58 research outputs found
Polarization dependent Landau level crossing in a two-dimensional electron system in MgZnO/ZnO-heterostructure
We report electrical transport measurements in a tilted magnetic field on a
high-mobility two-dimensional electron system confined at the MgZnO/ZnO
heterointerface. The observation of multiple crossing events of spin-resolved
Landau levels (LLs) enables the mapping of the sequence of electronic states.
We further measure the renormalization of electron spin susceptibility at zero
field and the susceptibility dependence on the electron spin polarization. The
latter manifests the deviation from the Pauli spin susceptibility. As the
result, the crossing of spin-resolved LLs shifts to smaller tilt angles and the
first Landau level coincidence event is absent even when the magnetic field has
only a perpendicular component to the 2DES plane.Comment: 5 pages, 4 figure
Temperature dependent magnetotransport around = 1/2 in ZnO heterostructures
The sequence of prominent fractional quantum Hall states up to =5/11
around =1/2 in a high mobility two-dimensional electron system confined at
oxide heterointerface (ZnO) is analyzed in terms of the composite fermion
model. The temperature dependence of \Rxx oscillations around =1/2
yields an estimation of the composite fermion effective mass, which increases
linearly with the magnetic field. This mass is of similar value to an enhanced
electron effective mass, which in itself arises from strong electron
interaction. The energy gaps of fractional states and the temperature
dependence of \Rxx at =1/2 point to large residual interactions between
composite fermions.Comment: 5 pages, 4 Figure
Air-gap gating of MgZnO/ZnO heterostructures
The adaptation of “air-gap” dielectric based field-effect transistor technology to controlling the MgZnO/ZnO heterointerface confined two-dimensional electron system (2DES) is reported. We find it possible to tune the charge density of the 2DES via a gate electrode spatially separated from the heterostructure surface by a distance of 5 μm. Under static gating, the observation of the quantum Hall effect suggests that the charge carrier density remains homogeneous, with the 2DES in the 3 mm square sample the sole conductor. The availability of this technology enables the exploration of the charge carrier density degree of freedom in the pristine sample limit
Air-gap gating of MgZnO/ZnO heterostructures
The adaptation of “air-gap” dielectric based field-effect transistor technology to controlling the MgZnO/ZnO heterointerface confined two-dimensional electron system (2DES) is reported. We find it possible to tune the charge density of the 2DES via a gate electrode spatially separated from the heterostructure surface by a distance of 5 μm. Under static gating, the observation of the quantum Hall effect suggests that the charge carrier density remains homogeneous, with the 2DES in the 3 mm square sample the sole conductor. The availability of this technology enables the exploration of the charge carrier density degree of freedom in the pristine sample limit
Composite fermion liquid to Wigner solid transition in the lowest Landau level of zinc oxide
Interactions between the constituents of a condensed matter system can drive it through a plethora of different phases due to many-body effects. A prominent platform for it is a dilute two-dimensional electron system in a magnetic field, which evolves intricately through various gaseous, liquid and solid phases governed by Coulomb interaction. Here we report on the experimental observation of a phase transition between the composite fermion liquid and adjacent magnetic field induced phase with a character of Wigner solid. The experiments are performed in the lowest Landau level of a MgZnO/ZnO two-dimensional electron system with attributes of both a liquid and a solid. An in-plane magnetic field component applied on top of the perpendicular magnetic field extends the Wigner-like phase further into the composite fermion liquid phase region. Our observations indicate the direct competition between a composite fermion liquid and a Wigner solid formed either by electrons or composite fermions
Even-denominator fractional quantum Hall physics in ZnO
The fractional quantum Hall (FQH) effect emerges in high-quality two-dimensional electron systems exposed to a magnetic field when the Landau-level filling factor, ν_e, takes on a rational value. Although the overwhelming majority of FQH states have odd-denominator fillings, the physical properties of the rare and fragile even-denominator states are most tantalizing in view of their potential relevance for topological quantum computation. For decades, GaAs has been the preferred host for studying these even-denominator states, where they occur at ν_e = 5/2 and 7/2. Here we report an anomalous series of quantized even-denominator FQH states outside the realm of III–V semiconductors in the MgZnO/ZnO 2DES electron at ν_e = 3/2 and 7/2, with precursor features at 9/2; all while the 5/2 state is absent. The effect in this material occurs concomitantly with tunability of the orbital character of electrons at the chemical potential, thereby realizing a new experimental means for investigating these exotic ground states
Temperature-Dependent Magnetotransport around ν=1/2 in ZnO Heterostructures
The sequence of prominent fractional quantum Hall states up to ν = 5/11 around ν = 1/2 in a high-mobility two-dimensional electron system confined at oxide heterointerface (ZnO) is analyzed in terms of the composite fermion model. The temperature dependence of R_(xx) oscillations around ν = 1/2 yields an estimation of the composite fermion effective mass, which increases linearly with the magnetic field. This mass is of similar value to an enhanced electron effective mass, which in itself arises from strong electron interaction. The energy gaps of fractional states and the temperature dependence of R_(xx) at ν = 1/2 point to large residual interactions between composite fermions
Temperature-Dependent Magnetotransport around ν=1/2 in ZnO Heterostructures
The sequence of prominent fractional quantum Hall states up to ν = 5/11 around ν = 1/2 in a high-mobility two-dimensional electron system confined at oxide heterointerface (ZnO) is analyzed in terms of the composite fermion model. The temperature dependence of R_(xx) oscillations around ν = 1/2 yields an estimation of the composite fermion effective mass, which increases linearly with the magnetic field. This mass is of similar value to an enhanced electron effective mass, which in itself arises from strong electron interaction. The energy gaps of fractional states and the temperature dependence of R_(xx) at ν = 1/2 point to large residual interactions between composite fermions
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