Today was the first day of interviews at my school.
All the men I did see were wearing dark suits, white shirts and a variety of ties. There may have been a few without jackets, but I didn't see them. I know a few did go without jackets at my interview a few years ago.
Get yourself a suit! Every man should have at least one good conservative suit in his wardrobe. You may need it during the school year...we've had a few functions that required business professional attire, and one black tie optional gala.