Author: Lotfi Mahyari, Zahra
Tremendous effort continues to be devoted to elucidating the anomalous normal state of high-temperature cuprate superconductors. Experiments on underdoped cuprates have revealed a rich phase above the superconducting transition temperature (Tc) with the presence of electronic nematicity, charge-density-wave order, anomalous weak magnetic order, Cooper pairing, and superconducting fluctuations. A key finding has been the observation of nanoscale electronic inhomogeneity at the surface of Bi2Sr2CaCu2O8+δ by scanning tunneling microscopy (STM). Understanding the role played by the electronic inhomogeneity in the various observed phenomena requires answers to the following questions: (i) Is there a similar degree of electronic inhomogeneity in the bulk? (ii) Does the electronic inhomogeneity observed in Bi2Sr2CaCu2O8+δ have any relevance to other cuprate superconductors? To address these questions one needs a bulk technique that can distinguish between a spatially uniform and inhomogeneous system. The present thesis reports on the results of a muon spin rotation (µSR) study of the bulk of Bi2+xSr2-xCaCu2O8+δ , as well as pure and Ca-doped YBa2Cu3O7-δ, which together with prior measurements reveal a universal inhomogeneous magnetic-field response of hole-doped cuprates extending to temperatures far above Tc. In particular, the inhomogeneous line broadening above Tc is found to scale with the maximum value 〖T_c〗^max for each cuprate family, indicating that the inhomogeneity in the normal state is controlled by the same energy scale as Tc. Since the degree of chemical disorder is very different in the materials we have measured, the observed scaling constitutes strong evidence for an intrinsic electronic tendency toward inhomogeneity in the normal-state, from which bulk superconductivity emerges at lower temperatures.
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Thesis advisor: Sonier, Jeff
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