- A New Look at the Phase Diagram of the Kondo Lattice:The Role of Umklapp Scattering. P.S. Riseboroug
- 26.07.2016 16.00 h
- Anfiteatro Antônio Cabral - Porto Alegre
- Colóquios 2016
A New Look at the Phase Diagram of the Kondo Lattice: The Role of Umklapp Scattering
Palestrante: Peter Stephen Riseborough
Autores:M. Abele and P.S. Riseborough
The Kondo Lattice model describes the magnetic exchange scattering of conduction electrons from a set of localized magnetic moments located at the sites of a periodic array. It is considered as being the simplest model that describes the loss of magnetism in the rare-earth heavy fermion compounds, such as CeAl3, CeCu6 and CeCoIn5. The model is based on an antiferromagnetic Heisenberg-like interaction between the each local moment and the magnetization density of the conduction electrons at that site (the Kondo interaction). For a single magnetic site, a non-magnetic (spin-singlet) ground state is formed when a cloud of conduction electrons with a compensating spin density is bound to the magnetic site. In the limit of half-filled conduction bands, the Kondo Lattice model can also describe the semiconducting phase, such as that found in Ce3Bi4Pt3. At half-filling, the non-magnetic semiconducting state can be viewed as a state in which every conduction electron is bound to a site, such that there are no free carriers.
We re-examine the phase diagram of the Kondo lattice, and investigate the stability of the non-magnetic phase relative to magnetic phases, such as spin-density wave. We show that umklapp scattering has an important effect in stabilizing the magnetic phases relative to the non-magnetic Kondo states. We argue that umklapp scattering is responsible for the anomalously high Neel temperatures found in the almost half-filled materials such as CeRu2Al10 and CeOs2Al10. For TN = 27 K (Ru) and 29 K (Os),[i] whereas for GdRu2Al10 the corresponding ordering temperature is only16.5 K,[ii] despite the large Ce–Ce distance (5.26 Å) and the small Ce moments of 0.32 B. We show that at half-filling, the umklapp scattering may stabilize a semiconducting phase with unusual magnetic properties.
[i] Nishioka, T. et al. Novel Phase Transition and the Pressure Effect in YbFe2Al10-type CeT2Al10(T = Fe, Ru, Os). J. Phys. Soc. Jpn. 78, 123705 (2009).
[ii] Kobayashi, R. et al. Magnetic Phase Diagram of Ce1-xGdxRu2Al10 Single Crystals. J. Phys. Soc. Jpn. Suppl. 80SA, SA044 (2011).; Sera, M. et al. Unusual temperature-dependent exchange interaction in GdFe2Al10 in comparison with GdRu2Al10. Phys. Rev. B 88, 100404 (2013).
- Anfiteatro Antônio Cabral
- Porto Alegre
- Rio Grande do Sul
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