Scientific article
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c -Axis Optical Sum Rule and a Possible New Collective Mode in La2−xSrxCuO4

Published inPhysical review letters, vol. 91, no. 3, 037004
Publication date2003-07-18
First online date2003-07-18

We present the c -axis optical conductivity σ 1 c ( ω , T ) of underdoped ( x = 0.12 ) and optimally doped ( x = 0.15 ) L a 2 − x S r x C u O 4 from 4 meV to 1.8 eV obtained by a combination of reflectivity and transmission spectra. In addition to the opening of the superconducting gap, we observe an increase of conductivity above the gap up to 270 meV with a maximal effect at about 120 meV. This may indicate a new collective mode at a surprisingly large energy scale. The Ferrell-Glover-Tinkham sum rule is violated for both doping levels. Although the relative value of the violation is much larger for the underdoped sample, the absolute increase of the low-frequency spectral weight, including that of the condensate, is higher in the optimally doped regime. Our results resemble in many respects the observations in Y B a 2 C u 3 O 7 − δ .

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Citation (ISO format)
KUZMENKO, Alexey et al. c -Axis Optical Sum Rule and a Possible New Collective Mode in La<sub>2−x</sub>Sr<sub>x</sub>CuO<sub>4</sub>. In: Physical review letters, 2003, vol. 91, n° 3, p. 037004. doi: 10.1103/PhysRevLett.91.037004
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ISSN of the journal0031-9007

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