Magnetic field-tuned quantum critical point in CeAuSb$_2$

Here we report on the anomalous metallic properties of CeAuSb$_ {2}$. At $H$ = 0, CeAuSb$_{2}$ displays AF ordering at $T_{N}$ = 6.0 K. Above $T_{N}$, the resistivity \textit{$\rho $} displays a $T^{\alpha }$ dependence with $\alpha \quad <$ 1 and $C_{e}$/$T$ has the -\textit{lnT} dependence characteristic of NFL behavior. For $T \quad <$ $T_{N}$, $\rho $ has the \textit{AT}$^{2}$ FL-like dependence and the extrapolation of $C_{e}$/$T$ to $T$ = 0 yields a Sommerfeld coefficient of $\gamma \quad \sim $ 0.1 J/mol.K$^{2}$, so that CeAuSb$_{2}$ is to be considered a heavy- Fermion system. A magnetic field along the inter-plane direction leads to two subsequent metamagnetic transitions and the concomitant \textit {continuous} suppression of $T_{N}$ to $T$ = 0 at $H_{C}$ = 5.3 $\pm $ 0.2 T. As the AF phase boundary is approached from the paramagnetic (PM) phase, $\gamma $ is enhanced and the $A$ coefficient of the resistivity diverges as $H-H_{C}^{-1}$. As $T$ is lowered for $H \quad \sim \quad H_{C}$, the $T$-dependence of \textit {$\rho $} and $C_{e}$/$T$ is sub-linear and -\textit{ln} $T$, respectively. These observations suggest the existence of a field-induced QCP at $H_{C}$. At higher fields an unconventional $T^{3}$- dependence emerges and becomes more prominent as $H$ increases, suggesting that the FL state is \textit{not} recovered for $H \quad >> \quad H_{C}$.