41,668 research outputs found
Quantum critical behaviour of the plateau-insulator transition in the quantum Hall regime
High-field magnetotransport experiments provide an excellent tool to
investigate the plateau-insulator phase transition in the integral quantum Hall
effect. Here we review recent low-temperature high-field magnetotransport
studies carried out on several InGaAs/InP heterostructures and an InGaAs/GaAs
quantum well. We find that the longitudinal resistivity near the
critical filling factor ~ 0.5 follows the universal scaling law
, where . The critical exponent equals ,
which indicates that the plateau-insulator transition falls in a non-Fermi
liquid universality class.Comment: 8 pages, accepted for publication in Proceedings of the Yamada
Conference LX on Research in High Magnetic Fields (August 16-19, 2006,
Sendai
Quantum phase transition in the Dicke model with critical and non-critical entanglement
We study the quantum phase transition of the Dicke model in the classical
oscillator limit, where it occurs already for finite spin length. In contrast
to the classical spin limit, for which spin-oscillator entanglement diverges at
the transition, entanglement in the classical oscillator limit remains small.
We derive the quantum phase transition with identical critical behavior in the
two classical limits and explain the differences with respect to quantum
fluctuations around the mean-field ground state through an effective model for
the oscillator degrees of freedom. With numerical data for the full quantum
model we study convergence to the classical limits. We contrast the classical
oscillator limit with the dual limit of a high frequency oscillator, where the
spin degrees of freedom are described by the Lipkin-Meshkov-Glick model. An
alternative limit can be defined for the Rabi case of spin length one-half, in
which spin frequency renormalization replaces the quantum phase transition.Comment: 1o pages, 10 figures, published versio
Photon-Photon Collisions with SuperChic
The SuperChic Monte Carlo generator provides a common platform for
QCD-mediated, photoproduction and photon-induced Central Exclusive Production
(CEP), with a fully differential treatment of soft survival effects. In these
proceedings we summarise the processes generated, before discussing in more
detail those due to photon-photon collisions, paying special attention to the
correct treatment of the survival factor. We briefly consider the
light-by-light scattering process as an example, before discussing planned
extensions and refinements for the generator.Comment: 6 pages, 2 figures. Submitted to proceedings of the PHOTON 2017
conferenc
Structural and magnetic transition in CeFeAsO: separated or connected?
Using an adapted Sn-flux growth technique we obtained comparatively large
CeFeAsO single crystals of better quality than previously reported polycrystals
or single crystals, as evidenced by much sharper anomalies at the structural
and magnetic phase transitions as well as a much higher residual resistivity
ratio of 12. In the magnetically ordered phase we observe a very pronounced
metallic behavior of the in-plane resistivity, which excludes a Mott insulator
regime at low temperature. The separation Delta_T = T_0 - T_N between
structural and magnetic ordering temperatures decreases with increasing sample
quality, from 18 K in the initial reports to 6 K in the present single
crystals, demonstrating that this separation is not an intrinsic property of
the RFeAsO systems. Our results indicate that the coupling between magnetic
ordering and structural distortion is very similar in AFe2As2 and RFeAsO type
of compounds, much more similar than previously thought. The implications of
our experimental results give arguments both in favor and against the nematic
phase model.Comment: published in PRB with the title 'Coupling between the structural and
magnetic transition in CeFeAsO
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