20 results on '"Moody, Galan"'
Search Results
2. Advances in multi-dimensional coherent spectroscopy of semiconductor nanostructures.
- Author
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Moody, Galan and Cundiff, Steven T.
- Published
- 2017
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3. Trion formation dynamics in monolayer transition metal dichalcogenides.
- Author
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Singh, Akshay, Moody, Galan, Tran, Kha, Scott, Marie E., Overbeck, Vincent, Berghäuser, Gunnar, Schaibley, John, Seifert, Edward J., Pleskot, Dennis, Gabor, Nathaniel M., Jiaqiang Yan, Mandrus, David G., Richter, Marten, Malic, Ermin, Xiaodong Xu, and Xiaoqin Li
- Subjects
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TRIONS (Nuclear physics) , *MONOMOLECULAR films , *PHASE transitions , *CHALCOGENIDES , *DOPING agents (Chemistry) , *ENERGY consumption - Abstract
We report charged exciton (trion) formation dynamics in doped monolayer transition metal dichalcogenides, specifically molybdenum diselenide (MoSe2), using resonant two-color pump-probe spectroscopy. When resonantly pumping the exciton transition, trions are generated on a picosecond time scale through excitonelectron interaction. As the pump energy is tuned from the high energy to low energy side of the inhomogeneously broadened exciton resonance, the trion formation time increases by ~50%. This feature can be explained by the existence of both localized and delocalized excitons in a disordered potential and suggests the existence of an exciton mobility edge in transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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4. Coherent Electronic Coupling in Atomically Thin MoSe2.
- Author
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Singh, Akshay, Moody, Galan, Sanfeng Wu, Yanwen Wu, Ghimire, Nirmal J., Jiaqiang Yan, Mandrus, David G., Xiaodong Xu, and Xiaoqin Li
- Subjects
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SPECTRUM analysis , *COUPLING constants , *BINDING energy , *EXCITON theory , *TRANSITION metals - Abstract
We report the first direct spectroscopic evidence for coherent electronic coupling between excitons and trions in atomically thin transition metal dichalcogenides, specifically monolayer MoSe2. Signatures of coupling appear as isolated cross-peaks in two-color pump-probe spectra, and the line shape of the peaks reveals that the coherent coupling originates from many-body interactions. Excellent agreement between the experiment and density matrix calculations suggests that coherent exciton-trion coupling leads to the formation of a correlated state with a remarkably large binding energy. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
5. Coherent Excitonic Coupling in an Asymmetric Double InGaAs Quantum Well Arises from Many-Body Effects.
- Author
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Nardin, Gaël, Moody, Galan, Singh, Rohan, Autry, Travis M., Hebin Li, Morier-Genoud, François, and Cundiff, Steven T.
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QUANTUM wells , *SPECTRUM analysis , *OPTICAL spectra , *EXCITON theory , *DENSITY matrices - Abstract
We study an asymmetric double InGaAs quantum well using optical two-dimensional coherent spectroscopy. The collection of zero-quantum, one-quantum, and two-quantum two-dimensional spectra provides a unique and comprehensive picture of the double well coherent optical response. Coherent and incoherent contributions to the coupling between the two quantum well excitons are clearly separated. An excellent agreement with density matrix calculations reveals that coherent interwell coupling originates from many-body interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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6. Biexcitons in semiconductor quantum dot ensembles.
- Author
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Moody, Galan, Singh, Rohan, Li, Hebin, Akimov, Ilya A., Bayer, Manfred, Reuter, Dirk, Wieck, Andreas D., Bracker, Allan S., Gammon, Daniel, and Cundiff, StevEN T.
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EXCITON theory , *ELECTRONS , *SEMICONDUCTOR quantum dots , *QUANTUM dots , *STATISTICAL ensembles - Abstract
The effects of confinement on biexciton renormalization in self-assembled InAs and interfacial GaAs quantum dot (QD) ensembles are studied using two-dimensional Fourier-transform spectroscopy. We find that in thermally annealed InAs QDs, changes in the biexciton transition energy are strongly correlated with those of the exciton and that the biexciton binding energy is similar for all QDs in the ensemble. These results are in contrast to those from GaAs QDs formed from interfacial fluctuations of a narrow quantum well (QW). In both the GaAs QW and QDs, correlation is reduced and the biexciton binding exhibits a strong dependence on localization. Comparison with simulations reveals how confinement and Coulomb interactions modify biexciton renormalization. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
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7. Vibrational Interferometry Enables Single-Scan Acquisition of all χ(3) Multi-Dimensional Coherent Spectra.
