Main Question or Discussion Point
Generally, a material is metal or insulator is simply determined by the gap. But if we view it in another way, to measure the resistance in different direction, says x and y, and there are usually different. And then measure the resistance change with temperature. Usually, the resistances goes up with temperature increases is metal, while resistances goes down is insulator, or semiconductor. If one finds that a material in x direction looks like metal in this resistance experimental, while in y no, is this situation possible? If so, could we say this material is metal just in x direction?