Resistively Detected NMR in Quantum Hall States: Investigation of the anomalous lineshape near ν=1\nu=1

A study of the resistively detected nuclear magnetic resonance (RDNMR) lineshape in the vicinity of $\nu=1$ was performed on a high-mobility 2D electron gas formed in GaAs/AlGaAs. In higher Landau levels, application of an RF field at the nuclear magnetic resonance frequency coincides with an observed minimum in the longitudinal resistance, as predicted by the simple hyperfine interaction picture. Near $\nu=1$ however, an anomalous dispersive lineshape is observed where a resistance peak follows the usual minimum. In an effort to understand the origin of this anomalous peak we have studied the resonance under various RF and sample conditions. Interestingly, we show that the lineshape can be completely inverted by simply applying a DC current. We interpret this as evidence that the minima and maxima in the lineshape originate from two distinct mechanisms.Comment: 5 pages, 3 figures, EP2DS 17, to be published in Physica

Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures

Chirality is a fundamental property of electrons with the relativistic spectrum found in graphene and topological insulators. It plays a crucial role in relativistic phenomena, such as Klein tunneling, but it is difficult to visualize directly. Here we report the direct observation and manipulation of chirality and pseudospin polarization in the tunneling of electrons between two almost perfectly aligned graphene crystals. We use a strong in-plane magnetic field as a tool to resolve the contributions of the chiral electronic states that have a phase difference between the two components of their vector wavefunction. Our experiments not only shed light on chirality, but also demonstrate a technique for preparing graphene’s Dirac electrons in a particular quantum chiral state in a selected valley

Energy scale of Dirac electrons in Cd3As2

Cadmium arsenide (Cd3As2) has recently became conspicuous in solid-state physics due to several reports proposing that it hosts a pair of symmetry-protected 3D Dirac cones. Despite vast investigations, a solid experimental insight into the band structure of this material is still missing. Here we fill one of the existing gaps in our understanding of Cd3As2, and based on our Landau-level spectroscopy study, we provide an estimate for the energy scale of 3D Dirac electrons in this system. We find that the appearance of such charge carriers is limited-contrary to a widespread belief in the solid-state community-to a relatively small energy scale (below 40 meV)

Resistively detected NMR in quantum Hall states: Investigation of the anomalous line shape near

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Gap like structure in a nonsuperconducting layered oxycarbonate Bi2+xSr4−xCu2CO3O8+δ single crystal

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Gap like structure in a nonsuperconducting layered oxycarbonate Bi2+xSr4−xCu2CO3O8+δ single crystal

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The contact hyperfine interaction and the integer and fractional quantumHall effects

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Integer quantum Hall effect in a PbTe quantum well

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Magnetotransport properties of nearly-free electrons in two-dimensional hexagonal metals and application to the Mn+1AXn phases

We propose a general, yet simple model for describing the weak field magnetotransport properties of nearly-free electrons in two-dimensional hexagonal metals. We modify this model so as to apply it to the magnetotransport properties of the Mn+1AXn phases, a particular class of nanolamellar carbides and nitrides. We argue that the values of the in-plane Hall coefficient and the in-plane parabolic magnetoresistance are due to the specific shape of the Fermi surface of almost two-dimensional hole and electron bands. If the contribution of the electron pockets to in-plane resistivity is often (but not always) predicted to be a minor one, in contrast, both holes and electrons should substantially contribute to the overall value of the in-plane Hall coefficient. The relevance of our model is supported by elementary considerations and a set of experimental data obtained from single crystals of V2AlC and Cr2AlC. In particular, we obtain a high ratio between the in-plane (ρab) and parallel to the c axis (ρc)resistivities

Determination of the Landau level shape via the transition to the spin polarized state in the integer quantum Hall effect

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