Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 43: Correlated Electrons: Heavy Fermions 2

TT 43.6: Vortrag

Donnerstag, 26. März 2009, 17:00–17:15, HSZ 301

Exotic Ground State of CeRu₄Sn₆ Investigated by Means of Specific-Heat and NMR — •Eva Maria Brüning¹, Manuel Brando¹, Michael Baenitz¹, André Strydom², Russel E. Walstedt³, and Frank Steglich¹ — ¹Max-Planck-Institut für Chemische Physik Fester Stoffe, Dresden, Germany — ²Physics Department, University of Johannesburg, South Africa — ³Physics Department, University of Michigan, MI, USA

The tetragonal compound CeRu₄Sn₆ is a narrow-gap semi-metal and shows no phase transition down to 50 mK. We performed field-sweep ¹¹⁹Sn NMR measurements at different frequencies (47, 70, 100 and 119 MHz) down to 2 K as well as specific-heat measurements in magnetic fields up to 10 T and temperatures down to 65 mK. The spin-lattice-relaxation rate 1/T₁ in the high-T range (300 K to 20 K) is field independent and could be consistently fitted with a model for a narrow gap semi-metal (1/T₁ ∝ Texp(−Δ /k_BT)) with a gap of Δ/k_B ≃ 30 K. This confirms the results from resistivity and thermopower measurements. Below 10 K, 1/T₁ becomes strongly field dependent, whereas higher fields lead to a stronger reduction of 1/T₁. The low-T range could be fitted with an activated behavior (1/T₁ ∝ exp(−Δ/k_BT)), where Δ/k_B increases with increasing field. This scenario is strongly supported by specific-heat investigations. Both results can be described consistently by assuming a double Cauchy-Lorentz function for the residual in-gap density of states N(E). The ground state is governed by these correlated states which show Zeeman-type splitting in magnetic fields.