# What does it mean for a Hamiltonian or system to be gapped or gapless?

+ 9 like - 0 dislike
1584 views

I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean?

Edit: Is an XX spin chain in a magnetic field gapped? Why or why not?

This post imported from StackExchange Physics at 2014-04-04 16:13 (UCT), posted by SE-user Jane