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

摘要

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 quantumphase transitions -- one magnetic and one of so far unknown origin -- can becrossed as a function of pressure \cite{Yuan 2003a}. We examine the associatedanomalous normal state by detailed measurements of the low temperatureresistivity ($\rho$) power law exponent $\alpha$. At the lower critical point(at $p_{c1}$, $1\leq\alpha\leq 1.5$) $\alpha$ depends strongly on Geconcentration $x$ and thereby on disorder level, consistent with aHlubina-Rice-Rosch scenario of critical scattering off antiferromagneticfluctuations. By contrast, $\alpha$ is independent of $x$ at the upper quantumphase transition (at $p_{c2}$, $\alpha\simeq 1$), suggesting criticalscattering from local or Q=0 modes, in agreement with a density/valencefluctuation approach.