6,439 research outputs found
Coherent Magnetotransport Through an Artificial Molecule
The conductance in an extended multiband Hubbard model describing linear
arrays of up to ten quantum dots is calculated via a Lanczos technique. A
pronounced suppression of certain resonant conductance peaks in an applied
magnetic field due to a density-dependent spin-polarization transition is
predicted to be a clear signature of a coherent ``molecular'' wavefunction in
the array. A many-body enhancement of localization is predicted to give rise to
a {\em giant magnetoconductance} effect in systems with magnetic scattering.Comment: 4 pages, REVTEX 3.0, 5 figures included as postscript file
The quasiparticle spectral function in doped graphene
We calculate the real and imaginary electron self-energy as well as the
quasiparticle spectral function in doped graphene taking into account
electron-electron interaction in the leading order dynamically screened Coulomb
coupling. Our theory provides the basis for calculating {\it all} one-electron
properties of extrinsic graphene. Comparison with existing ARPES measurements
shows broad qualitative agreement between theory and experiment. We also
calculate the renormalized graphene momentum distribution function, finding a
typical Fermi liquid discontinuity at k_F. We also provide a critical
discussion of the relevant many body approximations (e.g. RPA) for graphene.Comment: 5 pages, 3 figure
Dissipationless transport in low density bilayer systems
In a bilayer electronic system the layer index may be viewed as the
z-component of an isospin-1/2. An XY isospin-ordered ferromagnetic phase was
observed in quantum Hall systems and is predicted to exist at zero magnetic
field at low density. This phase is a superfluid for opposite currents in the
two layers. At B=0 the system is gapless but superfluidity is not destroyed by
weak disorder. In the quantum Hall case, weak disorder generates a random gauge
field which probably does not destroy superfluidity. Experimental signatures
include Coulomb drag and collective mode measurements.Comment: 4 pages, no figures, submitted to Phys. Rev. Let
How to make semiconductors ferromagnetic: A first course on spintronics
The rapidly developing field of ferromagnetism in diluted magnetic
semiconductors, where a semiconductor host is magnetically doped by transition
metal impurities to produce a ferromagnetic semiconductor (e.g. Ga_{1-x}Mn_xAs
with x ~ 1-10 %), is discussed with the emphasis on elucidating the physical
mechanisms underlying the magnetic properties. Recent key developments are
summarized with critical discussions of the roles of disorder, localization,
band structure, defects, and the choice of materials in producing good magnetic
quality and high Curie temperature. The correlation between magnetic and
transport properties is argued to be a crucial ingredient in developing a full
understanding of the properties of ferromagnetic semiconductors.Comment: 8 pages; to appear in the special issue 'Quantum Phases at Nanoscale'
of Solid State Communication
Shape-dependence of transmission, reflection and absorption eigenvalue densities in disordered waveguides with dissipation
The universal bimodal distribution of transmission eigenvalues in lossless
diffusive systems un- derpins such celebrated phenomena as universal
conductance fluctuations, quantum shot noise in condensed matter physics and
enhanced transmission in optics and acoustics. Here, we show that in the
presence of absorption, density of the transmission eigenvalues depends on the
confinement geometry of scattering media. Furthermore, in an asymmetric
waveguide, densities of the reflection and absorption eigenvalues also depend
of the side from which the waves are incident. With increas- ing absorpotion,
the density of absorption eigenvalues transforms from single-peak to
double-peak function. Our findings open a new avenue for coherent control of
wave transmission, reflection and absorption in random media.Comment: 9 pages 8 figure
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