenwart

Spin waves and revised crystal structure of honeycomb iridate Na2IrO3.

We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order below T(N)=15.3  K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90° Ir-O-Ir bonds required for dominant Kitaev exchange.

High-temperature superconductivity in Eu 0.5 K 0.5 Fe 2 As 2

Subsequent to our recent report of SDW type transition at 190 K and antiferromagnetic order below 20 K in EuFe2As2, we have studied the effect of K-doping on the SDW transition at high temperature and AF order at low temperature. 50% K doping suppresses the SDW transition and in turn gives rise to high-temperature superconductivity below T_c = 32 K, as observed in the electrical resistivity, AC susceptibility as well as magnetization. A well defined anomaly in the specific heat provides additional evidence for bulk superconductivity.

Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycombα−Li2IrO3

The layered honeycomb magnet

Unique phase diagram with narrow superconducting dome in EuFe 2 (As 1 − x P x ) 2 due to Eu 2 + local magnetic moments

\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}

Effect of isoelectronic doping on the honeycomb-lattice iridate A2 IrO3

has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled

Optical investigations of chemically pressurized EuFe 2 ( As 1 − x P x ) 2 : An s -wave superconductor with strong interband interactions

{j}_{\mathrm{eff}}=1/2

Effect of nonmagnetic dilution in the honeycomb-lattice iridatesNa2IrO3andLi2IrO3

magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counterrotating on nearest-neighbor sites. This unexpected type of magnetic structure for a honeycomb magnet cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes

Optical properties of the iron-pnictide analog BaMn 2 As 2

\ensuremath{\beta}

Local magnetism and spin dynamics of the frustrated honeycomb rhodate Li2RhO3

- and

Persistent low-temperature spin dynamics in the mixed-valence iridate Ba3InIr2O9

\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}