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The Janus-face of the localized carrier in cuprates: Generating the pseudogap and high temperature superconductivity

Periodic Reporting for period 3 - TheONE (The Janus-face of the localized carrier in cuprates: Generating the pseudogap and high temperature superconductivity)

Reporting period: 2020-09-01 to 2022-02-28

The phenomenon of high-temperature (high-Tc) superconductivity (SC) is one of the most exciting, thoroughly investigated yet still unresolved problems in physics. A major difficulty in understanding high-Tc systems lies in the complexity of the materials and phase diagram. The delicate balance between material-specific properties, disorder and the number of electronic phases superimpose to make it difficult to identify the leading interactions. Consequently, theoretical models attempting to describe the high-Tc SC are significantly disparate and identifying the mechanism of SC at elevated temperatures is full of hardship.
Due to the proximity of the antiferromagnetic phase, the strong electronic interactions, the appearance of a pseudogap phenomenon etc., the electronic phase is considered an exotic, a non-Fermi Liquid and the coupling mechanism for Cooper pairs strange. However, led by novel experimental results, that are obtained within my ERC project, a phenomenological model was developed. It comprehensively captures key unconventional experimental results, including the temperature and the doping dependence of the pseudogap phenomenon, the strange-metal linear temperature dependence of the planar resistivity, and the doping dependence of the superfluid density. The experimental results, obtained within the project, and the success and simplicity of the presented model essentially confirmed the main hypotheses of the project. Namely:
•the charge carriers which couple to give high temperature superconductivity follow the well-known Fermi- liquid behavior;
•the pseudogap phenomenon corresponds to a gradual (Mott-like) localization of exactly ONE charge carrier per unit cell;
•and the “Glue” for pairing stems from a bosonic excitation of ONE localized carrier leading to a novel excitonic mechanism for SC.
Our findings greatly demystify the cuprate phase diagram and point to a particular “excitonic”, very local, superconducting pairing mechanism. Testing the proposed mechanism is in the current focus of my research. Several experimental probes, which combine uniaxial pressure, are presently being developed. Potentially our findings will give an enormous boost to the field of high-Tc superconductivity and correlated systems. Beyond finding the solution of a 30-year-old enigma, it would enable an educated search for new materials with potentially even higher Tc's
Simplicity of Hg1201 compared to YBCO. N. Barišić et al. Nature Phys. 9,761 (2013).