We provide a phenomenological formula that describes the low-frequency optical absorption of charge carriers in disordered systems with localization. This allows us to extract, from experimental data ...on the optical conductivity, the relevant microscopic parameters determining the transport properties, such as the carrier localization length and the elastic and inelastic scattering times. This general formula is tested and applied here to organic semiconductors, where dynamical molecular disorder is known to play a key role in the transport properties. The present treatment captures the basic ideas underlying the recently proposed transient localization scenario for charge transport, extending it from the dc mobility to the frequency domain. When applied to existing optical measurements in rubrene fieldeffect transistors, our analysis provides quantitative evidence for the transient localization phenomenon. Possible applications to other disordered electronic systems are briefly discussed.
It has recently been argued that inverse-
β
nuclear transmutations might occur at an impressively high rate in a thin layer at a metallic hydride surface under specific conditions. In this note we ...present a calculation of the transmutation rate, which shows that there is little room for such a remarkable effect.
A model describing the low-density carrier state in an organic single-crystal field-effect transistor (FET) with high-κ gate dielectrics is studied. The interplay between charge-carrier coupling with ...intermolecular vibrations in the bulk of the organic material and the long-range interaction induced at the interface with a polar dielectric is investigated. This interplay is responsible for the stabilization of a polaronic state with an internal structure extending on few lattice sites, at much lower coupling strengths than expected from the polar interaction alone. This effect could drive the carriers close to self-trapping in high-κ organic FETs without invoking unphysically large values of the carrier-interface interaction.
Recent experiments have demonstrated that the performances of organic FETs strongly depend on the dielectric properties of the gate insulator. In particular, it has been shown that the temperature ...dependence of the mobility evolves from a metallic-like to an insulating behavior upon increasing the dielectric constant of the gate material. This phenomenon can be explained in terms of the formation of small polarons, due to the polar interaction of the charge carriers with the phonons at the organic/dielectric interface. Building on this model, the possible consequences of the Coulomb repulsion between the carriers at high concentrations are analyzed.
Optical and spectral properties of carriers in the presence of strong antiferromagnetic correlations and interacting with optical phonon modes are analyzed using Dynamical Mean Field Theory. We ...interpret the mid-infrared band in
σ(
ω) in term of mixed spin lattice polaronic excitations which arise from the stabilization of the lattice polaron due to the antiferromagnetic correlations. We compare our results with experimental data in NCCO showing that the doping and temperature dependences of the optical conductivity in this compound is naturally reproduced within a spin/lattice polaronic model.
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The two-site Holstein model represents a first non-trivial paradigm for the interaction between an itinerant charge with a quantum oscillator, a very common topic in different ambits. Exact results ...can be achieved both analytically and numerically, nevertheless it can be useful to compare them with approximate, semi-classical techniques in order to highlight the role of quantum effects. In this paper we consider the adiabatic limit in which the oscillator is slower than the electron. A density matrix approach is introduced for studying the charge dynamics and the exact results are compared with two different approximations: a Born-Oppenheimer-based Static Approximation for the oscillator (SA) and a Quantum-classical (QC) dynamics.
Isotope effects (IEs) are powerful tools to probe directly the dependence of many physical properties on lattice dynamics. In this Letter we investigate the onset of anomalous IEs in the spinless ...Holstein model by employing the dynamical mean field theory. We show that the isotope coefficients of the electron effective mass and of the dressed phonon frequency are sizable also far away from the polaronic crossover and mark the importance of nonadiabatic lattice fluctuations. We draw a nonadiabatic phase diagram in which we identify a novel crossover, not related to polaronic features, where the IEs attain their largest anomalies.
We calculate the optical conductivity of small polarons in the Holstein and Holstein-
t-
J models, by applying the dynamical mean field theory. We show that the antiferromagnetic correlations tend to ...increase the region of the parameters where polaronic signatures are found in the optical spectra, and shift the polaronic absorption band to higher frequencies compared to the case of purely lattice polarons. On the other hand, the electron–lattice interaction is essential in order to have polaronic features in the optical absorption.
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