Pressure influence on the valence and magnetic state of Yb ions in noncentrosymmetric heavy-fermion YbNiC2

Abstract

We present studies of neutron diffraction, electrical resistivity, magnetic susceptibility, magnetization, and specific heat of noncentrosymmetric YbNiC 2 . At normal pressure, YbNiC 2 is a moderate heavy-fermion compound with Kondo lattice. At 16 K we observe an anomaly in the temperature dependence of specific heat which is ascribed to an abrupt valence change of Yb ions. At pressures above 7 GPa, the valence change and the Kondo lattice state are suppressed, and near a temperature of 10 K we detect the appearance of magnetic order. Above 5 GPa, the temperature dependence of the resistivity behaves similarly to other compounds of the CeNiC 2 -type family, indicating the formation of charge density waves. This is attributed to the nesting properties of the Fermi surface (FS) found within the density functional theory + dynamical mean field theory treatment. Our ab initio calculations also show that the valence of Yb in YbNiC 2 at normal conditions is 2.85, which increases with temperature and pressure. The FS of YbNiC 2 is anisotropic in shape in comparison with the 3D surface of YbCoC 2 .

Pressure Evolution of the Magnetism and Fermi Surface of YbPtBi Probed by a Tunnel Diode Oscillator Based Method

“…[8] These result are in line with those typically found for Yb-based heavy fermion compounds under pressure, since pressure enhances the strength of the RKKY interaction relative to the Kondo effect, enhancing magnetic order and leading to more localized 4𝑓 electrons. [28][29][30][31] In the high field region, distinct quantum oscillations are observed. Figure 3(a) displays the quantum oscillations between 10 and 15 T at different pressures at 0.35 K, where a background polynomial term has been subtracted.…”