Quantum Criticality of the Quasi-One-Dimensional Heavy Fermion Material YbFe5P3

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. A central, unresolved issue is the role of quantum fluctuation dimensionality on the properties of the system. Most work to date has focused on quantum criticality with two-dimensional (2-D) and three-dimensional (3-D) fluctuations. Strong quantum fluctuations are expected in quasi-1-D materials. Furthermore, these 1-D systems may be treated exactly by theoretical tools such as Density Matrix Renormalization Group, providing robust and accurate methods for accounting for the strong correlations 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 A, while the inter-chain Yb-Yb spacing is 5.61 A. Below about 5 K, the electrical resistivity reflects the presence of strong quantum fluctuations. Specific heat measurements show a similar strong enhancement at low temperatures reaching a constant value of C/T=1.5 J/mol-K2 below T = 0.5 K, indicating a heavy Fermi liquid state. No magnetic ordering is observed down to 80 mK. Magnetic fields up to 8 T rapidly suppress the magnetic fluctuations, while resistivity measurements under pressure up to 2.5 GPa indicate the enhancement of quantum fluctuations, although still no order is observed down to 0.3 K. Density functional theory calculations suggest the presence of quasi-1D Fermi surface sheets together with 3-D electronic pockets. Chemical substation of Co or Ru for Fe drives YbFe5P3 to a quantum critical point. A magnetically ordered state is found for Co concentrations greater than 20%, beyond the quantum critical point. In this talk, I will describe the physical properties of the quasi-1D heavy fermion material YbFe5P3 and the nature of quantum criticality in Yb(Fe1-xMx)5P3 (M=Co, Ru).