中觀接頭的時變場效應及相位不相干效應

Abstract

我們研究在中觀接頭中傳輸的時變場效應，這些接頭包括(一)量子井、(二)雙位壘和(三)超導-常態金屬 -超導接頭。並把Buttiker研究直流場相位不相干效應提出的散射矩陣模型推展到時變場的情況下。這些 時變場導致同調非彈性散射，另外，在相位不相干散射矩陣作用下，則有部份不同調非彈性散射。作 用在有限範圍的時變閘極電位使電子沿著傳輸方向的動量可以不守恆，引起次能帶躍遷。 在（一）、（二）的常態接頭，時變場引起的次能帶躍遷對微分電導產生Fano結構，在（三）的超導 接頭，時變場引起的次能帶躍遷對超導電流積分元產生Fano結構，這些結構都與准束縛態的形成有關 。Fano結構的寬窄和時變場的強弱有關，Fano結構的形狀和時變場的位置有關。在（三）中，時變場 雖然造成Andreev能態散逸，使得束縛態電流消失，但是散射態因次能帶躍遷引起的Fano結構卻能部份 補回束縛態失去的電流。 在含時變場的相位不相干散射矩陣作用下，部份不同調非彈性散射會使因時變場造成的Fano結構變寬 平。

We have studied the transport effects of time-modulated potential in mesoscopic junctions. These junctions include (1) quantum dot, (2) double-barrier and (3) superconductor-normal-metal-superconductor junction. And we extend the scattering-matrix model, proposed by B\"{u}ttiker for studying the phase incoherent effects in dc potential, to the situation in time-modulated potential. The time-modulated potential leads to scattering that is phase coherent and inelastic. Besides, there is partial scattering that is phase incoherent and inelastic, in the action of phase incoherent scattering matrix. The finite-range time-modulated gate-potential makes the momentum in the transport direction variable, inducing sideband transition. The sideband transition induced by time-modulated potential produces Fano structure to differential conductance in (1), (2) normal junctions. The sideband transition induced by time-modulated potential produces Fano structure to the integrand of superconducting current in (3) superconducting junction. The width of the Fano structure is related to the strength of the time-modulated potential. The configuration of the Fano structure is related to the position of the time-modulated potential. Although the time-modulated potential makes the Andreev level leaking in (3), the Fano structure induced by sideband transition in scattering state can partially recontribute the current that bound state lost. In the action of phase incoherent scattering matrix including time-modulated potential, the partial incoherent and inelastic scattering can make the Fano structure induced by time-modulated potential wide and low.