Optical Investigation of the Superconducting Phase Transition in YBa2Cu3O7 Crystals

Koch, B.; Dürrler, M.; Geserich, H. P.; Wolf, Th.; Roth, Georg; Zaehmann, G.

doi:10.1007/978-3-642-84345-7_55

Cited by 10 publications

(9 citation statements)

References 7 publications

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“…Optimally and overdoped YBCO also show a gap-like depression in low frequency conductivity but the gap appears at T c and has been associated with the superconducting gap [24,43,50]. This gap does not have the flat bottomed shape of the underdoped materials.…”

Section: The Pseudogap In the C-axis Conductivitymentioning

confidence: 98%

The mysterious pseudogap in high temperature superconductors: an infrared view

Timusk

2003

Solid State Communications

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We review the contribution of infrared spectroscopy to the study of the pseudogap in high temperature superconductors. The pseudogap appears as a depression of the frequency dependent conductivity in the c-axis direction and seems to be related to a real gap in the density of states. It can also be seen in the Knight shift, photoemission and tunneling experiments. In underdoped samples it appears near room temperature and does not close with temperature. Another related phenomenon that has been studied by infrared is the depression in the ab-plane scattering rate. Two separate effects can be discerned. At high temperatures there is broad depression of scattering below 1000 cm −1 which may be related to the gap in the density of states. At a lower temperature a sharper structure is seen, which appears to be associated with scattering from a mode at 300 cm −1 , and which governs the carrier life time at low temperatures. This mode shows up in a number of other experiments, as a kink in ARPES dispersion, and a resonance at 41 meV in magnetic neutron scattering. Since the infrared technique can be used on a wide range of samples it has provided evidence that the scattering mode is present in all high temperature cuprates and that its frequency in optimally doped materials scales with the superconducting transition temperature. The lanthanum and neodymium based cuprates do not follow this scaling and appear to have depressed transition temperatures.

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Section: The Pseudogap In the C-axis Conductivitymentioning

confidence: 98%

The mysterious pseudogap in high temperature superconductors: an infrared view

Timusk

2003

Solid State Communications

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“…Temperature-dependent reflectance measurements were carried out to 5000 cm −1 . The room-temperature measurements of Koch et al [29] were used from 5000 cm −1 to 3.5 × 10 5 cm −1 and above this frequency free-electron behavior was assumed: R ∝ ω −4 .…”

Section: Optical Conductivitymentioning

confidence: 99%

“…In previous single crystal work with polished samples, these features were broad and weak, suggesting either poor oxygen homogeneity, or that polishing the sample has induced surface damage or altered the oxygen con-tent of the material in the surface layers, particularly in the chains. Furthermore, an examination of the reflectance of polished c-axis crystals [29,30] shows that they bear a strong similarity to the reflectance of freshly-annealed ceramics.…”

Section: Temperature Dependence Of the Phonon Parametersmentioning

confidence: 99%

Optical phonons polarized along the c axis of YBa₂Cu₃O_6+x, for x = 0.5 → 0.95

Homes¹,

Timusk²,

Bonn³

et al. 1995

Can. J. Phys.

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The c-axis polarized phonon spectra of single crystals of YBa2Cu3O6+x, were measured for the doping range x = 0.5 → 0.95, between 10 K and 300 K. The low background electronic conductivity, determined by Kramers-Kronig analysis of the reflectance, leads to a rich phonon structure. With decreased doping the five normally-active B1u modes broaden and the high-frequency apical oxygen mode splits into two components. We associate the higher of these with the two-fold coordinated copper "sticks". The 155 cm −1 low-frequency mode, which involves the apical and the chainoxygens, splits into at least three components with decreasing doping. Some phonon anomalies which occur near Tc in the highly-doped material occur well above Tc in the oxygen-reduced systems. An unusual broad phonon band develops in the normal state at ≈ 400 cm −1 , which becomes more intense at low doping and low temperatures, borrowing oscillator strength from apical and plane oxygen modes resulting in a major transformation of the phonon spectrum below ≈ 150 K.Résumé : Les spectres de phonons polarisés suivant l'axe c, dans des monocristaux de YBa2Cu3O6+x ontété measurés, pour l'intervalle de dopage x = 0, 5à 0, 95, entre 10 et 300 K. La faible condutivitéélectronique de fond, déterminée par analyse Kramers-Kronig de la réflectance, donne lieuà une riche structure de phonons. Lorsqu'on diminue le dopage, les cinque modes B1u normalement actifs s'élargissent, et le mode apicalà haute fréquence de l'oxygène se divise en deux composantes. Nous associons la plus haute de ces composantes aux « bâtons » de cuivreà coordinence deux. Le mode de basse fréquence,à 155 cm −1 , qui implique les oxygènes apical et en chaîne, se sépare en au moins trois composantes lorsque le dopage diminue. Certaines anomalies de phonons, présentes au voisinage de Tc dans les cristaux faiblement dopés, apparaissentà des températures bien plus grandes que Tc dans les systèmes avec moins de l'óxygène. A environ 400 cm −1 , il se développe dans l'état normal une bande large insolite qui devient plus intenseà faible dopage et a basse température, avec une force d'ocsillateur empruntée aux modes apical et plan de l'oxygène, ce quie entraîne une transformation majeure des spectres de phonons au-dessous d'environ 150 K.[Traduit par la rédaction]

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“…Polarized reflection measurements from Y Ba 2 Cu 3 O 7 crystals have been carried out by Koch et al [1]. For the radiation polarized perpendicularly to the CuO 2 planes a striking difference has been discovered between the reflectivity spectra in the normal and in the superconducting state.…”

Section: Introductionmentioning

confidence: 99%

“…The superconducting and the normal plasma frequencies, Ω s and Ω n , are related to the corresponding BCS densities n s and n n in the same way as in eq. (1). The absorption is characterized by some temperaturedependent attenuation coefficient 1/τ .…”

Section: Introductionmentioning

confidence: 99%