In the study of high-Tc superconducting cuprates, our group was the first to develop the capability of high-resolution spectroscopy as a function of temperature on these compounds — enabling direct visualization of the Cooper pair formation in these compounds as they are cooled.[M. Vershinin et al, Science 303, 1995, (2004), K. Gomes et al, Nature 447, 569 (2007). With these experiments, we showed that superconducting pairing first occurs in nanoscale regions at temperatures well above the superconducting transition temperature.[K. Gomes et al, Nature 447, 569 (2007)] Detailed measurements of the formation of the pairing gap allowed us to demonstrate that the pairing strength in these compounds is controlled by the electronic correlation of the normal state rather than coupling to bosons as in conventional superconductors.[ A. N. Pasupathy et al, Science 320, 196, (2008)]
Extending such measurements further, we focused on understanding how superconductivity is suppressed in the underdoped regime and explored the formation of the mysterious high temperature pseudogap state in this regime. We demonstrated that suppression of Tc is most likely caused by the competition with the pseudogap that reduced the phase space for the pairing interaction in these compounds.[A. Pushp et al, Science 324, 1689, (2009)] One of the intriguing aspects of the pseudogap state has been the observation of local charge ordering that was first reported by our group and made possible with high temperature STM studies.[M. Vershinin et al, Science 303, 1995, (2004)] With precise mapping of electronic states with temperature, we have shown that charge organization in underdoped samples initially turn on at the so-called pseudogap temperature [C. V. Parker et al, Nature 468, 677 (2010)] but are suppressed as superconductivity dominates the properties of the system below Tc. [E. H. da Silva Neto et al, Science, 343, 393 (2014)]
Our group was the first to correlate spectroscopic information from STM measurements on the charge order phase of the cuprates with results from x-ray studies on the same sample.[E. H. da Silva Neto et al, Science, 343, 393 (2014)] By providing high-resolution spatial and spectroscopic information on the electronic properties of cuprates that constrain theoretical models of these compounds, our group’s efforts have had a significant impact on research in this field.
VIDEO> The video below shows the evolution of superconducting gap mapped in an overdoped high-Tc cuprate sample with Tc=61K. The gapped regions survive to 77K well above Tc. (video is from the Yazdani Lab at Princeton University). Note: this video does not use audio.
References: Gomes et al, Nature 447 (2007), Pasupathy et al, Science 320 (2008).
Color scale to interpret plotting in the video: White=no gap and no pairs; Red=Strong gap and pairs.