1,721,126 research outputs found
Electronic transport and quantum localization effects in organic semiconductors
No full textWe explore the charge transport mechanism in organic semiconductors based on a model that accounts for the thermal intermolecular disorder at work in pure crystalline compounds, as well as extrinsic sources of disorder that are present in current experimental devices. Starting from the Kubo formula, we describe a theoretical framework that relates the time-dependent quantum dynamics of electrons to the frequency-dependent conductivity. The electron mobility is then calculated through a relaxation time approximation that accounts for quantum localization corrections beyond Boltzmann theory, and allows us to efficiently address the interplay between highly conducting states in the band range and localized states induced by disorder in the band tails. The emergence of a “transient localization” phenomenon is shown to be a general feature of organic semiconductors that is compatible with the bandlike temperature dependence of the mobility observed in pure compounds. Carrier trapping by extrinsic disorder causes a crossover to a thermally activated behavior at low temperature, which is progressively suppressed upon increasing the carrier concentration, as is commonly observed in organic field-effect transistors. Our results establish a direct connection between the localization of the electronic states and their conductive properties, formalizing phenomenological considerations that are commonly used in the literature
Band dispersion and electronic lifetimes in crystalline organic semiconductors
No full textThe consequences of several microscopic interactions on the photoemission spectra of crystalline organic semiconductors are studied theoretically. It is argued that their relative roles can be disentangled by analyzing both their temperature and their momentum-energy dependence. Our analysis shows that the polaronic thermal band narrowing, which is the foundation of most theories of electrical transport in organic semiconductors, is inconsistent in the range of microscopic parameters appropriate for these materials. An alternative scenario is proposed to explain the experimental trends
Re-switching and the Austrian business-cycle theory: A rejoinder
No full textIn these few pages I discuss some points concerning Lewin and Cachanosky’s Review of Austrian Economics, (2019) comment on my note (Fratini Review of Austrian Economics, 2019) about the implication of re-switching for the working of the Austrian business-cycle theory
Absolute advantages and capital mobility in international trade theory
No full textCapital mobility has the potential of undermining the validity of Ricardo’s theory of comparative advantage. Within this context, the tendency towards a uniform rate of profit makes absolute costs relevant for the analysis of specialisation patterns. A historical and analytical reconstruction is resented of a few significant contributions addressing this point, with a particular focus on the possibility of exclusion from trade and production “desertification” caused by a country’s low profitability of capital. A generalisation of a result obtained by Parrinello is provided
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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