@article{findik_biliroglu_seyitliyev_mendes_barrette_ardekani_lei_dong_so_gundogdu_2021, title={High-temperature superfluorescence in methyl ammonium lead iodide}, volume={15}, ISSN={1749-4885 1749-4893}, url={http://dx.doi.org/10.1038/s41566-021-00830-x}, DOI={10.1038/s41566-021-00830-x}, abstractNote={Light–matter interactions can create and manipulate collective many-body phases in solids1–3, which are promising for the realization of emerging quantum applications. However, in most cases, these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin film, exhibits such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high-energy electron–hole pairs, which quickly relax to lower energy domains and then develop a macroscopic quantum coherence through spontaneous synchronization. The excitation fluence dependence of the spectroscopic features and the population kinetics in such films unambiguously confirm all the well-known characteristics of superfluorescence. These results show that the creation and manipulation of collective coherent states in hybrid perovskites can be used as the basic building blocks for quantum applications4,5. A collective coherent quantum many-body phase, namely superfluorescence, is observed in CH3NH3PbI3 at 78 K. The excitation fluence dependence of the spectroscopic features and the population kinetics confirm all its well-known characteristics.}, number={9}, journal={Nature Photonics}, publisher={Springer Science and Business Media LLC}, author={Findik, Gamze and Biliroglu, Melike and Seyitliyev, Dovletgeldi and Mendes, Juliana and Barrette, Andrew and Ardekani, Hossein and Lei, Lei and Dong, Qi and So, Franky and Gundogdu, Kenan}, year={2021}, month={Jun}, pages={676–680} }
 @article{dunlap-shohl_barraza_barrette_dovletgeldi_findik_dirkes_liu_jana_blum_you_et al._2019, title={Tunable internal quantum well alignment in rationally designed oligomer-based perovskite films deposited by resonant infrared matrix-assisted pulsed laser evaporation}, volume={6}, ISSN={["2051-6355"]}, DOI={10.1039/c9mh00366e}, abstractNote={RIR-MAPLE enables thin-film deposition of organic–inorganic materials with tunable synergistic photophysics.}, number={8}, journal={MATERIALS HORIZONS}, author={Dunlap-Shohl, Wiley A. and Barraza, E. Tomas and Barrette, Andrew and Dovletgeldi, Seyitliyev and Findik, Gamze and Dirkes, David J. and Liu, Chi and Jana, Manoj K. and Blum, Volker and You, Wei and et al.}, year={2019}, month={Oct}, pages={1707–1716} }
 @article{dunlap-shohl_barraza_barrette_gundogdu_stiff-roberts_mitzi_2018, title={MAPbI(3) Solar Cells with Absorber Deposited by Resonant Infrared Matrix-Assisted Pulsed Laser Evaporation}, volume={3}, ISSN={["2380-8195"]}, DOI={10.1021/acsenergylett.7b01144}, abstractNote={Resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) is a gentle thin-film deposition technique that combines the facile chemical control of solution processing with the growth control of vapor-phase deposition, yet one that has not been widely applied to crystalline organic–inorganic hybrid materials. In this work, we investigate the optoelectronic quality of RIR-MAPLE-deposited CH3NH3PbI3 (MAPbI3) perovskite films and report on the fabrication of perovskite solar cells in which the absorber is deposited by RIR-MAPLE. We find the composition, morphology, and optical properties of these perovskite films to be comparable to those produced by more conventional methods, such as spin coating. The champion device reaches a stabilized power conversion efficiency of over 12%, a high value for perovskite solar cells deposited by a laser ablation process, highlighting the ability of this new technique to produce device-quality films.}, number={2}, journal={ACS ENERGY LETTERS}, author={Dunlap-Shohl, Wiley A. and Barraza, E. Tomas and Barrette, Andrew and Gundogdu, Kenan and Stiff-Roberts, Adrienne D. and Mitzi, David B.}, year={2018}, month={Feb}, pages={270–275} }
