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Over the course of extensive experimental studies of copper oxide superconductor films synthesized by molecular beam epitaxy, we discovered strange behaviors in their superconducting, metallic and insulting states. In the superconducting state at overdoped side, the measured linear dependence of the superconducting transition temperature on the superfluid density1, defies the Bardeen-Cooper-Schrieffer (BCS) theory and lends support to an electronic Bose-Einstein Condensation (BEC) picture. In the insulating state at underdoped side2, the strong quantum fluctuations and hysteresis in the Hall effect reveals the true ground state competing with the superconductivity is a charge-cluster glass state3. In the normal state, our transport measurements show the rotational symmetry of the electron fluid is spontaneously broken4, occurs in a large temperature and doping region. The superconducting state always emerges out of this electronic nematic state. With these insights, we shined light on the mechanism of the high temperature superconductivity. I will also present our results in searching for electronic nematicity in other unconventional superconductors, such as spin-triplet superconductors, e.g. ruthenates, and Fe-based superconductors, implying it may be universal among strongly-correlated materials.
1. I. Bo?ovi?, X. He, J. Wu and A. T. Bollinger, Nature 536, 309-311 (2016).
2. J. Wu et al., Nature Materials 12, 877 (2013).
3. J. Wu, A. T. Bollinger, Y.-J. Sun and I. Bo?ovi?, Proc. Natl. Acad. Sci. USA 113, 4284-4289 (2016).
4. J. Wu, A. T. Bollinger, X. He and I. Bo?ovi?, Nature 547, 432–435 (2017).
Dr. Jie Wu received his Bachelor’s and Master’s degree from Fudan University in China. He later attended the graduate school of the Physics department of University of California at Berkeley and studied the magnetism at lower dimensions. By synthesizing and fabricating magnetic heterostructures and nanostructures, he is a leading expert in the explorations of novel spin properties at the atomic scale. For instance, the world’s first photo of the antiferromagnetic vortex was taken by him with magnetic microscopy. After Dr. Wu received his Ph.D degree at the year of 2010, he became a postdoctoral fellow at the National High Magnetic Field Laboratory of USA, switching to the field of the transport properties of high temperature superconductors. At 2012, he joined the oxide molecular beam epitaxy (oxide-MBE) group at Brookhaven National Laboratory of USA and was promoted step by step from assistant physicist to associate physicist and to physicist. His work covers a vast body of the frontiers of quantum materials, including interface superconductivity, quantum critical behavior, BCS-BEC crossover etc., and particularly he pioneers in the discovery of the electronic nematicity, an intriguing metallic state, in unconventional superconductors.