Electric fields can polarize a variety of these substances often placed between capacitor plates.
In one class of these substances, helical edge states give rise to the quantum spin Hall effect in the absence of external magnetic fields. These substances lack density of states at the Fermi energy which, for them, lies in a large band gap. Strong interelectronic repulsion explains why (*) nickel oxide is one of these substances according to Mott-Hubbard theory. Electric fields can polarize a variety of these substances often placed between capacitor plates. Dielectrics are an example of - for 10 points - what substances which do not conduct electricity?
In one class of these substances, helical edge states give rise to the quantum spin Hall effect in the absence of external magnetic fields.
electrical insulators [accept topological insulators or Mott insulators, accept antiferromagnets before "Fermi" is read; prompt on dielectrics]