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Renker, B.; Rietschel, H.; Pintschovius, L.; Gläser, W.; Brüesch, P.; Kuse, D.; Rice, Michael J.

doi:10.1103/physrevlett.30.1144

Cited by 209 publications

(42 citation statements)

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“…3 clearly shows, that the phonon energies over the range 0.3 ≤ h ≤ 0.5 are renormalized across the CDW transition. This large range in h is in contrast to compounds, where a sharp FS nesting drives the CDW formation and renormalized phonon energies are observed only over a much smaller q range [25,26].…”

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Electron-Phonon Coupling and the Soft Phonon Mode inTiSe2

et al. 2011

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We report high-resolution inelastic x-ray measurements of the soft phonon mode in the chargedensity-wave compound TiSe2. We observe a complete softening of a transverse optic phonon at the L point, i.e. q = (0.5, 0, 0.5), at T ≈ TCDW . Renormalized phonon energies are observed over a large wavevector range (0.3, 0, 0.5) ≤ q ≤ (0.5, 0, 0.5). Detailed ab-initio calculations for the electronic and lattice dynamical properties of TiSe2 are in quantitative agreement with experimental frequencies for the phonon branch involving the soft mode. The observed broad range of renormalized phonon frequencies is directly related to a broad peak in the electronic susceptibility stabilizing the chargedensity-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe2 although other mechanisms might further boost the transition temperature.PACS numbers: 71.45. Lr, 63.20.kd, 63.20.dd, 63.20.dk The origin of charge-density-wave (CDW ) order, i.e., a periodic modulation of the electronic density, is a long-standing problem relevant to a number of important issues in condensed matter physics, such as the role of stripes in cuprates [1] and charge fluctuations in the colossal magnetoresistive manganites [2]. Chan and Heine derived the criterion for a stable CDW phase with a modulation wavevector q as [3]where η q is the electron-phonon coupling (EPC) matrix element associated with a mode at an unrenormalized energy of ω bare , χ q is the dielectric response of the conduction electrons, and U q and V q are their Coulomb and exchange interactions. Static CDW order typically is taken as a result of a divergent electronic susceptibility χ q due to nesting, i.e. parallel sheets of the Fermi surface (FS) separated by twice the Fermi wavevector 2k f . Electron-phonon coupling (EPC) is required to stabilize the structural distortion and, hence, an acoustic phonon mode at the CDW wavevector q CDW = 2k f softens to zero energy at the transition temperature T CDW [3,4]. However, when electronic probes reported only small and not well nested Fermi surfaces this scenario has been discarded for the prototypical CDW compound TiSe 2 [5][6][7].Alternative scenarios such as indirect or band-type Jahn-Teller effects [6][7][8] and, most prominently, exciton formation [5,9,10] are discussed in the theoretical as well as experimental literature. More recently, van Wezel et al. have invoked a model including exciton formation as well as EPC [11] and have shown that it can explain data from angle-resolved photoemission spectroscopy (ARPES) [12], formerly taken as evidence of an excitonic insulating phase in TiSe 2 [9]. Determining the origin of CDW formation in TiSe 2 is all the more important with respect to the nature of superconductivity, which emerges both as function of pressure [13] and Cu intercalation [14]. In particular, pressure induced superconductivity is expected to be closely linked to the nature of the parent CDW state.I...

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Electron-Phonon Coupling and the Soft Phonon Mode inTiSe2

et al. 2011

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“…For the metals with nested Fermi surfaces, the above effect is much more pronounced, resulting in considerable phonon softening at q = 2k F (giant Kohn anomaly) [25,26]. This leads to a great depression at q = 2k F in the phonon dispersion curve, which sometimes is so drastic that ω(2k F ) becomes zero, thus making the phonon mode with q = 2k F be frozen to a static lattice distortion.…”

Section: Cdw Ground States Stabilized By Electron-phonon Couplingmentioning

confidence: 99%

Surface Peierls transition on Cu(001) covered with heavier p-block metals

Aruga

2006

Surface Science Reports

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The Cu(001) surface covered with submonolayer coverages of In and Sn undergoes phase transitions at around 350-400 K. The transition is associated with the surface electronic structure change between low-temperature gapped and high-temperature ungapped ones. The energy gap positions in the k space coincide with the surface Brillouine zone boundaries of the low-temperature phases. These observations imply that the phase transitions are classified into the Peierls-type charge density wave (CDW) phase transition. The CDW ground states are characterized by large overall CDW gaps and long CDW correlation lengths. Structural studies show that the transitions are associated with order-disorder processes. This suggests that these are in strong-coupling regime. However, the associated gapped-ungapped change suggests that the electronic terms play significant role, in contradiction with the strong-coupling scenario. Based on the results of recent works on precise temperature dependence of the CDW gap and critical X-ray scattering, the origin of this dual nature and the detailed mechanism of the phase transition is discussed. It is suggested that the electronic entropy of the CDW ground state is not governed by the overall energy gap but by the gap between the upper band minimum and the Fermi level of the whole system. The dual nature of the surface Peierls transition on Cu(001) originates, on one hand, from the existence at metal surfaces of the two characteristic energy gaps: the overall gap, which determines the CDW stabilization energy, and the upper gap, which governs the electronic entropy. On the other hand, the CDW correlation length is suggested to play another significant role in determining the nature of the Peierls transition. The classification of the Peierls transisions according to the CDW correlation length and the gap size is discussed. It is suggested that the surface Peierls transition on metal-covered Cu(001) covered with heavier p-block metallic elements are qualitatively different from both the weak-coupling CDW transition, with long CDW correlation length and small gaps, and the strong-coupling CDW transitions, with short correlation lengths and large gaps, and should be classified into the third class, which is characterized by long coherence and strong coupling.

