2014 Fiscal Year Research-status Report
Lattice and Charge Engineering of Spin Ice
| Project/Area Number |
26400339
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
JAUBERT LUDOVIC 沖縄科学技術大学院大学, Theory of Quantum Matter Unit, 研究員 (10727209)
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| Co-Investigator(Kenkyū-buntansha) |
宇田川 将文 東京大学, 工学(系)研究科(研究院), 助教 (80431790)
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| Project Period (FY) |
2014-04-01 – 2017-03-31
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| Keywords | frustrated magnetism / spin ice / spin liquids / magneto-electric |
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| Outline of Annual Research Achievements |
As planned for FY2014, we have investigated the question of spontaneous Hall effect in Pr2Ir2O7, based on the spin ice model. The RKKY interactions could be effectively recast as nearest-neighbour interactions between monopoles. We studied the phase diagram of this monopole representation, both at equilibrium by L. Jaubert and dynamically by M. Udagawa. The possibility to visit each other at the University of Tokyo and at OIST greatly helped us to build a comprehensive picture of the problem together. Our main findings are i) the metastable stabilization of a promising mixed phase where long-range monopole order co-exists with a spin liquid, and ii) the existence of a new phase made of branched structures of monopoles which we illustratively named "monopole jellyfish". These structures encode the information of time-reversal symmetry breaking and are thus possibly relevant to the spontaneous Hall effect in Pr2Ir2O7. This work has already been presented by M. Udagawa at a YITP workshop and the writing of the paper is well-advanced.
In parallel, L. Jaubert has written a Monte Carlo code able to account for the emergence of electric polarization on magnetic monopoles. Based on this code, we are now studying the magneto-electric effect in pyrochlores, especially in an external field.
During FY2014, we were also very fortunate to have become co-editors of the first book on "Spin Ice", at the request of Springer-Verlag, which represents the coordination of approximately 20 co-authors across Japan, USA, Canada and Europe.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
Becoming editors of the first book on "Spin Ice" is a unique opportunity to disseminate our research on a broad scale, Springer-Verlag being one of the main scientific publishers in the world. The edition of the book is currently a work-in-progress and has been very time-consuming to organize the structure of the book, to find approximately 20 co-authors, and to supervise the contributions of everyone. This was not originally planned and we had to adapt to this new situation. This is probably why our original plan has been slightly delayed, but we are confident about the future of our project. Indeed, the main part of our first-year project is almost complete with a paper already in preparation. As for the magneto-electric coupling, the technical part is finished (namely developing a working Monte Carlo code). This code has been written in order to be very flexible and to explore a diversity of magneto-electric effects in spin ice in the next two years.
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| Strategy for Future Research Activity |
For the coming year, our goals are first to finish the paper related to the spontaneous Hall effect and to extensively study the magneto-electric effects in spin ice materials in an external field. As originally planned for the second year, we expect this magneto-electric project to help understanding the intriguing and yet poorly understood physics of Pr2Zr207. Another part of our second year project will be the investigation of the thermal Hall effect in pyrochlores, which will probably require the inclusion of quantum fluctuations and spin-lattice coupling, and has become extremely timely since a very recent experimental work published in Science has observed this thermal Hall effect in Tb2Ti2O7 [1].
[1] Hirschberger et al. Science, 348, pp 106 (2015)
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| Causes of Carryover |
As the first year of our project, initiating the projects, as well as becoming editors of the "Spin Ice" book, took a large part of our efforts. The costs were thus less than what were expected, and we have preferred to save money during the first year, which will be used during the next two years, especially concerning the publication costs and travel costs to present our results at conferences.
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| Expenditure Plan for Carryover Budget |
We are planning to use this money to pay for the visits of M. Udagawa at OIST and the visits of L. Jaubert at Gakushuin University, and also to present our work to conferences. For example, L. Jaubert has already been accepted for an oral presentation at the International Conference on Magnetism to be held in Barcelona, Spain on July 2014. Additionally, we will invite international researchers to give seminars and lectures in OIST and Tokyo: Professor John Chalker from Oxford has provisionally accepted to visit us in September 2015.
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Research Products
(1 results)
