## Dissertations from ProQuest

#### Title

Thermal transport and phase behavior of cuprate superconductors

1997

Article

#### Degree Name

Doctor of Philosophy (Ph.D.)

#### First Committee Member

Joshua L. Cohn, Committee Chair

#### Abstract

We present extensive, systematic doping dependent studies of thermal conduction in $\rm YBa\sb2Cu\sb3O\sb{6+x}$ (YBCO) and $\rm HgBa\sb2Ca\sb{n-1}Cu\sb{n}O\sb2\sb{(n+1)+\delta}$ (n = 1,2,3). The doping level of the specimens p (hole concentration per planar Cu site), was determined from thermoelectric power (S) measurements, and it was modified by thermal annealing. The temperature dependence of ($\kappa$) was measured at various dopings covering both the underdoped ($p1.6$) regions of the phase diagram. We were able to demonstrate the correlation between the p dependence of the temperature slope change in thermoconductivity at $\rm T\sb{c},\ \Gamma = {-}d(\kappa\sp{s}/\kappa\sp{n})/dt\vert\sb{t\to1}$, and that of the electronic specific heat jump $\Delta\gamma$ for YBCO. This correlation reflects the effect on the heat transport of the low energy spectral weight suppression due to the opening of the normal-state pseudogap.A generic, parabolic, doping dependence of the normal state thermoconductivity was found for the three layers Hg-compound. An additional scattering mechanism peaking at p = 1/8 (the point where the charge stripes are commensurate with the lattice) overlaps the generic behavior in the case of the one and two layers Hg-compounds and YBCO. The trend in the magnitude of the scattering mechanism suggests a causal connection with the oxygen vacancy structures of the doping unit (Hg-O layers and Cu-O chains). Moreover, $\Gamma$ for the Hg-compounds is suppressed similar to the normal state thermal conductivity over the same doping intervals. These findings lead us to conclude that there is a close connection between the doping dependencies of the: normal-state thermal conductivity, thermal conductivity temperature slope change at T$\rm\sb{c}$ and electronic specific heat jump.

#### Keywords

Physics, Condensed Matter