


2019-01-18
ION HANCU
ION HANCU

2019-01-29
MARIA MAFFEI
MARIA MAFFEI

2019-02-13
BORIS BOURDONCLE
BORIS BOURDONCLE

2019-02-15
JORDI MORALES DALMAU
JORDI MORALES DALMAU

2019-02-22
FRANCESCO RICCI
FRANCESCO RICCI

2019-03-06
CLARA GREGORI
CLARA GREGORI

2019-03-26
ALEXIA SALAVRAKOS
ALEXIA SALAVRAKOS

2019-04-12
SENAIDA HERNANDEZ SANTANA
SENAIDA HERNANDEZ SANTANA

2019-04-15
DAVID RAVENTÓS RIBERA
DAVID RAVENTÓS RIBERA

2019-04-16
PETER SCHMIDT
PETER SCHMIDT

2019-04-29
CALLUM O’DONNELL
CALLUM O’DONNELL

2019-05-02
LUCIANA VIDAS
LUCIANA VIDAS

2019-05-03
HANYU YE
HANYU YE

2019-05-10
TANJA DRAGOJEVIC
TANJA DRAGOJEVIC

2019-05-17
FLAVIO BACCARI
FLAVIO BACCARI

2019-06-04
MARTINA GIOVANNELLA
MARTINA GIOVANNELLA

2019-07-02
OZLEM YAVAS
OZLEM YAVAS

2019-07-03
ALESSANDRO SERI
ALESSANDRO SERI

2019-07-11
RENWEN YU
RENWEN YU

2019-09-06
ALEXANDER BLOCK
ALEXANDER BLOCK

2019-10-04
MARCO PAGLIAZZI
MARCO PAGLIAZZI

2019-10-07
RINU MANIYARA
RINU MANIYARA

2019-10-15
ALEJANDRO POZAS-KERSTJENS
ALEJANDRO POZAS-KERSTJENS
Exploring Intersubbands in 2D Materials


Dr PETER SCHMIDT
April 16th, 2019
PETER SCHMIDT
Quantum Nano-Optoelectronics
ICFO-The Institute of Photonic Sciences
Transition metal dichalcogenides (TMDs) are semiconducting layered materials that can be isolated up to the limit of a single atomic layer. Next to graphene, they are some of the most intensively studied materials within the larger family of 2D materials. TMDs have been studied thoroughly for both their electrical and optical properties showing intriguing phenomena. All optical studies have so far been limited to the visible to near-infrared wavelength region, exploiting interband transitions from the valence to the conduction band. This is surprising, since the two-dimensionality of TMDs gives rise to additional transitions within the conduction and valence band. These intersubband transitions typically lie in the mid-infrared to THz wavelength region and are a direct consequence of the quantum confinement of the charge carriers’ wave functions in the out-of-plane direction, leading to quantized energy states. In systems such as III-V semiconductor heterostructures, intersubband transitions have been well studied and have led to the development of quantum cascade lasers and quantum well infrared photodetectors. Intersubband transitions in TMDs are particularly promising, as the layered nature of 2D materials leads to atomically sharp interfaces between different materials thus limiting the detrimental effects of interface roughness. Furthermore, due to the TMDs’ weak van der Waals interactions in the out-of-plane direction, there are no lattice matching conditions. Intersubband transitions can therefore be combined with all kinds of two- and three-dimensional materials, including waveguides and cavities. In this thesis, we explore intersubband transitions in 2D materials. We first lay the theoretical framework for intersubband transitions in TMDs by using ab initio DFT calculations. We then demonstrate their first experimental observation using scattering scanning near-field optical microscopy (s-SNOM). We employ a doping modulation technique that provides the necessary sensitivity to observe intersubband absorption within a single quantum well. Our measurement technique allows us to quantitatively observe intersubband absorption with a nanometer scale spatial resolution, which is the highest reported spatial resolution of intersubband transitions in any class of material. We perform spectrally resolved measurements, which are in good agreement with our theoretical calculations and show signatures of many-body interactions and non-vertical transitions due to the momentum provided by the sharp AFM tip apex. Finally, we investigate the interaction of intersubband transitions with graphene plasmons and hBN hyperbolic phonon polaritons by transfer matrix method and finite difference time domain simulations and fabricate various van der Waals heterostructures in order to experimentally explore these interactions.
Tuesday, April 16, 10:00. ICFO Auditorium
Thesis Advisor: Prof Dr Frank Koppens
ICFO-The Institute of Photonic Sciences
Transition metal dichalcogenides (TMDs) are semiconducting layered materials that can be isolated up to the limit of a single atomic layer. Next to graphene, they are some of the most intensively studied materials within the larger family of 2D materials. TMDs have been studied thoroughly for both their electrical and optical properties showing intriguing phenomena. All optical studies have so far been limited to the visible to near-infrared wavelength region, exploiting interband transitions from the valence to the conduction band. This is surprising, since the two-dimensionality of TMDs gives rise to additional transitions within the conduction and valence band. These intersubband transitions typically lie in the mid-infrared to THz wavelength region and are a direct consequence of the quantum confinement of the charge carriers’ wave functions in the out-of-plane direction, leading to quantized energy states. In systems such as III-V semiconductor heterostructures, intersubband transitions have been well studied and have led to the development of quantum cascade lasers and quantum well infrared photodetectors. Intersubband transitions in TMDs are particularly promising, as the layered nature of 2D materials leads to atomically sharp interfaces between different materials thus limiting the detrimental effects of interface roughness. Furthermore, due to the TMDs’ weak van der Waals interactions in the out-of-plane direction, there are no lattice matching conditions. Intersubband transitions can therefore be combined with all kinds of two- and three-dimensional materials, including waveguides and cavities. In this thesis, we explore intersubband transitions in 2D materials. We first lay the theoretical framework for intersubband transitions in TMDs by using ab initio DFT calculations. We then demonstrate their first experimental observation using scattering scanning near-field optical microscopy (s-SNOM). We employ a doping modulation technique that provides the necessary sensitivity to observe intersubband absorption within a single quantum well. Our measurement technique allows us to quantitatively observe intersubband absorption with a nanometer scale spatial resolution, which is the highest reported spatial resolution of intersubband transitions in any class of material. We perform spectrally resolved measurements, which are in good agreement with our theoretical calculations and show signatures of many-body interactions and non-vertical transitions due to the momentum provided by the sharp AFM tip apex. Finally, we investigate the interaction of intersubband transitions with graphene plasmons and hBN hyperbolic phonon polaritons by transfer matrix method and finite difference time domain simulations and fabricate various van der Waals heterostructures in order to experimentally explore these interactions.
Tuesday, April 16, 10:00. ICFO Auditorium
Thesis Advisor: Prof Dr Frank Koppens