Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session T2: Quantum Fluctuations and Magnetic Frustration in Strongly Correlated Metals |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Zachary Fisk, Los Alamos National Laboratory Room: Oregon Ballroom 202 |
Wednesday, March 17, 2010 2:30PM - 3:06PM |
T2.00001: Mapping the effect of frustration on the Kondo Lattice Invited Speaker: The effect of quantum zero point fluctuations on strongly correlated electron systems, and their ability to transform the state of matter through a quantum phase transition, constitutes a major area of interest in condensed matter systems. I will discuss efforts, both experimental [1,2] and theoretical [3] to unify our understanding of zero point fluctuations in the context of frustrated quantum antiferromagnets, with our understanding of the Kondo lattice that describes heavy electron materials on the brink of magnetism. One of the interesting predictions of a unified approach, is the existence of a new kind of ``spin liquid metal" phase perched between the antiferromagnet and the heavy electron Fermi liquid. I will discuss our efforts to describe this state theoretically and present recent candidate observations of this phenomenon. \\[4pt] [1] Sven Friedemann et al., Nature Physics, {\bf 5}, 465 (2009).\\[0pt] [2] Jeroen Custers et al., to be published (2010).\\[0pt] [3] Andriy Nevidomskyy and P. Coleman, to be published (2010). [Preview Abstract] |
Wednesday, March 17, 2010 3:06PM - 3:42PM |
T2.00002: Heavy Fermions and Geometric Frustration on the Shastry-Sutherland Lattice Invited Speaker: Many of the $R_{2}T_{2}X$ ($R$=rare earth, $T$=transition metal, $X$=Mg, Cd, In, Sn, and Pb) form layered compounds where the $R$ atoms lie on triangular units in the geometically frustrated Shastry-Sutherland lattice (SSL). Depending on the relative strengths of the first and second neighbor exchange interactions, these compounds either order antiferromagnetically or show spin liquid properties. These $R_{2}T_{2}X$ compounds are metallic, and thus offer the promise of studying the effects of geometric frustration on quantum criticality. Yb$_{2}$Pt$_{2}$Pb and Ce2Pt2Pb are of special interest, as they lie very near this antiferromagnetic quantum critical point. Yb$_{2}$Pt$_{2}$Pb orders antiferromagnetically at 2 K, with unusually strong fluctuations in the paramagnetic state. The ordered state is Fermi liquid-like with a Sommerfeld coefficient $\gamma=0.03$ J/Yb-mol K$^{2}$. The phase behavior with magnetic field is very complex, terminating in a sequence of magnetization plateaux, as observed previously in insulating SSL systems. In contrast, Ce$_{2}$Pt$_{2}$Pb appears to be on the spin liquid side of the QCP, and here the ground state is heavy fermion-like, with $\gamma=0.6$ J/Ce-mol K$^{2}$. Our results suggest that heavy-fermion behavior occurs near the quantum critical point in this class of SSL compounds, as for unfrustrated heavy fermion compounds, but is strongly suppressed by magnetic ordering. [Preview Abstract] |
Wednesday, March 17, 2010 3:42PM - 4:18PM |
T2.00003: Kondo breakdown and Berry phase effect in local-moment systems Invited Speaker: Experiments in heavy fermion metals have indicated quantum-critical behavior with inherently new quantum modes, raising the question of how quantum fluctuations lead local-moment systems into a new class of quantum critical points. We theoretically study the effect of Kondo breakdown, with an emphasis on how the Berry phase influences the critical behavior. The Berry phase has embodied quantum mechanics ever since Berry's seminal work in the early 1980s showing that the adiabatic evolution of a quantum system is characterized by a geometrical phase, the Berry phase, on top of the dynamical phase. It has found fruitful applications in all areas of physics ranging from atomic physics to quantum field theory. We consider the Bose-Fermi Kondo model, which plays an important role in the theoretical approaches to Kondo-breakdown quantum criticality. We address the model in terms of a coherent-state spin-path-integral representation, which explicitly brings out a Berry phase term in the action. We demonstrate that, the Kondo-destroying fixed point is an interacting one and is therefore beyond a description in terms of order-parameter fluctuations alone [1,2,3]. The implications for the nature of the critical point in local moment systems with easy-axis symmetry will be discussed as well [4]. \\[4pt] [1] S. Kirchner, Q. Si, and K. Ingersent, PRL 102, 166405 (2009). \\[0pt] [2] S. Kirchner and Q. Si, arXiv:0808.2647. \\[0pt] [3] S. Kirchner and Q. Si, Physica B 404, 2904 (2009). \\[0pt] [4] S. Kirchner and Q. Si, PRL 100, 026403 (2008); J.-X. Zhu, S. Kirchner, R. Bulla, and Q. Si, PRL 99, 227204 (2007). [Preview Abstract] |