- Author
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Travis, M. Autry, Moody, Galan, McDonald, Corry, James, M. Fraser, Richard, P. Mirin, Kevin, L. Silverman, Cerullo, G., Ogilvie, J., Kärtner, F., Khalil, M., and Li, R.
- Subjects
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VIBRATIONAL spectra , *COHERENCE (Optics) , *NANOSTRUCTURES , *HETERODYNE detection , *MIXING - Abstract
We demonstrate a new method for multidimensional coherent spectroscopy of nanostructures. We use a heterodyne technique implemented with a confocal microscope to record the amplitude and phase of all degenerate third-order wave-mixing processes. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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8. Optical Multidimensional Spectroscopy of Atomic Vapor.
- Author
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Hebin Li, Moody, Galan, Bristow, Alan D., Siemens, Mark E., and Cundiff, Steven T.
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OPTICAL spectroscopy , *HAMILTONIAN systems , *VAPORS , *GASES at high temperatures , *DNA folding , *PHOTOSYNTHESIS , *FOURIER transform spectroscopy - Abstract
Optical single- and double-quantum three-dimensional Fourier-transform spectra are obtained for atomic vapors. We show that three-dimensional spectra can be used to identify the Hamiltonian of complex systems and to reveal the nature of many-body interactions [ABSTRACT FROM AUTHOR]
- Published
- 2013
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- View/download PDF
9. Multi-dimensional coherent optical spectroscopy of semiconductor nanostructures: Collinear and non-collinear approaches.
- Author
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Nardin, Gaël, Autry, Travis M., Moody, Galan, Singh, Rohan, Hebin Li, and Cundiff, Steven T.
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OPTICAL spectroscopy , *SEMICONDUCTOR nanoparticles , *NANOSTRUCTURES , *GEOMETRY , *QUANTUM dots - Abstract
We review our recent work on multi-dimensional coherent optical spectroscopy (MDCS) of semiconductor nanostructures. Two approaches, appropriate for the study of semiconductor materials, are presented and compared. A first method is based on a non-collinear geometry, where the Four-Wave-Mixing (FWM) signal is detected in the form of a radiated optical field. This approach works for samples with translational symmetry, such as Quantum Wells (QWs) or large and dense ensembles of Quantum Dots (QDs). A second method detects the FWM in the form of a photocurrent in a collinear geometry. This second approach extends the horizon of MDCS to sub-diffraction nanostructures, such as single QDs, nanowires, or nanotubes, and small ensembles thereof. Examples of experimental results obtained on semiconductor QW structures are given for each method. In particular, it is shown how MDCS can assess coupling between excitons confined in separated QWs. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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10. Prospects and challenges of quantum emitters in 2D materials.
- Author
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Azzam, Shaimaa I., Parto, Kamyar, and Moody, Galan
- Subjects
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TRANSITION metal nitrides , *BORON nitride , *PHOTONS - Abstract
The search for an ideal single-photon source has generated significant interest in discovering emitters in materials as well as developing new manipulation techniques to gain better control over the emitters' properties. Quantum emitters in atomically thin two-dimensional (2D) materials have proven to be very attractive with high brightness, operation under ambient conditions, and the ability to be integrated with a wide range of electronic and photonic platforms. This Perspective highlights some of the recent advances in quantum light generation from 2D materials, focusing on hexagonal boron nitride and transition metal dichalcogenides. Efforts in engineering and deterministically creating arrays of quantum emitters in 2D materials, their electrical excitation, and their integration with photonic devices are discussed. Finally, we address some of the challenges the field is facing and the near-term efforts to tackle them. We provide an outlook toward efficient and scalable quantum light generation from 2D materials to controllable and addressable on-chip quantum sources. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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11. Microsecond Valley Lifetime of Defect-Bound Excitons in Monolayer WSe2.
