Conductivity peak, relaxation dynamics, and superconducting gap of YBa{sub 2}Cu{sub 3}O{sub 7} studied by terahertz and femtosecond optical spectroscopies

Journal Article · Mon Jul 01 04:00:00 EDT 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.54.1355· OSTI ID:288998

Frenkel, A; Gao, F; Liu, Y; Whitaker, J F; Uher, C ^[1]; Hou, S Y; Phillips, J M ^[2]

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1. Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States)
2. AT&T Bell Laboratory, Murray Hill, New Jersey 07974 (United States)

Recent measurements at microwave, terahertz (THz), and infrared frequencies have revealed a peak in {sigma}{sub 1} below {ital T}{sub {ital c}}. Based on our THz measurements, which were performed on high quality, single crystal films of YBCO (900 and 500 A), we have found that {sigma}{sub 1} features a peak which increases in amplitude and shifts to lower temperatures as frequency changes from 1.2 to 0.4 THz. Although the quasiparticle relaxation time extracted from these results using the two-fluid Drude model exhibits an enhancement below {ital T}{sub {ital c}}, the analysis may not be adequate to account for the strong frequency dependence of the conductivity peak by the competition between the drop in scattering rate and the decreasing normal fluid density with temperature. On the contrary, we were able to account for the frequency dependent {sigma}{sub 1} by fitting with Mattis-Bardeen theory (modified to include scattering) using a slower average rate of increase of the anisotropic gap than for the BCS case as temperature decreases below {ital T}{sub {ital c}}. This is consistent with the higher normal fluid density (higher than Gorter-Casimir values) from the two-fluid model interpretation of our THz results. Thus, we have found evidence of BCS coherence factors in a high-{ital T}{sub {ital c}} superconductor with a slower than BCS gap increase below {ital T}{sub {ital c}}. We have discussed the role of coherence factors to account for the presence of the conductivity peak and the absence of the peak in NMR relaxation rate. Furthermore, we have presented a model for the quasiparticle relaxation time measured by the femtosecond pump-probe spectroscopy. This model allowed us to find a fit to the temperature-dependent energy gap function which is also consistent with the slower gap increase below {ital T}{sub {ital c}}.

• OSTI ID: 288998
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 2 Vol. 54; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BARIUM
BARIUM OXIDES
BCS THEORY
CUPRATES
ELECTRIC CONDUCTIVITY
ENERGY GAP
FREQUENCY DEPENDENCE
FS RANGE
HIGH-TC SUPERCONDUCTORS
MONOLAYERS
OPTICAL PROPERTIES
RELAXATION TIME
SUPERCONDUCTING FILMS
TEMPERATURE DEPENDENCE
TRANSITION TEMPERATURE
VISIBLE SPECTRA
YTTRIUM OXIDES