We present numerical calculations of the conductance of an interface between a phase-coherent two-dimensional electron gas and a superconductor with a quantum point contact in the normal region. Using a scattering matrix approach we reconsider the geometry of De Raedt, Michielsen, and Klapwijk [Phys. Rev. B 50, 631 (1994)] which was studied within the time-dependent Bogoliubov�de Gennes formalism. We find that the factor-of-2 enhancement of the conductance GNS compared to the normal state conductance GN for ideal interfaces may be suppressed for interfaces with a quantum point contact with only a few propagating modes. The suppression is found to depend strongly on the position of the Fermi level. We also study the suppression due to a barrier at the interface and find an anomalous behavior caused by quasiparticle interference. Finally, we consider the limit of sequential tunneling and find a suppression of the factor-of-2 enhancement which may explain the absence of conductance enhancement in experiments on metal-superconductor structures.
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机译：我们提出了一种在相干二维电子气与在正常区域中具有量子点接触的超导体之间的界面电导的数值计算。使用散射矩阵方法，我们重新考虑了De Raedt，Michielsen和Klapwijk [Phys。 Rev. B 50，631（1994）]，这是在时间依赖的BogoliubovâdeGennes形式主义中进行的。我们发现，对于具有仅少数传播模式的量子点接触的界面，对于理想界面，与正常状态电导GN相比，电导GNS的2因子增强可能受到抑制。发现抑制很大程度上取决于费米能级的位置。我们还研究了由于界面处的障碍而引起的抑制，并发现了由准粒子干扰引起的异常行为。最后，我们考虑了顺序隧穿的极限，并发现了2因子增强的抑制作用，这可以解释在金属超导体结构实验中电导没有增强的现象。
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