Differential conductance of a saddle-point constriction with a time-modulated gate-voltage

TL;DR

This paper investigates how a time-modulated gate voltage influences the differential conductance in a saddle-point constriction, revealing features like assisted and suppressed conductance, dip structures, and mini-steps depending on parameters.

Contribution

It introduces a model for the effect of a time-modulated gate voltage on conductance in saddle-point constrictions, highlighting new features and regimes not previously characterized.

Findings

Gate-voltage-assisted and suppressed features depend on chemical potential and modulation frequency.

Dip structures appear in the suppressed regime.

Mini-steps occur when the gate voltage is far from the constriction center.

Abstract

The effect of a time-modulated gate-voltage on the differential conductance $G$ of a saddle-point constriction is studied. The constriction is modeled by a symmetric saddle-point potential and the time-modulated gate-voltage is represented by a potential of the form $V_{0} \theta(a/2-|x-x_{c}|) \cos (\omega t)$. For $\hbar\omega$ less than half of the transverse subband energy level spacing, gate-voltage-assisted (suppressed) feature occurs when the chemical potential $\mu$ is less (greater) than but close to the threshold energy of a subband. As $\mu$ increases, $G$ is found to exhibit, alternatively, the assisted and the suppressed feature. For larger $\hbar\omega$, these two features may overlap with one another. Dip structures are found in the suppressed regime. Mini-steps are found in the assisted regime only when the gate-voltage covers region far enough away from the center of the constriction.