Inelastic X-ray scattering in YBa2Cu3O6.6 reveals giant phonon anomalies and elastic central peak due to charge-density-wave formation

Tacon, M. Le; Bosak, A.; Souliou, S. M.; Dellea, G.; Loew, T.; Heid, R.; Bohnen, K.‐P.; Ghiringhelli, G.; Krisch, M.; Keimer, B.

doi:10.1038/nphys2805

Cited by 286 publications

(320 citation statements)

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“…2e shows mode softening by approximately 25% at Q CDW , with a corresponding broadening of the fitted peak width, indicating that the short-ranged ordered CDW unambiguously affects the lattice. This observation is reminiscent of the bond-stretching phonon anomaly reported in the stripedordered cuprates 24 and the acoustic phonon anomaly in YBCO 25 , where CDW correlation lengths are notably longer. Curiously, the The fits (solid lines) are superimposed on the raw data (black circles).…”

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confidence: 68%

Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

et al. 2017

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Experimental evidence on high-T c cuprates reveals ubiquitous charge density wave (CDW) modulations 1-10 , which coexist with superconductivity. Although the CDW had been predicted by theory 11-13 , important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap 10,14 . Here, we use ultrahigh-resolution resonant inelastic X-ray scattering to reveal new CDW character in underdoped Bi 2.2 Sr 1.8 Ca 0.8 Dy 0.2 Cu 2 O 8+δ . At low temperature, we observe dispersive excitations from an incommensurate CDW that induces anomalously enhanced phonon intensity, unseen using other techniques. Near the pseudogap temperature T * , the CDW persists, but the associated excitations significantly weaken with an indication of CDW wavevector shift. The dispersive CDW excitations, phonon anomaly, and analysis of the CDW wavevector provide a comprehensive momentumspace picture of complex CDW behaviour and point to a closer relationship with the pseudogap state.With sufficient energy resolution, resonant inelastic X-ray scattering (RIXS) can be an ideal probe for revealing the CDW excitations in cuprates. By tuning the incident photon energy to the Cu L 3 -edge (Fig. 1a), the resonant absorption and emission processes can leave the system in excited final states, which couple to a variety of excitations arising from orbital, spin, charge, and lattice degrees of freedom 15 . Thus, information of these elementary excitations in energy and momentum space can be deduced from analysing the RIXS spectra as functions of the energy loss and the momentum transfer of the photons (Fig. 1a). This is highlighted by the pivotal role that RIXS has recently played in revealing orbital and magnetic excitations in cuprates [16][17][18][19][20] . In addition, RIXS provided the first X-ray scattering evidence for an incommensurate CDW in (Y,Nd)Ba 2 Cu 3 O 6+δ (ref. 4), owing to energy resolution that separated the quasi-elastic CDW signal (bright spot in Fig. 1b, limited by the instrumental resolution ∼130 meV) from other intense higher-energy excitations. Notably this quasi-elastic signal is asymmetric with respect to zero energy loss (Fig. 1c), which indicates the possible existence of additional low-energy excitations near the CDW wavevector (Q CDW ).In this work, we exploit the newly commissioned ultrahighresolution RIXS instrument at the European Synchrotron Radiation Facility to reveal these low-energy excitations near the CDW. We choose the double-layer cuprate Bi 2.2 Sr 1.8 Ca 0.8 Dy 0.2 Cu 2 O 8+δ (Bi2212), whose electronic structure has been extensively studied by surface-sensitive spectroscopy, such as scanning tunnelling microscopy 21 and angle-resolved photoemission 22 , and in which a short-range CDW order was recently reported 7,8 . With improved energy resolution up to 40 meV, we see additional features in the pre...

