高等固体与物理-维度.ppt

Two dimensional helium Since helium is attracted to almost anything* , it will form a 2D film. Most long-range order is forbidden in 2D (Mermin-Wagner theorem), e.g. BEC not allowed for T0 because the system is susceptible to long-range phase decoherence. However, it does become a superfluid. The transition is called the Kosterlitz-Thouless transition. Superfluid-normal fluid transition is caused by vortex-anti-vortex unbinding. KT predicts algebraic decay of single particle density matrix 2d helium energetics In contrast to 3D the energy is a smooth function of temperature. Bump in Cv above the transition. No feature at the transition (only an essential singularity) Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 新进展 观察到分数电荷涨落. FQHE 的Ginsburg Landau 理论. 费米, 玻色 和分数统计. 边缘态和共形场论. … 利用一维结观察分数电荷 C.L. Kane and M.P.A. Fisher, Shot in the Arm for Fractional Charge, Nature 389, 119 (1997). Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. The Quantum Hall effect (QHE) is one example of a quantum phenomenon that occurs on a truly macroscopic scale. The signature of QHE is the quantization plateaus in the Hall resistance (Rxy) and vanishing magnetoresistance (Rxx) in a magnetic field. The QHE, exclusive to two-dimensional metals, has led to the establishment of a new metrological standard, the resistance quantum, , that contains only fundamental constant. As with many other quantum phenomena, the observation of the QHE usually requires low temperatures (previously reported highest temperature was 30 K). In graphene, a single atomic layer of graphite, however, we have observed a well-defined QHE at room temperature owing to the unusual electronic band structure and the relativistic nature of the charge carriers of gra