Who says barbell has to mean "use two hands?" Narrow-minded thinking will only translate to narrow lats. This one-arm barbell exercise is brutally effective for lat development.
One-Arm Barbell Row
Simply stand beside the loaded barbell, reach down and grasp the bar, and start rowing. If you expect this to feel like a regular dumbbell row, then be prepared to be humbled. These are unique, to say the least. When done correctly, you'll feel it from the top of your lat to the bottom.
Performance Notes
Really emphasize the stretch on the way down.
Use 25-pound plates to extend the range of motion, allowing for the greatest possible stretch.
Raise the hip on the side you're lifting higher than the other hip. Most people do these or dumbbell rows with "square" shoulders, so they're really missing out on the awesome pre-stretch and extra range of motion that can be had. Try this and you'll understand.