The Experts below are selected from a list of 20007 Experts worldwide ranked by ideXlab platform
Fabian Grusdt - One of the best experts on this subject based on the ideXlab platform.
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imaging magnetic Polarons in the doped fermi hubbard model
Nature, 2019Co-Authors: Joannis Koepsell, Fabian Grusdt, Eugene Demler, Jayadev Vijayan, Pimonpan Sompet, Timon A Hilker, Guillaume Salomon, Immanuel BlochAbstract:Polarons—electronic charge carriers ‘dressed’ by a local polarization of the background environment—are among the most fundamental quasiparticles in interacting many-body systems, and emerge even at the level of a single dopant1. In the context of the two-dimensional Fermi–Hubbard model, Polarons are predicted to form around charged dopants in an antiferromagnetic background in the low-doping regime, close to the Mott insulating state2–7; this prediction is supported by macroscopic transport and spectroscopy measurements in materials related to high-temperature superconductivity8. Nonetheless, a direct experimental observation of the internal structure of magnetic Polarons is lacking. Here we report the microscopic real-space characterization of magnetic Polarons in a doped Fermi–Hubbard system, enabled by the single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of doublons by a local reduction—and even sign reversal—of magnetic correlations, which originates from the competition between kinetic and magnetic energy in the system. The experimentally observed Polaron signatures are found to be consistent with an effective string model at finite temperature7. We demonstrate that delocalization of the doublon is a necessary condition for Polaron formation, by comparing this setting with a scenario in which a doublon is pinned to a lattice site. Our work could facilitate the study of interactions between Polarons, which may lead to collective behaviour, such as stripe formation, as well as the microscopic exploration of the fate of Polarons in the pseudogap and ‘bad metal’ phases. Magnetic Polarons are imaged with single-site spin and density resolution in the low-doping regime of the atomic Fermi–Hubbard model, showing that mobile delocalized doublons are necessary for Polaron formation.
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imaging magnetic Polarons in the doped fermi hubbard model
arXiv: Quantum Gases, 2018Co-Authors: Joannis Koepsell, Fabian Grusdt, Eugene Demler, Jayadev Vijayan, Pimonpan Sompet, Timon A Hilker, Guillaume Salomon, Immanuel BlochAbstract:Polarons are among the most fundamental quasiparticles emerging in interacting many-body systems, forming already at the level of a single mobile dopant. In the context of the two-dimensional Fermi-Hubbard model, such Polarons are predicted to form around charged dopants in an antiferromagnetic background in the low doping regime close to the Mott insulating state. Macroscopic transport and spectroscopy measurements related to high $T_{c}$ materials have yielded strong evidence for the existence of such quasiparticles in these systems. Here we report the first microscopic observation of magnetic Polarons in a doped Fermi-Hubbard system, harnessing the full single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of mobile doublons by a local reduction and even sign reversal of magnetic correlations, originating from the competition between kinetic and magnetic energy in the system. The experimentally observed Polaron signatures are found to be consistent with an effective string model at finite temperature. We demonstrate that delocalization of the doublon is a necessary condition for Polaron formation by contrasting this mobile setting to a scenario where the doublon is pinned to a lattice site. Our work paves the way towards probing interactions between Polarons, which may lead to stripe formation, as well as microscopically exploring the fate of Polarons in the pseudogap and bad metal phase.
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Polaronic mass renormalization of impurities in bose einstein condensates correlated gaussian wave function approach
Physical Review A, 2016Co-Authors: Yulia E Shchadilova, Fabian Grusdt, A N Rubtsov, Eugene DemlerAbstract:We propose a class of variational Gaussian wavefunctions to describe Fr\"ohlich Polarons at finite momenta. Our wavefunctions give Polaron energies that are in excellent agreement with the existing Monte Carlo results for a broad range of interactions. We calculate the effective mass of Polarons and find smooth crossover between weak and intermediate impurity-bosons coupling. Effective masses that we obtain are considerably larger than those predicted by the mean-field method. A novel prediction based on our variational wavefunctions is a special pattern of correlations between host atoms that can be measured in time-of-flight experiments. We discuss atomic mixtures in systems of ultracold atoms in which our results can be tested with current experimental technology.
