Forum DQMP-MaNEP

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Day / Time
Date(s) - 29/09/2015
13 h 00 min - 14 h 00 min

Category


Auditoire Stückelberg

Ecole de physique

Tuesday, 29 September 2015 – 13h00

Coffee and tea will be available from

12h50 at the entrance of the Auditoire

 

Strong interface induced spin-orbit coupling in
graphene-on-WS2 heterostructure
Zhe Wang (group of Prof. Morpurgo)
Disorder-free graphene is the first predicted topological insulator, whose characteristics have not been
observed experimentally because the strength of intrinsic spin-orbit interaction (SOI) in graphene is too
weak. Here we explore this issue by exploiting interfacial interactions in graphene-on-WS2
heterostructure, whose basic transport characteristics confirm the high device quality. Robust weak
anti-localization effect is observed at all accessible carrier density range down to 250 mK, which is the
first time in graphene and constitutes unambiguous evidence of strong SOI induced in graphene. The
extracted spin-relaxation time is 2-3 order shorter than that in graphene on SiO2 or hexagonal boron
nitride (hBN) substrates, and is comparable to the intervalley scattering time. The experimental findings
are consistent with first-principle electronic structure calculations, which shows interfacial interactions
with WS2 substrate indeed induce strong SOI in graphene. Furthermore, the same analysis also
suggests opening of a gap due to SOI which can become a two-dimensional topological insulator. Our
work therefore clearly demonstrates strong SOI induced in high-quality graphene using interfacial
interactions with WS2, and opens a possible new route to access topological states of matter in
graphene-based systems.
Toward graphene based terahertz non-reciprocal isolator
Jean-Marie Poumirol (group of Prof. van der Marel)
The realization of non-reciprocal isolators is considered one of the most important open challenges in
terahertz science. The discovery of giant Faraday rotation in graphene has opened an interesting
avenue to tackle this problem. Electromagnetic time-reversal symmetry can be broken by applying a
magnetostatic biasing field perpendicular to a graphene sheet, the appearance of Faraday rotation
being a direct evidence of non-reciprocity. One of the major problems for using graphene in real
devices is that the Faraday rotation is maximum only at low frequency and decrease with increasing
energy, requiring large magnetic fields to obtain strong enough magneto-optical effect. In this
presentation, I report on two different ways envisaged to solve theses problems. Using multilayer
graphene combined with Fabry-Perot cavity we were able to strongly enhance the Faraday rotation
reaching 45° at 7T. In graphene periodic anti-dot lattice we show that delocalised plasmon allows the
resonant coupling between light and collective electron modes resulting in an enhancement of the
Faraday rotation close to the plasmon frequency, while keeping the opportunity to tune the carrier
density using electrostatic doping.
Forum Committee : L. Foini, C. Lichtensteiger, N. Ubrig (29.09.2015)

 

Réalisation : Sur Mesure concept