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Non-Fermi liquid states in the pressurized $CeCu_2(Si_{1-x}Ge_x)_2$ system: two critical points

H. Q. Yuan·F. M. Grosche·M. Deppe·G. Sparn·C. Geibel·F. Steglich
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Abstract

In the archetypal strongly correlated electron superconductor CeCu$_2$Si$_2$ and its Ge-substituted alloys CeCu$_2$(Si$_{1-x}$Ge$_{x}$)$_2$ two quantum phase transitions -- one magnetic and one of so far unknown origin -- can be crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated anomalous normal state by detailed measurements of the low temperature resistivity ($ρ$) power law exponent $α$. At the lower critical point (at $p_{c1}$, $1\leqα\leq 1.5$) $α$ depends strongly on Ge concentration $x$ and thereby on disorder level, consistent with a Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic fluctuations. By contrast, $α$ is independent of $x$ at the upper quantum phase transition (at $p_{c2}$, $α\simeq 1$), suggesting critical scattering from local or Q=0 modes, in agreement with a density/valence fluctuation approach.

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H. Q. Yuan, F. M. Grosche, M. Deppe, G. Sparn, C. Geibel, F. Steglich. 2005-10-12. Non-Fermi liquid states in the pressurized $CeCu_2(Si_{1-x}Ge_x)_2$ system: two critical points. https://doi.org/10.1103/physrevlett.96.047008

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