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 G(NS) 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 enhanced in experiments on metal-superconductor structures. [S0163-1829(99)07943-6].
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机译：我们提出了在相干二维电子气与具有正常区域中的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）]，它是在时间依赖的Bogoliubov-de Gennes形式主义中进行研究的。我们发现，对于具有仅几个传播模式的量子点接触的界面，电导率G（NS）相对于正常状态电导率GN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的实验中不存在电导增强的现象。 [S0163-1829（99）07943-6]。
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