  Quantum critical behavior has been associated with some of the most exotic
emergent states of matter including high-temperature superconductivity. Much of
the research into quantum critical point (QCP) physics has been hampered by the
lack of model systems simple enough to be analyzed by theory. Here, we show
that the concentrated solid solution fcc alloys, including the so-called
high-entropy alloys, are ideal model systems to study the effects of chemical
disorder on emergent properties near a quantum critical region. The face
centered cubic (fcc) alloy NiCoCrx with x near 1 is found to be close to the Cr
concentration where the ferromagnetic transition temperature, Tc, goes to 0.
Near this composition these alloys exhibit a resistivity linear in temperature
to 2 K, a linear magnetoresistance, an excess -TlnT contribution to the low
temperature heat capacity and excess low temperature entropy. All of the low
temperature electrical, magnetic and thermodynamic properties of the alloys
with compositions near x near 1 are not typical of a Fermi liquid and suggest
strong magnetic fluctuations associated with a quantum critical region. The
limit of extreme chemical disorder in these simple fcc materials thus provides
a novel and unique platform to study quantum critical behavior in a highly
tunable system.
