Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A2: Quantum Criticality of Strongly Correlated Metals |
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Sponsoring Units: DCMP Chair: Brian Maple, University of California-San Diego Room: LACC 151 |
Monday, March 21, 2005 8:00AM - 8:36AM |
A2.00001: Hall effect indicates destruction of large Fermi surface at a heavy-fermion quantum critical point Invited Speaker: Quantum critical points (QCPs) -– phase transitions at absolute zero in temperature -- are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet [1]. An important unsolved question concerns whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin density wave type [2], or suddenly as expected if the heavy electrons are abruptly localized by magnetism [3]. Here we report measurements of the low-temperature Hall coefficient ($R_H$) -- a measure of the Fermi surface volume -- in the heavy-fermion metal YbRh$_2$Si$_2$ upon field-tuning it from an antiferromagnetic to a paramagnetic state. $R_H$ undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP [4].\\[0.2cm] [1] R.~M.~Martin, {\em {Phys.\ Rev.\ Lett.}}{ \bf 48}, {362-- 365} (1982); P. ~Fulde, {in \em {Narrow-Band Phenomena -- Influence of Electrons with both Band and Localized Character}} (ed.\ Fuggle, J.~C.) 27--29 (Plenum Press, New York, 1988); M.~Oshikawa, {\em {Phys.\ Rev.\ Lett.}}{ \bf 84}, 3370--3373 (2000).\\[0.2cm] [2] J.~A.~Hertz, {\em {Phys.\ Rev.\ B}}{ \bf 14}, 1165--1184 (1976); A.~J.~Millis, {\em {Phys.\ Rev.\ B}}{ \bf 48}, 7183-- 7196 (1993).\\[0.2cm] [3] A.~Schr\"{o}der \emph{et~al.}, {\em {Nature}}{ \bf 407}, 351- -355 (2000); P.~Coleman \emph{et~al.}, {\em {J.\ Phys.: Condens.\ Matter}}{ \bf 13}, R723--R738 (2001); Q.~Si \emph{et~al.}, {\em Nature}{ \bf 413}, 804--808 (2001).\\[0.2cm] [4] S.~Paschen \emph{et~al.}, to appear in {\em Nature}.\\[0.2cm] In collaboration with: T.~L{\"u}hmann, S.~Wirth, P.~Gegenwart, O.~Trovarelli, C.~Geibel, F.~Steglich, P.~Coleman, and Q.~Si. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 9:12AM |
A2.00002: Emergent fluctuation hot spots on the Fermi surface of CeIn$_{3}$ in strong magnetic fields Invited Speaker: de Haas-van Alphen measurements on CeIn$_{3}$ in pulsed magnetic fields of up to 65 T reveal an increase in the quasiparticle effective mass with field concentrated at ``hot spots'' on the Fermi surface as the Neel phase is suppressed. As well as revealing the existence of fluctuations deep within the antiferromagnetic phase, these data suggest that a possible new type of quantum critical point may exist in strong magnetic fields that involves only parts of the Fermi surface. Recent specific heat and Hall effect data obtained at high magnetic fields will be discussed in this context. Work done in collaboration with A. Silhanek, N. Harrison, and T. Ebihara. [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:48AM |
A2.00003: Thermodynamic signature of quantum criticality: universally diverging Gr\"uneisen ratio Invited Speaker: At a generic quantum critical point where pressure acts as (or couples to) the zero-temperature control parameter, the Gr\"uneisen ratio $\Gamma$ (the ratio of thermal expansion to specific heat) is {\it divergent}[1]. This property provides a novel probe to quantum criticality from thermodynamics. When scaling applies, $\Gamma \sim 1/T^x$ at the critical pressure $p=p_c$, where the exponent $x$ measures the scaling dimension of the most singular operator coupled to pressure; in the alternative limit $T \to 0$ and $p \neq p_c$, $\Gamma = G_r/(p-p_c)$, where $G_r$ is a universal combination of critical exponents. The predicted divergence has been observed near the quantum critical points of several heavy fermion metals[2]. Analyses based on specific models relevant to these experiments are also presented. [1] L. Zhu, M. Garst, A. Rosch, and Q. Si, Phys. Rev. Lett. {\bf 91}, 066404 (2003). [2] R. K\"uchler {\it et al.}, Phys. Rev. Lett. {\bf 91}, 066405 (2003); {\it ibid.} {\bf 93}, 096402 (2004). [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:24AM |
A2.00004: Thermoelectricity as a probe of non-Fermi liquid physics Invited Speaker: Recently, the breakdown of the Fermi liquid picture in the vicinity of a Quantum Critical Point has become a subject of special attention. In this context, I will report on recent studies of thermoelectric coefficients in a number of heavy-fermion systems. In CeCoIn$_{5}$, when the system presents a strong departure from the standard Fermi-liquid behavior, a giant Nernst effect and an unusually reduced Seebeck coefficient emerge. The anomalous thermoelectricity disappears with the restoration of the Fermi liquid by the application of a magnetic field. Another example of anomalous thermoelectricity is provided by the hidden-order state of URu$_{2}$Si$_{2}$ which is host to a Nernst coefficient of unprecedented magnitude. Yet another remarkable case is the behavior of CeRu$_{2}$Si$_{2}$ close to the meta-magnetic transition. I will discuss the information extracted by probing the thermoelectric response of the system in each case. [Preview Abstract] |
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