Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Measuring the mass of 'massless' electrons: Taming graphene, Harvard-led researchers successfully measure collective mass of ‘massless’ electrons in motion

A schematic of the experimental setup. Ham and Yoon measured the change in phase of a microwave signal sent through the graphene.Image courtesy of Hosang Yoon, Harvard SEAS.
A schematic of the experimental setup. Ham and Yoon measured the change in phase of a microwave signal sent through the graphene.

Image courtesy of Hosang Yoon, Harvard SEAS.

Abstract:
Individual electrons in graphene are massless, but when they move together, it's a different story.

Graphene, a one-atom-thick carbon sheet, has taken the world of physics by storm—in part, because its electrons behave as massless particles. Yet these electrons seem to have dual personalities. Phenomena observed in the field of graphene plasmonics suggest that when the electrons move collectively, they must exhibit mass.

Measuring the mass of 'massless' electrons: Taming graphene, Harvard-led researchers successfully measure collective mass of ‘massless’ electrons in motion

Cambridge, MA | Posted on June 24th, 2014

After two years of effort, researchers led by Donhee Ham, Gordon McKay Professor of Electrical Engineering and Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS), and his student Hosang Yoon, Ph.D.'14, have successfully measured the collective mass of ‘massless' electrons in motion in graphene.

By shedding light on the fundamental kinetic properties of electrons in graphene, this research may also provide a basis for the creation of miniaturized circuits with tiny, graphene-based components.

The results of Ham and Yoon's complex measurements, performed in collaboration with other experts at Columbia University and the National Institute for Materials Science in Japan, have been published online in Nature Nanotechnology.

"Graphene is a unique material because, effectively, individual graphene electrons act as though they have no mass. What that means is that the individual electrons always move at a constant velocity," explains Ham. "But suppose we apply a force, like an electric field. The velocity of the individual electrons still remains constant, but collectively, they accelerate and their total energy increases—just like entities with mass. It's quite interesting."

Without this mass, the field of graphene plasmonics cannot work, so Ham's team knew it had to be there—but until now, no one had accurately measured it.

"One of the greatest contributions of this work is that it is actually an extremely difficult measurement," says Ham.

As Newton's second law dictates, a force applied to a mass must generate acceleration. Yoon and Ham knew that if they could apply an electric field to a graphene sample and measure the electrons' resulting collective acceleration, they could then use that data to calculate the collective mass.

But the graphene samples used in past experiments were replete with imperfections and impurities—places where a carbon atom was missing or had been replaced by something different. In those past experiments, electrons would accelerate but very quickly scatter as they collided with the impurities and imperfections.

"The scattering time was so short in those studies that you could never see the acceleration directly," says Ham.

To overcome the scattering problem, several smart changes were necessary.

First, Ham and Yoon joined forces with Philip Kim, a physics professor at Columbia who will join the Harvard faculty on July 1 as Professor of Physics and of Applied Physics. A Harvard graduate (Ph.D. '99), Kim is well known for his pioneering fundamental studies of graphene and his expertise in fabricating high-quality graphene samples. The team was now able to reduce the number of impurities and imperfections by sandwiching the graphene between layers of hexagonal boron nitride, an insulating material with a similar atomic structure. By also collaborating with James Hone, a professor of mechanical engineering at Columbia, they designed a better way to connect electrical signal lines to the sandwiched graphene. And Yoon and Ham applied an electric field at a microwave frequency, which allows for the direct measurement of the electrons' collective acceleration in the form of a phase delay in the current.

"By doing all this, we translated the situation from completely impossible to being at the verge of either seeing the acceleration or not," says Ham. "However, the difficulty was still very daunting, and Hosang [Yoon] made it all possible by performing very fine and subtle microwave engineering and measurements—a formidable piece of experimentation."

"To me, it was a victorious moment that finally justified a long-term effort, going through multiple trials and errors," says Yoon, lead author of the paper in Nature Nanotechnology. "Until then, I wasn't even sure if the experiment would really be possible, so it was like a ‘through darkness comes light' moment."

Collective mass is a key aspect of explaining plasmonic behaviors in graphene. By demonstrating that graphene electrons exhibit a collective mass and by measuring its value accurately, Yoon says, "We think it will help people to understand and design more sophisticated plasmonic devices with graphene."

The team's experiments also revealed that, in graphene, kinetic inductance (the electrical manifestation of collective mass) is several orders of magnitude larger than another, far more commonly exploited property called magnetic inductance. This is important in the push toward smaller and smaller electronic circuitry—the main theme of modern integrated circuits—because it means the same level of inductance can be achieved in a far smaller area. Furthermore, Ham and Yoon say that this miniature graphene-based kinetic inductor could enable the creation of a solid-state voltage-controlled inductor, complementary to the widely used voltage-controlled capacitor. It could be used to substantially increase the frequency tuning range of electronic circuits, which is an important function in communication applications.

For now, the challenge remains to improve the quality of graphene samples so that the detrimental effects of electron scattering can be further reduced.

##

Hosang Yoon is lead author of the paper in Nature Nanotechnology, with corresponding authors Donhee Ham at Harvard SEAS and Philip Kim at Columbia. Additional coauthors include Columbia professor James Hone, Columbia graduate students Carlos Forsythe and Lei Wang; Nikolaos Tombros, a former member of the Kim lab at Columbia, now at the University of Groningen in the Netherlands; Kenji Watanabe, chief researchers in optoelectronic materials at the National Institute for Materials Science (NIMS) in Japan; and Takashi Taniguchi, group leader in the Ultra-high Pressure Processes Group at NIMS.

