The Kondo Lattice Problem

Joe D Thompson (Los Alamos National Lab)

Heavy-electron systems, such as CeRhIn5 and CeCoIn5, are composed of a periodic lattice of Kondo ions, Ce3+ in these examples. At high temperatures, the 4f electrons of Ce are localized, but below a material-dependent low temperature, magnetic entropy associated with the 4f electrons creates a liquid of very heavy-mass quasiparticles. For nearly 30 years, our thinking about a lattice of Kondo ions has been guided by a model due to Doniach [1] who considered the competition between RKKY and Kondo interactions. The former promotes long-ranged magnetic order, and the latter compensates the local moments through an antiferromagnetic exchange with conduction electrons and renormalizes their effective mass. This model is intuitively very appealing but is unable to capture the complexity of states, such as the microscopic coexistence of magnetic order and unconventional superconductivity, that is found in CeRhIn5 [2] and CeCoIn5 [3]. As will be discussed, a recent reexamination of a large number of heavy-electron systems provides a qualitatively new framework for thinking about the Kondo-lattice problem.[4] Though this new phenomenology is far from completely developed, it holds promise for eventually understanding how complex states might emerge from a new state of matter, called a Kondo liquid.

[1] S. Doniach, Physica B 91, 231 (1977).

[2] T. Park et al., Nature 440, 65 (2006); PNAS 105, 6825 (2008); Nature, in press.

[3] M. Kenzelmann et al., Science 321, 1652 (2008).

[4] Y. Yang et al., Nature 454, 611 (2008).

  * in collaboration with T. Park, H-O. Lee, Z. Fisk, Y. Yang, D. Pines, M. Kenzelmann, R. Movshovich, E. D. Bauer, A. Bianchi, F. Ronning and V. A. Sidorov

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