- Author
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Moody, Galan, Tran, Kha, Xiaobo Lu, Autry, Travis, Fraser, James M., Mirin, Richard P., Li Yang, Xiaoqin Li, and Silverman, Kevin L.
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TUNGSTEN compounds , *SEMICONDUCTORS , *TRANSITION metals - Abstract
In atomically thin two-dimensional semiconductors such as transition metal dichalcogenides (TMDs), controlling the density and type of defects promises to be an effective approach for engineering light-matter interactions. We demonstrate that electron-beam irradiation is a simple tool for selectively introducing defect-bound exciton states associated with chalcogen vacancies in TMDs. Our first-principles calculations and time-resolved spectroscopy measurements of monolayer WSe2 reveal that these defect-bound excitons exhibit exceptional optical properties including a recombination lifetime approaching 200 ns and a valley lifetime longer than 1 μs. The ability to engineer the crystal lattice through electron irradiation provides a new approach for tailoring the optical response of TMDs for photonics, quantum optics, and valleytronics applications. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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12. Heterogeneous integration of superconducting thin films and epitaxial semiconductor heterostructures with lithium niobate.
- Author
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Lienhart, Michelle, Choquer, Michael, Nysten, Emeline D S, Weiß, Matthias, Müller, Kai, Finley, Jonathan J, Moody, Galan, and Krenner, Hubert J
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SEMICONDUCTOR thin films , *SUPERCONDUCTING films , *ACOUSTIC surface waves , *SEMICONDUCTOR quantum dots , *LITHIUM niobate , *ACOUSTIC resonators - Abstract
We report on scalable heterointegration of superconducting electrodes and epitaxial semiconductor quantum dots (QDs) on strong piezoelectric and optically nonlinear lithium niobate. The implemented processes combine the sputter-deposited thin film superconductor niobium nitride and III–V compound semiconductor membranes onto the host substrate. The superconducting thin film is employed as a zero-resistivity electrode material for a surface acoustic wave resonator with internal quality factors Q ≈ 17 000 representing a three-fold enhancement compared to identical devices with normal conducting electrodes. Superconducting operation of ≈ 400 M H z resonators is achieved to temperatures T > 7 K and electrical radio frequency powers P r f > + 9 d B m . Heterogeneously integrated single QDs couple to the resonant phononic field of the surface acoustic wave resonator operated in the superconducting regime. Position and frequency selective coupling mediated by deformation potential coupling is validated using time-integrated and time-resolved optical spectroscopy. Furthermore, acoustoelectric charge state control is achieved in a modified device geometry harnessing large piezoelectric fields inside the resonator. The hybrid QD—surface acoustic wave resonator can be scaled to higher operation frequencies and smaller mode volumes for quantum phase modulation and transduction between photons and phonons via the QD. Finally, the employed materials allow for the realization of other types of optoelectronic devices, including superconducting single photon detectors and integrated photonic and phononic circuits. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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13. All-silicon light-emitting diodes waveguide-integrated with superconducting single-photon detectors.
- Author
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Buckley, Sonia, Chiles, Jeffrey, McCaughan, Adam N., Moody, Galan, Silverman, Kevin L., Stevens, Martin J., Mirin, Richard P., Sae Woo Nam, and Shainline, Jeffrey M.
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LIGHT emitting diodes , *SILICON , *WAVEGUIDES , *PHOTON detectors , *NANOWIRES - Abstract
We demonstrate cryogenic, electrically injected, waveguide-coupled Si light-emitting diodes (LEDs) operating at 1.22 μm. The active region of the LED consists of W centers implanted in the intrinsic region of a p-i-n diode. The LEDs are integrated on waveguides with superconducting nanowire single-photon detectors (SNSPDs). We demonstrate the scalability of this platform with an LED coupled to eleven SNSPDs in a single integrated photonic device. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
14. Localization dynamics of excitons in disordered semiconductor quantum wells.
- Author
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Singh, Rohan, Richter, Marten, Moody, Galan, Siemens, Mark E., Hebin Li, and Cundiff, Steven T.
