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TT: Tiefe Temperaturen

TT 4: Schwere Fermionen, Kondo-Systeme

TT 4.3: Talk

Monday, March 24, 2003, 15:15–15:30, HSZ03

Universally diverging Grüneisen ratio and magnetocaloric effect close to quantum critical points — •Markus Garst¹, Lijun Zhu², Qimiao Si², and Achim Rosch¹ — ¹Institut für Theorie der Kondensierten Materie, Universität Karlsruhe, 76128 Karlsruhe — ²Department of Physics & Astronomy, Rice University, Houston, TX 77005 1892, USA

We show that close to a generic quantum critical point the thermal expansion α is much more singular than the specific heat c_p. Consequently, the Grüneisen ratio Γ = α/c_p diverges. With the help of a scaling analysis we find that for T → 0 the Grüneisen ratio behaves universally like Γ = − G_r/V_m (p−p_c) where V_m is the molar volume and G_r is a simple combination of critical exponents. At the critical pressure p=p_c it diverges like Γ ∼ T^{1/(ν z)} with a non-universal prefactor. Furthermore, we have determined the leading contribution to α and c_p and discuss corrections to scaling. In case of a magnetic-field driven quantum critical point the magnetocaloric effect plays the role of the Grüneisen ratio. The quantity Γ_H = −1/T ∂ T/∂ H |_S diverges universally upon approaching the quantum critical point for T → 0 as Γ_H = − G_r/H−H_c. Due to their singular behaviour the Grüneisen parameter and the magnetocaloric effect are very sensitive tools to investigate quantum criticality.