ω/T scaling and magnetic quantum criticality in BaFe2(As0.7P0.3)2

Abstract

We used transport and inelastic neutron scattering to study the optimally phosphorus-doped BaFe${}_2$(As${}_{0.7}$P${}_{0.3}$)${}_2$ superconductor ($T_c=30$ K). In the normal state, we find that the previously reported linear temperature dependence of the resistivity below room temperature extends to $\sim$ 500 K. Our analysis of the temperature and energy ($E=\hslash \omega$) dependence of spin dynamical susceptibility at the antiferromagnetic (AF) ordering wave vector ${\chi }^{\prime \prime }({\mathbf{Q}}_{\mathrm{AF}},\omega )$ reveal an $\omega /T$ scaling within $1.1<E/k_{B}T<110$. These results suggest that the linear temperature dependence of the resistivity is due to the presence of a magnetic quantum critical point in the cleanest iron pnictides near optimal superconductivity. Moreover, the results reconcile the strange-metal temperature dependences with the weakly first-order nature of the quantum transition out of the AF and nematic orders.

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