Frequency-dependent scattering rate

Models for the frequency-dependent scattering rate and effective mass... 

Keeping in mind possible caveats with respect to the interpretation of the results inferred from the extended Drude model, we find that this approach to the data analysis is extremely fruitful and provides important insights into the charge dynamics in cuprates. It is instructive to examine the behavior of the frequency-dependent scattering rate and of the effective mass within simple models. Here we restrict ourselves to one model developed... 

Fig. 7. Optical constants (in-plane) for a series of underdoped high-7J superconductors. Top row real part of the optical conductivity. Middle row frequency dependent scattering rate. Bottom row mass renormalization. Experimental data for Y123 and Y124 compounds from Basov et al. (1996) for Bi2212 compounds from Puchkov et al. (1996b). The scattering rate curves are essentially temperature independent above 1000 cm" but develop a depression at low temperature and at low frequency. The effective mass is enhanced at low temperature and at low frequency. Experimental results in the normal state at T s and in the superconducting state ate...

In the optimally doped materials, the frequency-dependent scattering rate varies linearly with temperature and energy. In underdoped compounds, there is a stronger suppression of l/r((u) at low frequencies and, at T > 7, this correlates with the opening of a pseudogap as detected by other experimental techniques. 

It is also fairly certain that the momentum dependence of the fluctuations must be much less important than their frequency dependence because that is the only way known to have the transport scattering rates be similar to the single-particle relaxation rates and to understand the NMR experiments on cu in the normal state. A specific form with dyanmical critical exponent of infinity has been proposed. 

In a stochastic approach the frequency-depiendent friction appears in the definition of the energy dependence of the relaxation rate P(E), defined by Eq. (4.12), and is evaluated for a Morse potential by Eq. (4.14). In this section the applicability of these relationships and the friction kernel B(d)( )) of Eq. (3.27) is tested in a variety of approaches for the case of u = 1, a diatomic. The use of frequency-dependent friction in the evaluation of D(E) for a system with many degrees of freedom is an area of ongoing activity. While many of the features of a stochastic approach to vibrational relaxation are found in inelastic scattering theories or master equation kernels, it is the characteristic of... 

However, the interpretation of /t (o) and m /m obtained from the one-component analysis is more difficult. Obviously, it is tempting to assign the frequency-dependent effective mass and the scattering rate to the real and imaginary parts of the electronic self-energy 2 (ty) = 2 i((y) -f-i22(o)) entering the equation for the spectral function of the electronic excitation A k, (w) ... 

Overdoped crystals. In overdoped samples, a threshold structure in the l/r(co) spectra is not observed (fig. 9). In sharp contrast to underdoped materials, the scattering rate shows a temperature dependence over a much broader frequency range, extending at least up to 2000 cm . There are indications that the frequency dependence of /r(co) becomes superlinear in the strongly overdoped cuprates. The overall magnitude of 1/t(co) is reduced compared to underdoped or even optimally doped materials. The effective... 

It should be noted that the data on the relaxation rates and spin dynamics of the diluted and mixed LiHopY pF4 (Reich et al. 1990), LiTbpYi pF4 (Lloyd and Mitchell 1990) and DyPpVi-p04 (Dirkmaat et al. 1987), obtained in the frequency dependent ac susceptibility measurements and in the inelastic neutron scattering experiments, demand special discussion. 

In noncubic sohds, the phonon mode frequencies of the polar lattice vibrations depend, in general, on the phonon mode propagation direction. Likewise, directionally dependent free-chargescattering rates and the anisotropic inverse effective freecarrier mass tensor will produce nonscalar free-charge-carrier contributions. The infrared dielectric function is then represented by a complex-valued second-rank tensor s, which can be expressed in Cartesian coordinates (x,y,z) as ... 

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