Evidence for modification of the electronic density of states by zero-point lattice motion in one dimension: Luminescence and resonance Raman studies of anMXsolid

Abstract

Luminescence spectra, both emission and excitation, and the excitation dependence of the resonance Raman spectra, have been measured for the quasi-one-dimensional charge-density-wave material

Effects of lattice fluctuations on electronic transmission in metal/conjugated-oligomer/metal structures

“…Thus both quantum and thermal fluctuations are considered. The fluctuation strength can be extracted from experiments, e.g., the width of the intragap ''tail'' states in the luminescence spectra of polymers, 14 and for polyacetylenelike polymers ϳ0.02.…”

Subpicosecond dynamics of excitons and photoexcited intrinsic polarons in the quasi-one-dimensional solid PtCl

“…Phonon-assisted absorption is possible, but unlikely, since the vibration most likely coupled is the symmetric stretch v 1 of the Cl atoms around the Pt 4 sites, which has an energy E p of only 0.038 eV. 4 In a linear system, excitation at 1.38 eV would therefore require absorption of about 19 of these phonons, an event that has a negligibly small probability. Although higher frequency, off-chain vibrations could also be involved in this process, a large number of quanta would still be required.…”

“…3 In contrast with conducting polymers, another class of 1D systems, M X solids grow as single crystals with primarily intrinsic disorder associated with zero-point motion and thermal fluctutations. 4 The excited electronic states of 1D compounds have traditionally been described by semiconductor band models. 5,6 Recently, however, there has been growing experimental evidence that excitations in conducting polymers more closely resemble those of their molecular analogs, the finite polyenes.…”

“…Similarly, for PtCl, in which excitations are very localized, 6 both experiments 8 and theory 9 indicate that an excitonic rather than band picture is more appropriate. The lowest energy odd-parity exciton ͉1u͘ has a threshold at 10 K of 2.4 eV, 4 and is associated with the transfer of an electron from the Pt 2ϩ band to the Pt 4ϩ band. Above the exciton band is another broad feature ͉2u͘, with a threshold of about 3 eV, which can be ascribed to either a continuum, a higher-energy exciton or a transition across the chains.…”

“…13 The situation in ordered M X solids is different because of the lack of structural inhomogeneity. 4 Instead of generating excitons, subgap excitation may give rise primarily to excited states of species that already exist as intrinsic defects, such as electron ͑P Ϫ ) and hole (P ϩ ) polarons, which are correlated with a subgap ''A'' band at 1.65 eV in the linear absorption of PtCl. 14,15 It is the purpose of this work to identify excited states and their relaxation dynamics as a function of excitation into three regions of the linear absorption-below, within, and above ͉1u͘-and to understand the nature of intrinsic versus extrinsic disorder, which characterizes photoexcited states in ordered M X solids and typical conducting polymers, respectively.…”