Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 18: Correlated Electrons: Quantum Impurities, Kondo Physics 2

TT 18.4: Vortrag

Dienstag, 27. März 2012, 10:15–10:30, H 3005

Complex charge ordering in CeRuSn — •Ralf Feyerherm¹, Esther Dudzik¹, Sergio Valencia¹, John A. Mydosh^2,3, Wilfried Hermes⁴, and Rainer Pöttgen⁴ — ¹Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin — ²MPI-CPFS, 01187 Dresden — ³Kamerlingh Onnes Laboratory, Leiden University, 2300RA Leiden, The Netherlands — ⁴Institut für Anorganische und Analytische Chemie, Universität Münster, 48149 Münster

At room temperature (RT), CeRuSn exhibits coexistence of trivalent Ce³⁺ and intermediate valent Ce^(4−δ)+ in a metallic environment. Charge ordering produces a doubling of the unit cell along the c-axis with respect to the basic CeCoAl type structure. Below RT, a phase transition with broad hysteresis has been observed in various bulk properties. The present x-ray diffraction results show that at low temperatures the doubling of the CeCoAl type structure is replaced by an ill-defined modulated ground state in which at least three modulation periods compete. The dominant mode is close to a tripling of the basic cell. XANES data suggest that the average Ce valence remains constant. We propose a qualitative structure model with modified stacking sequences of Ce³⁺ and Ce^(4−δ)+ layers in the various modulated phases. Surprisingly, far below 100 K the modulated state is sensitive to synchrotron x-ray irradiation. With a photon flux ≈ 10¹² s⁻¹, the modulated ground state is destroyed on a timescale of minutes and the doubling of the CeCoAl cell observed at room temperature is recovered. The final state is metastable at 10 K. Heating the sample above 60 K again leads to a recovery of the modulated state.