Experimental consequences at high temperatures of quantum critical points

We study the Cr_(1-x) Re_x phase diagram finding that its phase transition temperature towards an antiferromagnetic order T_N follows a quantum [(x_c-x)/x_c ]^ψ law, with ψ=1/2, from the quantum critical point (QCP) at x_c=0.25 up to T_N=600K. We compare this system to others in order to understand why this elemental material is affected by the QCP up to such unusually high temperatures. We determine a general criterion for the crossover, as function of an external parameter such as concentration, from the region controlled solely by thermal fluctuations to that where quantum effects become observable. The properties of materials with low coherence lengths will thus be altered far away from the QCP.

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