RequirePackage{filecontents}
begin{filecontents}{sample.bib}
@article{SNIa,
  title={Measurements of $Omega$ and $Lambda$ from 42 high-redshift supernovae},
  author={Perlmutter S. et al.},
  journal={ApJ},
  year={1995}
}
@article{Tegmark1998,
  title={Measuring the Galaxy Power Spectrum with Future Redshift Surveys},
  author={Tegmark M., Hamilton A.J.S., Strauss M.S., Szalay A.S.},
  journal={ApJ},
  pages={499-555.},
  year={1998}
}
end{filecontents}

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usepackage[style=ext-authoryear, backend=biber]{biblatex}
usepackage{hyperref}

...

% well displayed
SNIa cite{SNIa} et valid'ee depuis par d'autres d'observations

...
% bad displayed
dans le papier de cite{Tegmark1998}

author = {Sigfridsson, E.},

author = {Tegmark, M. and Hamilton, A. J. S. and Strauss, M. S. and Szalay, A. S.},

author={Perlmutter, S. and others},

WARN - Name "Tegmark M., Hamilton A.J.S., Strauss M.S., Szalay A.S." has too many commas:
       skipping name

RequirePackage{filecontents}
begin{filecontents}{jobname.bib}
@article{SNIa,
  title   = {Measurements of {$Omega$} and {$Lambda$} from 42 high-redshift supernovae},
  author  = {Perlmutter, S. and others},
  journal = {ApJ},
  year    = {1995},
}
@article{Tegmark1998,
  title   = {Measuring the Galaxy Power Spectrum with Future Redshift Surveys},
  author  = {Tegmark, M. and Hamilton, A. J. S. and Strauss, M. S. and Szalay, A. S.},
  journal = {ApJ},
  pages   = {499-555},
  year    = {1998}
}
end{filecontents}

documentclass[11pt,french,oneside]{report}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage[francais]{babel}
usepackage[style=ext-authoryear, backend=biber]{biblatex}
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addbibresource{jobname.bib}

begin{document}
SNIa autocite{SNIa} et validée depuis par d'autres d'observations
dans le papier de textcite{Tegmark1998}

printbibliography
end{document}