Phonon-order parameter coupling in YBa₂Cu₃O_{7- delta}as observed by infrared absorption spectroscopy

Abstract

Infrared absorption spectoscopy has been used to investigate the complete phonon frequency range (20c1n-~ -700cm-I) at temperatures between 10K and 300K. A direct coupling of bulk phonon modes in YBazCu307-6 with the superconductor order parameter is deduced from the critical temperature dependence in the superconducting low temperature phase (Tc -92K). The excess intensity and the frequency shift of the mode near 580cm-1 are shown to be proportional to the square of a BCS-like order parameter in agreement with the predictions of Hard Mode Spectroscopy.

Crystal structure and paramagnetic behaviour of

“…The physical properties of tungsten trioxide, WO 3 , and its slightly oxygen-deficient analogues, WO 3−x , have attracted renewed attention because their electronic properties may shed some light on one possible pairing mechanism in high-temperature superconductors, namely Bose condensation of pre-formed bipolaron charge carriers [1][2][3][4][5][6][7][8][9][10][11][12]. Experimental suggestions of possible Bose condensation stem from the departure of the nuclear spinrelaxation rate from the Korringa law [3], the heat capacity anomaly [4,5], and the softening of phonons above the pseudo-gap in the superconducting phase [7,8,[13][14][15].…”

Phonon softening and MIR absorption in superconducting

“…The observed phonon softening may well be correlated with polaron formation [10][11][12][13][14]24]. If this is the case, we find that such structural states are formed at temperatures well above T c .…”

“…The absorbance was calculated as the normalized difference between the sample spectrum and the reference spectrum, eliminating any spectrometer instabilities. The details of the experimental procedure were reported in [13].…”