부산대학교 도서관

Quite generally, an insulator is theoretically defined by a vanishingconductivity tensor at the absolute zero of temperature. In classicalinsulators, such as band insulators, vanishing conductivities lead to divergingresistivities. In other insulators, in particular when a high magnetic field(B) is added, it is possible that while the magneto-resistance diverges, theHall resistance remains finite, which is known as a Hall insulator. In thisletter we demonstrate experimentally the existence of another, more exotic,insulator. This insulator, which terminates the quantum Hall effect series in atwo-dimensional electron system, is characterized by a Hall resistance which isapproximately quantized in the quantum unit of resistance h/e^2. This insulatoris termed a quantized Hall insulator. In addition we show that for the samesample, the insulating state preceding the QHE series, at low-B, is of the HIkind.