 @article{yu_yu_xu_barrette_gundogdu_cao_2016, title={Fundamental limits of exciton-exciton annihilation for light emission in transition metal dichalcogenide monolayers}, volume={93}, DOI={10.1103/physrevb.93.201111}, abstractNote={We quantitatively evaluate the exciton-exciton annihilation (EEA) and its effect on light emission properties in monolayer TMDC materials, including WS2, MoS2, and WSe2. The EEA rate is found to be 0.3 cm2/s and 0.1 cm2/s for suspended WS2 and MoS2 monolayers, respectively, and subject to the influence from substrates, being 0.1 cm2/s and 0.05 cm2/s for the supported WS2 and MoS2 on sapphire substrates. It can substantially affect the luminescence efficiency of suspended monolayers even at an exciton concentration as low as 109 cm-2, but plays a milder role for supported monolayers due to the effect of the substrate. However, regardless the presence of substrates or not, the lasing threshold of the monolayer is always predominantly determined by the EEA, which is estimated to be 12-18 MW/cm2 if using 532 nm as the pumping wavelength.}, number={20}, journal={Physical Review B}, author={Yu, Y. L. and Yu, Y. F. and Xu, C. and Barrette, A. and gundogdu and Cao, L. Y.}, year={2016} }
 @article{gautam_barrette_mai_yan_zhang_danilov_you_ade_gundogdu_2015, title={Direct Optical Observation of Stimulated Emission from Hot Charge Transfer Excitons in Bulk Heterojunction Polymer Solar Cells}, volume={119}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.5b06557}, abstractNote={Charge transfer excitons (CTEs) play an important role in semiconducting polymer-based optoelectronic applications. In organic photovoltaics, they are an intermediate step between tightly bound excitons and free charges. Although CT state energies at the interface of bulk heterojunction organic solar cells have been reported using quantum chemical calculations and by sensitive external quantum efficiency (EQE) measurements, direct optical observation of CT states was limited to relaxed, low energy, CT levels. Here we used polarization anisotropy transient absorption experiments to measure emission from high-energy CT levels. These experimental methods provide means to study high energy CT state dynamics in BHJs with controlled molecular orientations and complement theoretical calculations of interfacial CT state energies.}, number={34}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Gautam, Bhoj R. and Barrette, Andy and Mai, Cong and Yan, Liang and Zhang, Qianqian and Danilov, Eygeny and You, Wei and Ade, Harald and Gundogdu, Kenan}, year={2015}, month={Aug}, pages={19697–19702} }
 @article{mai_semenov_barrette_yu_jin_cao_kim_gundogdu_2014, title={Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy}, volume={90}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.90.041414}, DOI={10.1103/physrevb.90.041414}, abstractNote={We measured the lifetime of optically created valley polarization in single layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). However the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single layer WS2. One process involves direct scattering of excitons from K to K' valleys with a spin flip-flop interaction. The other mechanism involves scattering through spin degenerate Gamma valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Gamma and K valleys.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Mai, Cong and Semenov, Yuriy G. and Barrette, Andrew and Yu, Yifei and Jin, Zhenghe and Cao, Linyou and Kim, Ki Wook and Gundogdu, Kenan}, year={2014}, month={Jul} }
 @inproceedings{barrette_mai_yu_semenov_jin_kim_cao_gundogdu_2014, title={Ultrafast valley relaxation dynamics in single layer semiconductors}, volume={9198}, booktitle={Ultrafast nonlinear imaging and spectroscopy ii}, author={Barrette, A. and Mai, C. and Yu, Y. F. and Semenov, Y. and Jin, Z. H. and Kim, K. W. and Cao, L. Y. and Gundogdu, K.}, year={2014} }
 @article{mai_barrette_yu_semenov_kim_cao_gundogdu_2013, title={Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2}, volume={14}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl403742j}, DOI={10.1021/nl403742j}, abstractNote={Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization.}, number={1}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Mai, Cong and Barrette, Andrew and Yu, Yifei and Semenov, Yuriy G. and Kim, Ki Wook and Cao, Linyou and Gundogdu, Kenan}, year={2013}, month={Dec}, pages={202–206} }