Zero-Bias Anomaly in Quantum Point Contacts

Quantum point contacts (QPCs) are narrow constrictions between large reservoirs of two-dimensional electron gas, with conductance quantized in units of $G = 2e^2/h$ at zero magnetic field. Despite decades of investigation, some conductance features of QPCs remain mysterious, one of which is known as the zero-bias anomaly (ZBA) --- a conductance peak centered at $V_{\mathrm{sd}}=0$ when the source-drain voltage $V_{\mathrm{sd}}$ is swept. Most previous work has focused on ZBAs around the 0.7 structure ($2e^2/h\ga G\ga e^2/h$). Here, we report measurements of the ZBA over a wide range of conductance, from the low-conductance limit ($G\sim10^{-4} e^2/ h$) to well above the first plateau ($G\sim4-6 e^2/h$). The qualitatively different dependences on in-plane magnetic field that are observed for ZBAs in different conductance regimes provide insight into the various physical mechanisms responsible for this feature.