Wurm Jürgen, Rycerz Adam, Adagideli Inanç, Wimmer Michael, Richter Klaus, Baranger Harold U
Institut für Theoretische Physik, Universität Regensburg, D-93040, Germany.
Phys Rev Lett. 2009 Feb 6;102(5):056806. doi: 10.1103/PhysRevLett.102.056806.
We study the symmetry classes of graphene quantum dots, both open and closed, through the conductance and energy level statistics. For abrupt termination of the lattice, these properties are well described by the standard orthogonal and unitary ensembles. However, for smooth mass confinement, special time-reversal symmetries associated with the sublattice and valley degrees of freedom are critical: they lead to block diagonal Hamiltonians and scattering matrices with blocks belonging to the unitary symmetry class even at zero magnetic field. While the effect of this structure is clearly seen in the conductance of open dots, it is suppressed in the spectral statistics of closed dots, because the intervalley scattering time is shorter than the time required to resolve a level spacing in the closed systems but longer than the escape time of the open systems.
我们通过电导和能级统计研究了开放和封闭的石墨烯量子点的对称类。对于晶格的突然终止，这些性质可以用标准的正交和酉系综很好地描述。然而，对于平滑的质量限制，与子晶格和能谷自由度相关的特殊时间反演对称性至关重要：即使在零磁场下，它们也会导致块对角哈密顿量和散射矩阵，其块属于酉对称类。虽然这种结构的影响在开放量子点的电导中清晰可见，但在封闭量子点的光谱统计中却受到抑制，因为能谷间散射时间比在封闭系统中分辨能级间距所需的时间短，但比开放系统的逃逸时间长。
