Quantum criticality in the (Cr98.4Al1.6)100-yMoy alloy system

Abstract

Indications of quantum critical behaviour (QCB), driven by electron-hole pair breaking effects through Mo doping of Cr98.4Al1.6 are reported. Previous studies on the electrical resistivity (ρ), Seebeck coefficient (S), Sommerfeld electronic specific heat coefficient (γ) and magnetic susceptibility (χ) as a function of temperature on the (Cr98.4Al1.6)100-yMoy alloy system point towards the existence of a quantum critical point (QCP) at yc ≈ 4.5. In the present study the Hall coefficient RH measurements and an analysis of the previous results are used to substantiate the presence of a QCP in the alloy system. The charge carrier density at 2 K, (qRH(2K))−1, of the alloy systems increases continuously with y from the antiferromagnetic (AFM) phase through yc ≈ 4.5 and into the paramagnetic (P) phase. Scaling relationships between the magnetic contribution to the electrical resistivity, Δρ2K, the magnetic contribution to the Sommerfeld electronic specific heat coefficient, Δγ, and (qRH(2K))−1, are furthermore used to support the presence of a QCP in the alloy system. dS/dT in the temperature limit T→ 2 K depicts an anomalous behaviour in the form of an upturn on decreasing y through the QCP, yc ≈ 4.5. The critical exponents in the vicinity of the QCP were found to be β = 0.5 ± 0.1 for the Δρ2K/ρ2K(y) curve and γ = 0.4 ± 0.1 for the TN(y) curve. The nature of the QCP in the present alloy system is classified as an incommensurate (I) spin-density-wave (SDW) type, driven mainly by electron-hole pair breaking effects.