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renormalization group approach to the frohlich Polaron model application to impurity bec problem
Scientific Reports, 2015Co-Authors: Fabian Grusdt, Yulia E Shchadilova, A N Rubtsov, Eugene DemlerAbstract:When a mobile impurity interacts with a many-body system, such as a phonon bath, a Polaron is formed. Despite the importance of the Polaron problem for a wide range of physical systems, a unified theoretical description valid for arbitrary coupling strengths is still lacking. Here we develop a renormalization group approach for analyzing a paradigmatic model of Polarons, the so-called Frohlich model, and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra cold atoms. Polaron energies obtained by our method are in excellent agreement with recent diagrammatic Monte Carlo calculations for a wide range of interaction strengths. They are found to be logarithmically divergent with the ultra-violet cut-off, but physically meaningful regularized Polaron energies are also presented. Moreover, we calculate the effective mass of Polarons and find a smooth crossover from weak to strong coupling regimes. Possible experimental tests of our results in current experiments with ultra cold atoms are discussed.
Eugene Demler - One of the best experts on this subject based on the ideXlab platform.
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imaging magnetic Polarons in the doped fermi hubbard model
Nature, 2019Co-Authors: Joannis Koepsell, Fabian Grusdt, Eugene Demler, Jayadev Vijayan, Pimonpan Sompet, Timon A Hilker, Guillaume Salomon, Immanuel BlochAbstract:Polarons—electronic charge carriers ‘dressed’ by a local polarization of the background environment—are among the most fundamental quasiparticles in interacting many-body systems, and emerge even at the level of a single dopant1. In the context of the two-dimensional Fermi–Hubbard model, Polarons are predicted to form around charged dopants in an antiferromagnetic background in the low-doping regime, close to the Mott insulating state2–7; this prediction is supported by macroscopic transport and spectroscopy measurements in materials related to high-temperature superconductivity8. Nonetheless, a direct experimental observation of the internal structure of magnetic Polarons is lacking. Here we report the microscopic real-space characterization of magnetic Polarons in a doped Fermi–Hubbard system, enabled by the single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of doublons by a local reduction—and even sign reversal—of magnetic correlations, which originates from the competition between kinetic and magnetic energy in the system. The experimentally observed Polaron signatures are found to be consistent with an effective string model at finite temperature7. We demonstrate that delocalization of the doublon is a necessary condition for Polaron formation, by comparing this setting with a scenario in which a doublon is pinned to a lattice site. Our work could facilitate the study of interactions between Polarons, which may lead to collective behaviour, such as stripe formation, as well as the microscopic exploration of the fate of Polarons in the pseudogap and ‘bad metal’ phases. Magnetic Polarons are imaged with single-site spin and density resolution in the low-doping regime of the atomic Fermi–Hubbard model, showing that mobile delocalized doublons are necessary for Polaron formation.
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imaging magnetic Polarons in the doped fermi hubbard model
arXiv: Quantum Gases, 2018Co-Authors: Joannis Koepsell, Fabian Grusdt, Eugene Demler, Jayadev Vijayan, Pimonpan Sompet, Timon A Hilker, Guillaume Salomon, Immanuel BlochAbstract:Polarons are among the most fundamental quasiparticles emerging in interacting many-body systems, forming already at the level of a single mobile dopant. In the context of the two-dimensional Fermi-Hubbard model, such Polarons are predicted to form around charged dopants in an antiferromagnetic background in the low doping regime close to the Mott insulating state. Macroscopic transport and spectroscopy measurements related to high $T_{c}$ materials have yielded strong evidence for the existence of such quasiparticles in these systems. Here we report the first microscopic observation of magnetic Polarons in a doped Fermi-Hubbard system, harnessing the full single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of mobile doublons by a local reduction and even sign reversal of magnetic correlations, originating from the competition between kinetic and magnetic energy in the system. The experimentally observed Polaron signatures are found to be consistent with an effective string model at finite temperature. We demonstrate that delocalization of the doublon is a necessary condition for Polaron formation by contrasting this mobile setting to a scenario where the doublon is pinned to a lattice site. Our work paves the way towards probing interactions between Polarons, which may lead to stripe formation, as well as microscopically exploring the fate of Polarons in the pseudogap and bad metal phase.
