split a \xrightarrow into two lines

I'm using the command \xrightarrow{}[] in a two column document. The problem is that the string above the arrow is too long and the arrow ends outside the column. Is there a way to "split" the arrow over two different lines?

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You can't really split a single symbol like that. And I'm not sure it would be a good idea to do so anyway. –  Seamus Jul 13 '12 at 14:31
But you probably can split in two lines the text over the arrow –  JLDiaz Jul 13 '12 at 14:59
Thanks Seamus and JLDiaz for your answers! Do you know how to split in two lines the text over the arrow??? Because \xrightarrow{text1 \\ text2}[] is no effective. –  taksun Jul 13 '12 at 15:06

$a \xrightarrow{\substack{x \to 0 \\ y \to 0}} b$