Zukunftskolleghttp://kops.uni-konstanz.de:80/handle/123456789/522019-08-20T15:11:57Z2019-08-20T15:11:57ZTunable Fröhlich polarons in organic single-crystal transistorsHulea, Iulian N.Fratini, SimoneXie, H.Mulder, Cornelis L.Iossad, Nikolai N.Rastelli, Gianlucapop242135Ciuchi, SergioMorpurgo, Alberto F.123456789/465512019-07-31T01:14:52Z2006-12Tunable Fröhlich polarons in organic single-crystal transistors
Hulea, Iulian N.; Fratini, Simone; Xie, H.; Mulder, Cornelis L.; Iossad, Nikolai N.; Rastelli, Gianluca; Ciuchi, Sergio; Morpurgo, Alberto F.
In organic field-effect transistors (FETs), charges move near the surface of an organic semiconductor, at the interface with a dielectric. In the past, the nature of the microscopic motion of charge carriers—which determines the device performance—has been related to the quality of the organic semiconductor. Recently, it was discovered that the nearby dielectric also has an unexpectedly strong influence. The mechanisms responsible for this influence are not understood. To investigate these mechanisms, we have studied transport through organic single-crystal FETs with different gate insulators. We find that the temperature dependence of the mobility evolves from metallic-like to insulating-like with increasing dielectric constant of the insulator. The phenomenon is accounted for by a two-dimensional Fröhlich polaron model that quantitatively describes our observations and shows that increasing the dielectric polarizability results in a crossover from the weak to the strong polaronic coupling regime. This represents a considerable step forward in our understanding of transport through organic transistors, and identifies a microscopic physical process with a large influence on device performance.
2006-12Hulea, Iulian N.Fratini, SimoneXie, H.Mulder, Cornelis L.Iossad, Nikolai N.Rastelli, GianlucaCiuchi, SergioMorpurgo, Alberto F.530In organic field-effect transistors (FETs), charges move near the surface of an organic semiconductor, at the interface with a dielectric. In the past, the nature of the microscopic motion of charge carriers—which determines the device performance—has been related to the quality of the organic semiconductor. Recently, it was discovered that the nearby dielectric also has an unexpectedly strong influence. The mechanisms responsible for this influence are not understood. To investigate these mechanisms, we have studied transport through organic single-crystal FETs with different gate insulators. We find that the temperature dependence of the mobility evolves from metallic-like to insulating-like with increasing dielectric constant of the insulator. The phenomenon is accounted for by a two-dimensional Fröhlich polaron model that quantitatively describes our observations and shows that increasing the dielectric polarizability results in a crossover from the weak to the strong polaronic coupling regime. This represents a considerable step forward in our understanding of transport through organic transistors, and identifies a microscopic physical process with a large influence on device performance.JOURNAL_ARTICLEeng10.1038/nmat17741476-11221476-4660982986512Nature Materials2019-07-30T11:45:43+02:00123456789/52Nature Materials ; 5 (2006), 12. - S. 982-986. - ISSN 1476-1122. - eISSN 1476-4660true2019-07-30T09:45:43ZtrueWigner crystallization in a polarizable mediumRastelli, Gianlucapop242135Ciuchi, Sergio123456789/465472019-07-27T01:14:45Z2005Wigner crystallization in a polarizable medium
Rastelli, Gianluca; Ciuchi, Sergio
We present a variational study of the two- and three-dimensional Wigner crystal phase of large polarons. The method generalizes that introduced by S. Fratini and P. Quémerais [Mod. Phys. Lett. B 12 1003 (1998)]. We take into account the Wigner crystal normal modes rather than a single mean frequency in the minimization procedure of the variational free energy. We calculate the renormalized modes of the crystal as well as the charge polarization correlation function and polaron radius. The solid phase boundaries are determined via a Lindemann criterion, suitably generalized to take into account the classical-to-quantum crossover. In the weak electron-phonon coupling limit, the Wigner crystal parameters are renormalized by the electron-phonon interaction, leading to a stabilization of the solid phase for low polarizability of the medium. Conversely, at intermediate and strong coupling, the behavior of the system depends strongly on the polarizability of the medium. For weakly polarizable media, a density crossover occurs inside the solid phase when the renormalized plasma frequency approaches the phonon frequency. At low density, we have a renormalized polaron Wigner crystal, whereas at higher densities the electron-phonon interaction is weakened irrespective of the bare electron-phonon coupling. For strongly polarizable media, the system behaves as a Lorentz lattice of dipoles. The abrupt softening of the internal polaronic frequency predicted by Fratini and Quemerais is observed near the actual melting point only at very strong coupling, leading to a possible liquid polaronic phase for a wider range of parameters.
