Electric and plasmonic control of THz magnetic circular dichroism and Faraday rotation in graphene

2 November 2016

Time: 10:30 - 12:00am
Venue: QMUL People’s Palace

Terahertz properties of graphene are determined by the electromagnetic Drude response and demonstrate an extraordinary sensitivity to the electrostatic doping and the magnetic field due to a tiny effective mass of the Dirac fermions.

Place and Time:

People’s Palace Room LG02, 10:30 am

Speaker:

prof. Alexey B. Kuzmenko, University of Geneva,

Abstract

Terahertz properties of graphene are determined by the electromagnetic Drude response and demonstrate an extraordinary sensitivity to the electrostatic doping and the magnetic field due to a tiny effective mass of the Dirac fermions. In particular, a giant Faraday rotation was observed by us in epitaxial graphene on SiC [1]. Recently, we studied magneto-optical properties of gated CVD graphene, where one can easily modulate the carrier concentration [2]. Large g-FET devices suitable for THz studies were fabricated, showing excellent transport properties, ambipolar doping and a strong magnetoresistance.

By applying both the electric and magnetic fields, a modulation of transmission exceeding 40% and the magnetic circular dichroism (MCD) of about 35% were achieved. Because of the unique properties of the Dirac fermions (significantly different from conventional 2D electron gases), we were able to tune the cyclotron frequency electrostatically up to 10 THz. Moreover, using ambipolar gating we were able to reverse the sign of the MCD and the Faraday rotation purely electrically at a constant magnetic field. In order to exploit the magneto-plasmonic degrees of freedom, we have also studied graphene with a square array of holes (antidots) [3]. In these structures we observed, apart from the Drude peak, two intense Bragg modes (at 5 and 7 THz). In magnetic field, the intensity of the Bragg modes (magnetoplasmons) increases dramatically for the left-hand- and decreases for the right-hand-circular polarized light. Our electromagnetic simulations reproduce nicely these magneto-plasmon experiments [2]. Our results show that gated antidot arrays allow a strong tunability of their magneto-optical and magneto-plasmonic properties.

We have experimentally demonstrated a first THz graphene-based Faraday isolator [4], where three graphene monolayers separated by thin PMMA layers, were put on top of a thin silicon substrate. The device showed an isolation of up to 17 dB at 3 and 7.5 THz (close to the Fabry-Perot resonances in Si) with the insertion loss below 7 dB in 7 T. Our simulations demonstrate that the characteristics of this proof-of-principle device can be greatly improved in the future using graphene with a higher mobility.

• [1] I. Crassee et al., Nature Phys. 48, 7 (2011).
• [2] J.-M. Poumirol et al., submitted.
• [3] P.Q.. Liu et al., Optica 2, 135 (2015).
• [4] M. Tamagnone et al., Nature Comm., 7, 11216 (2016).

 

About the Speaker

Current research interests:

• 2D crystals (graphene, transition-metal dichalcogenides, topological insulators)
• Strongly correlated electron systems and quantum-spin systems (cuprates, nickelates)
• Broadband optical (UV-Visible-IR-THz) and Raman spectroscopy/microscopy
• Scanning near-field optical microscopy (SNOM)
• Magneto-optics and plasmonics

Principal investigator in:

• Several research projects in Swiss National Science Foundation (2008 - now)
• EU Project Graphene Flagship (2013 - now)

Awards:

• 2012: Ludwig-Genzel Prize (LEES 2012 conference, Napa Valley). Formulation: “For his seminal work on graphene and for his important contributions to the optical investigations of novel superconductors”
• Landau Fellowship, Forschungszentrum Julich (1996, 1997)
• George Soros Fellowship (1995, 1998, 1999)

Software:

RefFIT: versatile, user-friendly and free computer software to model optical spectra (https://sites.google.com/site/reffitprogram/). Used by >100 research groups in the world.