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Title: Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe

Abstract

While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Director. Office of Science. Basic EnergySciences
OSTI Identifier:
919514
Report Number(s):
LBNL-60117
Journal ID: ISSN 0163-1829; PRBMDO; R&D Project: 403005; BnR: KC0302030; TRN: US0806423
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B: Rapid Communications; Journal Volume: 75; Journal Issue: 1; Related Information: Journal Publication Date: 01/2007
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION SPECTRA; DEFECTS; IMPURITIES; NEUTRONS; SCATTERING; STOICHIOMETRY; THERMAL EXPANSION; VALENCE; YTTERBIUM

Citation Formats

Booth, C.H., Christianson, A.D., Lawrence, J.M., Pham, L., Lashley, J., and Drymiotis, F.R.. Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe. United States: N. p., 2006. Web.
Booth, C.H., Christianson, A.D., Lawrence, J.M., Pham, L., Lashley, J., & Drymiotis, F.R.. Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe. United States.
Booth, C.H., Christianson, A.D., Lawrence, J.M., Pham, L., Lashley, J., and Drymiotis, F.R.. Mon . "Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe". United States. doi:. https://www.osti.gov/servlets/purl/919514.
@article{osti_919514,
title = {Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe},
author = {Booth, C.H. and Christianson, A.D. and Lawrence, J.M. and Pham, L. and Lashley, J. and Drymiotis, F.R.},
abstractNote = {While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.},
doi = {},
journal = {Physical Review B: Rapid Communications},
number = 1,
volume = 75,
place = {United States},
year = {Mon May 08 00:00:00 EDT 2006},
month = {Mon May 08 00:00:00 EDT 2006}
}
  • While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with nominally 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.
  • While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with nominally 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.
  • We propose a lattice action including unphysical Wilson fermions with a negative mass m{sub 0} of the order of the inverse lattice spacing. With this action, the exact zero mode of the Hermitian Wilson-Dirac operator H{sub W}(m{sub 0}) cannot appear and near-zero modes are strongly suppressed. By measuring the spectral density {rho}({lambda}{sub W}), we find a gap near {lambda}{sub W}=0 on the configurations generated with the standard and improved gauge actions. This gap provides a necessary condition for the proof of the exponential locality of the overlap-Dirac operator by Hernandez, Jansen, and Luescher. Since the number of near-zero modes ismore » small, the numerical cost to calculate the matrix sign function of H{sub W}(m{sub 0}) is significantly reduced, and the simulation including dynamical overlap fermions becomes feasible. We also introduce a pair of twisted mass pseudofermions to cancel the unwanted higher mode effects of the Wilson fermions. The gauge coupling renormalization due to the additional fields is then minimized. The topological charge measured through the index of the overlap-Dirac operator is conserved during continuous evolutions of gauge field variables.« less
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