Nanoscale heterogeneity induced by nonmagnetic Zn dopants in the quantum critical metal CeCoIn 5 : In 115 NQR/NMR and Co 59 NMR study

Antiferromagnetism in a prototypical quantum critical metal ${\mathrm{CeCoIn}}_{5}$ is known to be induced by slight substitutions of nonmagnetic Zn atoms for In. In nominally 7% Zn-substituted ${\mathrm{CeCoIn}}_{5}$, an antiferromagnetic (AFM) state coexists with heavy fermion superconductivity. Heterogeneity of the electronic states is investigated in Zn-doped ${\mathrm{CeCoIn}}_{5}$ by means of nuclear quadrupole and magnetic resonances (NQR and NMR). Site-dependent NQR relaxation rates $1/{T}_{1}$ indicate that the AFM state is locally nucleated around Zn substituents in the matrix of a heavy fermion state, and percolates through the bulk at the AFM transition temperature ${T}_{\mathrm{N}}$. At lower temperatures, an anisotropic superconducting (SC) gap below the SC transition temperature ${T}_{\mathrm{c}}$, and the SC state permeates through the AFM regions via a SC proximity effect. Applying an external magnetic field induces a spin-flop transition near 5 T, reducing the volume of the AFM regions. Consequently, a short-ranged inhomogeneous AFM state survives and coexists with a paramagnetic Fermi liquid state at high fields.