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The even-denominator states have attracted considerable attention owing to their possible applications in future quantum technologies. In this letter, we first report a 3/2 diagonal resistance, indicating the existence of a 3/2 state in a nanometer-sized triple-gated quantum point contact (QPC) fabricated on a high-mobility (not ultra-high-mobility) single-layer two-dimensional (2D) GaAs wafer. The center gate plays a crucial role in realizing the QPC’s 3/2 state. Our observation of the 3/2 state using a conventional QPC device, which is a suitable building block for semiconductor quantum devices, paves a new path for the development of semiconductor-based quantum technologies.

We demonstrate a way to polarize and detect nuclear spin in a gate-defined quantum point contact operating at high Landau levels. Resistively-detected Nuclear Magnetic Resonance (RDNMR) can be achieved up to the 5th Landau level and at a magnetic field lower than 1 T. We are able to retain the RDNMR signals in a condition where the spin degeneracy of the first 1D subband is still preserved. Furthermore, the effects of orbital motion on the first 1D subband can be made smaller than those due to electrostatic confinement. This developed RDNMR technique is a promising means to study electronic states in a quantum point contact near zero magnetic field. PACS numbers:In a quantum Hall setting, generation of nuclear spin polarization and NMR detection are mostly carried out at the lowest Landau level (LL). Examples include quantum Hall edge channels 1-8 , breakdown of integer and fractional quantum Hall effect 9-15 , spin transitions of integer and fractional quantum Hall effect [16][17][18][19][20][21][22][23][24][25][26][27][28] . A few Tesla magnetic field is typically required to reach the lowest LL. Here, we advance the existing body of works by demonstrating local generation and detection of nuclear spin polarization in a quantum point contact at half-integer quantum Hall effect operating at up to the 5 th LL. This way we manage to push the lowest field down to less than 1 Tesla without relying on spin injection from ferromagnetic contacts 29-32 .One important application of this RDNMR techniques is to probe many body electronic states in the lowest 1D subband such as the 0.7 × 2e 2 /h anomalous conductance 33-50 , whose microscopic origin is still under active discussion. Early NMR measurement in the quantum point contact by Kawamura et al. 49 reveals that the 0.7 anomaly does not arise from a bound state formation. The measurement itself is carried out in an in plane magnetic field of 4.5 T to polarize the nuclei in a quantum point contact, but at the expense of almost fully lifting the spin degeneracy of the first 1D subband. It is not obvious whether the conclusion remains the same in the case where the spin is degenerate. In particular, a scanning gate microscope measurement by Brun et al. 45,50 observing an interference pattern of electron waves between a tip and a quantum point contact at zero magnetic field agrees with a single or multiple bound states formation scenario. Finding a way to perform NMR in a quantum point contact without lifting the spin degeneracy of the first 1D subband therefore is crucially important and hence the main focus of this paper.Although in a quantum Hall setting the out of plane field exerts circular motion on electrons, we found that the effects on the 1D subband can be made smaller than those due to electrostatic confinement. This makes it possible to preserve the electrons motion at the lowest subband in the quantum point contact so that the motion is as close as possible to that without a magnetic field.The layout and dimensions of the present devices displayed in Fig. 1(...

Resistively‐detected nuclear magnetic resonance (RDNMR) is a unique characterization method enabling highly sensitive NMR detection for a single quantum nanostructure, such as a quantum point contact (QPC). In many studies, dynamic nuclear polarization and RDNMR detection are used in a quantum Hall breakdown regime of a local QPC filling factor of 1 (νqpc = 1). However, the RDNMR lineshapes are complicated and still not fully understood yet. Herein, the nuclear spins are systematically polarized by current pumping from the close vicinity of the νqpc = 1 conductance plateau all the way down to pinch‐off point, providing clear evidence that the spin‐flip scattering between two edge channels at the lowest Landau level still occurs in the constriction even when it is close to the pinch off point. The collected RDNMR spectra reveal two sets of distinguished features. First, in a strong to intermediate tunneling regime, we observe an ordinary resistance dip lineshape with snake‐like transition frequencies, indicative of spatial modulation of electron density in the QPC. Second, in a weak tunneling regime, the spectrum turns into a dispersive lineshape, which is interpreted due to the build‐up of two sets of nuclear spin polarization that are in contact with different electron spin polarization.

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