Infrared study of valence transition compound YbInCu4 using cleaved surfaces

TL;DR

This study uses infrared reflectivity measurements on cleaved and polished YbInCu4 surfaces to reveal that the valence transition causes a sudden electronic structure change, with surface preparation affecting observed transition behavior.

Contribution

It demonstrates that cleaved surfaces reveal a sharp valence transition, unlike polished surfaces, highlighting the importance of surface quality in infrared spectroscopy of YbInCu4.

Findings

Cleaved surfaces show a rapid change in reflectivity at T_v

Polished surfaces exhibit gradual changes due to disorder

Electronic structure undergoes a sudden change at valence transition

Abstract

Optical reflectivity R(w) of YbInCu4 single crystals has been measured across its first-order valence transition at T_v ~ 42 K, using both polished and cleaved surfaces. R(w) measured on cleaved surfaces Rc(w) was found much lower than that on polished surface Rp(w) over the entire infrared region. Upon cooling through T_v, Rc(w) showed a rapid change over a temperature range of less than 2 K, and showed only minor changes with further cooling. In contrast, Rp(w) showed much more gradual and continuous changes across T_v, similarly to previously reported data on polished surfaces. The present result on cleaved surfaces demonstrates that the microscopic electronic structures of YbInCu4 observed with infrared spectroscopy indeed undergo a sudden change upon the valence transition. The gradual temperature-evolution of Rp(w) is most likely due to the compositional and/or Yb-In site disorders caused by polishing.