As crowd-pulling operatic divas go, most of the attention goes to the sopranos. But a select number of mezzos have the same kind of following, and Latvia's Elina Garanča is high on that list. There are just a few roles where the mezzo is the main character of the opera (many of the others are "witches and bitches", as Garanča puts it), and the big one of those is Carmen.