What's the meaning of "Incompressible" for FQHE?

[howl]

Someone says The fractional quantum Hall effect is an incompressible quantum liquid, what's the meaning?

 

[atyy]

There is a description of incompressibility in Allan Macdonald's notes: https://arxiv.org/abs/cond-mat/9410047.

 

[howl]

There is a description of incompressibility in Allan Macdonald's notes: https://arxiv.org/abs/cond-mat/9410047.

It's helpful, thanks.