M. Cerchez

Effect of edge transmission and elastic scattering on the resistance of magnetic barriers : Experiment and theory

Strong magnetic barriers are defined in two-dimensional electron gases by magnetizing dysprosium ferromagnetic platelets on top of a Ga[Al]As heterostructure. A small resistance across the barrier is observed even deep inside the closed regime. We have used semiclassical simulations to explain this behavior quantitatively in terms of a combined effect of elastic electron scattering inside the barrier region and E x B drift at the intersection of the magnetic barrier with the edge of the Hall bar.

Quantized Magnetic Confinement in Quantum Wires

Ballistic quantum wires are exposed to longitudinal profiles of perpendicular magnetic fields composed of a spike and a homogeneous part. An asymmetric magnetoconductance peak as a function of the homogeneous magnetic field is found, comprising quantized conductance steps in the interval where the homogeneous magnetic field and the magnetic barrier have identical polarities, and a characteristic shoulder with several resonances in the interval of opposite polarities. The observations are interpreted in terms of inhomogeneous diamagnetic shifts of the quantum wire modes leading to magnetic confinement.

Dynamics of hydrogen sensing with Pt/TiO2 Schottky diodes

The dynamics of hydrogen sensing with nanoporous Pt/TiO2 Schottky barriers is studied by time-resolved electronic transport measurements. The development with time of the doping density, the average Schottky barrier height, and the built-in voltage are determined from current-voltage and capacitance-voltage characteristics. The current-voltage characteristics change from exponential towards Ohmic behavior as time proceeds. This is interpreted in terms of local areas that switch from diodic to Ohmic response due to a combination of increasing doping density and decreasing Schottky barrier height.

Magnetic-barrier-induced conductance fluctuations in quantum wires

Quasiballistic semiconductor quantum wires are exposed to localized perpendicular magnetic fields, also known as magnetic barriers. Pronounced, reproducible conductance fluctuations as a function of the magnetic barrier amplitude are observed. The fluctuations are strongly temperature dependent and remain visible up to temperatures of approximate to 10 K. Simulations based on recursive Greens functions suggest that the conductance fluctuations originate from parametric interferences of the electronic wave functions, which experience scattering between the magnetic barrier and the electrostatic potential landscape.

Influence of magnetic field offsets on the resistance of magnetic barriers in two-dimensional electron gases: Experiment and simulations

Strongly localized, magnetic field structures oriented perpendicular to two-dimensional electron gases, also known as magnetic barriers, are shifted in

Interdependence of electroforming and hydrogen incorporation in nanoporous titanium dioxide

B

Correction factor in nondiffusive Hall magnetometry

space by homogeneous, perpendicular magnetic fields. The magnetoresistance across the barrier shows a characteristic asymmetric dip in the regime where the polarity of the homogeneous magnetic field is opposite to that of the magnetic barrier. The measurements are in quantitative agreement with semiclassical simulations, which reveal that the magnetoresistance originates from the interplay of snake orbits with

Observation of quantum states without a semiclassical equivalence bound by a magnetic field gradient

E\ifmmode\times\else\texttimes\fi{}B

Probing magnetic microstructures with quasi-ballistic Hall crosses

drift at the edges of the Hall bar and with elastic scattering.

Commensurability oscillations by snake-orbit magnetotransport in two-dimensional electron gases

It is shown that in nanoporous titanium dioxide films, sensitivity to atmospheric hydrogen exposure and electroforming can coexist and are interdependent. The devices work as conventional hydrogen sensors below a threshold electric field while above it, the well-known electroforming is observed. Offering hydrogen in this regime accelerates the electroforming process, and in addition to the usual reversible increase of the conductance in response to the hydrogen gas, an irreversible conductance decrease is superimposed. The behavior is interpreted in terms of a phenomenological model where current carrying, oxygen-deficient filaments with hydrogen-dependent conductivities form inside the TiO2 matrix.