Unveiling competing fluctuations at an unconventional quantum critical point
Lekhanath Poudel (University of Tennessee)
CeCu6-xAux is a well-known heavy fermion series that hosts an unconventional quantum critical point (QCP). Near the QCP, the dynamic susceptibility exhibits E/T-scaling with an anomalous fractional exponent α = 0.75. This observation is uncommon among Ce-based QCPs and inconsistent with an established approach provided by Hertz-Millis-Moriya (HMM). In the recent years, the debate as to correct the theoretical description has intensified as additional models of the quantum critical behavior have been proposed. Hence, further work to compare the competing theoretical descriptions with experiment is essential. To that end, we have studied closely related systems CeCu6-xTx (T=Ag, Pd). We find that CeCu6-xTx (T = Ag, Pd) are magnetically similar to the CeCu6-xAux despite that the evolution of structural properties is different in these series. Our inelastic neutron scattering spectroscopy (INS) measurement of QCP composition CeCu5.8Ag0.2 shows diffuse patterns of magnetic scattering in both (H0L) and (HK0) scattering planes. The dynamic susceptibility at different temperatures, energy transfers and wave-vectors in the (H0L) scattering plane fits well with a single phenomenological equation that yields E/T scaling with an almost identical anomalous scaling exponent α = 0.72(1). Our analysis also reveals that the diffuse pattern in (H0L) scattering plane comprises at least two distinct antiferromagnetic correlations that compete at the QCP, only one of which is expected to go critical. While the observation of E/T scaling suggests anomalous critical behavior similar to CeCu6-xAux, the critical part of the dynamic susceptibility is more consistent with the framework of the HMM model.
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