Kondo effect and quantum criticality in Ce-based pnictides

The pnictides have not only triggered enthusiasm in searches for high-$T_{c}$ superconductors, but also paved a new way for investigating the Kondo effect and quantum criticality. In this talk, I will start with the phase diagram of CeFeAs$_{\mathrm{1-x}}$P$_{x}$O which hosts two possible quantum critical points (QCPs) [1]. Due to the entanglement of 3$d$ and 4f magnetism, CeFeAsO is not a good candidate for investigating quantum criticality, therefore we turned to CeNiAsO. The Ce-sublattice shows two successive AFM transitions at $T_{N1}=$9.3 K and $T_{N2}=$7.3 K, while the Ni-sublattice is nonmagnetic [2]. Under pressure, both AFM transitions are suppressed, and a QCP is obtained at $p_{c}=$6.5 kbar. Similar phenomenon was also observed by P/As-substitution, which leads to a critical doping at $x_{c}=$0.4. The quantum fluctuations near these QCPs are discussed, and the possibility of a Kondo-destruction type QCP is addressed [3]. Finally, I will briefly talk about the pressure effect on the 122 cousin, CeNi$_{2}$As$_{2}$ [4], which seems to provide a rare paradigm of quantum criticality in the low carrier density limit. \\[4pt] In collaboration with: Z. Xu, J. Dai, G. Cao, L. Pourovskii, Q. Si, N. P. Ong, and J. D. Thompson \textit{et al.} \\[4pt] [1] Y. Luo \textit{et al.}, Phys. Rev. B \textbf{81,} 134422 (2010).\\[0pt] [2] Y. Luo \textit{et al.}, J. Phys.: Condens. Matter \textbf{23}, 175701 (2011).\\[0pt] [3] Y. Luo \textit{et al.}, Nature Materials \textbf{13}, 777 (2014).\\[0pt] [4] Y. Luo \textit{et al.}, Phys. Rev. B \textbf{86}, 245130 (2012).