(physics) valence band; a highest range of electron energies in an insulator or semiconductor that can be populated; it corresponds to the valence electrons of the constituent atoms

difficult / hard, probably impossible

to exceed, to go over, to be more than, to cross / to surpass, to excel / to transcend

prohibition, ban, embargo, taboo

to prohibit

obi - the sash worn with a kimono / paper wrapper (on books, CD, etc.)

electron / (attributive) the quality of being electronic

material, substance

band, belt

belt / sash / band / girdle