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many body interferometry of magnetic Polaron dynamics
Physical Review B, 2018Co-Authors: Yuto Ashida, Richard Schmidt, Leticia Tarruell, Eugene DemlerAbstract:The physics of quantum impurities coupled to a many-body environment is among the most important paradigms of condensed matter physics. In particular, the formation of Polarons, quasiparticles dressed by the polarization cloud, is key to the understanding of transport, optical response, and induced interactions in a variety of materials. Despite recent remarkable developments in ultracold atoms and solid-state materials, the direct measurement of their ultimate building block, the Polaron cloud, has remained a fundamental challenge. We propose and anlalyze a unique platform to probe time-resolved dynamics of Polaron-cloud formation with an interferometric protocol. We consider an impurity atom immersed in a two-component Bose-Einstein condensate, where the impurity generates spin-wave excitations that can be directly measured by the Ramsey interference of surrounding atoms. The dressing by spin waves leads to the formation of magnetic Polarons and reveals a unique interplay between few- and many-body physics that is signified by single- and multi-frequency oscillatory dynamics corresponding to the formation of many-body bound states. Finally, we discuss concrete experimental implementations in ultracold atoms.
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Polaronic mass renormalization of impurities in bose einstein condensates correlated gaussian wave function approach
Physical Review A, 2016Co-Authors: Yulia E Shchadilova, Fabian Grusdt, A N Rubtsov, Eugene DemlerAbstract:We propose a class of variational Gaussian wavefunctions to describe Fr\"ohlich Polarons at finite momenta. Our wavefunctions give Polaron energies that are in excellent agreement with the existing Monte Carlo results for a broad range of interactions. We calculate the effective mass of Polarons and find smooth crossover between weak and intermediate impurity-bosons coupling. Effective masses that we obtain are considerably larger than those predicted by the mean-field method. A novel prediction based on our variational wavefunctions is a special pattern of correlations between host atoms that can be measured in time-of-flight experiments. We discuss atomic mixtures in systems of ultracold atoms in which our results can be tested with current experimental technology.
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renormalization group approach to the frohlich Polaron model application to impurity bec problem
Scientific Reports, 2015Co-Authors: Fabian Grusdt, Yulia E Shchadilova, A N Rubtsov, Eugene DemlerAbstract:When a mobile impurity interacts with a many-body system, such as a phonon bath, a Polaron is formed. Despite the importance of the Polaron problem for a wide range of physical systems, a unified theoretical description valid for arbitrary coupling strengths is still lacking. Here we develop a renormalization group approach for analyzing a paradigmatic model of Polarons, the so-called Frohlich model, and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra cold atoms. Polaron energies obtained by our method are in excellent agreement with recent diagrammatic Monte Carlo calculations for a wide range of interaction strengths. They are found to be logarithmically divergent with the ultra-violet cut-off, but physically meaningful regularized Polaron energies are also presented. Moreover, we calculate the effective mass of Polarons and find a smooth crossover from weak to strong coupling regimes. Possible experimental tests of our results in current experiments with ultra cold atoms are discussed.
Richard Schmidt - One of the best experts on this subject based on the ideXlab platform.
