Wednesday, September 12, 2018

condensed matter - Can gapped state and gapless state be adiabatically connected to each other?


Is it possible that we can construct a gapped state and a gapless state which are adiabatically connected?


Here adiabatically connected I mean:


there exists a class of Hamiltonians $H(g)$ with ground state $|\phi(g)>$($g\in[0,1]$), such that $|\phi(0)>$ is gapless and $|\phi(1)>$ is gapped. And the ground state average of any local operator $(g)$ doesn't has singularity for all $g\in[0,1]$





  1. If it's possible, can some one give me an example?




  2. If it's impossible. Does it imply we can always find a topological order or a normal order parameter to distinguish a gapped phase from a gapless phase.






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