Spectroscopic evidence for a charge-density-wave condensate in a charge-ordered manganite: Observation of a collective excitation mode inPr0.7Ca0.3

Abstract

THz time-domain spectroscopy was used to directly probe the low-energy (0.5-5 meV) electrodynamics of the charge-ordered manganite Pr0.7Ca0.3MnO3. We revealed the existence of a finite peak structure around 2-3 meV well below the charge gap ∼ 300 meV. In analogy to the low-energy optical properties of the well-studied low-dimensional materials, we attributed this observed structure to the collective excitation mode arising from the charge-density-wave condensate. This finding provides the importance role of the quasi-one dimensional nature of the charge and orbital ordering in Pr0.7Ca0.3MnO3.

Boson peak in overdoped manganites La1−xCaxMnO3

“…Similar asymmetric absorption bands in LCMO were observed previously [8][9][10][11][12] and assigned to collective excitations of the CDW ground state. However, there are good arguments against this interpretation: (i) The bands consist of two or even more spectral components that could only be explained by multi-phonon Peierls coupling, as in the case of organic mixed stack compounds [26].…”

“…One of the most popular approaches is based on the charge-density wave (CDW) scenario [5] because the systems seem to possess the necessary ingredients like the Fermi surface nesting and lattice superstructure [6,7]. Low-energy excitations in the THz frequency range are frequently taken as evidence in favor of this mechanism as they are ascribed to the CDW-condensate phase or amplitude modes [8][9][10][11][12]. There is, however, some dispute about this Peierls-Fröhlich scenario [13,14].…”

“…Similar effects are expected in La 1−x Ca x MnO 3 for incommensurate calcium contents x that leads to a certain degree of disorder in the lattice ions positions. To which extent the disorder-driven renormalization of the phonon DOS can be responsible for the low-energy physics of manganites and in particular for the soft excitations reported in the literature [8][9][10][11][12][19][20][21][22], remains unclear.…”

Anomaly in the dielectric response at the charge-orbital-ordering transition ofPr0.67Ca0.33MnOMercone1, Wahl2, Pautrat3 et al. 2004Phys. Rev. B713410View full textAdd to dashboardCite

“…To add to this scenario of differing views, recent spectroscopy experiments 21,22 have suggested the development of a charge-density-wave (CDW). This is supported by the quasione-dimensional electronic structure proposed by Asaka et al 23 in the light of their lowtemperature TEM measurements.…”

Investigation of the electronic structure of the charge-ordered phase in epitaxial and polycrystallineLa1−xCaxMnO3Schmidt1 2008Phys. Rev. B370901View full textAdd to dashboardCite

“…Electronically "soft" phases with weak electron-lattice coupling have been suggested 17 and a phenomenological Ginzburg-Landau theory was postulated 16 to describe these phases in a delocalised charge-density wave (CDW) picture. 22,23 At this point, it has to be stated that any CO pattern could be regarded as some kind of CDW. However, the term CDW is conventionally used only for systems which undergo a Peierls transition by cooling below the Peierls transition temperature T PE .…”