Collapse of the Gd3+ ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor CeFe

Abstract

Gd+ ESR spectra displays a fine structure with lorentzian line shape, typical of insulating media. The electronic gap is attributed to the large hybridization present in the coherent regime of a Kondo lattice, and MeanField calculations suggest that the electron-phonon interaction is fundamental at explaining such hybridization. The resulting electronic structure is strongly temperature dependent, and at * 160 T ≈ K the system undergoes an insulator-tometal transition induced by the withdrawal of 4f-electrons from the Fermi volume, the system becoming metallic and non-magnetic. The 3 Gd + ESR fine structure coalesces into a single dysonian resonance, as in metals. Still, our simulations suggest that exchange-narrowing via the usual Korringa mechanism, is not enough to describe the thermal behavior of the 3 Gd + ESR spectra in the entire temperature region (4.2 -300 K). We propose that temperature activated fluctuating-valence of the Ce ions is the key ingredient that fully describes this unique temperature dependence of the 3 Gd + ESR fine structure.

Hard x-ray spectroscopy of the itinerant magnets RFe4Sb12 (R=Na, K, Mounssef1, Cantarino2, Bittar3 et al. 2019Phys. Rev. B6090View full textAdd to dashboardCite

“…Indeed, the large pre-edge intensity (see Fig4(b)) observed for CaFe 4 Sb 12 connects the local disorder to local electronic properties, since the large local disorder would favor the on site Fe 3d-4p mixing, that is otherwise much too small due to symmetry constraints. This finding connects the unconventional vibrational dynamics of skutterudites to its electronic structure, that in some instances is known to affect their many body electronic structure [42].…”

Slow crystalline electric field fluctuations in the Kondo lattice SmB$_{6}$

“…It was shown that the lineshape evolves from a symmetric Lorentzian to an asymmetric Dysonian upon temperature increase. This behavior, together with an enhanced conductivity, is associated with a monotonic crossover from insulator-to-metal phases occurring within 6 K ≤ T ≤ 12 K and provides strong evidence for the local closure of the hybridization gap caused in part by the electron-phonon (rattling) interactions [33] The linewidth behavior according to Eq. ( 6), and showed in Figure 4(a), describes reasonably well the Gd 3+ ESR linewidth in the low-T and high-T regimes.…”

“…In order to study the T -evolution of the ESR fine structure in a mixed valence insulator, one should also consider the T -dependent relaxation process due to the valence fluctuation (VF) between the 4f n and 4f n+1 configurations of Sm ions. This causes a fast fluctuating field at the Gd 3+ site [33,[46][47][48] which homogeneously broadens the linewidth of the individual resonances leading to the narrowing of the Gd 3+ CEF fine structure.…”

“…where the first term is the residual linewidth and b the usual Korringa relaxation rate [49] associated to a possible relaxation process due to the exchange interaction, J f s , between the Gd 3+ localized magnetic moment and the ce. The last term is the exponential contribution to the Gd 3+ relaxation due to the Sm 2.6+ VF [48], where A is a constant and E ex is the interconfigurational excitation energy, i.e., the energy necessary to exchange an electron between the ce-band and the Sm 4f states [33,48], actually, the energy to excite an electron from the hybridized valence band into the hybridized conduction band (indirect gap). T -evolution of the X-band Gd 3+ ESR spectra shown in Figure 1, where we have used Eq.…”

“…The absorption response with exchange narrowing effects due to the exchange interaction between the Gd 3+ local moment and the ce, is obtained by calculating the transverse dynamic susceptibility χ + (ω). Assuming no bottleneck relaxation effects, χ + (ω) can be approximated by [31][32][33][34]:…”