Thermal transport and phase behavior of cuprate superconductors

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Joshua L. Cohn, Committee Chair


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.


Physics, Condensed Matter

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