Superfluid Density Measurements of High-Temperature Superconducting Films
Osborn, Kevin Daniel
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https://hdl.handle.net/2142/31326
Description
Title
Superfluid Density Measurements of High-Temperature Superconducting Films
Author(s)
Osborn, Kevin Daniel
Issue Date
2001
Doctoral Committee Chair(s)
Van Harlingen, Dale J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
superfluid density
superconducting films
Language
en
Abstract
We have constructed a precision two-coil inductive system suitable for measuring the
superfluid density of superconducting films. With this system we measure several
intrinsic properties of YBa2Cu3O7-x (YBCO) and Bi2Sr2CaCu2O8+δ (Bi-2212) films. Two
competing models of the pseudogap are compared to the temperature dependence of the
superfluid density as a function of doping in Bi-2212. Near zero temperature, a
maximum in the superfluid density as a function of hole doping is observed at
approximately 0.19 holes per unit Cu, in agreement with a model of the pseudogap with
competing order. At temperatures close to the Tc, the superfluid density exhibits critical
phase fluctuations described by an XY model. These phase fluctuations are compared to
a model of the pseudogap described by preformed pairs. In contrast to previous reports
on YBCO films, we find that the phase transition in a YBCO film is described by 3D-XY
critical fluctuations. In heavily underdoped Bi-2212, we find a drop in superfluid density
that is approximately described by a Kosterlitz-Thouless-Berezinskii (KTB) transition.
However, in Bi-2212 films near optimal and critical doping, we find evidence for 3D-XY
static and dynamic fluctuations. The dynamic critical exponent, z, in thin optimally-doped
Bi-2212 films is directly observed as diffusive (z=2) at Tc when the correlation
length exceeds the film thickness (D=2). In the 3D regime we find evidence for z≈1.5,
indicative of a propagating mode.
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