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Quantum criticality occurs as a result of competing interactions, and influences physical properties over a wide temperature and parameter ranges. Magnetic heavy fermion metals represent a prototype system in this context, and have in particular provided the setting to study local quantum criticality that involves not only order-parameter fluctuations but also a Kondo breakdown [1]. Surprisingly, recent theoretical and experimental developments have revealed some unusual phases proximate to the heavy-fermion quantum critical points, thereby opening up an entirely new frontier on the relationship between quantum criticality and emergent phases. I will discuss the relevant recent experiments [2] within the framework of a global phase diagram that was put forward several years ago [3] and has recently been studied more extensively. The theoretical considerations of the global phase diagram emphasize the interplay between two effects. One is the Kondo screening and its breakdown, and the other is the fluctuations in the quantum magnetism of local moments alone. The global phase diagram is influenced by Berry phase and topologically nontrivial configurations of the spin system. I will discuss this effect and illustrate it in the one-dimensional Kondo-lattice Hamiltonian [4].
[1] Q. Si and F. Steglich, Science 329, 1161 (2010). [2] S. Friedemann et al., Nature Phys. 5, 465 (2009); J. Custers et al., PRL 104, 186402 (2010). [3] Q. Si, Physica B 378, 23 (2006); S. J. Yamamoto and Q. Si, PRL 99, 016401 (2007). [4] P. Goswami and Q. Si, "Effects of Berry phase and instantons in one dimensional Kondo-Heisenberg model",arXiv:1012.6041. |
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