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“…In order to see if electronic quasiparticles are responsible for the giant phonon anomaly, we first checked if the phonon wavevector spans parallel sheets of the Fermi surface, near h=0.25 or 0.3, since such FS nesting can give the phonon anomaly 25 . Fig.…”

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Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La2−xSrxCuO
Park
¹
,
Fukuda
²
,
Hamann
³

et al. 2014
Phys. Rev. B
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In superconducting copper oxides some Cu-O bond-stretching phonons around 70meV show anomalous giant softening and broadening of electronic origin and electronic dispersions have large renormalization kinks near the same energy. These observations suggest that phonon broadening originates from quasiparticle excitations across the Fermi surface and the electronic dispersion kinks originate from coupling to anomalous phonons. We measured the phonon anomaly in underdoped (x=0.05) and overdoped (x=0.20,0.25) La2−xSrxCuO4 by inelastic neutron and x-ray scattering with high resolution. Combining these and previously published data, we found that doping-dependence of the magnitude of the giant phonon anomaly is very different from that of the ARPES kink, i.e. the two phenomena are not connected. We show that these results provide indirect evidence that the phonon anomaly originates from novel collective charge excitations as opposed to interactions with electron-hole pairs. Their amplitude follows the superconducting dome so these charge modes may be important for superconductivity.PACS numbers: 74.25.Kc, 63.20.kd, 74.20.Mn Lattice vibrations in metals can be damped and/or softened by either electronic quasiparticles or collective charge excitations (e.g. plasmons). Giant phonon softening and line broadening of electronic origin of the longitudinal Cu-O bond stretching phonons near half-way to the zone boundary (giant anomaly) was observed in copper oxide high temperature superconductors (HTSCs) 1-11 . It was previously found at superconducting compositions and was also absent in undoped and overdoped nonsuperconducting copper oxides [5][6][7] .First reports interpreted the phonon anomaly as a signature of unit cell doubling 3 followed by a different interpretation 6 in terms of coupling of the phonon to dynamic charge stripes. Subsequently, close kinematic relationship between the longitudinal Cu-O bond stretching mode dispersion and renormalization of electronic quasiparticles in Bi 2 Sr 1.6 La 0.4 CuO 6 (Bi2201) indicated that the phonon anomaly may originate from the coupling of phonons to electronic quasiparticles 11 . t − J modelbased calculations also predicted strong coupling of optical phonons to electron-hole excitations 12 .If phonons couple strongly to electronic quasipaticles, then a BCS-type mechanism of superconductivity may still be valid. Alternatively, the phonon anomaly would arise from a novel collective charge excitations at low energies (at least 70 meV). Then such collective mode may provide the pairing interaction 13-15 .We measured Cu-O bond-stretching phonons in La 2−x Sr x CuO 4 for undoped x=0.00, nonsuperconducting underdoped x=0.05, and superconducting overdoped x=0.20, 0.25. x=0.05 did not show characteristic signatures of the giant phonon anomaly. x=0.20 showed a very strong phonon anomaly, which was dramatically reduced already at x=0.25. On the other hand, the magnitude of the kink in the electronic dispersions gradually decreases from x=0.05 to x=0.30 16,17 . The new data, combine...

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Observation of Giant Kohn Anomaly in the One-Dimensional ConductorK2Pt(CN)

Cited by 209 publications

References 10 publications

Electron-Phonon Coupling and the Soft Phonon Mode inTiSe2

Electron-Phonon Coupling and the Soft Phonon Mode inTiSe2

Surface Peierls transition on Cu(001) covered with heavier p-block metals

Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La2−xSrxCuO
Park
¹
,
Fukuda
²
,
Hamann
³

et al. 2014
Phys. Rev. B
Self Cite
46
0
36
2
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Observation of Giant Kohn Anomaly in the One-Dimensional ConductorK2Pt(CN)

Cited by 209 publications

References 10 publications

Electron-Phonon Coupling and the Soft Phonon Mode inTiSe2

Electron-Phonon Coupling and the Soft Phonon Mode inTiSe2

Surface Peierls transition on Cu(001) covered with heavier p-block metals

Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La2−xSrxCuOPark1, Fukuda2, Hamann3 et al. 2014Phys. Rev. BSelf Cite460362View full textAdd to dashboardCite

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Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La2−xSrxCuO
Park
¹
,
Fukuda
²
,
Hamann
³

et al. 2014
Phys. Rev. B
Self Cite
46
0
36
2
View full text Add to dashboard Cite