Soft-x-ray high-resolution photoemission study on the valence transitions inYbInCu4

Abstract

Valence-band electronic structure of YbInCu 4 has been investigated by means of high-resolution photoemission spectroscopy with an excitation energy of hϭ800 eV. With decreasing temperature from 50 to 40 K, the intensity of the Yb 2ϩ 4 f peak increases remarkably, while that of the Yb 3ϩ 4 f multiplet structures decreases due to the valence transition at 42 K. The Yb valence directly derived from the photoemission spectra is z ϳ2.81 at 100 K, decreases continuously to 50 K and changes sharply to zϳ2.68 at 40 K. The larger valence compared with the other photoemission experiments with smaller probing depth suggests that there is a subsurface region in YbInCu 4 . We have also found that the Yb 3ϩ 4 f multiplet structures shift toward the deeper binding-energy side by ϳ50 meV with decreasing temperature from 50 to 40 K. This energy shift is assumed to reflect that the energy to add the bare Yb 4 f hole increases for the low-temperature region in accordance with the valence transition.

Yb 4f states of YbXCu4 (X=Cd, Mg, Zn and Sn) investigated by high-resolution soft X-ray photoemission spectroscopy

“…In addition, the Yb 3+ 4f structures slightly shift toward deeper binding-energy side with decreasing temperature. These temperature dependences of the Yb 2+ and Yb 3+ 4f spectra are observed in the higher temperature phase of YbInCu 4 [5], suggesting that the electronic structure of YbCdCu 4 is close to that of YbInCu 4 .…”

“…1 shows the SX-PES spectrum of YbCdCu 4 measured at 20 K with hν = 800 eV. The basic feature of the spectrum is similar to that of YbInCu 4 [5]. The spectrum almost reflects the Yb 4f states except for the Cu 3d states at 2.5-5 eV and the Cd 4d states at 10-12 eV taking into account the photoionization cross-sections of photoelectrons [10].…”

“…9. Recently, we have investigated the Yb 4f states of YbInCu 4 by means of high-resolution soft X-ray photoemission spectroscopy (SX-PES) with the excitation energy of hν = 800 eV and successfully observed the change of the Yb 4f states in accordance of the valence transition at T V : (i) the intensity of the Yb 2+ 4f peaks remarkably increases while that of the Yb 3+ 4f multiplet structures decreases from high to low temperature phases and (ii) the Yb 3+ 4f structures shift toward the deeper binding-energy side by ∼50 meV below T V [5]. * Corresponding author.…”

“…[5], are estimated to be ∼2.78 at 150 K and ∼2.75 at 20 K. Here, it should be noticed that with decreasing the Yb valence, the Yb 3+ 4f structures shift toward the deeper binding-energy side. This relation is clearly observed just at the valence transition of YbInCu 4 [5]. The energy position of the Yb 3+ 4f shallowest peak around 6 eV, furthermore, almost linearly depends on the Yb valence both for YbInCu 4 and YbCdCu 4 .…”

“…The energy position of the Yb 3+ 4f shallowest peak around 6 eV, furthermore, almost linearly depends on the Yb valence both for YbInCu 4 and YbCdCu 4 . This means that an amount of ε f + U [5] is closely related to the Yb valence, where ε f and U represent the energy to add the bare 4f hole and the Coulomb interaction energy between the 4f holes, respectively. Similar energy shift is also detected for the valence transition compound EuPd 2 Si 2 [11].…”