Volume 10 Issue 6, June 2014

Will government intervene if private-sector investment conflicts with national research interests?

Among physics students there exists a wide variety of misconceptions, generally thought to be robust and resistant to change. But our analysis of the path of progress has changed our conception of how students learn physics.

Brownian motion in a feedback-controlled optical trap provides a minimal experimental realization of a Szilárd engine, confirming fluctuation theorems and demonstrating the importance of spontaneous symmetry breaking in small thermodynamic systems.

Friction involves a complex set of phenomena spanning a large range of length scales, but experiments assessing the evolution of the slip-front between two dry sliding bodies now reveal that slip can be reasonably well described by linear fracture mechanics theory.

Without a well-defined cavity, there is no obvious way to control the resonant modes in a random laser. Experiments now show that shaping the optical pump allows for controlled single-mode operation at predetermined lasing wavelengths.

Properties of companion galaxies strengthen the idea that the probability of the inner regions of an active galaxy being hidden from our view by dust depends on environmental and evolutionary factors.

An active galactic nucleus is the brightest source of electromagnetic radiation in the Universe, believed to be powered by a supermassive black hole at its core. There are two main types of active galactic nuclei, though the differences may be down to varying viewing angles. Or are they?

When the charge density wave state in TiSe₂ is suppressed by hydrostatic pressure or chemical doping, superconductivity appears. This suggests the presence of a quantum critical point. Yet a high pressure X-ray study unexpectedly finds that the quantum critical point is nowhere near the superconducting dome.

Random lasers generate the optical feedback required for stimulated emission by scattering light from disordered particles. Their inherent randomness, however, makes controlling the emission wavelength difficult. It is now shown that this problem can be remedied by carefully matching the pump laser to the specific random medium. The concept is applied to a one-dimensional optofluidic device, but could also be applicable to other random lasers.

Nanoscale metallic tips are a useful source of electrons for material characterization. It is now shown how terahertz radiation can provide precision control and enhancement of photoelectron emission from these sources. The approach can shape the spectrum of the electron pulse, which could pave the way to improvements in ultrafast electron diffraction and transmission electron microscopy.

Magnetoresistance measurements on underdoped La_2−xSr_xCuO₄, a cuprate superconductor, reveal quantum-critical behaviour of the resistivity—the signature of a superconductor–insulator transition. The magnetic-field-driven transition involves an intermediate state, which is only superconducting at zero temperature.

The effect of structural disorder on superconductivity can be subtle: for two crystalline arrangements of superconducting lead monolayers deposited on silicon, there are unexpected spatial variations that result in macroscopically different behaviour.

A single layer of graphene on top of a hexagonal boron-nitride sheet can stretch to form a commensurate structure, or not — depending on the rotation angle between the two layers. In the case of commensurability, strain gets concentrated in domain walls, resulting in soliton-like structures.

The spontaneous breaking of a system’s symmetry results in an entropy decrease. Now, an experiment involving a particle subject to a potential with a shape that changes from a single- to a double-well demonstrates that the associated entropy changed is detectable. Moreover, the experimental setup enables the realization of a Szilard engine.

Interactive lessons.