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(b). Spin-orbital effects in frustrated antiferromagnets Oleg A. Starykh, University of Utah, DMR 0808842.

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**(b)**Spin-orbital effects in frustrated antiferromagnetsOleg A. Starykh, University of Utah, DMR 0808842 Electron spin resonance (ESR) measures absorption of radiation (due to oscillating magnetic field h1eiwt) in the presence of static magnetic field H0. We showed that uniform Dzyaloshinskii-Moriya (DM) interaction DSnxSn+1, which originates from atomic spin-orbit coupling, acts as an internal momentum-dependent magnetic field and splits the ESR absorption line into two separate lines, as shown in Figure (b) on the right. The splitting can be understood as an effective gauge-field-induced momentum boost, proportional to D/J, of the spinon continuum of the Heisenberg chain, as shown in Figure (b). Amazingly, exactly this behavior was found in experiments on frustrated spin-1/2 antiferromagnet Cs2CuCl4, performed in Kapitza Institute in Moscow. Figure (a): experimental data showing splitting of ESR line at T=1.3 K (red line). Two contributions, centered at different magnetic fields, are shown in green. Figure (b): modification of spinon continuum of the Heisenberg chain by the uniform DM interaction. The main effect is a shift of the continuum along the horizontal (momentum) axis. As a result, ESR signal, which measures absorption at q=0, becomes the sum of two contributions centered around upper and lower edges of the spinon continuum. Ref: Povarov et al.,Phys. Rev. Lett. 107, 037204 (2011). (a) Two ESR peaks due to DM interaction**Spin-orbital effects in frustrated antiferromagnetsOleg A.**Starykh, University of Utah, DMR 0808842 • Broader impact: • This grant initiated collaboration between the P.I. and experimental groups of Prof. Yasu Takano (University of Florida) and Dr. Alexander Smirnov (Kapitza Institute for Physical Problems, Moscow, Russia). • Graduate students involved in the projects supported by this grant: Ms. Rachel Glenn (University of Utah; she is Research Assistant funded by the grant), Ms. Huejin Ju and Ms. Ru Chen (UC Santa Barbara; these are graduate students of Prof. Balents, and we are collaborating on the topic of Bose-Einstein condensation of magnons in frustrated geometries), Mr. Kirill Povarov (Kapitza Institute, Moscow; conducting ESR experiments in Cs2CuCl4), Mr. Christian Griset (currently a graduate student at UCSB; while an undergraduate at Caltech, he took part in the investigation of the role of DM interaction on the phase diagram of Cs2CuBr4 - extensive results are described in the recent preprint arxiv:1107.0772). • Postdoctoral researcher involved in the grant-supported project on Majorana fermions in the interacting quantum wire with spin-orbital interaction and in proximity with superconductor: Dr. Miles Stoudenmire, UC Irvine. • As a part of outreach to undergraduate students at the University of Utah, PI has given well-attended lecture “A spin on ice” in which he describes fascinating connections between crystal structure of water ice (H2O) and magnetic properties of pyrochlores with predominantly Ising interactions between spins (spin ice). The emergence of magnetic monopoles in these materials caused real excitement among students. • Main research topics supported by the grant are reviewed in web-based notes at the PI’s web page, see http://www.physics.utah.edu/~starykh/research/research.html.

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