Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 22: Correlated Electrons: Quantum-Critical Phenomena 2
TT 22.2: Vortrag
Mittwoch, 25. März 2009, 10:00–10:15, HSZ 03
Low-temperature thermal expansion of Nb1−yFe2+y — •Stefan Lausberg1, Manuel Brando1, Rafik Ballou2, F Malte Grosche3, and Frank Steglich1 — 1Max-Planck-Institut für Chemische Physik fester Stoffe Nöthnitzer Str. 40, 01187 Dresden, Germany — 2Laboratoire Louis Néel, CNRS, B.P. 166, 38042 Grenoble Cedex 9, France — 3Cavendish Laboratory, Cambridge CB30HE, United Kingdom
The hexagonal C14 Laves phase system Nb1−yFe2+y exhibits a magnetically ordered ground state, the nature of which strongly depends on the concentration y. Stoichiometric NbFe2 shows low-temperature (TN=10 K) spin-density-wave (SDW) order, while slight Fe-excess induces low-moment ferromagnetism (FM). A quantum critical point (QCP) is expected on the Nb-rich side at y∼ −0.015, where signatures of logarithmic Fermi-liquid breakdown have been reported [1]. The presence of a QCP can be thermodynamically tested by measuring the thermal expansion coefficient α(T): In metals close to a QCP, a divergence of the Grüneisen ratio Γ = α / cp has been proposed, since α is more singular than cp, while in metals with a Fermi-liquid ground state, α / T and cp/T are constant. We report measurements of α for different single crystals with y close to the QCP. Surprisingly, we find an extremely large α coefficient, similar to that of heavy-fermion materials [2], and it increases with decreasing temperature. The behavior of the resulting Γ parameter will be discussed.
[1] M. Brando et al., PRL 101, 026401 (2008).
[2] R. Küchler et al., Physica B 378-380, 36 (2006).