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Title: Recombination and propagation of quasiparticles in cuprate superconductors

Abstract

Rapid developments in time-resolved optical spectroscopy have led to renewed interest in the nonequilibrium state of superconductors and other highly correlated electron materials. In these experiments, the nonequilibrium state is prepared by the absorption of short (less than 100 fs) laser pulses, typically in the near-infrared, that perturb the density and energy distribution of quasiparticles. The evolution of the nonequilibrium state is probed by time resolving the changes in the optical response functions of the medium that take place after photoexcitation. Ultimately, the goal of such experiments is to understand not only the nonequilibrium state, but to shed light on the still poorly understood equilibrium properties of these materials. We report nonequilibrium experiments that have revealed aspects of the cup rates that have been inaccessible by other techniques. Namely, the diffusion and recombination coefficients of quasiparticles have been measured in both YBa2Cu3O6.5 and Bi2Sr2CaCu2O8+x using time-resolved optical spectroscopy. Dependence of these measurements on doping, temperature and laser intensity is also obtained. To study the recombination of quasiparticles, we measure the change in reflectivity ΔR which is directly proportional to the nonequilibrium quasiparticle density created by the laser. From the intensity dependence, we estimate β, the inelastic scattering coefficient and γthmore » thermal equilibrium quasiparticle decay rate. We also present the dependence of recombination measurements on doping in Bi2Sr2CaCu2O8+x. Going from underdoped to overdoped regime, the sign of ΔR changes from positive to negative right at the optimal doping. This is accompanied by a change in dynamics. The decay of ΔR stops being intensity dependent exactly at the optimal doping. We provide possible interpretations of these two observations. To study the propagation of quasiparticles, we interfered two laser pulses to introduce a spatially periodic density of quasiparticles. Probing the evolution of the initial density through space and time yielded the quasiparticle diffusion coefficient, and both inelastic and elastic scattering rates. Measured diffusion coefficient suggests that the quasiparticles induced by the laser occupy primarily states near the antinodal regions of the Brillouin zone.« less

Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
842568
Report Number(s):
LBNL-55855
R&D Project: 504601; TRN: US0503620
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: doctoral thesis, Ph.D, University of California, Berkeley, Berkeley, CA
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION; BRILLOUIN ZONES; CUPRATES; DECAY; DIFFUSION; ELASTIC SCATTERING; ELECTRONS; ENERGY SPECTRA; INELASTIC SCATTERING; LASERS; RECOMBINATION; REFLECTIVITY; RESPONSE FUNCTIONS; SPECTROSCOPY; SUPERCONDUCTORS; THERMAL EQUILIBRIUM; superconductivity cuprates quasiparticles

Citation Formats

Gedik, Nuh. Recombination and propagation of quasiparticles in cuprate superconductors. United States: N. p., 2004. Web. doi:10.2172/842568.
Gedik, Nuh. Recombination and propagation of quasiparticles in cuprate superconductors. United States. https://doi.org/10.2172/842568
Gedik, Nuh. 2004. "Recombination and propagation of quasiparticles in cuprate superconductors". United States. https://doi.org/10.2172/842568. https://www.osti.gov/servlets/purl/842568.
@article{osti_842568,
title = {Recombination and propagation of quasiparticles in cuprate superconductors},
author = {Gedik, Nuh},
abstractNote = {Rapid developments in time-resolved optical spectroscopy have led to renewed interest in the nonequilibrium state of superconductors and other highly correlated electron materials. In these experiments, the nonequilibrium state is prepared by the absorption of short (less than 100 fs) laser pulses, typically in the near-infrared, that perturb the density and energy distribution of quasiparticles. The evolution of the nonequilibrium state is probed by time resolving the changes in the optical response functions of the medium that take place after photoexcitation. Ultimately, the goal of such experiments is to understand not only the nonequilibrium state, but to shed light on the still poorly understood equilibrium properties of these materials. We report nonequilibrium experiments that have revealed aspects of the cup rates that have been inaccessible by other techniques. Namely, the diffusion and recombination coefficients of quasiparticles have been measured in both YBa2Cu3O6.5 and Bi2Sr2CaCu2O8+x using time-resolved optical spectroscopy. Dependence of these measurements on doping, temperature and laser intensity is also obtained. To study the recombination of quasiparticles, we measure the change in reflectivity ΔR which is directly proportional to the nonequilibrium quasiparticle density created by the laser. From the intensity dependence, we estimate β, the inelastic scattering coefficient and γth thermal equilibrium quasiparticle decay rate. We also present the dependence of recombination measurements on doping in Bi2Sr2CaCu2O8+x. Going from underdoped to overdoped regime, the sign of ΔR changes from positive to negative right at the optimal doping. This is accompanied by a change in dynamics. The decay of ΔR stops being intensity dependent exactly at the optimal doping. We provide possible interpretations of these two observations. To study the propagation of quasiparticles, we interfered two laser pulses to introduce a spatially periodic density of quasiparticles. Probing the evolution of the initial density through space and time yielded the quasiparticle diffusion coefficient, and both inelastic and elastic scattering rates. Measured diffusion coefficient suggests that the quasiparticles induced by the laser occupy primarily states near the antinodal regions of the Brillouin zone.},
doi = {10.2172/842568},
url = {https://www.osti.gov/biblio/842568}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat May 01 00:00:00 EDT 2004},
month = {Sat May 01 00:00:00 EDT 2004}
}

Thesis/Dissertation:
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