Nav: Home

Time-resolved measurement of the anomalous velocity

December 16, 2015

The movement of charge carriers perpendicular to an electric driving field - even without a magnetic field - constitutes one of the most intriguing properties of carriers in solids. This anomalous velocity is at the origin of fascinating physical phenomena - with the spin Hall effect and the anomalous Hall effect being two prominent examples - and might be important for future spintronic applications or even new quantum computers. At the Physikalisch-Technische Bundesansstalt (PTB), the German National Metrology Institute, researchers have now succeeded in detecting the anomalous velocity in a semiconductor made of GaAs with a sub-picosecond time resolution. On the one hand, this work gives new insight into the microscopic origins of the anomalous velocity. On the other hand, it opens a new area of research for studying important physical effects on ultrafast time scales. The results have been published in the present issue of the renowned journal Physical Review Letters.

The anomalous velocity has different microscopic origins; one typically distinguishes between intrinsic and extrinsic contributions. The intrinsic contribution depends on the intrinsic properties of the solid (i.e. on the so-called Berry curvature), while the extrinsic contribution is caused by carrier scattering. Despite intensive investigations of the anomalous velocity in the past years, no simple technique has been developed which would enable the distinction between intrinsic and extrinsic contributions in a straightforward way. Moreover, the anomalous velocity has not yet been studied on ultrafast time scales on which factors such as coherent effects might significantly influence the anomalous velocity.

At PTB, the anomalous velocity has now, for the first time, been detected with sub-picosecond time resolution. For this purpose a semiconductor made of GaAs was excited by means of an optical femtosecond laser and a pulsed high-frequency electric field. While the optical laser pulse excites carriers with a particular spin direction, the high-frequency field accelerates these carriers. During this process, the carriers gain not only a velocity parallel to the electric field, but also the anomalous velocity perpendicular to it. This velocity was detected by a time-resolved study of the electromagnetic radiation emitted from the sample.

The PTB researchers have shown that the time-resolved detection of the anomalous velocity is very important for its further understanding. On the one hand, such investigations enable the distinction between intrinsic and extrinsic contributions, since these contributions have different time-domain shapes. On the other hand, it is now possible to investigate the dependence of the anomalous velocity on the momentum and energy of the carriers involved which, in turn, allows new studies of other important physical phenomena.

Mark Bieler, Working Group 2.54 Femtosecond Measurement Techniques, phone: +49 531 592-2540, e-mail:

Publication link

S. Priyadarshi, K. Pierz, M. Bieler: Detection of the anomalous velocity with sub-picosecond time resolution in semiconductor nanostructures. Phys. Rev. Lett. 115, 257401 (2015)

Physikalisch-Technische Bundesanstalt (PTB)

Related Electric Field Articles:

Electric tech could help reverse baldness
Reversing baldness could someday be as easy as wearing a hat, thanks to a noninvasive, low-cost hair-growth-stimulating technology developed by engineers at the University of Wisconsin-Madison.
Is it safe to use an electric fan for cooling?
The safety and effectiveness of electric fans in heatwaves depend on the climate and basing public health advice on common weather metrics could be misleading, according to a new study from the University of Sydney.
Dowsing for electric fields in liquid crystals
Nematic liquid crystals can be oriented in a curious way termed the 'dowser texture', which is sensitive to external conditions.
Electric-field-controlled superconductor-ferromagnetic insulator transition
Xianhui Chen's group at University of Science and Technology of China observed an electric-field controlled reversible transition from superconductor to ferromagnetic insulator in (Li,Fe)OHFeSe thin flake using the latest SIC-FET gating technique.
IU researchers develop electric field-based dressing to help heal wound infections
Researchers at Indiana University School of Medicine have found a way to charge up the fight against bacterial infections using electricity.
More Electric Field News and Electric Field Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...