2005Rastelli, GianlucaCiuchi, Sergio530We present a variational study of the two- and three-dimensional Wigner crystal phase of large polarons. The method generalizes that introduced by S. Fratini and P. Quémerais [Mod. Phys. Lett. B 12 1003 (1998)]. We take into account the Wigner crystal normal modes rather than a single mean frequency in the minimization procedure of the variational free energy. We calculate the renormalized modes of the crystal as well as the charge polarization correlation function and polaron radius. The solid phase boundaries are determined via a Lindemann criterion, suitably generalized to take into account the classical-to-quantum crossover. In the weak electron-phonon coupling limit, the Wigner crystal parameters are renormalized by the electron-phonon interaction, leading to a stabilization of the solid phase for low polarizability of the medium. Conversely, at intermediate and strong coupling, the behavior of the system depends strongly on the polarizability of the medium. For weakly polarizable media, a density crossover occurs inside the solid phase when the renormalized plasma frequency approaches the phonon frequency. At low density, we have a renormalized polaron Wigner crystal, whereas at higher densities the electron-phonon interaction is weakened irrespective of the bare electron-phonon coupling. For strongly polarizable media, the system behaves as a Lorentz lattice of dipoles. The abrupt softening of the internal polaronic frequency predicted by Fratini and Quemerais is observed near the actual melting point only at very strong coupling, leading to a possible liquid polaronic phase for a wider range of parameters.JOURNAL_ARTICLEeng10.1103/PhysRevB.71.1843030163-18291095-37957118Physical Review B2019-07-26T14:54:21+02:00123456789/52Physical Review B ; 71 (2005), 18. - 184303. - ISSN 0163-1829. - eISSN 1095-3795true2019-07-26T12:54:21ZtrueOptical and spectral properties of quantum domain-walls in the generalized Wigner latticeFratini, SimoneRastelli, Gianlucapop242135123456789/465462019-07-27T01:14:44Z2007Optical and spectral properties of quantum domain-walls in the generalized Wigner lattice
Fratini, Simone; Rastelli, Gianluca
We study the spectral properties of a system of electrons interacting through long-range Coulomb potential on a one-dimensional chain. When the interactions dominate over the electronic bandwidth, the charges arrange in an ordered configuration that minimizes the electrostatic energy, forming Hubbard's generalized Wigner lattice. In such strong coupling limit, the low energy excitations are quantum domain-walls that behave as fractionalized charges, and can be bound in excitonic pairs. Neglecting higher order excitations, the system properties are well described by an effective Hamiltonian in the subspace with one pair of domain-walls, which can be solved exactly. The optical conducitivity $\sigma(\omega)$ and the spectral function $A(k,\omega)$ can be calculated analytically, and reveal unique features of the unscreened Coulomb interactions that can be directly observed in experiments.
2007Fratini, SimoneRastelli, Gianluca530We study the spectral properties of a system of electrons interacting through long-range Coulomb potential on a one-dimensional chain. When the interactions dominate over the electronic bandwidth, the charges arrange in an ordered configuration that minimizes the electrostatic energy, forming Hubbard's generalized Wigner lattice. In such strong coupling limit, the low energy excitations are quantum domain-walls that behave as fractionalized charges, and can be bound in excitonic pairs. Neglecting higher order excitations, the system properties are well described by an effective Hamiltonian in the subspace with one pair of domain-walls, which can be solved exactly. The optical conducitivity $\sigma(\omega)$ and the spectral function $A(k,\omega)$ can be calculated analytically, and reveal unique features of the unscreened Coulomb interactions that can be directly observed in experiments.JOURNAL_ARTICLEeng10.1103/PhysRevB.75.1951030163-18291095-37957519Physical Review B2019-07-26T14:51:00+02:00123456789/52Physical Review B ; 75 (2007), 19. - 195103. - ISSN 0163-1829. - eISSN 1095-3795true2019-07-26T12:51:00ZtrueEnhancement of Wigner crystallization in quasi-low-dimensional solidsRastelli, Gianlucapop242135Quémerais, PascalFratini, Simone123456789/465422019-07-27T01:14:51Z2006-01-25Enhancement of Wigner crystallization in quasi-low-dimensional solids
Rastelli, Gianluca; Quémerais, Pascal; Fratini, Simone
The crystallization of electrons in quasi-low-dimensional solids is studied in a model that retains the full three-dimensional nature of the Coulomb interactions. We show that restricting the electron motion to layers (or chains) gives rise to a rich sequence of structural transitions upon varying the particle density. In addition, the concurrence of low-dimensional electron motion and isotropic Coulomb interactions leads to a sizable stabilization of the Wigner crystal, which could be one of the mechanisms at the origin of the charge-ordered phases frequently observed in such compounds.
2006-01-25Rastelli, GianlucaQuémerais, PascalFratini, Simone530The crystallization of electrons in quasi-low-dimensional solids is studied in a model that retains the full three-dimensional nature of the Coulomb interactions. We show that restricting the electron motion to layers (or chains) gives rise to a rich sequence of structural transitions upon varying the particle density. In addition, the concurrence of low-dimensional electron motion and isotropic Coulomb interactions leads to a sizable stabilization of the Wigner crystal, which could be one of the mechanisms at the origin of the charge-ordered phases frequently observed in such compounds.JOURNAL_ARTICLEeng10.1103/PhysRevB.73.1551030163-18291095-37957315Physical Review B2019-07-26T11:07:48+02:00123456789/52Physical Review B ; 73 (2006), 15. - 155103. - ISSN 0163-1829. - eISSN 1095-3795true2019-07-26T09:07:48Ztrue