K. Nagase

Resistively detected nuclear magnetic resonance via a single InSb two-dimensional electron gas at high temperature

We report on the demonstration of the resistively detected nuclear magnetic resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at elevated temperatures up to 4 K. The RDNMR signal of I115n in the simplest pseudospin quantum Hall ferromagnet triggered by a large direct current shows a peak-dip line shape, where the nuclear relaxation time T1 at the peak and the dip is different but almost temperature independent. The large Zeeman, cyclotron, and exchange energy scales of the InSb 2DEG contribute to the persistence of the RDNMR signal at high temperatures.

Gate depletion of an InSb two-dimensional electron gas

We investigated the gate control of a two-dimensional electron gas (2DEG) confined to InSb quantum wells with an Al2O3 gate dielectric formed by atomic layer deposition on a surface layer of Al0.1In0.9Sb or InSb. The wider bandgap of Al0.1In0.9Sb compared to InSb resulted in a linear, sharp, and non-hysteretic response of the 2DEG density to gate bias in the structure with an Al0.1In0.9Sb surface layer. In contrast, a nonlinear, slow, and hysteretic (nonvolatile-memory-like) response was observed in the structure with an InSb surface layer. The 2DEG with the Al0.1In0.9Sb surface layer was completely depleted by application of a small gate voltage (∼ −0.9u2009V).

Characterization of InSb quantum wells with atomic layer deposited gate dielectrics

We report magnetotransport measurements of a gated InSb quantum well (QW) with high quality Al2O3 dielectrics (40u2009nm thick) grown by atomic layer deposition. The magnetoresistance data demonstrate a parallel conduction channel in the sample at zero gate voltage (Vg). A good interface between Al2O3 and the top InSb layer ensures that the parallel channel is depleted at negative Vg and the density of two-dimensional electrons in the QW is tuned by Vg with a large ratio of 6.5u2009×u20091014u2009m−2 V−1 but saturates at large negative Vg. These findings are closely related to layer structures of the QW as suggested by self-consistent Schrodinger-Poisson simulation and two-carrier model.

Resistively detected NMR line shapes in a quasi-one-dimensional electron system

We observe variation in the resistively-detected nuclear magnetic resonance (RDNMR) lineshapes in quantum Hall breakdown. The breakdown is locally occurred in a gate-defined quantum point contact (QPC) region. Of particular interest is the observation of a dispersive lineshape occured when the bulk 2D electron gas (2DEG) is set to

Scanning nuclear electric resonance microscopy using quantum-Hall-effect breakdown

nu_{rm{b}} = 2

Simultaneous measurement of resistively and optically detected nuclear magnetic resonance in the ν = 2 / 3 fractional quantum Hall regime

and the QPC filling factor to the vicinity of

Localized NMR Mediated by Electrical-Field-Induced Domain Wall Oscillation in Quantum-Hall-Ferromagnet Nanowire

nu_{rm{QPC}} = 1

Fabry-Pérot interference in a triple-gated quantum point contact

, strikingly resemble the dispersive lineshape observed on a 2D quantum Hall state. This previously unobserved lineshape in a QPC points to simultaneous occurrence of two hyperfine-mediated spin flip-flop processes within the QPC. Those events give rise to two different sets of nuclei polarized in the opposite direction and positioned at a separate region with different degree of electronic polarizations.

Resistive detection of optically pumped nuclear polarization with spin phase transition peak at Landau level filling factor 2/3

We present a scanning nuclear-spin resonance (NSR) method that incorporates resistive detection with electric-field induced NSR locally excited by a scanning metallic probe. In the quantum-Hall effect breakdown regime, NSR intensity mapping at both the fundamental NSR frequency f75As and twice the frequency 2f75As demonstrates the capability to probe the distribution of nuclear polarization, particularly in a semiconductor quantum well. We find that f75As NSR excitation drives not only local NSR but also spatially overlapped nonlocal NSR, which suppresses the maximum intensity of local NSR, while the 2f75As NSR yields purely local excitation conferring a larger intensity.

Transport characteristics of InSb trench-type in-plane gate quantum point contact

We observe nuclear magnetic resonance (NMR) in the fractional quantum Hall regime at the Landau-level filling factor of