Exploring the quantum critical point
Researchers using the HP-CAT 16-ID-B beamline at the APS are investigating the effects of the QCP on the crystal structure of the Yb valence of YbFe2Ge2. The quantum critical point (QCP) is a strong quantum fluctuation that gives rise to unusual, or non-Fermi, liquid temperature dependencies of physical properties. To explore the origin of QCP, the interplay between crystal structure and valence as a function of pressure is important.
High-pressure resonant x-ray emission spectroscopy and x-ray diffraction experiments on YbFe2Ge2 show a pressure-induced valence change under compression. Yb valence becomes nearly trivalent at ∼9 GPa.
The crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. The measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ∼9 GPa, where at low temperature a pressure-induced quantum critical state was reported.
Ravhi S. Kumar, Axel Svane, Ganapathy Vaitheeswaran, Venkatakrishnan Kanchana, Daniel Antonio, Andrew L. Cornelius, Eric D. Bauer, Yuming Xiao and Paul Chow, “Effect of Pressure on Valence and Structural Properties of YbFe2Ge2 Heavy Fermion Compound—A Combined Inelastic X-ray Spectroscopy, X-ray Diffraction, and Theoretical Investigation,” Inorganic Chemistry, Article ASAP, DOI: 10.1021/acs.inorgchem.5b01534, Published Online October 19, 2015.