Hour: From 12:00h to 13:00h
Place: Online (Zoom)
COLLOQUIUM: Atomically thin semiconductors : probing strongly correlated electrons using excitons
If the Coulomb repulsion between the electrons becomes significantly stronger than their kinetic energy, the itinerant electrons in the two-dimensional systems are expected to form a spatially-ordered state, termed a Wigner crystal [1]. According to former Quantum Monte Carlo calculations [2], the ratio rs of the two energy scales must exceed 30 for such a crystallization to occur in the absence of the magnetic field (B = 0). Owing to severe difficulties in satisfying this condition for conventional semiconductors (e.g., GaAs), prior experimental studies of the crystalline electronic states have mainly focused on the electrons confined to single Landau level under strong external magnetic field, which almost completely quenches the kinetic energy.
In this talk, I will describe recent experiments in atomically-thin transition metal dichalcogenides (TMDs) where it is possible to reach rs > 40. Our measurements provide a direct evidence that the electrons at densities < 3 · 1011 cm-2 in a pristine MoSe2 monolayer spontaneously break the continuous translation symmetry and form a Wigner crystal even at B = 0 [3]. This is revealed by our low-temperature (T = 80 mK) magneto-optical spectroscopy experiments that utilize a newly developed technique allowing to unequivocally detect charge order in an electronic Mott-insulator state [4]. This method relies on the modification of excitonic band structure arising due to the periodic potential experienced by the excitons interacting with a crystalline electronic lattice. Under such conditions, optically-inactive exciton states with finite momentum matching the reciprocal Wigner lattice vector k = kW get Bragg scattered back to the light cone, where they hybridize with the zero-momentum bright exciton states. This leads to emergence of a new, umklapp peak in the optical spectrum heralding the presence of periodically-ordered electronic lattice.
ZOOM LINK TO JOIN IN: http://s.ic.fo/AtacImamoglu041220
All interested may join this session. Participants will be asked to register upon entry.
Host: Darrick Chang
Hour: From 12:00h to 13:00h
Place: Online (Zoom)
COLLOQUIUM: Atomically thin semiconductors : probing strongly correlated electrons using excitons
If the Coulomb repulsion between the electrons becomes significantly stronger than their kinetic energy, the itinerant electrons in the two-dimensional systems are expected to form a spatially-ordered state, termed a Wigner crystal [1]. According to former Quantum Monte Carlo calculations [2], the ratio rs of the two energy scales must exceed 30 for such a crystallization to occur in the absence of the magnetic field (B = 0). Owing to severe difficulties in satisfying this condition for conventional semiconductors (e.g., GaAs), prior experimental studies of the crystalline electronic states have mainly focused on the electrons confined to single Landau level under strong external magnetic field, which almost completely quenches the kinetic energy.
In this talk, I will describe recent experiments in atomically-thin transition metal dichalcogenides (TMDs) where it is possible to reach rs > 40. Our measurements provide a direct evidence that the electrons at densities < 3 · 1011 cm-2 in a pristine MoSe2 monolayer spontaneously break the continuous translation symmetry and form a Wigner crystal even at B = 0 [3]. This is revealed by our low-temperature (T = 80 mK) magneto-optical spectroscopy experiments that utilize a newly developed technique allowing to unequivocally detect charge order in an electronic Mott-insulator state [4]. This method relies on the modification of excitonic band structure arising due to the periodic potential experienced by the excitons interacting with a crystalline electronic lattice. Under such conditions, optically-inactive exciton states with finite momentum matching the reciprocal Wigner lattice vector k = kW get Bragg scattered back to the light cone, where they hybridize with the zero-momentum bright exciton states. This leads to emergence of a new, umklapp peak in the optical spectrum heralding the presence of periodically-ordered electronic lattice.
ZOOM LINK TO JOIN IN: http://s.ic.fo/AtacImamoglu041220
All interested may join this session. Participants will be asked to register upon entry.
Host: Darrick Chang
All Colloquia
Hour: From 12:00h to 13:00h
Place: Online (Zoom)