Dehybridization of f and d states in the heavy-fermion system YbRh2Si2

Abstract

We report an optically induced reduction of the f-d hybridization in the prototypical heavyfermion compound YbRh2Si2. We use femtosecond time-and angle-resolved photoemission spectroscopy to monitor changes of spectral weight and binding energies of the Yb 4f and Rh 4d states before the lattice temperature increases after pumping. Overall, the f-d hybridization decreases smoothly with increasing electronic temperature up to ∼ 250 K but changes slope at ∼ 100 K. This temperature scale coincides with the onset of coherent Kondo scattering and with thermally populating the first excited crystal electrical field level. Extending previous photoemission studies, we observe a persistent f-d hybridization up to at least ∼ 250 K, which is far larger than the coherence temperature defined by transport but in agreement with the temperature dependence of the noninteger Yb valence. Our data underlines the distinction of probes accessing spin and charge degrees of freedom in strongly correlated systems characterized by spin-charge separation.

Strong spin-orbit coupling in the noncentrosymmetric Kondo lattice

“…We clearly see that the "neck" of the 4f -derived doughnut Fermi surface sheet mentioned above obviously becomes narrower with increasing temperature explicitly indicating the fundamental process of transition from a large to a small (holelike) Fermi surface in a Kondo lattice [58]. The issue of the transition from small to large FS is presently hotly discussed [63][64][65]. Most recent papers on this subject suggest that f -d hybridization persists at temperatures much higher than the Kondo temperature [64,65].…”

“…The issue of the transition from small to large FS is presently hotly discussed [63][64][65]. Most recent papers on this subject suggest that f -d hybridization persists at temperatures much higher than the Kondo temperature [64,65]. They suggest that the transition from the small to the large Fermi surface is a smooth process, however, it has not yet been experimentally established for YbT 2 Si 2 Kondo lattices.…”

Competing soft phonon modes at the charge-density-wave transitions in DyTe3

“…Regarding the high-temperature transition we discuss our results with respect to time-resolved pump-probe studies using reflectivity [36], resonant soft x-ray diffraction [37] and angle-resolved photoemission spectroscopy [38,39]. From the time dependence of the different experimental observations, the authors could deduce characteristic phonon frequencies of about 1.7-1.75 THz and 2.2-2.4 THz for (Tb/Dy)Te3 [36,38,39]. Results for CeTe3 [38] reveal larger frequencies of 2.2 THz and 2.7 THz as can be expected because of the higher CDW transition temperature [40].…”

“…From the time dependence of the different experimental observations, the authors could deduce characteristic phonon frequencies of about 1.7-1.75 THz and 2.2-2.4 THz for (Tb/Dy)Te3 [36,38,39]. Results for CeTe3 [38] reveal larger frequencies of 2.2 THz and 2.7 THz as can be expected because of the higher CDW transition temperature [40]. All of these measurements are sensitive to the amplitude mode in the ordered phase, i.e., below TCDW,1.…”

Thermopower Evolution in Yb( $$\hbox {Rh}_{1-x}\hbox {Co}_x$$ Rh 1 - x Co x

“…(2) The position of the maximum in S(T ) is almost independent of x, i.e., we compare thermopower values taken at practically constant T . (3) Recent ARPES experiments on YbRh 2 Si 2 revealed a temperature-independent Fermi surface up to about 100 K [30] and a significant hybridization between f and d states even up to at least 250 K [31]. In this sense, our thermopower minimum around 90 K is still lying in the low-T regime, and the charge carriers that participate in the transport at 90 K are related to those contributing to γ 0 taking into account thermal broadening.…”