Pressure versus magnetic-field tuning of a magnetic quantum phase transition

Abstract

Specific heat $C\left(T\right)\mathrm{}$ and electrical resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ of ${\mathrm{CeCu}}_{6\mathrm{-}x}{\mathrm{Au}}_x$ at very low temperatures T show distinctly different behavior depending on whether long-range antiferromagnetic order is suppressed by hydrostatic pressure p or an applied magnetic field B. p tuning yields $C/T=a\ln {(T}_0/T)$ and $\rho \approx {\rho }_0{+A}^{\prime }T,$ while B tuning shows $C/T={\gamma }_0-a^{\prime }{T}^{0.5}$ and $\rho \approx {\rho }_0{+A}^{″}{T}^{1.5}.$ This suggests that the spectrum of low-lying excitations that determines the behavior near these quantum phase transitions differs.