3,892 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
Stationary Entangled Radiation from Micromechanical Motion
Mechanical systems facilitate the development of a new generation of hybrid
quantum technology comprising electrical, optical, atomic and acoustic degrees
of freedom. Entanglement is the essential resource that defines this new
paradigm of quantum enabled devices. Continuous variable (CV) entangled fields,
known as Einstein-Podolsky-Rosen (EPR) states, are spatially separated two-mode
squeezed states that can be used to implement quantum teleportation and quantum
communication. In the optical domain, EPR states are typically generated using
nondegenerate optical amplifiers and at microwave frequencies Josephson
circuits can serve as a nonlinear medium. It is an outstanding goal to
deterministically generate and distribute entangled states with a mechanical
oscillator. Here we observe stationary emission of path-entangled microwave
radiation from a parametrically driven 30 micrometer long silicon nanostring
oscillator, squeezing the joint field operators of two thermal modes by
3.40(37) dB below the vacuum level. This mechanical system correlates up to 50
photons/s/Hz giving rise to a quantum discord that is robust with respect to
microwave noise. Such generalized quantum correlations of separable states are
important for quantum enhanced detection and provide direct evidence for the
non-classical nature of the mechanical oscillator without directly measuring
its state. This noninvasive measurement scheme allows to infer information
about otherwise inaccessible objects with potential implications in sensing,
open system dynamics and fundamental tests of quantum gravity. In the near
future, similar on-chip devices can be used to entangle subsystems on vastly
different energy scales such as microwave and optical photons.Comment: 13 pages, 5 figure
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
Evaluation of the institutional structure of sustainable forest management in the Netherlands
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