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dynamical variational approach to bose Polarons at finite temperatures
Physical Review Letters, 2020Co-Authors: David Dzsotjan, Richard Schmidt, Michael FleischhauerAbstract:We discuss the interaction of a mobile quantum impurity with a Bose-Einstein condensate of atoms at finite temperature. To describe the resulting Bose Polaron formation we develop a dynamical variational approach applicable to an initial thermal gas of Bogoliubov phonons. We study the Polaron formation after switching on the interaction, e.g., by a radio-frequency (rf) pulse from a noninteracting to an interacting state. To treat also the strongly interacting regime, interaction terms beyond the Frohlich model are taken into account. We calculate the real-time impurity Green's function and discuss its temperature dependence. Furthermore we determine the rf absorption spectrum and find good agreement with recent experimental observations. We predict temperature-induced shifts and a substantial broadening of spectral lines. The analysis of the real-time Green's function reveals a crossover to a linear temperature dependence of the thermal decay rate of Bose Polarons as unitary interactions are approached.
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observation of a smooth Polaron molecule transition in a degenerate fermi gas
arXiv: Quantum Gases, 2020Co-Authors: Gal Ness, Richard Schmidt, Constantine Shkedrov, Yanay Florshaim, Oriana K Diessel, Jonas Von Milczewski, Yoav SagiAbstract:Understanding the behavior of an impurity strongly interacting with a Fermi sea is a long-standing challenge in many-body physics. When the interactions are short-ranged, two vastly different ground states exist: a Polaron quasiparticle and a molecule dressed by the majority atoms. In the single-impurity limit, it is predicted that at a critical interaction strength, a first-order transition occurs between these two states. Experiments, however, are always conducted in the finite temperature and impurity density regime. The fate of the Polaron-to-molecule transition under these conditions, where the statistics of quantum impurities and thermal effects become relevant, is still unknown. Here, we address this question experimentally and theoretically. Our experiments are performed with a spin-imbalanced ultracold Fermi gas with tunable interactions. Utilizing a novel Raman spectroscopy combined with a high-sensitivity fluorescence detection technique, we isolate the quasiparticle contribution and extract the Polaron energy, spectral weight, and the contact parameter. As the interaction strength is increased, we observe a continuous variation of all observables, in particular a smooth reduction of the quasiparticle weight as it goes to zero beyond the transition point. Our observation is in good agreement with a theoretical model where Polaron and molecule quasiparticle states are thermally occupied according to their quantum statistics. At the experimental conditions, Polaron states are hence populated even at interactions where the molecule is the ground state and vice versa. The emerging physical picture is thus that of a smooth transition between Polarons and molecules and a coexistence of both in the region around the expected transition.
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quantum zeno fermi Polaron in the strong dissipation limit
arXiv: Quantum Gases, 2019Co-Authors: Tomasz Wasak, Richard Schmidt, Francesco PiazzaAbstract:The interplay between measurement and quantum correlations in many-body systems can lead to novel types of collective phenomena which are not accessible in isolated systems. In this work, we merge the Zeno-paradigm of quantum measurement theory with the concept of Polarons in condensed-matter physics. The resulting quantum-Zeno Fermi-Polaron is a quasi-particle which emerges for lossy impurities interacting with a quantum-degenerate bath of fermions. For loss rates of the order of the impurity-fermion binding energy the quasi-particle is short lived. However, we show that in the strongly dissipative regime of large loss rates a long-lived Polaron branch re-emerges. This quantum-Zeno Fermi-Polaron originates from the nontrivial interplay between the Fermi-surface and the surface of the momentum region forbidden by the quantum Zeno projection. The situation we consider here is realized naturally for polaritonic impurities in charge-tuneable semiconductors and can be also implemented using dressed atomic states in ultracold gases.
