Regensburg 2019 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 17: Poster Session: Correlated Electrons 1

TT 17.2: Poster

Monday, April 1, 2019, 15:00–18:30, Poster D

Thermopower evolution in Yb(Rh_1−xCo_x)₂Si₂ upon 4f localization — •Ulrike Stockert¹, Christoph Klingner¹, Cornelius Krellner², Veljko Zlatić³, Christoph Geibel¹, and Frank Steglich^1,4,5 — ¹MPI for Chemical Physics of Solids, Dresden — ²Physikalisches Institut, Goethe-Universität, Frankfurt/Main — ³Department of Physics, University of Split, Croatia — ⁴Center for Correlated Matter, Zhejiang University, Hangzhou, China — ⁵Institute of Physics, Chinese Academy of Science, Beijing, China

YbRh₂Si₂ is a heavy-fermion system, which exhibits a large negative thermopower S(T) with a single minimum around 80 K due to Kondo scattering from the full 4f multiplet. Substitution of Rh by Co leads to a strong reduction of the exchange coupling between the 4f and the conduction electron states and to a lowering of the Kondo scale T_K. This drives the system to a stable trivalent state in YbCo₂Si₂.

We performed thermopower measurements on Yb(Rh_1−xCo_x)₂Si₂ to study the evolution of S(T) upon 4f localization. As T_K decreases with increasing x we observe the appearance of a second minimum that shifts subsequently to lower T. Simultaneously, the absolute thermopower values are strongly reduced due to the weaker exchange coupling between the 4f and the conduction electron states. Pure YbCo₂Si₂ still exhibits two minima in S(T) indicative of weak residual Kondo scattering. The value at the high-T minimum is found to be proportional to the Sommerfeld coefficient for the whole series. We discuss this unexpected finding in relation to recent measurements of the valence and Fermi surface evolution with temperature.