Quantum beats due to excitonic ground-state splitting in colloidal quantum dots

Bylsma, Jason; Dey, Prasenjit; Paul, Jeffrey; Hoogland, Sjoerd; Sargent, Edward H.; Luther, Joseph M.; Beard, Matthew C.; Karaiskaj, D.

doi:10.1103/physrevb.86.125322

Cited by 24 publications

(18 citation statements)

References 43 publications

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“…In bulk PbS, the energy of the zero-wave-vector (Γpoint) transverse-optical phonon is 8.1 meV as observed through far-infrared absorption [41] spectroscopy and Raman spectroscopy [42,43]. Furthermore, vibronic quantum beats have also been observed in femtosecond optical spectroscopy [43,44] of PbS QDs. Phonon modes can also be observed in the inelastic ETS [45].…”

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confidence: 92%

Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

Wang

Lhuillier

et al. 2015

Phys. Rev. B

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We present a tunnel spectroscopy study of single PbS Quantum Dots (QDs) as function of temperature and gate voltage. Three distinct signatures of strong electron-phonon coupling are observed in the Electron Tunneling Spectrum (ETS) of these QDs. In the shell-filling regime, the 8× degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon sub-bands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon (FC) blockade. From the data, a Huang-Rhys factor in the range S ∼ 1.7 − 2.5 is obtained. Finally, in the shell tunneling regime, the optical phonons appear in the inelastic ETS d 2 I/dV 2 .PACS numbers: 73.21.-b, 73.22.-f, 73.23.-b, 71.38.-k Semiconducting nanocrystals are characterized by discrete electronic levels with size-tunable energies[1], giving these QDs unique electronic properties [2][3][4].While optical spectroscopy is usually used to characterize the properties of QDs, ETS is a more relevant characterization when the goal is to incorporate the QDs into electron conducting devices such as fieldeffect transistors [3] or light emitting diodes [5]. Indeed, the coupling of a QD to electrodes or neighboring QDs, in presence of Coulomb and electron-phonon interactions, strongly alters their electronic spectrum and, consequently, their electronic transmission coefficient.In this work, we have studied the ETS of PbS QDs. They are characterized by strong quantum confinement and a size-tunable band gap on a wide energy range, which is of interest for solar cells [6-9] and infra-red detectors [10].After synthesis of the PbS QDs, as described in Ref. [11,12] and shown on the TEM picture Fig. 1a., the organic ligands at their surface are replaced by short inorganic ligands, S 2− [10, 13], to reduce the thickness of the insulating tunnel barrier between the QD and the electrodes.To measure the ETS as function of temperature and carrier filling, we employed on-chip tunneling spectroscopy where the nanoparticle is trapped within a nanogap, i.e. two electrodes separated by a distance of about 10 nm, deposited on a p-doped silicon substrate used as a back-gate covered by a silicon oxide layer 300 nm thick. While Scanning Tunneling Microscopy (STM) has already been employed to study the ETS of several colloidal QDs systems[14-22], on-chip tunneling spectroscopy has been only employed a few times [23][24][25]. This method presents several advantages though. The junctions are highly stable at low temperature, which FIG. 1. a) TEM image of PbS QDs. b) SEM image of ∼ 10 nm spaced electrodes in which a QD has been deposited. c) QDs are projected onto the chip-circuit in high vacuum using a fast pulsed valve. d) After each projection, the tunnel current is measured (VDrain = 0.1 V, VGate = 0 V, T=300 K). When it exceeds the threshold, the projection stops.allows high resolution measurements of the elastic and inelastic ETS. A back gate ca...

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confidence: 92%

Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

Wang

Lhuillier

et al. 2015

Phys. Rev. B

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“…1 (d)) [37]. The advantages of multidimensional spectroscopy are well documented in the literature [38][39][40][41], where in semiconductor nanomaterials, 2DFT spectroscopy has provided insights into the microscopic details of the many-body interactions [12,[42][43][44][45][46].…”

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confidence: 99%

Strong Quantum Coherence between Fermi Liquid Mahan Excitons

et al. 2016

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In modulation doped quantum wells, the excitons are formed as a result of the interactions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the so-called "Mahan excitons." The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence destroyed as a result of the screening and electron-electron interactions. Surprisingly, we observe strong quantum coherence between the heavy hole and light hole excitons. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum two-dimensional Fourier transform spectra. Theoretical simulations based on the optical Bloch equations where many-body effects are included phenomenologically reproduce well the experimental spectra. Time-dependent density functional theory calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system.

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“…Coherent FWM spectroscopy is very suited to probe many-body interactions, because electron-phonon and exciton-exciton interactions lead to measurable changes of the dephasing 48 . Two-dimensional Fourier transform (2DFT) spectroscopy based on the coherent FWM signal has more recently emerged [49][50][51][52][53][54] and has been successfully applied to III-V semiconductors [55][56][57][58][59][60][61][62][63] , diamond nitrogenvacancy center 64 , biological photosynthetic centers [65][66][67][68][69][70] , peptides 52,71,72 , and two-dimensional materials [73][74][75] , providing important insights difficult to access using traditional time-integrated and spectrally resolved FWM spectroscopy. The advantages of 2DFT spectroscopy over traditional one-dimensional FWM have been well documented in the literature 51,[76][77][78][79][80][81][82] .…”

Section: Introductionmentioning

confidence: 99%

Coherent two-dimensional Fourier transform spectroscopy using a 25 Tesla resistive magnet

Paul

Smith

Dey

et al. 2019

Review of Scientific Instruments

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We performed nonlinear optical two-dimensional Fourier transform spectroscopy measurements using an optical resistive high-field magnet on GaAs quantum wells. Magnetic fields up to 25 Tesla can be achieved using the split helix resistive magnet. Two-dimensional spectroscopy measurements based on the coherent four-wave mixing signal require phase stability. Therefore, these measurements are difficult to perform in environments prone to mechanical vibrations. Large resistive magnets use extensive quantities of cooling water, which causes mechanical vibrations, making two-dimensional Fourier transform spectroscopy very challenging. Here we report on the strategies we used to overcome these challenges and maintain the required phase-stability throughout the measurement. A self-contained portable platform was used to setup the experiments within the time frame provided by a user facility. Furthermore, this platform was floated above the optical table in order to isolate it from vibrations originating from the resistive magnet. Finally, we present two-dimensional Fourier transform spectra obtained from GaAs quantum wells at magnetic fields up to 25 Tesla and demonstrate the utility of this technique in providing important details, which are obscured in one dimensional spectroscopy.

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Quantum beats due to excitonic ground-state splitting in colloidal quantum dots

Cited by 24 publications

References 43 publications

Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

Strong Quantum Coherence between Fermi Liquid Mahan Excitons

Coherent two-dimensional Fourier transform spectroscopy using a 25 Tesla resistive magnet

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