Harvard Condensed Matter Theory Seminars

Nai-Chang Yeh, California Institute of Technology

Effects of competing orders and quantum criticality on the quasiparticle tunneling spectroscopy and vortex dynamics of Cuprate superconductors
The effect of competing orders and quantum criticality on the macroscopic vortex dynamics and microscopic low-energy excitations of cuprate superconductors is investigated using high-field magnetic measurements and low-temperature scanning tunneling spectroscopy. Our experimental results suggest that significant field-induced quantum fluctuations at low temperatures are present in all cuprates investigated, suggesting that cuprate superconductors are in close proximity to a quantum critical point (QCP) that separates a pure superconducting phase (SC) from a phase consisting of coexisting SC and a competing order. The proximity of a cuprate to the QCP can be determined from a normalized characteristic field in the zero-temperature limit, and the characteristic field correlates well with the quasiparticle tunneling spectra, showing increasing spectral deviation from the mean-field behavior for samples of closer proximity to the QCP. Macroscopically, the presence of competing order can induce strong fluctuation effects in the cuprate superconductors, which is consistent with the extreme type-II nature of the cuprates. The relevant competing orders in different cuprates are examined by comparing theory and numerical calculations with experimental results and the physics implications of these studies are discussed.

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