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: mark.bieler@ptb.de

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 from Brightsurf:

Charging electric cars up to 90% in 6 minutes
POSTECH Professor Byoungwoo Kang's research team uncovers a new Li-ion battery electrode material that can achieve high-energy density and high power capability per volume without reducing particle size.

uOttawa researchers find cheaper, faster way to measure the electric field of light
Researchers at the University of Ottawa have created a new method to measure the temporal evolution of electric fields with optical frequencies.

How dangerous are burning electric cars?
What happens if an electric car burns in a road tunnel or an underground car park?

One more hit from rare Earth: Efficient coherent spin manipulation by the electric field
Researchers used rare earth ions to efficiently couple the electric and magnetic behaviors of material.

Battery breakthrough gives boost to electric flight and long-range electric cars
Researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with Carnegie Mellon University, have developed a new battery material that could enable long-range electric vehicles that can drive for hundreds of miles on a single charge, and electric planes called eVTOLs for fast, environmentally friendly commutes.

Deterministic reversal of single magnetic vortex circulation by an electric field
Chinese researchers discover a deterministic reversal of magnetic vortex circulation in a Ni79Fe21 (NiFe) island on top of a layered-perovskite Bi2WO6 (BWO) thin film using an electric field.

4D electric circuit network with topology
Researchers from China and Germany have proposed a design scheme to implement a four-dimensional topological insulating state in circuit network, which provides a convenient physical platform for studying high-dimensional states.

How we might recharge an electric car as it drives
Stanford engineers demonstrate a technology that could one day be scaled up to power a car moving down the road.

Electric cars better for climate in 95% of the world
Fears that electric cars could actually increase carbon emissions are unfounded in almost all parts of the world, news research shows.

O-FIB: Far-field-induced near-field breakdown for direct nanowriting in an atmospheric environment
Nanoscale texturing, drilling, cutting and spatial sculpturing require not only high accuracy, but also the capability of manufacturing in the atmospheric environment.

Read More: Electric Field News and Electric Field Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.