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Charge-density waves, quantum-anharmonicity, polar responses and resonant Raman in 1D conjugated systems
Full text linkSystems with reduced dimensionality are known to display many fascinating phenomena, with properties often showing pathological behaviors. In this context, one of the most studied aspect regards the insurgence of a modulation of the electronic charge density, i.e. a charge density wave (CDW). The interest in CDWs physics is very broad as they are present in many systems, ranging from 1D and 2D materials, to high Tc superconductors and transition metal dichalcogenides. CDWs usually manifest as a broken-symmetry state, that in 1D chains of atoms results in the presence of a bond-length alternation, commonly explained as a consequence of the interplay between an instability of electronic origin and the coupling between electronic and lattice degrees of freedom. It is commonly understood that the interplay of these elements in 1D systems regulates the competition between a dimerized, less symmetric, configuration and an undimerized, more symmetric, one. In particular, a diatomic chain of atoms presents a second-order phase transition between these two phases. However, a part for these two ingredients, many other different elements are actually at play in the creation of a CDW. Indeed, there are evidences that the presence of a CDW in the infinitely-long straight chains of carbon atoms, called carbyne, is strongly affected by quantum and anharmonic fluctuations, as well as from the effect of an external environment, as we confirm and discuss in our study. The aim of the present work is thus, on one hand, to unveil the contribution of each element to the manifestation of a CDW, and, on the other hand, to study the properties of 1D systems that host CDWs. Indeed, the instability at the boundaries of the structural phase transition suggests the presence of interesting and peculiar polar responses. Following this idea, in our work, we show how 1D systems such as conjugated polymers present a huge enhancement of the effective charges, with values up to 30 times that of the nominal electronic charge at the critical point of the transition, and of the piezoelectric coefficients, which in principle present a diverging behavior in proximity of the phase boundary. In the task of determining the properties of these materials, it is then fundamental to resort to particular experimental techniques, such as resonance Raman spectroscopy. However, at date, a theory which permits to accurately describe experimental results on 1D systems is lacking. We address this problem in our work, introducing a framework that allows for the calculation of resonance Raman spectra beyond the commonly adopted Placzek approximation, even in systems beyond the simple 1D case
Reply to Michael A. Gorin, Arthur I. Sagalowsky and Mark S. Soloway's Letter to the Editor re: S. Picozzi, C. Ricci, M. Gaeta et al. Upper urinary tract recurrence following radical cystectomy for bladder cancer: a meta-analysis on 13,185 patients. J Urol 2012; 188: 2046-54
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Re: the results of ureteral stenting after ureteroscopic lithotripsy for ureteral calculi: a systematic review and meta-analysis: S. Pengfei, L. Yutao, Y. Jie, W. Wuran, D. Yi, Z. Hao and W. Jia, J Urol 2011; 186: 1904-1909
No full textElectronic, morphological, and transport properties of 6,13 Pentacenequinone thin films: theory and experiments
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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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