arXiv subjects

J. Moser

Publications and source records attributed to J. Moser.

25 records · Page 2Linked to original sources

arXiv2007

Current-induced cleaning of graphene

A simple yet highly reproducible method to suppress contamination of graphene at low temperature inside the cryostat is presented. The method consists of applying a current of several mA through the graphene device, which is here typically a few $μ$m wide. This ultra-high current density is shown to remove contamination adsorbed on the surface. This method is well suited for quantum electron transport studies of undoped graphene devices, and its utility is demonstrated here by measuring the anomalous quantum Hall effect.

cond-mat.other↗

arXiv2006

Tunneling anisotropic magnetoresistance and spin-orbit coupling in Fe/GaAs/Au tunnel junctions

We report the observation of tunneling anisotropic magnetoresistance effect (TAMR) in the epitaxial metal-semiconductor system Fe/GaAs/Au. The observed two-fold anisotropy of the resistance can be switched by reversing the bias voltage, suggesting that the effect originates from the interference of the spin-orbit coupling at the interfaces. Corresponding model calculations reproduce the experimental findings very well.

cond-mat.mes-hall↗

arXiv2006

Bias dependent inversion of tunneling magnetoresistance in Fe/GaAs/Fe tunnel junctions

We investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions. The tunneling magnetoresistance effect (TMR) was probed for different types of Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is increased and observable at room temperature. If an epitaxial Fe/GaAs(001) interface is involved, the tunnel junction exhibits a bias dependent inversion of the TMR effect. This is a first experimental signature for band structure effects at a Fe/GaAs interface and relevant for spin injection experiments.

cond-mat.mes-hall↗

arXiv2006

Classical-to-stochastic Coulomb blockade cross-over in aluminum arsenide wires

We report low-temperature differential conductance measurements in aluminum arsenide cleaved-edge overgrown quantum wires in the pinch-off regime. At zero source-drain bias we observe Coulomb blockade conductance resonances that become vanishingly small as the temperature is lowered below $250 {\rm mK}$. We show that this behavior can be interpreted as a classical-to-stochastic Coulomb blockade cross-over in a series of asymmetric quantum dots, and offer a quantitative analysis of the temperature-dependence of the resonances lineshape. The conductance behavior at large source-drain bias is suggestive of the charge density wave conduction expected for a chain of quantum dots.

cond-mat.mes-hall↗

arXiv2005

Aluminum arsenide cleaved-edge overgrown quantum wires

We report conductance measurements in quantum wires made of aluminum arsenide, a heavy-mass, multi-valley one-dimensional (1D) system. Zero-bias conductance steps are observed as the electron density in the wire is lowered, with additional steps observable upon applying a finite dc bias. We attribute these steps to depopulation of successive 1D subbands. The quantum conductance is substantially reduced with respect to the anticipated value for a spin- and valley-degenerate 1D system. This reduction is consistent with disorder-induced, intra-wire backscattering which suppresses the transmission of 1D modes. Calculations are presented to demonstrate the role of strain in the 1D states of this cleaved-edge structure.

cond-mat.mes-hall↗

arXiv2004

High-field magnetoresistance of Fe/GaAs/Fe tunnel junctions

We investigate transport through 6 to 10 nm thin epitaxial GaAs(001) barriers sandwiched between polycrystalline iron films. Apart from a pronounced tunneling magnetoresistance effect (TMR) at low magnetic fields we observe a distinct negative magnetoresistance (MR) at low and a positive MR at higher temperatures. We show that the negative MR contribution is only observed for the ferromagnetic iron contacts but is absent if iron is replaced by copper or gold electrodes. Possible explanations of the negative MR involve suppression of spin-flip scattering or Zeeman splitting of the tunneling barrier.

cond-mat.mes-hall↗

arXiv2000

From spin-Peierls to superconductivity: (TMTTF)_2PF_6 under high pressure

The nature of the attractive electron-electron interaction, leading to the formation of Cooper-pairs in unconventional superconductors has still to be fully understood and is subject to intensive research. Here we show that the sequence spin-Peierls, antiferromagnetism, superconductivity observed in (TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagram universal. We argue that the suppression of the spin-Peierls transition under pressure, the close vicinity of antiferromagnetic and superconducting phases at high pressure as well as the existence of critical antiferromagnetic fluctuations above T_c strongly support the intriguing possibility that the interchain exchange of antiferromagnetic fluctuations provides the pairing mechanism required for bound charge carriers.

cond-mat.supr-con↗