NCTS (South)


DATE2011-04-22

TIME14:10

PLACE物理二館地下室 (49X04)

FIELDOther

SPEAKER Dr. Shigeki Onoda - Condensed Matter Theory Laboratory, RIKEN, Japan

TITLETheory of quantum spin ices for Pr and Yb pyrochlore oxides

ABSTRACTThe effective quantum pseudospin-1/2 model for interacting rare-earth magnetic moments, which are locally described with atomic doublets, is studied theoretically for magnetic pyrochlore oxides. It is derived microscopically for Pr_2TM_2O7 (TM = Zr, Sn, Hf, and Ir) and Yb_2TM_2O7 (TM =Ti and Sn) by taking into account Anderson’s superexchange processes. Remarkably, these systems form quantum variants of the spin ice, potentially showing large quantum effects and the quantum kinematics of magnetic monopoles. The effective model is then studied by means of a classical mean-field theory, a numerical exact diagonalization, and a lattice gauge theory. These calculations reveal appreciable quantum fluctuations leading to quantum phase transitions among various phases, including quantum spin liquid phases and long-range ordered phases. The possible relevance to experiments is discussed.

References: Y. Machida, S. Nakatsuji, S. Onoda, et al., Nature 463, 210 (2010). S. Onoda and Y. Tanaka, Phys. Rev. Lett. 105, 047201 (2010); Phys. Rev. B 83, 094411 (2011). S. Onoda, arXiv:1101.1230.