Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Channeling valleytronics in graphene

07.05.2015

Berkeley Lab researchers discover 1-D conducting channels in bilayer graphene

To the list of potential applications of graphene - a two-dimensional semiconductor of pure carbon that is stronger and much faster than silicon - we can now add valleytronics, the coding of data in the wavelike motion of electrons as they speed through a conductor. Berkeley Lab researchers have discovered topologically protected one-dimensional electron conducting channels at the domain walls of bilayer graphene. These conducting channels are "valley polarized," which means they can serve as filters for electron valley polarization in future devices such as quantum computers.


In this near-field infrared nanoscopy image of bilayer graphene, domain walls are revealed by bright lines that arise because of the walls' local electronic structures and IR responses.

Image courtesy of Feng Wang, Berkeley Lab

"Combining near-field infrared nanometer-scale microscopy and low-temperature electrical transport measurements, we have recorded the first experimental observations of 1D ballistic electron conducting channels at bilayer graphene domain walls," says Feng Wang, a condensed matter physicist with Berkeley Lab's Materials Sciences Division, who led this work. "These 1D valley-polarized conducting channels featured a ballistic length of about 400 nanometers at 4 kelvin. Their existence opens up opportunities for exploring unique topological phases and valley physics in graphene."

Wang, who also holds an appointment with the University of California (UC) Berkeley Physics Department and is a member of the Kavli Energy NanoScience Institute (Kavli-ENSI), is the corresponding author of a paper describing this research in the journal Nature. The lead authors of the paper are Long Ju and Zhiwen Shi, members of Wang's research group. (See here for full list of authors.)

Valleytronics is generating a lot of excitement in the high-tech industry as a potential avenue to quantum computing. Like spintronics, valleytronics offers a tremendous advantage in data processing speeds over the electrical charge used in classical electronics.

"In valleytronics, electrons move through the lattice of a 2D semiconductor as a wave with two energy valleys, each valley being characterized by a distinct momentum and quantum valley number," Wang says. "This quantum valley number can be used to encode information when the electrons are in a minimum energy valley."

Recent theoretical work suggested that domain walls between AB- and BA-stacked bilayer graphene could provide an attractive place to realize one-dimensional electron conducting channels for valleytronics because the smoothness of the domain walls preserves electron valleys, unlike the atomic defects at graphene edges that result in valley-mixing. Until now, however, there has been no experimental evidence of these channels.

Working at Berkeley Lab's Advanced Light Source (ALS), a DOE Office of Science User Facility, Wang, Ju, Shi and their colleagues used tightly focused beams of infrared light to image in situ bilayer graphene layer-stacking domain walls on device substrates. Field effect devices fabricated over these domain walls revealed the 1D conducting channels.

In the bilayer graphene imaging work by Feng Wang and his group, IR light (yellow) is focused onto the apex of a metal-coated AFM tip and the backscattered infrared radiation is collected and measured.

"The infrared measurements were carried out at ALS beamline 5.4," says Shi. "The near-field infrared capabilities of this beamline enable optical spectroscopy with spatial resolutions that are way beyond the diffraction limit, allowing us to image the nanometer-wide domain walls in bilayer graphene."

Adds Ju, "That we were able to image the domain walls with a technique that is compatible with device fabrication was key to our work. With near-field IR spectroscopy, we could directly fabricate field effect devices over the domain walls and detect the 1D conducting channels."

To date, most valleytronics research has focused on the 2D semiconductors known as MX2 materials, which consist of a single layer of transition metal atoms, such as molybdenum or tungsten, sandwiched between two layers of chalcogen atoms, such as sulfur. The results of this study demonstrate that protected topological phases can also be realized in bilayer graphene, which is a tunable semiconductor, making the 2D carbon sheets useful for valleytronic applications.

"Our next step is to increase the ballistic length of these 1D channels so we can utilize them as electron valley filters, as well as for other manipulations of electron valleys in graphene," Wang says.

###

This research was primarily funded by the DOE Office of Science.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.lbl.gov.

Media Contact

Lynn Yarris
lcyarris@lbl.gov
510-486-5375

 @BerkeleyLab

http://www.lbl.gov 

Lynn Yarris | EurekAlert!

More articles from Materials Sciences:

nachricht Glass's off-kilter harmonies
18.01.2017 | University of Texas at Austin, Texas Advanced Computing Center

nachricht Explaining how 2-D materials break at the atomic level
18.01.2017 | Institute for Basic Science

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland

19.01.2017 | Earth Sciences

Not of Divided Mind

19.01.2017 | Life Sciences

Molecule flash mob

19.01.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>