This research was supported by the Air Force Office of Scientific Research, the Office of Naval Research, the National Science Foundation, and the Samsung Advanced Institute of Technology and its Global Research Opportunity program. Additional support was provided by the Nano Material Technology Development Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning; the Columbia Optics and Quantum Electronics IGERT; and the Netherlands Organisation for Scientific Research.

####

For more information, please click here

Contacts:
Caroline Perry

617-496-1351

Copyright © Harvard University

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

GLOBALFOUNDRIES and Soitec Enter Into Long-term Supply Agreement on FD-SOI Wafers: Strategic milestone to help guarantee a secure, high-volume supply of FD-SOI technology September 20th, 2017

GLOBALFOUNDRIES Announces Availability of mmWave and RF/Analog on Leading FDX™ FD-SOI Technology Platform: Technology solution delivers ‘connected intelligence’ to next generation high-volume wireless and IoT applications with lower power and significantly reduced cost September 20th, 2017

GLOBALFOUNDRIES Announces Availability of Embedded MRAM on Leading 22FDX® FD-SOI Platform: Advanced embedded non-volatile memory solution delivers ‘connected intelligence’ by expanding SoC capabilities on the 22nm process node September 20th, 2017

Wireless/telecommunications/RF/Antennas/Microwaves

GLOBALFOUNDRIES Announces Availability of mmWave and RF/Analog on Leading FDX™ FD-SOI Technology Platform: Technology solution delivers ‘connected intelligence’ to next generation high-volume wireless and IoT applications with lower power and significantly reduced cost September 20th, 2017

GLOBALFOUNDRIES Delivers 8SW RF SOI Technology for Next-Generation Mobile and 5G Applications: Advanced 8SW 300mm SOI technology enables cost-effective, high-performance RF front-end modules for 4G LTE mobile and sub-6GHz 5G applications September 20th, 2017

GLOBALFOUNDRIES Unveils Vision and Roadmap for Next-Generation 5G Applications: Technology platforms are uniquely positioned to enable a new era of ‘connected intelligence’ with the transition to 5G September 20th, 2017

Graphene/ Graphite

New quantum phenomena in graphene superlattices September 18th, 2017

Graphene based terahertz absorbers: Printable graphene inks enable ultrafast lasers in the terahertz range September 13th, 2017

UConn chemist synthesizes pure graphene August 30th, 2017

Physics

New quantum phenomena in graphene superlattices September 18th, 2017

Bit data goes anti-skyrmions September 1st, 2017

Govt.-Legislation/Regulation/Funding/Policy

Copper catalyst yields high efficiency CO2-to-fuels conversion: Berkeley Lab scientists discover critical role of nanoparticle transformation September 20th, 2017

Solar-to-fuel system recycles CO2 to make ethanol and ethylene: Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis September 19th, 2017

New insights into nanocrystal growth in liquid: Understanding process that creates complex crystals important for energy applications September 14th, 2017

Magnetic cellular 'Legos' for the regenerative medicine of the future September 12th, 2017

Discoveries

Copper catalyst yields high efficiency CO2-to-fuels conversion: Berkeley Lab scientists discover critical role of nanoparticle transformation September 20th, 2017

Solar-to-fuel system recycles CO2 to make ethanol and ethylene: Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis September 19th, 2017

A new approach to ultrafast light pulses: Unusual fluorescent materials could be used for rapid light-based communications systems September 19th, 2017

New quantum phenomena in graphene superlattices September 18th, 2017

Announcements

GLOBALFOUNDRIES Delivers 8SW RF SOI Technology for Next-Generation Mobile and 5G Applications: Advanced 8SW 300mm SOI technology enables cost-effective, high-performance RF front-end modules for 4G LTE mobile and sub-6GHz 5G applications September 20th, 2017

GLOBALFOUNDRIES Unveils Vision and Roadmap for Next-Generation 5G Applications: Technology platforms are uniquely positioned to enable a new era of ‘connected intelligence’ with the transition to 5G September 20th, 2017

GLOBALFOUNDRIES Delivers Custom 14nm FinFET Technology for IBM Systems: Jointly developed 14HP process is world’s only technology that leverages both FinFET and SOI September 20th, 2017

GLOBALFOUNDRIES Introduces New 12nm FinFET Technology for High-Performance Applications September 20th, 2017

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

Copper catalyst yields high efficiency CO2-to-fuels conversion: Berkeley Lab scientists discover critical role of nanoparticle transformation September 20th, 2017

Solar-to-fuel system recycles CO2 to make ethanol and ethylene: Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis September 19th, 2017

A new approach to ultrafast light pulses: Unusual fluorescent materials could be used for rapid light-based communications systems September 19th, 2017

New quantum phenomena in graphene superlattices September 18th, 2017

Military

First on-chip nanoscale optical quantum memory developed: Smallest-yet optical quantum memory device is a storage medium for optical quantum networks with the potential to be scaled up for commercial use September 11th, 2017

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

2-faced 2-D material is a first at Rice: Rice University materials scientists create flat sandwich of sulfur, molybdenum and selenium August 14th, 2017

Moving at the Speed of Light: University of Arizona selected for high-impact, industrial demonstration of new integrated photonic cryogenic datalink for focal plane arrays: Program is major milestone for AIM Photonics August 10th, 2017

Research partnerships

GLOBALFOUNDRIES Delivers Custom 14nm FinFET Technology for IBM Systems: Jointly developed 14HP process is world’s only technology that leverages both FinFET and SOI September 20th, 2017

Solar-to-fuel system recycles CO2 to make ethanol and ethylene: Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis September 19th, 2017

A new approach to ultrafast light pulses: Unusual fluorescent materials could be used for rapid light-based communications systems September 19th, 2017

New insights into nanocrystal growth in liquid: Understanding process that creates complex crystals important for energy applications September 14th, 2017

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project