- Subjects
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QUANTUM wells , *LOCALIZATION (Mathematics) , *SEMICONDUCTORS - Abstract
Exciton transport in nanomaterials is sensitive to fluctuations in the confinement potential that are intrinsic to heterogeneous solid-state systems. Redistribution of exciton population manifests as spectral diffusion in which the exciton energy shifts. It is generally assumed that increase or decrease in the exciton energy are equally probable. We show that this assumption is not necessarily valid using two-dimensional coherent spectroscopy on a disordered GaAs quantum well. High-energy excitons relax into lower-energy localized states over a time scale of tens of picoseconds at low sample temperatures (~5K). A transition to uniform spectral diffusion of excitons is observed as the temperature is increased to ~20K. Numerical simulations reveal the contribution of exciton-phonon interactions to spectral diffusion of excitons. These results provide a perspective on the process of dynamic localization and the effect of the correlation length of disorder on spectral diffusion of excitons. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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15. Coherent and Incoherent Coupling Dynamics between Neutral and Charged Excitons in Monolayer MoSe2.
- Author
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Kai Hao, Lixiang Xu, Nagler, Philipp, Singh, Akshay, Tran, Kha, Dass, Chandriker Kavir, Schüller, Christian, Korn, Tobias, Xiaoqin Li, and Moody, Galan
- Subjects
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MOLYBDENUM selenides , *EXCITON theory , *OPTOELECTRONIC devices , *MONOMOLECULAR films , *OPTICAL properties , *CHARGE transfer - Abstract
The optical properties of semiconducting transition metal dichalcogenides are dominated by both neutral excitons (electron-hole pairs) and charged excitons (trions) that are stable even at room temperature. While trions directly influence charge transport properties in optoelectronic devices, excitons may be relevant through exciton-trion coupling and conversion phenomena. In this work, we reveal the coherent and incoherent nature of exciton-trion coupling and the relevant time scales in monolayer MoSe2 using optical two-dimensional coherent spectroscopy. Coherent interaction between excitons and trions is definitively identified as quantum beating of cross peaks in the spectra that persists for a few hundred femtoseconds. For longer times up to 10 ps, surprisingly, the relative intensity of the cross peaks increases, which is attributed to incoherent energy transfer likely due to phonon-assisted up-conversion and down-conversion processes that are efficient even at cryogenic temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
16. Pulse Propagation Effects in Optical 2D Fourier-TransformSpectroscopy: Experiment.
- Author
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Li, Hebin, Spencer, Austin P., Kortyna, Andrew, Moody, Galan, Jonas, David M., and Cundiff, Steven T.
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FOURIER transform spectroscopy , *CHEMISTRY experiments , *PHYSICAL & theoretical chemistry , *THICKNESS measurement , *VAPORS - Abstract
Inoptical two-dimensional Fourier-transform (2DFT) spectroscopy, understandinghow the spectral line shape is affected by pulse propagation in thesample is crucial for an accurate interpretation of spectra. We reportan experimental study of pulse propagation effects in 2DFT spectroscopyperformed in a dense atomic vapor. The spectral line shape can bedramatically distorted due to high optical density as well as thephysical thickness of a sample. The spectral distortion can be partiallycorrected by using a reference pulse copropagating with the signalcombined with appropriate data processing. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
17. Anisotropic homogeneous linewidth of the heavy-hole exciton in (110)-oriented GaAs quantum wells.
- Author
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Singh, Rohan, Autry, Travis M., Nardin, Gaël, Moody, Galan, Hebin Li, Pierz, Klaus, Bieler, Mark, and Cundiff, Steven T.
- Subjects
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ANISOTROPIC crystals , *EXCITON theory , *QUANTUM wells , *ENERGY-band theory of solids , *FOURIER transform spectroscopy - Abstract
The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance in a (110)-oriented GaAs multiple-quantum-well sample are measured using optical two-dimensional Fourier transform spectroscopy. By probing the optical nonlinear response for polarization along the in-plane crystal axes [110] and [110], we measure different homogeneous linewidths for the two orthogonal directions. This difference is found to be due to anisotropic excitation-induced dephasing, caused by a crystal-axis-dependent absorption coefficient. The extrapolated zero-excitation density homogeneous linewidth exhibits an activation-like temperature dependence. We find that the homogeneous linewidth extrapolated to zero excitation density and temperature is ∼34 μeV, while the inhomogeneous linewidth is 1.9 meV for both polarizations. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
