High-speed march through a layer of graphene

October 5, 2015
A laser pulse hits a two-dimensional layer of graphene and dislocates the electrons of the carbon ions. Credit: Christian Hackenberger

In cooperation with the Center for Nano-Optics of Georgia State University in Atlanta, scientists of the Laboratory for Attosecond Physics of the Max Planck Institute of Quantum Optics and the Ludwig-Maximilians-Universität have made simulations of the processes that happen when a layer of carbon atoms is irradiated with strong laser light.

Electrons hit by strong laser pulses change their location on ultrashort timescales, i.e. within a couple of attoseconds (1 as = 10-18 sec). In cooperation with the Center for Nano-Optics of Georgia State University in Atlanta (USA), scientists at the Laboratory for Attosecond Physics (LAP) of the Max Planck Institute of Quantum Optics (MPQ) and the Ludwig-Maximilians-Universität (LMU) have made simulations of processes that take place when electrons in a layer of interact with strong laser light. The purpose of these simulations is to gain insight into light-matter-interactions in the microcosm. A better understanding of the underlying physical processes could lead to light-wave driven electronics that would operate at light frequencies, which is a hundred thousand times faster than state-of-the-art technologies. Graphene with its exceptional properties is considered to be very well suited as an example system for prototype experiments.

The closer we observe the motion of electrons, the better we understand their interaction with light. Many phenomena that arise in condensed matter due to strong-field light-matter interaction are not yet fully understood. As the underlying processes occur within femto- or even attoseconds, it is difficult to access this intra-atomic cosmos: a femtosecond is a millionth of a billionth of a second; an attosecond is even a thousand times shorter. Experimental methods that shall cope with this challenge are at a development stage. However, it is possible to investigate these processes with the help of numerical simulations.

The team of scientists from LAP and Georgia State University has calculated what happens to electrons in graphene interacting with an intense laser pulse. The laser field excites and displaces electrons, changing thus the charge density distribution. During this process, an extremely short electron pulse is scattered off the probe. The diffraction map of these matter waves reflects how the electron density distribution inside the graphene layer has been altered because of the laser pulse.

These simulations have revealed complex relations between the excitation of by light and their subsequent ultrafast motion inside and between the carbon atoms in the graphene layer. Valence electrons are weakly bound and shared among neighbouring atoms. The scientists investigated their motion by identifying microscopic volumes that represent various chemical bonds and analysing the electric charge contained in these volumes. During a laser pulse, there is a significant redistribution of the charge; at the same time, the displacement of the caused by the electromagnetic field of the laser pulse is very small, less than a picometre (10-12 m). In addition to that, the calculations showed that the light-induced electric current has an inhomogeneous microscopic distribution, flowing along the chemical bonds between the carbon atoms.

These simulations should assist new ultrafast electron diffraction measurements. "We will possibly detect new phenomena, and perhaps observe deviations from our predictions", project leader Vladislav Yakovlev points out. "But we are pretty sure that quite some fundamental physics is waiting to be observed in challenging but feasible atomic-scale measurements."

Explore further: Attosecond electron catapult

More information: "Atomic-scale diffractive imaging of sub-cycle electron dynamics in condensed matter." Scientific Reports, 28 September 2015, DOI: 10.1038/srep14581

Related Stories

Attosecond electron catapult

August 12, 2015

A team of physicists and chemists from the Laboratory of Attosecond Physics at the Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics has studied the interaction of light with tiny glass particles.

Flashes of light out of the mirror

June 12, 2012

(Phys.org) -- A team of the Laboratory of Attosecond physics at the Max Planck Institute of Quantum Optics developed an alternative way of generating attosecond flashes of light. 

Recommended for you

Nano-decoy lures human influenza A virus to its doom

October 25, 2016

To infect its victims, influenza A heads for the lungs, where it latches onto sialic acid on the surface of cells. So researchers created the perfect decoy: A carefully constructed spherical nanoparticle coated in sialic ...

New method increases energy density in lithium batteries

October 24, 2016

Yuan Yang, assistant professor of materials science and engineering at Columbia Engineering, has developed a new method to increase the energy density of lithium (Li-ion) batteries. He has built a trilayer structure that ...

Nanofiber coating prevents infections of prosthetic joints

October 24, 2016

In a proof-of-concept study with mice, scientists at The Johns Hopkins University show that a novel coating they made with antibiotic-releasing nanofibers has the potential to better prevent at least some serious bacterial ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.