YbPtGe2: A multivalent charge-ordered system with an unusual spin pseudogap

Abstract

We performed a study of the structural and physical properties of YbPtGe 2 . This compound is a multivalent charge-ordered system presenting an unusual spin pseudogap below 200 K. The crystal structure of YbPtGe 2 is refined from single-crystal and powder high-resolution synchrotron x-ray diffraction data at different temperatures. Analysis of the structural features of YbPtGe 2 , together with a combined study of Yb L III x-ray absorption spectroscopy, magnetic susceptibility χ (T ), thermopower S(T ), and 171 Yb and 195 Pt NMR indicate half of the Yb atoms to be in an intermediate valence state with an electronic configuration close to 4f 13 (Yb 3+ ), while for the remaining Yb atoms the 4f 14 (Yb 2+ ) configuration with almost no valence fluctuations is most likely. A drastic drop of the magnetic susceptibility and a decrease of the isotropic shift 195 K iso (T ) with decreasing temperature in the temperature range of 50-200 K evidence the opening of a spin pseudogap with an activation energy of /k B ∼ 200 K. Surprisingly, transport properties do not show clear evidence for the opening of a charge gap, thus excluding a standard Kondo-insulator scenario. Possible origins for this unusual electronic (valence) behavior are discussed.

Intermediate valence to heavy fermion through a quantum phase transition inYb3(Rh1−xTx)Binod1, Oswald2, Chan3 et al. 2016Phys. Rev. B231170View full textAdd to dashboardCite

“…5) ranges from 35 to 55 mJ/mol Y b K 2 , consistent with other intermediate valence compounds. 39,41,42 On the other hand, the Ir-doped series shows large electron mass renormalization (Fig. 6), with γ > 1.2 J/mol K 2 for x = 0.50.…”

Unconventional magnetism in multivalent charge-ordered YbPtGe2probed by195Pt- and171Yb-NMR

“…18 Because of two inequivalent crystallographic sites of Yb with different electronic configurations, YbPtGe 2 is considered as a multivalent charge-ordered system. Moreover, a huge drop of the magnetic susceptibility (χ ) in the temperature range of 50-200 K could not be explained by the simple valence fluctuations model.…”

“…Moreover, a huge drop of the magnetic susceptibility (χ ) in the temperature range of 50-200 K could not be explained by the simple valence fluctuations model. 18 Such a drop in χ is reminiscent of correlated semiconductors and/or semimetals such as YbB 12 , 5 Ce 3 Bi 4 Pt 3 , 19 FeSi, 2 U 2 Ru 2 Sn, 11 and CeFe 2 Al 10 . 13 However, unlike the other Kondo semiconductors, we have not found any clear sign of a charge gap in the electrical resistivity of YbPtGe 2 .…”

“…Therefore NMR has been extensively and successfully applied to understand the microscopic magnetic properties of correlated semimetal and/or pseudogapped systems. While we have reported the 195 Pt NMR shift data incorporated with the bulk susceptibility data briefly, 18 we present here a more detailed and extended NMR study on YbPtGe 2 . YbPtGe 2 powder samples were prepared according to Ref.…”

“…YbPtGe 2 powder samples were prepared according to Ref. 18. The powder was mixed with paraffin in a small quartz tube, subsequently heated up and shaken up, and then cured to randomize the grains.…”