We use transport and neutron scattering to study the electronic phase diagram and spin excitations of ${\mathrm{NaFe}}_{1-x}{\mathrm{Cu}}_x\mathrm{As}$ single crystals. Similar to Co- and Ni-doped NaFeAs, a bulk superconducting phase appears near $x\approx 2\%$ with the suppression of stripe-type magnetic order in NaFeAs. Upon further increasing Cu concentration the system becomes insulating, culminating in an antiferromagnetically ordered insulating phase near $x\approx 50\%$. Using transport measurements, we demonstrate that the resistivity in ${\mathrm{NaFe}}_{1-x}{\mathrm{Cu}}_x\mathrm{As}$ exhibits non-Fermi-liquid behavior near $x\approx 1.8\%$. Our inelastic neutron scattering experiments reveal a single neutron spin resonance mode exhibiting weak dispersion along $c$ axis in ${\mathrm{NaFe}}_{0.98}{\mathrm{Cu}}_{0.02}\mathrm{As}$. The resonance is high in energy relative to the superconducting transition temperature $T_{\mathrm{c}}$ but weak in intensity, likely resulting from impurity effects. These results are similar to other iron pnictides superconductors despite that the superconducting phase in ${\mathrm{NaFe}}_{1-x}{\mathrm{Cu}}_x\mathrm{As}$ is continuously connected to an antiferromagnetically ordered insulating phase near $x\approx 50\%$ with significant electronic correlations. Therefore, electron correlations is an important ingredient of superconductivity in ${\mathrm{NaFe}}_{1-x}{\mathrm{Cu}}_x\mathrm{As}$ and other iron pnictides.

• Received 16 November 2016
• Revised 8 January 2017

DOI:https://doi.org/10.1103/PhysRevB.95.054501