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Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

et al. 2017

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“…The electronic excitations may ultimately regain their quasiparticle character, including possible polaronic behavior (13,14). Furthermore, the CDW transition in this material is correlated with a strong electron-phonon interaction (29,30). We further elaborate on these points below.…”

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confidence: 99%

Anomalous thermal diffusivity in underdoped YBa ₂ Cu ₃ O _6+x

Zhang

Levenson-Falk

Ramshaw

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The thermal diffusivity in the ab plane of underdoped YBCO crystals is measured by means of a local optical technique in the temperature range of 25-300 K. The phase delay between a point heat source and a set of detection points around it allows for high-resolution measurement of the thermal diffusivity and its in-plane anisotropy. Although the magnitude of the diffusivity may suggest that it originates from phonons, its anisotropy is comparable with reported values of the electrical resistivity anisotropy. Furthermore, the anisotropy drops sharply below the charge order transition, again similar to the electrical resistivity anisotropy. Both of these observations suggest that the thermal diffusivity has pronounced electronic as well as phononic character. At the same time, the small electrical and thermal conductivities at high temperatures imply that neither well-defined electron nor phonon quasiparticles are present in this material. We interpret our results through a strongly interacting incoherent electron-phonon "soup" picture characterized by a diffusion constant D ∼ v 2 B τ , where v B is the soup velocity, and scattering of both electrons and phonons saturates a quantum thermal relaxation time τ ∼ /k B T.thermal diffusivity | bad metals | electron-phonon T he standard paradigm for transport in metals relies on the existence of quasiparticles. Electronic quasiparticles conduct electricity and heat. Phonon quasiparticles, the collective excitations of the elastic solid (here, we discuss acoustic phonons) also conduct heat. Transport coefficients, such as electrical and thermal conductivities, can then be calculated using, for example, Boltzmann equations (1). However, such an approach fails when the quasiparticle mean free paths become comparable with the quasiparticle wavelength. For electrons, it is the Fermi wavelength (2-4), whereas for phonons, it is the larger of the interatomic distance or minimum excited phonon wavelength (5, 6). Understanding transport in nonquasiparticle regimes requires a new framework and has become a subject of intense theoretical effort in recent years, triggering an urgent need for experimental results that can shed light on such regimes. In particular, in ref. 7, the diffusivity was singled out as a key observable for incoherent nonquasiparticle transport, possibly subject to fundamental quantum mechanical bounds.In this work, we report high-resolution measurements of the thermal diffusivity of single-crystal underdoped YBCO6.60 (an ortho-II YBa2Cu3O6.60) and YBCO6.75 (an ortho-III YBa2Cu3O6.75). We are particularly interested in the anisotropy of the thermal diffusivity as measured along the principal axes a and b (which is the chain direction) in the temperature range 25-300 K. We use a noncontact optical microscope (see Fig. S1) to perform local thermal transport measurements on the scale of ∼10 µm, hence avoiding inhomogeneities, particularly twinning and grain boundary effects. Our principal experimental results are as follows. (i) The measured thermal diffusivity is...

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“…Early STM measurements revealed presence of checker board pattern consistent with charge ordering in the cores of the vortexes 14 then in heavily under doped samples 15 and moderately doped samples 16 . More recently series of high precision X-ray scattering experiments detected fluctuating charge density order within pseudo gap state [17][18][19] . All these findings point to the fact that pseudo gap is a manifestation of an ordered states or perhaps interplay of two ordered states involving charge and magnetic moment.…”

Section: Introductionmentioning

confidence: 99%

Pairing, pseudogap and Fermi arcs in cuprates

Kaminski

Kondo

Takeuchi

et al. 2014

Philosophical Magazine

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We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather then preformed pairs.Pairing does occur below T pair ∼ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below T pair , and its interplay with strong scattering creates "artificial" Fermi arcs for T c ≤ T ≤ T pair . However, above T pair , the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. We demonstrate that these findings resolve a number of seemingly contradictory scenarios.

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Inelastic X-ray scattering in YBa2Cu3O6.6 reveals giant phonon anomalies and elastic central peak due to charge-density-wave formation

Cited by 286 publications

References 44 publications

Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

Anomalous thermal diffusivity in underdoped YBa ₂ Cu ₃ O _6+x

Pairing, pseudogap and Fermi arcs in cuprates

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Inelastic X-ray scattering in YBa2Cu3O6.6 reveals giant phonon anomalies and elastic central peak due to charge-density-wave formation

Cited by 286 publications

References 44 publications

Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

Dispersive charge density wave excitations in Bi2Sr2CaCu2O8+δ

Anomalous thermal diffusivity in underdoped YBa 2 Cu 3 O 6+x

Pairing, pseudogap and Fermi arcs in cuprates

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Anomalous thermal diffusivity in underdoped YBa ₂ Cu ₃ O _6+x