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inelastic neutron scattering spectra of quantum magnets

Prof Radu Coldea

Professor of Physics

Research theme

  • Quantum materials

Sub department

  • Condensed Matter Physics

Research groups

  • Quantum magnetism and quantum phase transitions
Radu.Coldea@physics.ox.ac.uk
Telephone: 01865 (2)72335
Clarendon Laboratory, room 111.1
  • About
  • Publications

Single crystal growth from separated educts and its application to lithium transition-metal oxides

Scientific Reports Nature Publishing Group 6 (2016) 35362

Authors:

F Freund, Stephanie C Williams, Roger Johnson, Radu Coldea, P Gegenwart, A Jesche

Abstract:

Thorough mixing of the starting materials is the first step of a crystal growth procedure. This holds true for almost any standard technique, whereas the intentional separation of educts is considered to be restricted to a very limited number of cases. Here we show that single crystals of α-Li2IrO3 can be grown from separated educts in an open crucible in air. Elemental lithium and iridium are oxidized and transported over a distance of typically one centimeter. In contrast to classical vapor transport, the process is essentially isothermal and a temperature gradient of minor importance. Single crystals grow from an exposed condensation point placed in between the educts. The method has also been applied to the growth of Li2RuO3, Li2PtO3 and β-Li2IrO3. A successful use of this simple and low cost technique for various other materials is anticipated.
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Topological Triplon Modes and Bound States in a Shastry-Sutherland Magnet

(2016)

Authors:

PA McClarty, F Krüger, T Guidi, SF Parker, K Refson, AW Parker, D Prabakharan, R Coldea
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Magnetic field dependence of excitations near spin-orbital quantum criticality

(2016)

Authors:

A Biffin, Ch Rüegg, J Embs, T Guidi, A Loidl, V Tsurkan, R Coldea
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Spin dynamics of counterrotating Kitaev spirals via duality

(2016)

Authors:

Itamar Kimchi, Radu Coldea
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Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycomb $α$-Li$_2$IrO$_3$

Physical Review B American Physical Society 93:19 (2016) 195158

Authors:

Stephanie Williams, Roger D Johnson, Friedrich Freund, Sungkyun Choi, Anton Jesche, Itamar Kimchi, Soham Manni, Alessandro Bombardi, Pascal Manuel, Phillipp Gegenwart, Radu Coldea

Abstract:

The layered honeycomb magnet α-Li2IrO3 has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled jeff = 1=2 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 β-and γ-Li2IrO3, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in α-Li2IrO3, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li2IrO3 polytypes.
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