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UID:6a5970f8e35ba
DTSTART:20260720T090000Z
SEQUENCE:0
TRANSP:OPAQUE
LOCATION:ICFO Auditorium
SUMMARY:ICFO | ÁLVARO MORENO ABAJO
CLASS:PUBLIC
DESCRIPTION:Two-dimensional (2D) materials provide a powerful platform for 
 nanoscale engineering and control of geometry and energy landscapes withou
 t directly modifying the material\, owing to their interfacial nature. Thi
 s thesis explores how we can harness this potential by introducing in-plan
 e engineering in van der Waals heterostructures. We present two case studi
 es: in one\, the exciton dimensionality is reduced using a designed 1D ele
 ctrostatic trap\; in the other\, twisting two monolayers yields a chiral c
 onfiguration that modifies the interaction with other chiral systems. Toge
 ther\, these two parts demonstrate how inplane symmetry breaking (translat
 ional and mirror symmetry\, respectively) in 2D material platforms enables
  new modalities of control and sensing.\nIn the first part\, we investigat
 e electrostatically defined confinement of intralayer excitons in MoSe2. A
  p&ndash\;i&ndash\;n junction is induced in the monolayer by asymmetric ga
 ting\, creating a tight 1D potential with an effective exciton confinement
  length down to 10nm. Combining photoluminescence and reflectance-contrast
  spectroscopy\, we resolve a discrete spectrum of localized states arising
  from center-of-mass quantization\, with linear polarization aligned with 
 the trap geometry\, consistent with confinement-enhanced valley-exchange i
 nteractions. Importantly for the development of this technique\, we show t
 hat the confinement potential cannot be understood as a purely electrostat
 ic effect. Illumination reshapes device operation by inducing dissociation
 -driven photo-doping and Auger-assisted charge extraction\, thereby stabil
 izing a working p&ndash\;i&ndash\;n configuration. We resolve photoinduced
  carrier-redistribution dynamics on the scale of seconds and demonstrate t
 hat their dependence on excitation position produces sharp switching betwe
 en confined and unconfined excitonic responses. A rate-equation descriptio
 n captures the competition between dissociation and Auger processes\, high
 lighting a route to nonlocal optical control of carrier density and\, cons
 equently\, of the confinement potential. Programmable excitonic potentials
  that reach the 0D limit could enable quantum technologies such as single-
 photon sources or optically addressable qubits\, and open a route toward s
 trong exciton&ndash\;exciton interactions and Bose&ndash\;Hubbard physics.
 In the second part\, we leverage the structural chirality of twisted bilay
 er graphene (TBG) to realize a novel enantiomeric sensing strategy based o
 n chirality-dependent non-radiative energy transfer. In the presence of TB
 G\, the decay rate of chiral fluorophores is modified depending on handedn
 ess matching between molecule and substrate\, which we read out by measuri
 ng the fluorescence lifetime in time-resolved photoluminescence experiment
 s. The observed asymmetry is statistically tested by spatially resolving t
 he enantioselective contrast\, observing a sign reversal upon inversion of
  the TBG handedness\, and exploring the role of the twist angle as a contr
 ol parameter. We quantify the effect of chirality through a lifetime-based
  dissymmetry factor that reaches the 1 &ndash\; 10% level\, implying an en
 hancement of several orders of magnitude compared with the natural optical
  circular dichroism of both the molecule and TBG. The presented approach i
 s conceptually distinct from schemes that rely on electromagnetic field en
 gineering\, and achieves sensitivities down to the single-molecule layer w
 ithout requiring surface functionalization. This opens the door to develop
 ing a platform with tunable\, strong chiral light&ndash\;matter interactio
 ns with implications in optics\, sensing\, and chemistry\, including chira
 l catalysis and homochiral synthesis.\nMonday July 20\, 11:00 h. ICFO Audi
 torium Thesis Director: Prof. Dr. Frank Koppens and Prof. Dr. Antoine Rese
 rbat-Plantey
DTSTAMP:20260717T000200Z
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