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dynamical variational approach to bose Polarons at finite temperatures
arXiv: Quantum Gases, 2019Co-Authors: David Dzsotjan, Richard Schmidt, Michael FleischhauerAbstract:We discuss the interaction of a mobile quantum impurity with a Bose-Einstein condensate of atoms at finite temperature. To describe the resulting Bose Polaron formation we extend the dynamical variational approach of [Phys.Rev.Lett. 117, 11302 (2016)] to an initial thermal gas of Bogoliubov phonons. We study the Polaron formation after switching on the interaction, e.g., by a radio-frequency (RF) pulse from a non-interacting to an interacting state. To treat also the strongly-interacting regime, interaction terms beyond the Frohlich model are taken into account. We calculate the real-time impurity Green's function and discuss its temperature dependence. Furthermore, we determine the RF absorption spectrum and find good agreement with recent experimental observations. We predict temperature-induced shifts and a substantial broadening of spectral lines. The analysis of the real-time Green's function reveals a crossover to a linear temperature dependence of the thermal decay rate of Bose Polarons as unitary interactions are approached.
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many body interferometry of magnetic Polaron dynamics
Physical Review B, 2018Co-Authors: Yuto Ashida, Richard Schmidt, Leticia Tarruell, Eugene DemlerAbstract:The physics of quantum impurities coupled to a many-body environment is among the most important paradigms of condensed matter physics. In particular, the formation of Polarons, quasiparticles dressed by the polarization cloud, is key to the understanding of transport, optical response, and induced interactions in a variety of materials. Despite recent remarkable developments in ultracold atoms and solid-state materials, the direct measurement of their ultimate building block, the Polaron cloud, has remained a fundamental challenge. We propose and anlalyze a unique platform to probe time-resolved dynamics of Polaron-cloud formation with an interferometric protocol. We consider an impurity atom immersed in a two-component Bose-Einstein condensate, where the impurity generates spin-wave excitations that can be directly measured by the Ramsey interference of surrounding atoms. The dressing by spin waves leads to the formation of magnetic Polarons and reveals a unique interplay between few- and many-body physics that is signified by single- and multi-frequency oscillatory dynamics corresponding to the formation of many-body bound states. Finally, we discuss concrete experimental implementations in ultracold atoms.
Desheng Liu - One of the best experts on this subject based on the ideXlab platform.
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dynamical simulations of Polaron spin filtering and rectification in an organic magnetic nonmagnetic co oligomer the interfacial effect
Journal of Physical Chemistry C, 2019Co-Authors: Hui Wang, Kun Gao, Hongyan Shi, Jingfen Zhao, Xiaojuan Yuan, Wenjing Wang, Zaifa Yang, Wenli Guan, Desheng LiuAbstract:The interfacial effect on the dynamical properties of spin-dependent Polarons in an organic magnetic/nonmagnetic co-oligomer is investigated by using a tight-binding model coupled with a nonadiabatic dynamic method. It is found that the dynamical behaviors of spin-up and spin-down Polarons are quite different at the interface. In the presence of an external electric field, Polarons with a specific spin (up or down) can get trapped near the magnetic/nonmagnetic interface while the motion of Polarons with an opposite spin is not affected, which leads to the phenomenon of Polaron spin-filtering. Interestingly, when the electric field is reversely applied, only Polarons with opposite spin can pass through the co-oligomer and spin rectification can be observed. The spin-filtering and rectification can be improved by increasing the strength of the spin correlation in the magnetic part of the co-oligomer and they can also be affected by the strength of the interfacial electron–lattice coupling and the electronic...
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dynamical simulations of Polaron spin filtering and rectification in an organic magnetic nonmagnetic co oligomer the interfacial effect
The Journal of Physical Chemistry, 2019Co-Authors: Hui Wang, Kun Gao, Hongyan Shi, Jingfen Zhao, Xiaojuan Yuan, Wenjing Wang, Zaifa Yang, Wenli Guan, Desheng LiuAbstract:The interfacial effect on the dynamical properties of spin-dependent Polarons in an organic magnetic/nonmagnetic co-oligomer is investigated by using a tight-binding model coupled with a nonadiabatic dynamic method. It is found that the dynamical behaviors of spin-up and spin-down Polarons are quite different at the interface. In the presence of an external electric field, Polarons with a specific spin (up or down) can get trapped near the magnetic/nonmagnetic interface while the motion of Polarons with an opposite spin is not affected, which leads to the phenomenon of Polaron spin-filtering. Interestingly, when the electric field is reversely applied, only Polarons with opposite spin can pass through the co-oligomer and spin rectification can be observed. The spin-filtering and rectification can be improved by increasing the strength of the spin correlation in the magnetic part of the co-oligomer and they can also be affected by the strength of the interfacial electron–lattice coupling and the electronic transfer integral. These findings are useful for the design of organic-based spin logic devices.
