Scientists have a new way to gauge the growth of nanowires

In a new study, researchers from the U.S. Department of Energy’s Argonne and Brookhaven National Laboratories observed the formation of two kinds of defects in individual nanowires, which are smaller in diameter than a human hair.

These nanowires, made of indium gallium arsenide, could be useful for a wide range of applications in a field scientists have termed optoelectronics, which encompasses devices that work by converting light energy into electrical impulses. Fiber optic relays are a good example.

The effectiveness of these devices, however, can be affected by tiny defects in their components. These defects, which can change both the optical and electronic properties of these materials, interest scientists who seek to tailor them to boost the functionality of future optoelectronics, including materials that will be able to manipulate quantum information.

>Read more on the NSLS-II website and the Advanced Photon Source website

Image: Argonne and Brookhaven researchers observed two kinds of defects forming in individual nanowires, depicted here. These nanowires are smaller in diameter than a human hair.
Credit: Megan Hill/Northwestern University

Scientists measure accelerated emission

Grazing light for rapid events

An international team, including scientists from DESY,  has verified a prediction about the quantum-mechanical behaviour of resonant systems made more than 50 years ago. In experiments at SACLA, the Japanese X-ray laser, and at the European Synchrotron Radiation Facility ESRF in France, the group led by Aleksandr Chumakov from ESRF could show a dramatic reduction in the time to emit the first X-ray photon from an ensemble of excited nuclei when the number of X-rays for the excitation was increased. This behaviour is in good agreement with one limit of a superradiant system, predicted by the US physicist Robert Dicke in 1954, as the scientists report in the journal Nature Physics.

One of the broad challenges of science is to understand the behaviour of groups of atoms based on the response of a single atom in isolation, which is usually much simpler. A facet of this is understanding the behaviour of a group of identical oscillators. An analogy is a collection of bells that all have the same tone: one can easily imagine the sound of a single bell struck once – a clear tone ringing out with a volume that decays away over time.

But what happens if one gently taps all the bells in a large collection? Will the tone be the same as a single one? What about the volume? What about the direction – does it matter where you are standing when you listen to the sound? Does it matter if you tap them all at the same time?

>Read more on the FLASH website

Watching a Quantum Material Lose Its Stripes

Berkeley Lab study uses terahertz laser pulses to reveal ultrafast coupling of atomic-scale patterns

Stripes can be found everywhere, from zebras roaming in the wild to the latest fashion statement. In the world of microscopic physics, periodic stripe patterns can be formed by electrons within so-called quantum materials.

Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have now disentangled the intriguing dynamics of how such atomic-scale stripes melt and form, providing fundamental insights that could be useful in the development of novel energy materials.

>Read more on the ALS website

Image: Illustration of an ultrashort laser light striking a lanthanum strontium nickel oxide crystal, triggering the melting of atomic-scale stripes. The charges (yellow) quickly become mobile while the crystal distortions react only with delay, exposing the underlying interactions.
Credit: Robert Kaindl/Berkeley Lab

Precise test of quantum physical tunnel effect at DESY’s X-ray laser FLASH

Partnership at a distance: deep-frozen helium molecules

Helium atoms are loners. Only when you cool them to very low temperatures do they form extremely weakly bonded molecules. Yet even in this state, they are able to maintain an extremely large separation from each other thanks to quantum tunnelling. With the help of DESY’s free-electron laser FLASH, Frankfurt nuclear physicists have been able to confirm that the atoms spend more than 75 percent of their time so far apart from each other that their bond can only be explained by means of quantum tunnelling. The scientists have presented their findings in the US journal “Proceedings of the National Academy of Sciences” (PNAS).

The binding energy of a helium molecule is approximately one billionth of the binding energy of everyday molecules like oxygen or nitrogen. On top of this, the molecule is so huge that small viruses or soot particles could actually pass between the atoms. Physicists explain this in terms of quantum tunnelling. They visualise the bond in a classical molecule as a potential well, in which atoms cannot get further apart from each other than by going to opposite “walls”. However, quantum theory also allows atoms to tunnel inside these walls. “It is as if each of them were to dig a shaft without an exit,” explains Reinhard Dörner, a professor at the Institute of Nuclear Physics at the Goethe University in Frankfurt.

 

>Read more on the FLASH website

Cartoon: “When two loners are forced to share a bed, they move well beyond its edges to get away from each other.”
Credit: Peter Evers