Electron induced rippling in graphene

Physicists are really blessed by nature in the sense that, they have all the time been offered some new objects that admit very rich phenomena to be explored. Latest examples include Graphene and Topological Insulators. Since its discovery, graphene never stops yielding surprising things for physicists. This time comes something that (again, considering Dirac physics) parallels particle physics: the strain field associated with the flexural phonon condenses in the same way as the Higgs field in the Standard Model [1]. Don't miss reading it !

[1]PRL, 106:045502(2011)

A One-Way Wall of Silence

In a previous entry I highlighted this work. Here is another citation of it [http://www.sciencemag.org/content/331/6022/twil.full?sa_campaign=Email/toc/3316022twil]:

The recent development of metamaterials and photonic crystals has provided a route to control the propagation of electromagnetic waves through the engineered structure of a material. Combined with transformation optics, such control is rewriting the expected rules of behavior governing the propagation of electromagnetic waves, and offers myriad possibilities ranging from imaging to communications and stealth applications. Sound is also a wave, and so the manipulation of acoustic waves may be expected to carry over by analogy to their electromagnetic counterparts. Li et al. present a sonic crystal composed of a periodic array of steel rods, the geometry of which was selected to give rise to a band gap, whereby the transmission of sound waves in a specific frequency range is prohibited in one direction but allowed in the opposite direction. The authors also show that by mechanically changing the spacing of the array (by rotating the square steel rods), the diode-like behavior can be switched on and off. A range of applications might be expected to follow, from acoustic isolation and filtering to ultrasound imaging.

Phys. Rev. Lett. 106, 84301 (2011).

Accoustic diode

This is a device that allows one-way propagation of sound. Obviously, such device must break time reversal symmetry. [http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.084301]

The device consists of a two-dimensional sonic crystal arranged in a mesh of square steel rods. By rotating the steel rods, Li et al. are able to manipulate the unit cell of the sonic crystal element to turn the diode on (sound waves only propagate one way) and off (sound waves can move back and forth). Furthermore, Li et al. make their device entirely from linear acoustic materials, which allows them to control sound propagation with a simpler and more efficient process, over a broader bandwidth, and with lower power consumption, compared to existing nonlinear sonic-crystal-based devices.