18. Twist Angle-Dependent Interlayer Exciton Lifetimes in van der Waals Heterostructures.
- Author
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Junho Choi, Florian, Matthias, Steinhoff, Alexander, Erben, Daniel, Kha Tran, Dong Seob Kim, Liuyang Sun, Jiamin Quan, Claassen, Robert, Majumder, Somak, Hollingsworth, Jennifer A., Takashi Taniguchi, Kenji Watanabe, Keiji Ueno, Singh, Akshay, Moody, Galan, Jahnke, Frank, and Xiaoqin Li
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HETEROSTRUCTURES , *MOMENTUM space , *EXCITED states , *QUANTUM states , *MAGNITUDE (Mathematics) , *MONOMOLECULAR films , *VAN der Waals forces - Abstract
In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are formed and subject to both vertical and lateral confinement. We investigate how a unique control knob, the twist angle between the two monolayers, can be used to control the exciton dynamics. We observe that the interlayer exciton lifetimes in MoSe2/WSe2 twisted bilayers (TBLs) change by one order of magnitude when the twist angle is varied from 1° to 3.5°. Using a low-energy continuum model, we theoretically separate two leading mechanisms that influence interlayer exciton radiative lifetimes. The shift to indirect transitions in the momentum space with an increasing twist angle and the energy modulation from the moiré potential both have a significant impact on interlayer exciton lifetimes. We further predict distinct temperature dependence of interlayer exciton lifetimes in TBLs with different twist angles, which is partially validated by experiments. While many recent studies have highlighted how the twist angle in a vdW TBL can be used to engineer the ground states and quantum phases due to many-body interaction, our studies explore its role in controlling the dynamics of optically excited states, thus, expanding the conceptual applications of "twistronics". [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
19. Polarization-dependent exciton linewidth in semiconductor quantum wells: A consequence of bosonic nature of excitons.
- Author
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Singh, Rohan, Takeshi Suzuki, Autry, Travis M., Moody, Galan, Siemens, Mark E., and Cundiff, Steven T.
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QUANTUM wells , *POLARIZATION (Nuclear physics) , *NUCLEAR magnetic resonance , *QUANTUM amplifier , *MECHANICAL ability , *MATHEMATICAL models - Abstract
The exciton coherent signal decay rate in GaAs quantum wells, as measured in four-wave mixing experiments, depends on the polarization of the excitation pulses. Using polarization-dependent two-dimensional coherent spectroscopy, we show that this behavior is due to the bosonic character of excitons. Interference between two different quantum mechanical pathways results in a smaller decay rate for cocircular and colinear polarization of the optical excitation pulses. This interference does not exist for cross-linearly polarized excitation pulses resulting in a larger decay rate. Our result shows that the bosonic nature of excitons must be considered when interpreting ultrafast spectroscopic studies of exciton dephasing in semiconductors. This behavior should be considered while interpreting results of ultrafast spectroscopy experiments involving bosonlike excitations. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
20. Persistent exciton-type many-body interactions in GaAs quantum wells measured using two-dimensional optical spectroscopy.
- Author
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Turner, Daniel B., Wen, Patrick, Arias, Dylan H., Nelson, Keith A., Li, Hebin, Moody, Galan, Siemens, Mark E., and Cundiff, Steven T.
- Subjects
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EXCITON theory , *MANY-body problem , *GALLIUM arsenide , *QUANTUM wells , *OPTICAL spectroscopy , *SEMICONDUCTORS - Abstract
Studies have shown that many-body interactions among semiconductor excitons can produce distinct features in two-dimensional optical spectra. However, to the best of our knowledge, the dynamics of many-body interactions have not been measured in two-dimensional (2D) spectroscopy studies. Here we measure 2D spectra of GaAs quantum wells at many different "waiting" times and study the time dependence of the spectral features. Characteristic signatures of exciton polarization correlations manifest in the diagonal peaks decay at the exciton dephasing rate, consistent with theoretical predictions. Other many-body interactions manifest in off-diagonal features decay much more slowly. These persistent off-diagonal features must be due to many-body interactions involving exciton populations, and their persistence cannot be predicted by theoretical descriptions restricted to the coherent limit. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
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