13,671 research outputs found
Magnetic Field Induced Instabilities in Localised Two-Dimensional Electron Systems
We report density dependent instabilities in the localised regime of
mesoscopic two-dimensional electron systems (2DES) with intermediate strength
of background disorder. They are manifested by strong resistance oscillations
induced by high perpendicular magnetic fields B_{\perp}. While the amplitude of
the oscillations is strongly enhanced with increasing B_{\perp}, their position
in density remains unaffected. The observation is accompanied by an unusual
behaviour of the temperature dependence of resistance and activation energies.
We suggest the interplay between a strongly interacting electron phase and the
background disorder as a possible explanation.Comment: 5 pages, 4 figure
Possible evidence of a spontaneous spin-polarization in mesoscopic 2D electron systems
We have experimentally studied the non-equilibrium transport in low-density
clean 2D electron systems at mesoscopic length scales. At zero magnetic field
(B), a double-peak structure in the non-linear conductance was observed close
to the Fermi energy in the localized regime. From the behavior of these peaks
at non-zero B, we could associate them to the opposite spin states of the
system, indicating a spontaneous spin polarization at B = 0. Detailed
temperature and disorder dependence of the structure shows that such a
splitting is a ground state property of the low-density 2D systems.Comment: 7 pages, 5 figure
Quantized charge pumping through a quantum dot by surface acoustic waves
We present a realization of quantized charge pumping. A lateral quantum dot
is defined by metallic split gates in a GaAs/AlGaAs heterostructure. A surface
acoustic wave whose wavelength is twice the dot length is used to pump single
electrons through the dot at a frequency f=3GHz. The pumped current shows a
regular pattern of quantization at values I=nef over a range of gate voltage
and wave amplitude settings. The observed values of n, the number of electrons
transported per wave cycle, are determined by the number of electronic states
in the quantum dot brought into resonance with the fermi level of the electron
reservoirs during the pumping cycle.Comment: 8 page
Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses
The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems
Weak Value in Wave Function of Detector
A simple formula to read out the weak value from the wave function of the
measuring device after the postselection with the initial Gaussian profile is
proposed. We apply this formula for the weak value to the classical experiment
of the realization of the weak measurement by the optical polarization and
obtain the weak value for any pre- and post-selections. This formula
automatically includes the interference effect which is necessary to yields the
weak value as an outcome of the weak measurement.Comment: 3 pages, no figures, Published in Journal of the Physical Society of
Japa
Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites
Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance-curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second-phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass
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