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TT: Tiefe Temperaturen

TT 3: Correlated Electrons - Heavy Fermions

TT 3.5: Vortrag

Freitag, 4. März 2005, 11:15–11:30, TU H3027

Kondo-ion electron spin resonance of isotope clean ¹⁷⁴Yb Rh₂ Si₂ — •J. Wykhoff¹, J. Sichelschmidt¹, G. Knebel², G. Lapertot², J. Flouquet², J. Ferstl¹, H.-A. Krug von Nidda³, C. Geibel¹, and F. Steglich¹ — ¹Max-Planck-Institut für Chemische Physik fester Stoffe, D-01187 Dresden, Germany — ²Département de Recherche Fondamentale sur la Matière Condensée, SPSMS, CEA Grenoble, 38054 Grenoble, France — ³Experimentalphysik V, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany

The heavy-fermion compound Yb Rh₂ Si₂ is located very close to a magnetic field induced quantum critical point. The unexpected observation of electron spin resonance (ESR) of the Kondo-ion Yb³⁺ below the Kondo temperature (T_K≃25 K) might be a direct verification of the localized moment scenario of quantum criticality. We present the ESR of isotope clean ¹⁷⁴Yb Rh₂ Si₂ which was prepared at the CEA Grenoble. Its T behavior is very similar compared to that of Yb Rh₂ Si₂. Especially, for the ESR linewidth an exponential behavior above T≃12 K and a progressive reduction by decreasing T down to the lowest accessible T=1.7 K could be confirmed in ¹⁷⁴Yb Rh₂ Si₂. However, ¹⁷⁴Yb Rh₂ Si₂ shows a smaller residual linewidth and a strongly reduced thermal line broadening in the whole T region. Assuming a smaller disorder in ¹⁷⁴Yb Rh₂ Si₂ these observations further support our previous finding that introducing disorder in Yb Rh₂ Si₂ by La- or Ge-doping causes a more effective Yb³⁺ ESR relaxation. The question arises whether an ESR bottleneck effect could be responsible for the extremely narrow linewidth.