New way to measure electron pair interactions

Feb 11, 2014
A view inside the photoemission chamber, "Hydra," shows the entry point for one time-of-flight electron spectrometer (on the left, opposite the larger open round hole), as well as a second time-of-flight electron spectrometer (on the left front side looking toward the sample, which is a round silver crystal covered by an ultrathin layer of nickel oxide). Credit: M.Huth/Max Planck

Shoot a beam of light or particles at certain special materials and you will liberate electrons—pairs of them—a phenomenon known as "electron pair emission," which can reveal fundamental properties of the solid and reveal information necessary to design novel materials for future applications.

Measuring electron pair emission has always been difficult, however, because they were traditionally done using highly expensive synchrotron light sources, which are available in only a few laboratories worldwide. Nobody has found a way to routinely measure electron pair interactions on a standard lab bench.

Now a team led by researchers at the Max Planck Institute of Microstructure Physics in Halle, Germany has done just that. They developed a new way to measure the emission of directly by combining two common laboratory instruments called time-of-flight spectrometers, a setup they describe in the journal Applied Physics Letters.

"Einstein received the Nobel Prize for his explanation of the photoelectric effect, which was published in 1905. Einstein considered the possibility that the photon energy can be transferred to more than one electron," explained Michael Huth, a postdoctoral researcher at the Max Planck Institute of Microstructure Physics. "The existence of this process provides direct access to the electron correlation strength."

An electron pair is "excited" by a single photon; from an experimental point of view, this requires the combination of a suitable light source and electron spectrometers.

Developing such a setup involved "a significant effort," according to Huth. Comically, the team dubbed their setup's photoemission chamber "Hydra," because its two time-of-flight spectrometers give the chamber an appearance of having multiple heads.

As a proof-of-principle experiment, the team chose to investigate (NiO), which, in theory, should have strong electron correlation effects. While measuring the energy distribution, they were surprised to discover that in contrast to the metal, the energy sum of the electron pair shows no prominent features.

What's the significance? "Our observation is that metals and nickel oxide behave very differently," Huth said. "This implies that our technique allows us to quantify the electron correlation strength."

Quantifying a solid-state material's electron correlation strength is important because it allows researchers to characterize its useful properties, including superconductivity, metal-insulator transition and long-range magnetic ordering. "Our experimental data will guide theory toward understanding the of solids, and one day help to design novel functional materials," Huth noted.

Next, the researchers' sights are set on exploring different materials to gain a more complete picture of electron correlation by running experiments at different photon energies. "We also plan to optimize the efficiency and stability of our new setup for ongoing experiments," Huth said.

Explore further: How to make graphene superconducting

More information: The article, "Electron pair emission detected by time-of-flight spectrometers: Recent progress" by Michael Huth, Cheng-Tien Chiang, Andreas Trützschler, Frank O. Schumann, Jürgen Kirschner, and Wolf Widdra appears in the journal Applied Physics Letters ( DOI: 10.1063/1.4820430 ). The article will be published online on February 11, 2014.

Related Stories

How to make graphene superconducting

Feb 11, 2014

Whenever a new material is discovered, scientists are eager to find out whether or not it can be superconducting. This applies particularly to the wonder material graphene. Now, an international team around ...

A new look below the surface of nanomaterials

Aug 16, 2011

Scientists can now look deeper into new materials to study their structure and behavior, thanks to work by an international group of researchers led by UC Davis and the Lawrence Berkeley National Laboratory and published ...

Recommended for you

Using antineutrinos to monitor nuclear reactors

5 hours ago

When monitoring nuclear reactors, the International Atomic Energy Agency has to rely on input given by the operators. In the future, antineutrino detectors may provide an additional option for monitoring. ...

Imaging turns a corner

9 hours ago

( —Scientists have developed a new microscope which enables a dramatically improved view of biological cells.

Mapping the road to quantum gravity

23 hours ago

The road uniting quantum field theory and general relativity – the two great theories of modern physics – has been impassable for 80 years. Could a tool from condensed matter physics finally help map ...

User comments : 0

More news stories

Phase transiting to a new quantum universe

( —Recent insight and discovery of a new class of quantum transition opens the way for a whole new subfield of materials physics and quantum technologies.

A 'quantum leap' in encryption technology

Toshiba Research Europe, BT, ADVA Optical Networking and the National Physical Laboratory (NPL), the UK's National Measurement Institute, today announced the first successful trial of Quantum Key Distribution ...

When things get glassy, molecules go fractal

Colorful church windows, beads on a necklace and many of our favorite plastics share something in common—they all belong to a state of matter known as glasses. School children learn the difference between ...

Autism Genome Project delivers genetic discovery

A new study from investigators with the Autism Genome Project, the world's largest research project on identifying genes associated with risk for autism, has found that the comprehensive use of copy number variant (CNV) genetic ...

Study links California drought to global warming

While researchers have sometimes connected weather extremes to man-made global warming, usually it is not done in real time. Now a study is asserting a link between climate change and both the intensifying California drought ...