Spin hall effect of light.

I cant help keeping a record of this piece of work, which shows a fast light split. By incidenting a beam of linearly polarized light upon the interface between two media with differing refraction indice, they obtain two closely separated beams of light with oppositely polarized circular helicity.

We experimentally demonstrate a general optical pump-probe technique to observe the spin Hall effect of light SHEL in an absorbing medium. In essence, a locally confined pump-induced modification of a material’s absorptivity can effectively be used as an induced aperture allowing one to detect the transversely displaced
circular polarization components of an incident beam through differential transmission techniques. We consider linear absorption mechanisms such as free-carrier absorption and Pauli blocking as well as nonlinear absorption processes such as two-photon absorption. For absorption mechanisms that do not depend on light polarization, the SHEL of the probe beam is obtained directly, while polarization-dependent properties give an effective SHEL displacement that depends on the action of the SHEL on both pump and probe beams. Using 150 fs pump, 820 nm pump and probe pulses we observe SHEL effects in silicon via free-carrier absorption. SHEL effects are also observed via Pauli blocking at 820 nm and two-photon absorption at 1550 nm in GaAs using 150 fs pump and probe pulses.

PHYSICAL REVIEW B 82, 045303 2010

Type-2 superconductors used as tweezers

A just published work (PRA, 81, 063408, 2010) did calculations on how type-2 superconductors might be used to trap atoms or other tiny particles. In comparison with other choices, the scheme there-proposed has less loss of coherences. Their calculations proved type-2 SC as a very versatile device in that direction. What holds the key as tweezers is the formation of vortice, which allows the existence of local magnetic field. Such vortice appear in type-2 SC, but not in type-1.

An aternative to Einstein's GRT

Einstein constructed his general relativity theory about a century ago. Adhering to two basic principles, namely, (1)general relativity principle and (2)Equivalence principle, he arrived at his celebrated action, which had also been proposed by Hilbert and led to Einstein's equation. However, there are some seemingly inherent singularity that has been plaguing physicists. Such singularity concerns the beginning of time and space. Now, a very interesting paper [1] has just appeared in PRL, addressing such issues by a different GRT, as first suggested by Eddington. This new action is also invariant under general coordinate transformations. And, in this paper, it was shown that, due to some extra terms particularly relevant in large density regions, this new theory may get around those long standing issues.

Eddington’s Theory of Gravity and Its Progeny
Ma´ximo Ban˜ados, P. Universidad Cato´lica de Chile, Avenida Vicuna Mackenna 4860, Santiago, Chile Astrophysics, University of Oxford, DWB, Keble Road, Oxford, OX1 3RH, United Kingdom Pedro G. Ferreira, Astrophysics, University of Oxford, DWB, Keble Road, Oxford, OX1 3RH, United Kingdom
(Received 21 March 2010; published 2 July 2010)
We resurrect Eddington’s proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we
find that there is a minimum length (and maximum density) at early times, clearly pointing to analternative theory of the big bang.We thus argue that the modern formulation of Eddington’s theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe.
DOI: 10.1103/PhysRevLett.105.011101 PACS numbers: 04.50. h, 98.80. k

[1]PRL 105, 011101 (2010)

Negative specific heat

It is usually thought that, specific heat of a thermodynamic system is positive, that is, energy must be invested to heat the system. How, these authors demonstrated that[1], such a common sense shall be violated if the system does not obey Boltzman statistics or goes out of equilibrium in the presence of long range interactions. They have considered a particular example to illustrate the statement.

[1]PRL 105, 010601 (2010)

Sodium atoms

Here is a summary of the properties of the D lines of sodium atoms, which are frequently used in quantum optics.

A new superconductor: LaNiC

I knew nothing about this supercondutor until I had just a small poster about it. I found this poster on the following blog site:
http://blogs.kent.ac.uk/strongcorrelations/

This superconductor seems abberent in its symmetry, as perfectly summarized in that poster, which I'd like to share in my blog.

soccer balls spinning in the air

The World Cup this round is now near its climax. I'm not a soccer fan, though it is my interest to know how the soccer balls traverse the air. One finds here a good and terse essay on this. It talks of how the trajectory of a soccer through the air is affected by the drag force and Magnus force, both of which are of course exterted by the air. An exact solution of such problem is only numerically or experimentally possible. Even today, after nearly three centuries since Euler equation, some very fundamental issues as regards the transition from laminar and turbulent flow are not concluded.