A Raman study of the charge-density-wave state in A<sub>0.3</sub>MoO<sub>3</sub>(A = K, Rb)

Sagar, D. M.; Fausti, Daniele; Yue, Song; Kuntscher, C. A.; Smaalen, Sander van; Loosdrecht, P.H.M. van

doi:10.1088/1367-2630/10/2/023043

Cited by 27 publications

(35 citation statements)

References 31 publications

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“…9(b)-9(d)). In particular, its energy softens by over 10% upon heating from 10 K to 45 K. While such an amount of softening is considerably smaller than those observed in quasi-2D [19] and 3D materials [53], it is not uncommon among quasi-1D systems [54], in which the effect of fluctuations is expected to strongly reduce the actual transition temperature from its mean-field value. Therefore we attribute this feature to the CDW amplitude excitation.…”

Section: F the Cdw Amplitude Excitationmentioning

confidence: 87%

Charge density waves and phonon-electron coupling inZrTe3

Zheng

Ren

et al. 2015

Phys. Rev. B

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Charge-density-wave (CDW) order has long been interpreted as arising from a Fermi-surface instability in the parent metallic phase. While phonon-electron coupling has been suggested to influence the formation of CDW order in quasi-two-dimensional (quasi-2D) systems, the presumed dominant importance of Fermi-surface nesting remains largely unquestioned in quasi-1D systems.Here we show that phonon-electron coupling is also important for the CDW formation in a model quasi-1D system ZrTe 3 . Our joint experimental and computational study reveals that particular lattice vibrational patterns possess exceedingly strong coupling to the conduction electrons, and are directly linked to the lattice distortions associated with the CDW order. The dependence of the coupling matrix elements on electron momentum further dictates the opening of (partial) electronic gaps in the CDW phase. Since lattice distortions and electronic gaps are the defining signatures of CDW order, our result demonstrates that the conventional wisdom based on Fermisurface geometry needs to be substantially supplemented by phonon-electron coupling even in the simplest quasi-1D case. As prerequisites for the CDW formation, the highly anisotropic electronic structure and strong phonon-electron coupling in ZrTe 3 give rise to a distinct Raman scattering effect, namely, measured phonon linewidths depend on the direction of momentum transfer in the scattering process.

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Section: F the Cdw Amplitude Excitationmentioning

confidence: 87%

Charge density waves and phonon-electron coupling inZrTe3

Zheng

Ren

et al. 2015

Phys. Rev. B

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“…Because of their strong coupling to the electronic order, several phonon modes are folded back to the Brillouin zone center and appear in infrared [11] and Raman spectra [12,13]. The amplitudes, frequencies, and damping of these collective excitations hold important information on the density of the ordered charges [14].…”

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confidence: 99%

Dynamical Stability Limit for the Charge Density Wave in K0.3MoO3

et al. 2017

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We study the response of the one-dimensional charge density wave in K 0.3 MoO 3 to different types of excitation with femtosecond optical pulses. We compare direct excitation of the lattice at midinfrared frequencies with injection of quasiparticles across the low energy charge density wave gap and with charge transfer excitation in the near infrared. For all three cases, we observe a fluence threshold above which the amplitude-mode oscillation frequency is softened and the mode becomes increasingly damped. We show that all the data can be collapsed onto a universal curve in which the melting of the charge density wave occurs abruptly at a critical lattice excursion. These data highlight the existence of a universal stability limit for a charge density wave, reminiscent of the Lindemann criterion for the melting of a crystal lattice. DOI: 10.1103/PhysRevLett.118.116402 One-dimensional charge-density waves (CDWs) are a prototypical example of a broken symmetry state, in which the energy is lowered by the modulation of the conduction electron density at a wave vector q CDW that nests two regions of the Fermi surface [1]. This modulation in the real space charge distribution is typically also associated with a distortion of the lattice [2] and with the appearance of new excitations that can be observed in optical or Raman spectroscopy. Charge density waves are especially interesting in systems in which nesting occurs between two different bands, for which the order is often incommensurate with the lattice, resulting in highly anomalous and nonlinear dc conductivity.Here, we study the response of the one-dimensional charge density wave material K 0.3 MoO 3 (blue bronze) to short pulse optical excitation, which so far has been investigated extensively at near-infrared wavelengths [3][4][5]. In these studies, a collapse of the CDW gap [6] and the rearrangement of the lattice along the coordinate of the amplitude mode [7] were reported.We seek to provide a new perspective into these dynamics by inducing melting of the same charge density wave by three different types of optical stimulation. We study excitation of the lattice alone, of charge quasiparticles immediately above the low-energy CDW gap and of charges across a high-energy charge transfer resonance. The third mechanism is the one studied in previous experiments and is analyzed here as a reference point. We find evidence for a universal dynamical instability that occurs always at specific lattice displacement, which we estimate to be of approximately 20% of the CDW-induced equilibrium lattice distortion.

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“…Further, the frequency softening of certain phonons ͑364 and 220 cm −1 ͒ and the frequency saturation below 100 K very much resemble the behavior of soft modes, for instance, seen in the prototypical CDW system-blue bronze. 2 The saturation of frequency and linewidth of 220 cm −1 mode above 200 K very much implies a strong electron-phonon coupling. In general, phonon line-width broadening may come from either phononphonon interaction in which case an optical phonon decays into two acoustic phonon modes, or due to an anharmonicity arising from electron-phonon coupling.…”

Section: Discussionmentioning

confidence: 99%

“…These physical properties often originate from a strong coupling between various elementary excitations in solids, such as phonons, phasons, 1 amplitudons, 2 and plasmarons. 3 Among the transition-metal oxides, tungsten bronzes have attained considerable attention due to their interesting physical properties which depend on the kind of alkali-metal atom and its composition.…”

Section: Introductionmentioning

confidence: 99%

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Raman signatures of charge ordering inK0.3WO3

et al. 2010

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We present polarization-and temperature-dependent Raman spectroscopic study of hexagonal tungsten bronze, K 0.3 WO 3 . The observed asymmetry in phonon line shapes indicate the presence of strong lattice anharmonicity arising due to the nonstoichiometry of the material. We observed a broad multipeak Raman feature at low frequency due to the local modes of K atoms known as local structural excitations. The observed vibrational features indicate a second-order phase transition around T = 200 K accompanied by a frequency softening of low-frequency phonon modes. The observed phonon anomalies hint a physical picture involving a continuous symmetry change toward a charge-ordered state below 200 K. These observations indicate that K 0.3 WO 3 may exhibit a weak charge-density-wave ground state at low temperatures.

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A Raman study of the charge-density-wave state in A_0.3MoO₃(A = K, Rb)

Cited by 27 publications

References 31 publications

Charge density waves and phonon-electron coupling inZrTe3

Charge density waves and phonon-electron coupling inZrTe3

Dynamical Stability Limit for the Charge Density Wave in K0.3MoO3

Raman signatures of charge ordering inK0.3WO3

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A Raman study of the charge-density-wave state in A0.3MoO3(A = K, Rb)

Cited by 27 publications

References 31 publications

Charge density waves and phonon-electron coupling inZrTe3

Charge density waves and phonon-electron coupling inZrTe3

Dynamical Stability Limit for the Charge Density Wave in K0.3MoO3

Raman signatures of charge ordering inK0.3WO3

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A Raman study of the charge-density-wave state in A_0.3MoO₃(A = K, Rb)