Resistively‐detected NMR lineshapes in a local filling ν <1 quantum Hall breakdown

Resistively-detected NMR (RDNMR) is a unique characterization method enabling highly-sensitive detection for single quantum nanostructure, such as point contact (QPC). In many studies, we use dynamic nuclear polarization and RDNMR in Hall breakdown regime of local QPC filling factor 1 ($\nu_{\rm{qpc}} = 1$). However, the lineshapes signal are proved to be complicated still not fully understood yet. Here, systematically polarize spins by current-pumping from close vicinity $\nu_{\rm{qpc}} 1$ conductance plateau all way down pinch-off point, providing clear evidence that spin-flip scattering between two edge channels at lowest Landau level occurs constriction even when it pinch off ($G \approx 10^{-2}$ $2e^{2}/h$). The collected spectra reveal sets distinguished features. First, strong intermediate tunneling regime, observe an ordinary resistance dip lineshape but interestingly its transition frequency follows snake-like pattern, indicative spatial modulation electron density QPC. Second, weak spectrum turns into dispersive which interpret due build up spin with different polarization.