Phonon-electron decoupling

When a model for a CUORICINO detector (see Section 15.3.2) was formulated and the pulses simulated by the model were compared with those detected by the front-end electronics, it was evident that a large difference of about a factor 3 in the pulse rise time existed. This discrepancy was mainly attributed to the uncertainty in the values of carrier-phonon decoupling parameter. For the thermistor heat capacity, a linear dependence on temperature was assumed down to the lowest temperatures. As we shall see, this assumption was wrong. 

The carrier-phonon interaction decreases with the lowering of temperature, since the emission and absorption of phonons by carriers is proportional to the number of final states available to carriers and phonons. At sufficiently low temperatures, the interaction between the two subsystems can be so weak that there is no thermal equilibrium between them, and the energy is distributed among electrons more rapidly than it is distributed to the lattice, resulting in a different temperature for electron and phonon subsystems, giving rise to the so-called electron-phonon decoupling . 

For example in copper, a metal used in nuclear adiabatic demagnetization (see Section 7.4), electron and phonon systems are decoupled the power transferred between the two systems is [18] ... 

The HEM is a thermal model which represents a doped semiconductor thermistor (e.g. Ge NTD) as made up of two subsystems carriers (electrons or holes) and phonons. Each subsystem has its own heat capacity and is thermally linked to the other one through a thermal conductance which takes into account for the electron-phonon decoupling (see Fig. 15.2). 

The nature of G s is different from that of The latter represents the phenomenon of electron-phonon decoupling, the former represents the contact resistance to the heat sink. 

As we saw in Section 4.4, g s(T) is expected to depend on temperature approximately as T3 (there is always an electrical insulating layer in the contact between the thermistor and the metallic support at the temperature of the heat sink) (Fig. 15.3). For a review of the few existing measurements of electron-phonon decoupling, see ref. [20]. 

Figure 15.8 shows the thermal scheme of one detector there are six lumped elements with three thermal nodes at Tu T2, r3, i.e. the temperatures of the electrons of Ge sensor, Te02 absorber and PTFE crystal supports respectively. C), C2 and C3 are the heat capacity of absorber, PTFE and NTD Ge sensor respectively. The resistors Rx and R2 take into account the contact resistances at the surfaces of PTFE supports and R3 represents the series contribution of contact and the electron-phonon decoupling resistances in the Ge thermistor (see Section 15.2.1.3). 

For R3j a l/T4 dependence on temperature was chosen as a representative average between the l/T3 (contact resistance) and 1/r4 5 (electron-phonon decoupling) scaling. 

We take into account that (1,01 (f)l 1,0) = 0.). In systems with continuous phonon spectrum, the function under this integral differs essentially from zero only for t — t2 cr-1 < cS-1. For such a small time difference, electronic and vibrational motions are only weakly correlated this allows one to use the following decoupling of the electronic and the vibrational degrees of freedom ... 

In the JT case, electron-phonon coupling is represented by a matrix Hamiltonian, similar to (1), or (3). Diagonalization of Hn decouples the matrix of potential energy into a multisheet APES. In addition to their diabatic admixture, another difficult side of the JT effect is strong anharmonicity of the APES. As a rule, it has... 

GPa, but then increases at 13 GPa. This has been attributed to a redistribution of intensity between the resonant vibronic and electronic states when the electron-phonon coupling is greater (between 11-12 GPa), followed by the commencement of decoupling of the electronic and vibronic states, at... 

In summary, using the electron—lattice dynamics theory, we have been able to explore the details of the intrachain polaron motion. In particular, we have shown that the velocity of the polaron can exceed the sound velocity of the system. This is achieved by the decoupling of acoustic phonons from the polaron. With this knowledge about the intrachain behavior of the polaron dynamics, we will now go on to discuss the interchain transport of polarons. 

Such decoupling in the liquid may be strictly justified only in the long-wave approximation.In this sense, such a procedure is justified for the macroscopic description. However, one should remember that this is the correct method in a number of cases also for short wavelengths. For example, this is the case for phonons in solids. In other cases, such as the electron gas in metals (plasmons), acoustic phonons in quantum liquids and so on, this decoupling may be considered as the self-consistent field method or the random phase approximation (the analog of the superposition approximation in the classical theory of liquids). 

The second-order derivatives of the energy with respect to the nuclear coordinates are involved in lattice djmamics, in particular, in the calculation of vibrational (phonon) spectra. We shall begin from the molecular case, [669]. The decoupling of the nuclear from the electronic motion is made in the adiabatic approximation (see Chap. 4). 

Another way to enhance ZT is by decoupling the electronic and thermal properties to design PGEC , i.e. a Phonon Glass and Electrical... 

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