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SUMMARY:Electron optics in suspended graphene
DTSTART:20141121T141500
DTSTAMP:20260414T032132Z
UID:88204cbc1d119a56abf2fbdc350d710cc2fb6dd21907633b3fbac87b
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Christian Schönenberger\, Swiss Nanoscience Institute\,
  University of Basel\nGraphene is an intriguing material: electrons are ch
 iral Dirac particles yielding a plethora of new phenomena such as Klein tu
 nneling\, fractional quantum Hall plateaus and unconventional Andreev refl
 ection. All these effects require graphene of high quality and low carrier
  density. In the language of graphene\, one needs to approach the so-calle
 d charge neutrality point\, also known as the Dirac point\, as close as po
 ssible. However\, in real devices there is typically a considerable random
  potential present due to charge impurities in the substrate or adsorbates
  on graphene itself. Mobilities in most practical devices are modest. Thou
 gh values two orders of magnitude larger than in silicon devices can easil
 y be obtained\, typical graphene devices are way off state-of-the-art high
  mobility III-V heterojunction layers\, where mobilities in 10^3  m2/Vs a
 re possible.\nTo overcome this problem\, we have developed a versatile tec
 hnology that allows to suspend graphene and complement it with arbitrary b
 ottom and top-gate structures. Using current annealing we demonstrate exce
 ptional high mobilities in monolayer graphene approaching 10^2 m2/Vs. Thes
 e suspended devices are ballistic over micrometer length scales and displa
 y intriguing interference patterns in the electrical conductance when diff
 erent gate potentials are applied. Specifically I will discuss different t
 ypes of Fabry-Perot resonances that appear in different gate voltage regim
 es of ballistic pn devices [1]. I will also present recent electric transp
 ort measurements in magnetic field\, where intriguing features appear in t
 he intermediate field range in between the low-field Klein-tunneling regim
 e and the quantum Hall regime. We observe a large number of non-dispersing
  states which might be due to so-called snake states confined to the pn in
 terface.\nFurthermore\, I will use the opportunity to discuss first result
 s on electron guiding in ultraclean monolayer graphene. Similar to light g
 uiding\, electrons can be confined by total internal reflection due to dif
 ferent effective refractive indices. In graphene\, the latter can be obtai
 ned simply by changing the carrier density through gating. Unlike a conven
 tional unipolar material\, one can in addition guide electron waves throug
 h the formation of bipolar boundaries. This should yield a high guiding ef
 ficiency. Finally\, I will briefly mention our efforts in realizing lensin
 g using negative refractive electron optics in graphene.\nReference: P. Ri
 ckhaus et al.\, Nature Communications 4\, 2342 (2013)\nBio: Christian Sch
 önenberger holds a degree as an electrical engineer in applied sciences (
 1979) and a diploma in physics (1986). He did his PhD at the IBM Zurich Re
 search Lab in the group of Dr. H. Rohrer and Dr. S. Alvarado. His PhD is e
 ntitled “Understanding Magnetic Force Microscopy” which was awarded wi
 th a medal from the ETH-Zurich and the Swiss Physical Society price (1991)
 . Subsequently\, he worked at the Philips Research Lab. at Eindoven (NL)\,
  first as a postdoc\, and later as a permanent staff member.\nIn 1994 he w
 as awarded a fellowship from the Swiss National Science Foundation (Profil
 -II). Soon afterwards he was elected to a full chair at the Univ. of Basel
  (1995). Since then\, Christian Schönenberger has setup a group whose res
 earch focuses on charge transport in nanoscaled devices. He has co-authore
 d over 80 refereed journal publications. He has participated in several EU
  programs and is currently directing the Swiss Nanoscience Institute at th
 e University of Basel and the Swiss-NSF center on Nanoscale Science and Te
 chnology: http://www.nanoscience.ch
LOCATION:PH L1 503 (Aquarium) http://plan.epfl.ch/?room=PHL1503
STATUS:CONFIRMED
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