Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 25: Correlated Electrons - Poster Session
TT 25.54: Poster
Mittwoch, 29. März 2006, 14:30–18:30, P1
Systematic Study of the Grüneisen-ratio near Quantum Critical Points — •Robert Küchler1, Philipp Gegenwart1, Niels Oeschler1, Christoph Geibel1, Frank Steglich1, Karsten Heuser2, and Ernst-Wilhelm Scheidt2 — 1Max-Planck Institut for Chemical Physics of Solids, D-01187 Dresden, Germany — 2Chemische Physik und Materialwissenschaften, Universität Augsburg, 86159 Augsburg, Germany
Recent theoretical work has shown that the Grüneisen ratio Γ ∝ β / C of thermal expansion , β(T), to specific heat, C(T), is a highly sensitive probe of quantum criticality. This is because Γ is divergent as T goes to zero at any quantum critical point (QCP) and the associated critical exponent can be used to distinguish between different types of QCPs. We report thermal expansion and Grüneisen ratio measurements in the temperature range 50 mK ≤ T ≤ 6 K on different Heavy-fermion systems close to magnetic QCPs. Our studies revealed the first-ever observation of a Grüneisen ratio divergence in four heavy fermion systems, which are located in the vicinity of antiferromagnetic QCPs. For CeNi2Ge2 and CexIn3−xSnx, Γ ∝ 1/T in accordance with the SDW scenario for three-dimensional critical spinfluctuations. By contrast, the observed singularity of Γ for YbRh2(Si0.95Ge0.05)2 cannot be explained by the SDW theory, but is consistent with not yet published theoretical results of the locally scenario. Furthermore, the system CeCu5.8Ag0.2 has been studied, which shows a similar temperature dependence as found in YbRh2(Si0.95Ge0.05)2 on a reduced temperature scale T/T0, with T0 ≈ TK, the Kondo temperature.