Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 21: FS: Quantum Criticality in Strongly Correlated Metals

TT 21.1: Invited Talk

Wednesday, March 24, 2010, 09:30–10:10, H20

Quantum Criticality, Kondo Breakdown, and Fermi Surfaces — •Qimiao Si — Dept of Physics & Astro, Rice U, Houston, TX, USA

Quantum criticality describes the collective fluctuations of matter undergoing a second order phase transition at zero temperature. Magnetic heavy fermion metals represent a prototype setting for quantum critical points (QCPs). Studies here have demonstrated quantum criticality as a mechanism for both non-Fermi liquid behavior and unconventional superconductivity. They have also illustrated the general notion of quantum criticality beyond the orthodox theory of order-parameter fluctuations. Here, I discuss these issues in the broader contexts, and address two types of antiferromagnetic QCPs, including a local quantum critical point [1] which contains the physics of a critical breakdown of the Kondo effect. Across such a QCP, there is a sudden collapse of a large Fermi surface to a small one. I also consider the proximate antiferromagnetic and paramagnetic phases, and these considerations lead to a global phase diagram [2]. Finally, I discuss the pertinent experiments, briefly address the case of ferromagnetic heavy fermions [3], and outline some issues for future studies.

[1] J.-X. Zhu, S. Kirchner, R. Bulla, & Q. Si, PRL 99, 227204 (2007) and to be published; Q. Si, S. Rabello, K. Ingersent & J. L. Smith, Nature 413, 804 (2001).

[2] Q. Si, arXiv:0912.0040; Physica B378, 23-27 (2006); S. J. Yamamoto and Q. Si, PRL 99, 016401 (2007).

[3] S. J. Yamamoto and Q. Si, arXiv:0812.0819.