Note to players: Description acceptable. For a system of quantum particles with this property, solutions to Harper’s equation with varying flux ratio produce Hofstadter’s butterfly. Frank Wilczek hypothesized quasiparticles with fractional spin states called “anyons” (15[1])(“EN-ee-ons”) that have only been observed in systems with this property. (15[1])Extreme magnetoresistance and a lack of inversion centers allow for spin-valley coupling in a class of materials with this property known as transition-metal di·chalco·genides. An electron gas model of systems with this property exhibits discretized resistance in the (*) quantum Hall effect. Andre Geim and Konstantin Novoselov used micromechanical exfoliation to produce a material with this topological (10[1])property by peeling it away from a more common carbon allotrope with Scotch tape. For 10 points, crystalline materials like graphene have what general property of being as thin as possible? ■END■