Paper published in Science Advances

Our paper on cavity materials – how to manipulate matter with pure vacuum fluctuations of light – was published in Science Advances. Here is the press release.

The vacuum fluctuations of light (yellow wave) are amplified in an optical cavity (upper and lower reflecting mirrors). Crystal lattice vibrations (red atoms) at a two-dimensional interface surf this strong light wave. The thus mixed light-vibrational waves couple particularly strongly to electrons in a two-dimensional atomically thin material (green and yellow atoms), changing its properties.
© Jörg M. Harms / MPSD

Gabriel’s paper in Nature Communications

A wave of laser light hits the magnetic material, shaking the electron spins (arrows). This weakens magnetism and induces Weyl fermions in the laser-shaken material. © J.M. Harms / MPSD

Gabriel’s paper is out in Nature Communications: G. E. Topp et al., Nature Communications 9, 4452 (2018). Here is a link to the press release “Shedding light on Weyl fermions” on the MPSD website (click here for a German version).

Congratulations, Gabriel!

Charge pumping in graphene

Riku’s paper with Mike Ridley on charge pumping in ac-driven graphene nanoribbons has been published in Physical Review B. Congrats!

Popular summary: Typically, electronic current flowing through a conductor needs a net voltage to be applied across the conductor. However, applying an alternating voltage, which is zero on average, may induce a direct current. This mechanism is known in the engineering literature as AC-DC conversion or rectification. Here we investigated this mechanism in a quantum transport setup consisting of graphene nanoribbons, and derived some general “rules of thumb” for quantum pumping.

How to make a material more correlated with light

From top to bottom, electronic spectra show more and more coherence-incoherence spectral weight transfer, indicative of enhanced electron-lattice coupling in the strongly driven system.

Our preprint “Light-enhanced electron-phonon coupling from nonlinear electron-phonon coupling” is available on arXiv. In this work, it is shown how one can amplify electron-lattice coupling by using lasers that are tuned to a phonon, that is coupled quadratically to the electrons of the material. Such enhanced electron-lattice coupling can lead to the formation of polarons – electrons coupled to a “cloud” of lattice distortion – or even make the system superconducting. It has recently been debated how possible light-induced superconductivity in carbon football molecular crystal (“fullerenes”) may come about, and nonlinear electron-phonon coupling might play an important role. Similarly, more direct signatures of light-enhanced electron-lattice coupling have been observed in metallic bilayers of the carbon flatland material graphene. Now experiments have to be performed to check the hypothesis of our theory paper.

Elementary-particle physics in laser-driven materials

Dancing Weyl cones: When excited by tailored laser pulses (white spiral), the cones in a Dirac fermion material dance on a path (8-shape) that can be controlled by the laser light. This turns a Dirac material into a Weyl material, changing the nature of the quasiparticles in it. One of the cones hosts right-handed Weyl fermions; the other cone hosts left-handed ones. [less] © Jörg M. Harms/MPSD
Dancing Weyl cones: When excited by tailored laser pulses (white spiral), the cones in a Dirac fermion material dance on a path (8-shape) that can be controlled by the laser light. This turns a Dirac material into a Weyl material, changing the nature of the quasiparticles in it. One of the cones hosts right-handed Weyl fermions; the other cone hosts left-handed ones. © Jörg M. Harms/MPSD

Our work “Creating stable Floquet-Weyl semimetals by laser-driving of 3D Dirac materials” was published in Nature Communications (doi:10.1038/ncomms13940).

Further reading:
Studying fundamental particles in materials

Understanding the energy flow in a high-temperature superconductor

Microscopic image of one of the bismuth strontium calcium copper oxide samples the scientists studied using a new high-speed imaging technique. Color changes show changes in sample height and curvature to dramatically reveal the layered structure and flatness of the material. Credit: Brookhaven National Laboratory Read more at: http://phys.org/news/2016-12-laser-pulses-scientists-complex-electron.html#jCp
Microscopic image of one of the bismuth strontium calcium copper oxide samples the scientists studied using a new high-speed imaging technique. Color changes show changes in sample height and curvature to dramatically reveal the layered structure and flatness of the material. Credit: Brookhaven National Laboratory

Our work “Energy Dissipation from a Correlated System Driven Out of Equilibrium” was published in Nature Communications (doi:10.1038/ncomms13761).

Further reading:
Laser pulses help scientists tease apart complex electron interactions
Energiefluss im Supraleiter
Laserpulse helfen Forschern, komplexe Elektronenwechselwirkungen zu entflechten