Charged excitations

In view of this apparent contradictory outcome from the transport and magnetic properties, we were motivated to investigate the dynamics of the charge excitation spectrum by optical methods. In fact, the optical measurement is a powerful contactless experimental tool which should in principle allow to unfold the disagreement between and p(7 since the optical response of a metal... 

An important property of the dimerized Peierls stale is the existence of gaps in the spectra of spin and charge excitations. For free electrons (//ci-ci=0) both gaps are equal, while in the presence of Coulomb repulsion the spin gap is smaller than the charge gap [23, 24]. In what follows, we will assume the temperature to be much smaller than these two gaps, so that we can neglect electronic excitations and replace Hcl [ A (.v)] by its ground state expectation value. 

Direct evidence for the competition of two counteracting contributions to the transient absorption changes stems from the temporal evolution of the transmission change at 560 nm. From Figure 10-3 it can be seen that the positive transmission change due to the stimulated emission decays very fast, on a time scale of picoseconds. On the other hand the typical lifetime of excitations in the 5, slate is in the order of several hundred picoseconds. Therefore, one has to conclude that the stimulated emission decay is not due to the decay of the. Sj-population (as is typically the case in dye solutions). The decay is instead attributed to the transiei.i build up of spatially separated charged excitations that absorb at this wavelength. 

AR Brown, K Pichler, NC Greenham, DDC Bradley, RH Friend, and AB Holmes, Optical spectroscopy of triplet excitons and charged excitations in poly(p-phenylenevinylene) light-emitting diodes, Chem. Phys. Lett., 210 61-66, 1993. 

Coulomb correlation energy, I/44, and thereby showed how the cationic and anionic energy levels were both equally important. These workers calculated the gap arising in the charge excitation spectrum of a single transition-metal impurity hybridizing with a... 

For a strongly degenerate carrier liquid fIMb7 1, as well as neglecting the spin-orbit interaction, xc = p/4, where p is the total density-of-states for intra-band charge excitations, which in the 3D case is given by p =. In general, however, xc... 

Now we look on the minimal excitation energies of the quasiparticles which reflect the presence of gaps in the charge-excitation-channel of the superconductor. 

Polaron Pair State. There are a number of experimental observations which can be interpreted neither by invoking charged excitations injected or photo-generated in the polymer, nor by excitons. However, it may happen that the singlet exciton is broken, as described above, and a pair of charges, negative P and positive P+ polarons, are separated onto adjacent chains, but still bound by the Coulomb attraction. These pairs will be referred to as polaron pairs. Polaron pairs are intermediate states between electronic molecular excitations and free charge carriers. They are formed by excitation of the photo-conductivity in polymers and other molecular solids, as well as... 

Mid-temperature process II This process extends over mid-range temperatures (300-400 K) and over low to moderate frequencies (up to 105 Hz). The mid-temperature process was associated with the percolation of charge excitation within the developed fractal structure of connected pores at low... 

In the presence of umklapp processes, the charge bosons are no longer free. They are bound by a cosine potential energy term of amplitude g3 /2ir, so the charge excitations have a gap of this magnitude which can be felt at low temperatures. Under those circumstances, only the SDW susceptibility remains singular with ySDW = 1 (see, however, the refinement when umklapp are present in Section IV.B.3.d). 

The solutions of Eq. (16) for which the umklapp is relevant (i.e., g3 flows to strong-coupling values) are for 2g2 - gi > —1. A Hubbard gap forms for repulsive charge-excitation interactions. At temperatures below Tp E0 exp(-l/g3) [see Eq. (10)], when the gap in the charge excitations is felt, the perturbative RG results have to be discarded in favor of more exact ones. The calculations of Voit [41] show that the susceptibility power... 

Figure 5 Phase diagram of the interacting electron gas showing the competing response functions with positive power law exponent in the presence of umklapp processes. Those in parentheses have a smaller prefactor. There is a gap in the charge excitations to the right of the - g3 line and one in the spin excitations for negative gl.

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