Phonon dispersion, phonon specific heat, and Debye temperature of high-temperature superconductors
1992; American Physical Society; Volume: 46; Issue: 22 Linguagem: Inglês
10.1103/physrevb.46.14922
ISSN1095-3795
AutoresF. W. de Wette, Anil D. Kulkarni,
Tópico(s)Quantum, superfluid, helium dynamics
ResumoA simple model representing the low-frequency acoustical and optical modes of the high-temperature superconductors (HTSC's) leads to a surprisingly realistic representation of the low-temperature specific heats ${\mathit{c}}_{\mathit{v}}$(T) and the corresponding Debye temperatures FTHETA(T) of the HTSC's. The model allows us to relate the characteristics and peculiarities of ${\mathit{c}}_{\mathit{v}}$(T) and FTHETA(T) directly to various features of the low-frequency phonon dispersion, and it is found that ${\mathit{c}}_{\mathit{v}}$ and FTHETA can exhibit rather well the identifiable features of phonon anomalies. For instance, a surprising result is that optic Einstein-like modes at ${\ensuremath{\nu}}_{\mathit{E}}$=2 THz (h${\ensuremath{\nu}}_{\mathit{E}}$/${\mathit{k}}_{\mathit{B}}$=96 K) in our model begin to have an effect at 6 K. This behavior has potentially important consequences for the procedure of separating the phonon contribution from the measured specific heat, in order to obtain the nonphonon specific-heat contributions. Another consequence of the occurrence of these Einstein modes is the presence of low-frequency phonons with large wave vectors, which means that umklapp scattering can begin to play a role at temperatures lower than usually assumed. This, in turn, may require a modification of the customary qualitative picture of the low-temperature electrical and thermal conductivities.
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