Wednesday, March 17, 2010 4:18PM - 4:54PM |
T2.00004: Hidden order in URu2Si2 Invited Speaker: Complex electronic matter exhibit subtle forms of self organization which are almost invisible to the available experimental tools, but which have dramatic physical consequences. One prominent example is provided by the actinide based heavy fermion material URu$_2$Si$_2$. At high temperature, the U-5f electrons in URu$_2$Si$_2$ carry a very large entropy. This entropy is released at 17.5K via a second order phase transition to a state which remains shrouded in mystery, and which was termed a ``hidden order'' state. We developed a first principles theoretical method to analyze the electronic spectrum of correlated materials as a function of the position inside the unit cell of the crystal, and we used it to identify the low energy excitations of the URu$_2$Si$_2$ and to identify the possible candidate for the order parameter of the hidden order state. The first principles calculation for URu$_2$Si$_2$ show that U-5f electrons undergo a multichannel Kondo effect below 70K, which is arrested at lower temperature (35K) by the crystal field splitting. At even lower temperatures, two broken symmetry states can be stabilized, characterized by a complex order parameter $psi$. A real $psi$ describes the hidden order phase, and an imaginary $psi$ corresponds to the large moment antiferromagnetic phase, thus providing a unified picture of the two broken symmetry phases, which are realized in this material. [Preview Abstract] |
Wednesday, March 17, 2010 4:54PM - 5:30PM |
T2.00005: Analysis of the antiferromagnetic phase transitions of the 2D Kondo lattice Invited Speaker: The Kondo lattice continues to present an interesting and relevant challenge, with its interactions between Kondo, RKKY, and coherent order. We present our study[1] of the antiferromagnetic quantum phase transitions of a 2D Kondo-Heisenberg square lattice. Starting from the nonlinear sigma model as a model of antiferromagnetism, we carry out a renormalization group analysis of the competing Kondo-RKKY interaction to one-loop order in an $\varepsilon $-expansion. We find a new quantum critical point (QCP) strongly affected by Kondo fluctuations. Near this QCP, there is a breakdown of hydrodynamic behavior, and the spin waves are logarithmically frozen out. The renormalization group results allow us to propose a new phase diagram near the antiferromagnetic fixed point of this 2D Kondo lattice model. The T=0 phase diagram contains four phases separated by a tetracritical point, the new QCP. For small spin fluctuations, we find a stable local magnetic moment antiferromagnet. For stronger coupling, region II is a metallic quantum disordered paramagnet. We find in region III a paramagnetic phase driven by Kondo interactions, with possible ground states of a heavy fermion liquid or a Kondo driven spin-liquid. The fourth phase is a spiral phase, or a large-Fermi-surface antiferromagnetic phase. We will describe these phases in more detail, including possible experimental confirmation of the spiral phase. The existence of the tetracritical point found here would be expected to affect the phase diagram at finite temperatures as well. In addition, It is hoped that these results, and particularly the Kondo interaction paramagnetic phase, will serve to bridge to solutions starting from the opposite limit, of a Kondo effect leading to a heavy fermion ground state. Work in collaboration with T. Tzen Ong. \\[4pt] [1] T. Ong and B. A. Jones, Phys. Rev. Lett. \textbf{103}, 066405 (2009). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700