Riku receives Academy of Finland funding

Riku Tuovinen has been granted an Academy of Finland 3-year independent funding award starting in September 2019. In his project “Ultrafast many-body correlations in quantum transport and spectroscopy” Riku will develop and apply novel theoretical and computational methods for many-body quantum phenomena out of equilibrium. Congratulations, Riku!

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