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dynamical study of Polaron biPolaron scattering in conjugated polymers
Organic Electronics, 2010Co-Authors: Zhaopeng Sun, Kun Gao, Desheng Liu, Shijie XieAbstract:Abstract We simulate the scattering processes between a negative Polaron and a positive biPolaron in a conjugated polymer chain using mixed quantum classical molecular dynamics. The simulations are performed based on the Su–Schrieffer–Heeger (SSH) model modified to include electron–electron interactions, a Brazovskii–Kirova symmetry-breaking term, and an external electric field. It is found that there exist a critical electric field, below which the Polaron and biPolaron can scatter into an excited Polaron. If the external electric field is higher than the critical electric field, the Polaron and biPolaron will pass through each other and continue moving as isolated ones. Because the excited Polaron can decay to the Polaron state through emitting a photon, our results indicate that the interactions between Polarons and biPolarons can open a channel for electroluminescence.
Cesare Soci - One of the best experts on this subject based on the ideXlab platform.
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Polaron self localization in white light emitting hybrid perovskites
Journal of Materials Chemistry C, 2017Co-Authors: Daniele Cortecchia, Jeanluc Bredas, Jun Yin, Annalisa Bruno, Gagik G Gurzadyan, Subodh Mhaisalkar, Cesare SociAbstract:Two-dimensional (2D) perovskites with the general formula APbX4 are attracting increasing interest as solution processable, white-light emissive materials. Recent studies have shown that their broadband emission is related to the formation of intra-gap colour centres. Here, we provide an in-depth description of the charge localization sites underlying the generation of such radiative centres and their corresponding decay dynamics, highlighting the formation of small Polarons trapped within their lattice distortion field. Using a combination of spectroscopic techniques and first-principles calculations to study the white-light emitting 2D perovskites (EDBE)PbCl4 and (EDBE)PbBr4, we infer the formation of Pb23+, Pb3+, and X2− (where X = Cl or Br) species confined within the inorganic perovskite framework. Due to strong Coulombic interactions, these species retain their original excitonic character and form self-trapped Polaron–excitons acting as radiative colour centres. These findings are expected to be relevant for a broad class of white-light emitting perovskites with large Polaron relaxation energy.
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Polaron self localization in white light emitting hybrid perovskites
arXiv: Materials Science, 2016Co-Authors: Daniele Cortecchia, Jeanluc Bredas, Jun Yin, Annalisa Bruno, Gagik G Gurzadyan, Subodh Mhaisalkar, Cesare SociAbstract:Two-dimensional (2D) perovskites with general formula $APbX_4$ are attracting increasing interest as solution processable, white-light emissive materials. Recent studies have shown that their broadband emission is related to the formation of intra-gap color centers; however, the nature and dynamics of the emissive species have remained elusive. Here we show that the broadband photoluminescence of the 2D perovskites $(EDBE)PbCl_4$ and $(EDBE)PbBr_4$ stems from the localization of small Polarons within the lattice distortion field. Using a combination of spectroscopic techniques and first-principles calculations, we infer the formation of ${Pb_2}^{3+}$, $Pb^{3+}$, and ${X_2}^-$ (where X=Cl or Br) species confined within the inorganic perovskite framework. Due to strong Coulombic interactions, these species retain their original excitonic character and form self-trapped Polaron-excitons acting as radiative color centers. These findings are expected to be applicable to a broad class of white-light emitting perovskites with large Polaron relaxation energy.
