Quantum criticality has been an organizing principle to explain the behavior of many families of quantum materials including the high-temperature cuprate and iron-based superconductors and f-electron heavy fermion compounds.  Most work to date has focused on quantum criticality with two-dimensional (2-D) and 3-D fluctuations.  Strong quantum fluctuations are expected in quasi-1-D materials and have recently been explored in 1-D f-electron materials such as CeRh₆Ge₄ [1], Yb₂Pt₂Pb [2], and YbAlO₃ [3].

YbFe₅P₃ crystallizes in the orthorhombic YCo₅P₃ structure type [4] with 1-D Yb chains along the b-axis with an Yb-Yb distance of 3.65 Å, while the inter-chain Yb-Yb spacing is 5.61 Å. Specific heat measurements show a strong enhancement at low temperatures reaching a constant value of C/T=1.5 J/mol K² below T = 0.5 K, indicating Fermi liquid behavior. Chemical substitution of Co for Fe drives YbFe₅P₃ to a quantum critical point (QCP). For x_Co = 0.08, the specific heat diverges as C/T~ -log(T), indicating close proximity to a QCP.  Magnetic order is found for x_Co  > 0.2.  Neutron diffraction measurements for x_Co = 0.4 are consistent with antiferromagnetic order with a wavevector k = (0,0,0), in either a canted or alternating arrangement of Yb moments.  In this talk, I will describe the physical properties and nature of quantum criticality in Yb(Fe_1-xCo_x)₅P₃.

[1] B. Shen et al. Nature 579, 51 (2020); [2] L. S. Wu et al. Science 352, 1206 (2016); [3] L. S. Wu et al. Nature Comm. 10, 698 (2019); [4] W. Jeitschko et al. J. Solid State Chem. 55, 331 (1984)