| speaker: | Qimiao Si Rice University, USA |
| time: | Th., 23.08, 14:50-15:40 |
collaborator: Stefan Kirchner
In recent years, quantum criticality and the associated non-Fermi liquid behavior have taken a center stage in the study of strongly correlated systems, and heavy fermion metals represent a prototype system in this context. Historically, theoretical work on heavy fermion systems had centered around the formation of heavy Fermi liquid out of Kondo effect. Recent studies have instead focused attention on the critical destruction of the Kondo effect on the verge of an antiferromagnetic transition at zero temperature. It is natural to ask whether related effects can be studied in nanostructures, given the extensive work in recent years that have been devoted to the Kondo effects in such structures.
This talk will a) briefly summarize the theoretical aspects of local quantum criticality[1] and the experimental evidences coming from heavy fermion metals[2], and b) describe how a single-electron transistor attached to ferromagnetic leads can be used as a tunable quantum impurity model system for Kondo-destroying quantum criticality [3]. The magnetic nanostructure can undergo a continuous quantum phase transition as its gate voltage is varied. The corresponding quantum critical point separates a Fermi liquid phase from a non-Fermi liquid one. The manifestation of the quantum phase transition in the transport properties is studied through an effective Bose-Fermi Kondo model. Non-equilibrium aspects will also be addressed.
[1] Q. Si et al., Nature 413, 804 (2001); P. Coleman et al., J. Phys. Cond. Matt. 13, R723 (2001); H. v. Loehneysen et al., cond-mat/0606317.
[2] S. Paschen et al., Nature 432, 881 (2004); P. Gegenwart et al., Science 315, 969 (2007).
[3] S. Kirchner et al., PNAS 102, 18824 (2005); arXiv:0707.0062.