Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 31: Correlated Electrons: Low-Dimensional Systems -Materials 1
TT 31.5: Talk
Tuesday, March 12, 2013, 10:30–10:45, H41
Competing soft phonon modes in TbTe3 — •Michael Maschek1, Rolf Heid1, Stefan Rosenkranz2, Ayman Said2, Bogdan Leu2, Paula Giraldo-Gallo3, and Ian Fisher3 — 1Institute of Solid State Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany — 2Material Science Division, Argonne National Laboratory, Argonne, USA — 3Geballe Laboratory for Advanced Materials, Stanford University, Stanford, USA
We report high energy resolution inelastic x-ray measurements of competing soft phonon modes in the vicinity of the charge-density-wave (CDW) phase transition in TbTe3. We investigated two phonon modes having each a transverse polarization within the basal plane of the nearly tetragonal unit cell (a=4.308, b=25.57, c=4.314) but are dispersing along the reciprocal (100) and the (001) directions. Only the latter one is expected to go soft at qCDW = (0, 0, 0.296) and TCDW = 332 K. We found that both phonon modes go soft approaching TCDW from high temperatures. The softenings are identical down to T = 350 K, and only for T < 350 K we see a significantly stronger softening of the mode at qCDW. Our results are corroborated by lattice dynamical calculations demonstrating the degeneracy between the two crystallographic axes with respect to the formation of CDW order.