Scaling of Magnetic Fluctuations near a Quantum Phase Transition

Abstract

We use inelastic neutron scattering to measure the magnetic fluctuations in a single crystal of the heavy fermion alloy ${\mathrm{CeCu}}_{5.9}{\mathrm{Au}}_{0.1}$ close to the antiferromagnetic quantum critical point. The energy ( $E$), wave vector ( $Q$), and temperature ( $T$) dependent spectra obey $E/T$ scaling at $Q$ near (1,0,0). The neutron data and earlier bulk susceptibility are consistent with the form ${\chi }^{-1\mathrm{}}\sim f\left(Q\right)+(-iE+aT{)}^{\alpha }$, with an anomalous exponent $\alpha \approx 0.8\ne 1$. We confirm the earlier observation of quasilow dimensionality and show how both the magnetic fluctuations and the thermodynamics can be understood in terms of a quantum Lifshitz point.