3,325 research outputs found
The FIR-absorption of short period quantum wires and the transition from one to two dimensions
We investigate the FIR-absorption of short period parallel quantum wires in a
perpendicular quantizing magnetic field. The external time-dependent electric
field is linearly polarized along the wire modulation. The mutual Coulomb
interaction of the electrons is treated self-consistently in the ground state
and in the absorption calculation within the Hartree approximation. We consider
the effects of a metal gate grating coupler, with the same or with a different
period as the wire modulation, on the absorption. The evolution of the
magnetoplasmon in the nonlocal region where it is split into several Bernstein
modes is discussed in the transition from: narrow to broad wires, and isolated
to overlapping wires. We show that in the case of narrow and not strongly
modulated wires the absorption can be directly correlated with the underlying
electronic bandstructure.Comment: 15 pages, 9 figures, Revtex, to appear in Phys. Rev.
Magnetic structure and phase diagram of TmB4
Magnetic structure of single crystalline TmB4 has been studied by
magnetization, magnetoresistivity and specific heat measurements. A complex
phase diagram with different antiferromagnetic (AF) phases was observed below
TN1 = 11.7 K. Besides the plateau at half-saturated magnetization (1/2 MS),
also plateaus at 1/9, 1/8 and 1/7 of MS were observed as function of applied
magnetic field B//c. From additional neutron scattering experiments on TmB4, we
suppose that those plateaus arise from a stripe structure which appears to be
coherent domain boundaries between AF ordered blocks of 7 or 9 lattice
constants. The received results suggest that the frustration among the Tm3+
magnetic ions, which maps to a geometrically frustrated Shastry-Sutherland
lattice lead to strong competition between AF and ferromagnetic (FM) order.
Thus, stripe structures in intermediate field appear to be the best way to
minimize the magnetostatic energy against other magnetic interactions between
the Tm ions combined with very strong Ising anisotropy.Comment: 4 pages, 4 figures, conference contribution - CSMAG 0
Analysis of interface conversion processes of ballistic and diffusive motion in driven superlattices
We explore the non-equilibrium dynamics of non-interacting classical
particles in a one-dimensional driven superlattice which is composed of domains
exposed to different time-dependent forces. It is shown how the combination of
directed transport and conversion processes from diffusive to ballistic motion
causes strong correlations between velocity and phase for particles passing
through a superlattice. A detailed understanding of the underlying mechanism
allows us to tune the resulting velocity distributions at distinguished points
in the superlattice by means of local variations of the applied driving force.
As an intriguing application we present a scheme how initially diffusive
particles can be transformed into a monoenergetic pulsed particle beam whose
parameters such as its energy can be varied
Magnetic-field induced multiferroicity in a quantum critical frustrated spin liquid
Dielectric spectroscopy is used to check for the onset of polar order in the
quasi one-dimensional quantum spin system Sul-Cu2Cl4 when passing from the
spin-liquid state into the ordered spiral phase in an external magnetic field.
We find clear evidence for multiferroicity in this material and treat in detail
its H-T phase diagram close to the quantum-critical regime.Comment: 5 pages, 4 figures. Revised according to suggestions of referee
Mechanical On-Chip Microwave Circulator
Nonreciprocal circuit elements form an integral part of modern measurement
and communication systems. Mathematically they require breaking of
time-reversal symmetry, typically achieved using magnetic materials and more
recently using the quantum Hall effect, parametric permittivity modulation or
Josephson nonlinearities. Here, we demonstrate an on-chip magnetic-free
circulator based on reservoir engineered optomechanical interactions.
Directional circulation is achieved with controlled phase-sensitive
interference of six distinct electro-mechanical signal conversion paths. The
presented circulator is compact, its silicon-on-insulator platform is
compatible with both superconducting qubits and silicon photonics, and its
noise performance is close to the quantum limit. With a high dynamic range, a
tunable bandwidth of up to 30 MHz and an in-situ reconfigurability as beam
splitter or wavelength converter, it could pave the way for superconducting
qubit processors with integrated and multiplexed on-chip signal processing and
readout.Comment: References have been update
Dynamics of a thin liquid film with surface rigidity and spontaneous curvature
The effect of rigid surfaces on the dynamics of thin liquid films which are
amenable to the lubrication approximation is considered. It is shown that the
Helfrich energy of the layer gives rise to additional terms in the
time-evolution equations of the liquid film. The dynamics is found to depend on
the absolute value of the spontaneous curvature, irrespective of its sign. Due
to the additional terms, a novel finite wavelength instability of flat rigid
interfaces can be observed. Furthermore, the dependence of the shape of a
droplet on the bending rigidity as well as on the spontaneous curvature is
discussed.Comment: 4 pages, 5 figure
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