3,198 research outputs found
Renormalization of hole-hole interaction at decreasing Drude conductivity
The diffusion contribution of the hole-hole interaction to the conductivity
is analyzed in gated GaAs/InGaAs/GaAs heterostructures. We show
that the change of the interaction correction to the conductivity with the
decreasing Drude conductivity results both from the compensation of the singlet
and triplet channels and from the arising prefactor in the
conventional expression for the interaction correction.Comment: 6 pages, 5 figure
Resonant Tunneling in a Dissipative Environment
We measure tunneling through a single quantum level in a carbon nanotube
quantum dot connected to resistive metal leads. For the electrons tunneling
to/from the nanotube, the leads serve as a dissipative environment, which
suppresses the tunneling rate. In the regime of sequential tunneling, the
height of the single-electron conductance peaks increases as the temperature is
lowered, although it scales more weekly than the conventional 1/T. In the
resonant tunneling regime (temperature smaller than the level width), the peak
width approaches saturation, while the peak height starts to decrease. Overall,
the peak height shows a non-monotonic temperature dependence. We associate this
unusual behavior with the transition from the sequential to the resonant
tunneling through a single quantum level in a dissipative environment.Comment: 5 pages, 5 figure
Simplicial quantum dynamics
Present-day quantum field theory can be regularized by a decomposition into
quantum simplices. This replaces the infinite-dimensional Hilbert space by a
high-dimensional spinor space and singular canonical Lie groups by regular spin
groups. It radically changes the uncertainty principle for small distances.
Gaugeons, including the gravitational, are represented as bound fermion-pairs,
and space-time curvature as a singular organized limit of quantum
non-commutativity.
Keywords: Quantum logic, quantum set theory, quantum gravity, quantum
topology, simplicial quantization.Comment: 25 pages. 1 table. Conference of the International Association for
Relativistic Dynamics, Taiwan, 201
Disordered electron liquid in double quantum well heterostructures: Renormalization group analysis and dephasing rate
We report a detailed study of the influence of the electron-electron
interaction on physical observables (conductance, etc.) of a disordered
electron liquid in double quantum well heterostructure. We find that even in
the case of common elastic scattering off electrons in both quantum wells, the
asymmetry in the electron-electron interaction across and within quantum wells
decouples them at low temperatures. Our results are in quantitative agreement
with recent transport experiments on the gated double quantum well
AlGaAs/GaAs/AlGaAs heterostructures.Comment: 15 pages; 5 figure
Clifford algebra as quantum language
We suggest Clifford algebra as a useful simplifying language for present
quantum dynamics. Clifford algebras arise from representations of the
permutation groups as they arise from representations of the rotation groups.
Aggregates using such representations for their permutations obey Clifford
statistics. The vectors supporting the Clifford algebras of permutations and
rotations are plexors and spinors respectively. Physical spinors may actually
be plexors describing quantum ensembles, not simple individuals. We use
Clifford statistics to define quantum fields on a quantum space-time, and to
formulate a quantum dynamics-field-space-time unity that evades the
compactification problem. The quantum bits of history regarded as a quantum
computation seem to obey a Clifford statistics.Comment: 13 pages, no figures. Some of these results were presented at the
American Physical Society Centennial Meeting, Atlanta, March 25, 199
Structural origin of the anomalous temperature dependence of the local magnetic moments in the CaFeAs family of materials
We report a combination of Fe K x-ray emission spectroscopy and
-intio calculations to investigate the correlation between structural and
magnetic degrees of freedom in CaFe(AsP). The
puzzling temperature behavior of the local moment found in rare earth-doped
CaFeAs [\textit{H. Gretarsson, et al., Phys. Rev. Lett. {\bf 110},
047003 (2013)}] is also observed in CaFe(AsP). We
explain this phenomenon based on first-principles calculations with scaled
magnetic interaction. One scaling parameter is sufficient to describe
quantitatively the magnetic moments in both CaFe(AsP) () and CaLaFeAs at all
temperatures. The anomalous growth of the local moments with increasing
temperature can be understood from the observed large thermal expansion of the
-axis lattice parameter combined with strong magnetoelastic coupling. These
effects originate from the strong tendency to form As-As dimers across the Ca
layer in the CaFeAs family of materials. Our results emphasize the
dual local-itinerant character of magnetism in Fe pnictides
Theory of quantum metal to superconductor transitions in highly conducting systems
We derive the theory of the quantum (zero temperature) superconductor to
metal transition in disordered materials when the resistance of the normal
metal near criticality is small compared to the quantum of resistivity. This
can occur most readily in situations in which ``Anderson's theorem'' does not
apply. We explicitly study the transition in superconductor-metal composites,
in an s-wave superconducting film in the presence of a magnetic field, and in a
low temperature disordered d-wave superconductor. Near the point of the
transition, the distribution of the superconducting order parameter is highly
inhomogeneous. To describe this situation we employ a procedure which is
similar to that introduced by Mott for description of the temperature
dependence of the variable range hopping conduction. As the system approaches
the point of the transition from the metal to the superconductor, the
conductivity of the system diverges, and the Wiedemann-Franz law is violated.
In the case of d-wave (or other exotic) superconductors we predict the
existence of (at least) two sequential transitions as a function of increasing
disorder: a d-wave to s-wave, and then an s-wave to metal transition
Anderson Transitions: Criticality, Symmetries, and Topologies
The physics of Anderson transitions between localized and metallic phases in
disordered systems is reviewed. We focus on the character of criticality as
well as on underlying symmetries and topologies that are crucial for
understanding phase diagrams and the critical behavior.Comment: 36 pages. Published in "50 Years of Anderson Localization", ed. by E.
Abrahams (World Scientific, 2010); reprinted in IJMP
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