Nonlinear optical spectroscopy of excited states in disubstituted polyacetylene

Abstract

We used a variety of nonlinear optical ͑NLO͒ spectroscopies for studying the excited states order and primary photoexcitations in disubstituted polyacetylene ͑DPA͒. The NLO spectroscopies include ultrafast pump-probe photomodulation in a broad spectral range of 0.2-2.5 eV, two-photon absorption in the range of 3.2-4.2 eV, and electroabsorption ͑EA͒ in the range of 2.3-4.1 eV. For completeness we also measured the linear-absorption and photoluminescence spectra. We found that the primary photoexcitations in DPA are singlet excitons with three photoinduced absorption ͑PA͒ bands, PA 0 at 0.6 eV, PA 1 at 1 eV, and PA 2 at 1.6 eV, respectively, and a stimulated emission band at ϳ2.5 eV. This is in contrast to other -conjugated polymers where the singlet excitons are characterized by two PA bands and a stimulated emission ͑SE͒ band. We conclude that in addition to the four essential excited states known to determine the NLO spectra of -conjugated polymers, namely, 1A g , 1B u , mA g , and nB u ; in DPA there is another important complex of states at ϳ3.3 eV that contains almost degenerate states with odd and even parity symmetries ͑dubbed here transverse excited state or TES͒ that is probably reminiscent of the 2A g state in unsubstituted trans-polyacetylene, which lies in between the 1B u and mA g of which dipole moment has a strong component perpendicular to the chain direction. In support for this model we found that the depolarization ratio of the EA spectrum drastically changes around the TES from a value of ϳ2 for ប Ͻ 3 eV to ϳ0.5 for ប Ͼ 3.3 eV.

Ultrafast intersystem-crossing in platinum containing π-conjugated polymers with tunable spin-orbit coupling

“…The EA spectrum of Pt-3 (Fig. 1(d)) at similar photon energies shows a modulation spectral feature with two zero crossings at 4.1 eV and 4.35 eV, respectively, which we ascribed to m A g and n B u that mix under the influence of the electric field21.…”

Experimental high-dimensional quantum secret sharing with spin-orbit-structured photons

“…Spin-orbit coupled states, e.g. vector modes, have been used to complete the entanglement purification in photon pairs for polarization Bell states [41,42]. Similar they have been used to overcome the limiting channel capacity of superdense coding [43] and to realise a high capacity QKD protocol [44].…”

Interacting resonant-level model with long-range interactions: Fast screening and suppression of the zero-bias conductance

“…The final equations are exact in the uncontacted case as well as in the noninteracting case and several analytic results are obtained in the steadystate, including a Meir-Wingreen-like formula for the current. We benchmarked this formula against recent results with SR interaction obtained using field theoretical methods, 9 DMRG, 9,14 and other renormalization group approaches, [11][12][13] and found the same qualitative behavior.…”

“…Recently, a short-range (SR) dot-lead interaction has been shown to reduce the quasiparticle gap in equilibrium [4][5][6][7] and to reopen it at sufficiently large biases. 8 In the interacting resonant level model (IRLM) the SR interaction is also at the origin of a negative differential conductance with an interaction-dependent power-law decay [9][10][11][12] as well as of an overall enhancement of the off-resonance conductance. 13,14 In recent years the experimental progress in producing low-dimensional conducting wires has been accompanied by an increasing number of theoretical studies on the IRLM with single-channel leads.…”