New method provides answers to long lasting dispute about electrical insulators

Sep 25, 2012
Laser system for generating ultra short x-ray pulses used in the experiment to make the recordings. Copyright: CAU, Photo: Rohwer et al.

Experts have been heavily discussing why exactly electrically insulating materials insulate as they do. Based on different mechanisms, a classification scheme for insulators has been in use since the 1960s – a theoretical one. However, it has been yet impossible to distinctly classify all insulators due to a lack of suitable experimental approaches. A team of physicists from Kiel University (Germany) and the University of Colorado in Boulder has now developed a new method to distinguish different insulators unambiguously. The study was published in the online journal Nature Communications.

No notebook, no cell phone, no digital camera would be functional without electrical insulators. The hunt for precise knowledge about state-of-the-art or future insulators is just as rapid as the development of new, better electronic devices. For this reason, research is currently one of the hottest topics in solid-state science.

Following the common scientific procedures in physics, such insulators are first described using universal equations and simulated by computer models. The theoretical results about materials then need to be verified by experiments in the lab. It is this that failed for a number of insulators in the past. "For many years, expert discussions went round and round without any final answer about the insulator class", says project leader Kai Rossnagel from the Institute of Experimental and Applied Physics of Kiel University. The study presented now provides a completely new experimental approach to classifying the insulating behavior of materials objectively.

The materials used in the insulator study were produced by the scientists in a crystal breeding lab in Kiel. Copyright: CAU, Photo: Maack

The science team made use of a special effect: some turn into insulators when strongly cooled down. At the same time, their electric state changes, and when the materials warm up again, their also change. The scientists now use the speed of this change to distinguish different classes of insulators.

Inconceivably small time scales are applied in this method: For the classification, they use a laser beam camera to produce a film from individual images taken within femtoseconds. For comparison: If you took one picture every femtosecond for a period of one second, you would end up with 1.000.000.000.000.000 single pictures, while a regular film camera takes only 24 images per second. "The electronic changes visible in the film, take about one to 50 femtoseconds for some materials and 100 to 200 femtoseconds for others", Rossnagel explains. In this manner, the scientists can distinguish one insulator class from another.

One of the heavily discussed insulator materials, titanium diselenide (TiSe2), was now precisely classified. On top of the precise classification of TiSe2, the scientists gave the first experimental evidence for a new class of insulators, the so-called excitonic insulators. "We believe that our results may terminate the discussion about titanium diselenide after decades"; says Rossnagel but admits: "Only after several years of cross-checking our results, we will know for sure if our method is as useful as we think now".

The new classification method uses a camera technique presented by the same team of researchers in the journal Nature in March 2011. It is called "femtosecond time-resolved photoelectron spectroscopy with extreme UV radiation". The current study was the first systematic application of the new camera technique to a scientific question. The study was carried out within the Kiel Nano and Surface Science, one out of four major research themes at Kiel University. It was funded on the German side by the German Federal Ministry for Education and Research (BMBF).

Explore further: Global scientific team 'visualizes' a new crystallization process (w/ video)

More information: S. Hellmann, T. Rohwer, M. Kalläne, K. Hanff, C. Sohrt, A. Stange, A. Carr, M.M. Murnane, H.C. Kapteyn, L. Kipp, M. Bauer, K. Rossnagel (2012): Time-domain classification of charge-density-wave insulators, Nature Communications 3: 1069, doi: 10.1038/ncomms2078

add to favorites email to friend print save as pdf

Related Stories

Unfazed by imperfections

Jul 08, 2011

While insulating against electrical currents in their interior, the surface of materials called topological insulators permits the flow of electron spins relatively unhindered. The almost lossless flow ...

Researchers create working Mott transistor prototype

Jul 26, 2012

(Phys.org) -- Engineers from several research organizations working together in Japan have developed a working prototype of a Mott transistor, a possible alternative to the standard silicon based field-effect ...

Seeking dark matter on a desktop

Mar 15, 2010

Desktop experiments could point the way to dark matter discovery, complementing grand astronomical searches and deep underground observations. According to recent theoretical results, small blocks of matter ...

Recommended for you

Novel technique opens door to better solar cells

Apr 14, 2014

A team of scientists, led by Assistant Professor Andrivo Rusydi from the Department of Physics at the National University of Singapore's (NUS) Faculty of Science, has successfully developed a technique to ...

Probing metal solidification nondestructively

Apr 14, 2014

(Phys.org) —Los Alamos researchers and collaborators have used nondestructive imaging techniques to study the solidification of metal alloy samples. The team used complementary methods of proton radiography ...

Glasses strong as steel: A fast way to find the best

Apr 13, 2014

Scientists at Yale University have devised a dramatically faster way of identifying and characterizing complex alloys known as bulk metallic glasses (BMGs), a versatile type of pliable glass that's stronger than steel.

User comments : 0

More news stories

Progress in the fight against quantum dissipation

(Phys.org) —Scientists at Yale have confirmed a 50-year-old, previously untested theoretical prediction in physics and improved the energy storage time of a quantum switch by several orders of magnitude. ...

Simplicity is key to co-operative robots

A way of making hundreds—or even thousands—of tiny robots cluster to carry out tasks without using any memory or processing power has been developed by engineers at the University of Sheffield, UK.

Meteorites yield clues to Martian early atmosphere

(Phys.org) —Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks. Their study, published ...