How to write “ä” and other umlauts and accented letters in bibliography?

Question

How to write in bibliography (package natbib) letter "a" with two dots above? Specially, I mean the word Birkhäuser.

Is there a general rule or way how to write such umlauts or other accented letters in bibliographies?

Answer 1

To typeset accented characters inside bibliography fields for processing with BibTeX, encase them in curly braces. To list but a few accented characters:

{\"a} {\^e} {\`i} {\o} {\'u} {\aa} {\c c} {\u g} {\l} {\~n} {\H o} {\v r} {\ss}

The word Birkhäuser should therefore be entered as Birkh{\"a}user.

---

Addendum: There is an obvious follow-up question to the "How does one enter a special character for use in BibTeX?" question. Namely: Why is it necessary to encase these "special characters" in this manner? Or: Why is the ordinary LaTeX method of entering these characters -- say, \"{a} or even \"a -- not quite good enough for BibTeX?

The main issue to grasp is that the contents of bibliographic fields -- certainly author and editor fields, but potentially other fields as well, including title, booktitle, and organization fields -- are frequently used to sort entries alphabetically. How does one sort characters with Umlaute, diacritics, and other special features relative to the basic 26 characters of the Latin alphabet? How is one supposed to sort three authors named, say, Peter Hauser, Anna Häuser, and John Hill?

For some pretty sound reasons (but which are way too ancient and obscure to go into any adequate level of detail here; to explore these reasons properly, it's crucial to have Appendix C of the TeXBook handy...), a decision was made in the design of BibTeX to "purify" (the BibTeX function that does this job really is called purify$!) the contents of various fields as follows (this method conforms, probably not surprisingly, to US and UK sorting criteria; it needn't be "correct" outside of English-speaking regions, as I will note below):

• {\"a}, {\'a}, {\^a}, etc are all made equivalent for sorting purposes to a,
• {\"o}, {\'o}, {\H o} and {\o} all become equivalent to o,
• {\l} and {\L} become equivalent to l and L, respectively,
• {\ss} becomes equivalent to ss,
• {\aa} becomes equivalent to aa,
• and so on for the other "accented" characters,
• finally, any characters that do not fit into this scheme, including ä, are moved to the very end, i.e., after z. (This may seem arbitrary and ill-informed from today's vantage point, but back when BibTeX was created more than 20 years ago the only relevant character encoding and sorting system was ASCII.)

As you can immediately appreciate, this purification step is greatly simplified and made more robust if the "special" characters are all entered consistently in the manner suggested in the first part of this answer.

Turning to the earlier case of Peter Hauser, Anna Häuser, and John Hill: How will they appear in the bibliography (assuming the entries are to be sorted alphabetically by the authors' last names)? If Anna's last name is entered as H{\"a}user, the three authors will end up being listed as Häuser, A. - Hauser, P. - Hill, J.. In contrast, if Anna's last name had been entered as Häuser, the sorting order will be Hauser - Hill - Häuser. For most English-speaking readers, the second ordering will look completely wrong.

Some specialists from, say, Sweden, may object that this approach to sorting characters that aren't among the basic 26 characters of the Latin alphabet doesn't meet the specific national standards of, say, Sweden. [I don't mean to pick on any Swedes, of course. I mention them because I remember having read somewhere that in the Swedish alphabet, ä does come after z and hence is definitely not equivalent (not even for sorting purposes!) to a.] My answer to this objection is: If you're a Swedish author writing in Swedish for a Swedish target audience, you had better conform to specific Swedish customs. On the other hand, if you're a Swede writing in English in a journal that's exclusively published in English, it'll do you no good at all if you try to insist on obeying Swedish sorting customs in your paper's bibliography. Of course, the very inability of BibTeX to be easily adaptable to non-English sorting customs is one of the reasons for the development and adoption of BibLaTeX and Biber. However, that's a topic for another day, isn't it?

The issue of how BibTeX sorts bibliographic entries (as well as many other fascinating issues!) is examined at length and explained admirably in the surprisingly readable (given the enormous dryness of the subject!) essay Tame the BeaST by Nicolas Markey. If you have TeXLive or MikTeX as your TeX distribution, you can also access this document by typing "texdoc tamethebeast" at a command prompt.

Answer 2

When using \usepackage[uft8]{inputenc} you can have it directly.

Consider the .bib file:

@BOOK
  {Goe,
   AUTHOR  = "Gödel",
   TITLE   = "Die Vollständigkeit der Axiome des logischen Funktionenkalküls.",
   PUBLISHER = "Monatshefte für Mathematik und Physik",
   YEAR = 1930
  }

for example. Then

\documentclass{article}
\usepackage[utf8]{inputenc}

\begin{document}
\bibliographystyle{plain}

\section{Introduction}
Hällo Wörld\cite{Goe}

\bibliography{encodingInBib}

\end{document}

yields the desired result. Or, you could also use biblatex and the following code:

\documentclass{article} 
\usepackage[utf8]{inputenc}
\usepackage{biblatex} 
\bibliography{ref}
\begin{document} 
Hällo Wörld\cite{Goe} 
\printbibliography
\end{document}

In the final result, using either method, the umlauts are inserted automatically.