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SUMMARY:Ultraclean graphene: from record mobility to suspended moiré supe
 rlattices
DTSTART:20261019T141500
DTSTAMP:20261017T055716Z
UID:6caee47cbce799e5a026543f6152836bd163544d40b45032fdaea746
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Alexey Berdyugin National University of Singapore\nAbstr
 act:  \nThe quality of an electronic system\, typically quantified by it
 s mobility\, doping homogeneity and\, in moiré materials\, twist-angle un
 iformity\, determines the visibility and robustness of quantum phenomena. 
 Since its discovery\, graphene has been recognized as an exceptionally cle
 an material with a vanishingly small number of intrinsic defects\, yet rea
 lizing its intrinsic potential has remained challenging. In this talk\, I 
 will present three developments that overcome established limitations of v
 an der Waals devices and open new routes for the exploration of electronic
  and structural phenomena.\nFirst\, I will describe graphene devices with 
 engineered Coulomb screening\, created either by proximal graphite gates o
 r by encapsulating graphene between other graphene layers decoupled by a l
 arge twist angle. These devices yield mobilities up to 6 × 107 cm2 V-1 s-
 1\, the highest reported for any material\, and show how engineering the d
 ielectric environment reveals electronic quality previously masked by extr
 insic disorder.\nSecond\, I will show how a related architecture allows us
  to probe and control interlayer hybridization in moiré systems. Although
  miniband formation is usually associated with twisted layers in direct co
 ntact\, graphene layers separated by a monolayer spacer retain sufficient 
 coupling to exhibit pronounced minibands and Brown-Zak oscillations\, whic
 h can now be controlled by displacement field. The spacer also suppresses 
 atomic reconstruction\, yielding highly uniform twist angles over macrosco
 pic distances\, with twist-angle disorder of just ~0.01°. The same signat
 ures appear in CVD-grown twisted structures\, opening a route towards scal
 able long-period superlattices.\nThird\, I will address a long-standing bo
 ttleneck in heterostructure assembly: residual contamination from polymer-
 based stacking. Replacing standard polymer stamps with mica crystals yield
 s devices with ultraclean surfaces and enables new architectures\, includi
 ng suspended twisted graphene superlattices. Atomic force microscopy revea
 ls moiré buckling of 0.1-0.7 nm at the nodes of the domain-wall network\,
  driven by relaxation toward low-energy stacking\, while heterostrain indu
 ces crinkling along the domain walls. The transition between these regimes
  is highly sensitive to the magnitude and anisotropy of heterostrain\, giv
 ing access to a rich family of moiré morphologies at fixed twist angle\, 
 and opening a promising direction for further research.\n\n 
LOCATION:PH L1 503 https://plan.epfl.ch/?room==PH%20L1%20503 https://epfl.
 zoom.us/j/69823646374?pwd=mYUfXk7hNOyXYh238nfzg8CTbqjaQO.1
STATUS:CONFIRMED
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