Periodic Reporting for period 4 - TheONE (The Janus-face of the localized carrier in cuprates: Generating the pseudogap and high temperature superconductivity)
Berichtszeitraum: 2022-03-01 bis 2023-08-31
The phenomenon of high-temperature (high-Tc) superconductivity (SC) remains one of the most intriguing and extensively studied yet unresolved challenges in physics. Beyond its conceptual significance, high-Tc SC harbors the formidable potential to revolutionize key societal aspects, including improvements in energy efficiency, the development of innovative transportation systems, advancements in medical diagnostics, enhancements in renewable energy technologies, revolutions in electronics, and applications in various industrial processes.
However, the complexity of cuprate compounds and their associated phase diagrams poses a formidable challenge in understanding high-Tc systems. Despite the similarity in the manifestation of superconductivity across all compounds, suggesting a common underlying mechanism, the intricate balance between material-specific properties, disorder, and the number of electronic phases makes it challenging to identify the leading interactions. Consequently, theoretical models attempting to describe high-Tc SC vary significantly, and identifying the mechanism of superconductivity at elevated temperatures proves to be a challenging task.
The primary objective of this project is to distinguish the key universal properties associated with superconductivity from those that are compound-specific. By pinpointing these universalities, the aim is to isolate those relevant to the superconducting mechanism. Additionally, by addressing compound-specific properties, the goal is to understand how superconducting properties are tuned. Ultimately, the project aims to propose an explanation for normal state properties and suggest a possible superconducting mechanism.
However, the complexity of cuprate compounds and their associated phase diagrams poses a formidable challenge in understanding high-Tc systems. Despite the similarity in the manifestation of superconductivity across all compounds, suggesting a common underlying mechanism, the intricate balance between material-specific properties, disorder, and the number of electronic phases makes it challenging to identify the leading interactions. Consequently, theoretical models attempting to describe high-Tc SC vary significantly, and identifying the mechanism of superconductivity at elevated temperatures proves to be a challenging task.
The primary objective of this project is to distinguish the key universal properties associated with superconductivity from those that are compound-specific. By pinpointing these universalities, the aim is to isolate those relevant to the superconducting mechanism. Additionally, by addressing compound-specific properties, the goal is to understand how superconducting properties are tuned. Ultimately, the project aims to propose an explanation for normal state properties and suggest a possible superconducting mechanism.
Due to the proximity of the insulating antiferromagnetic phase, strong electronic interactions, and the presence of the pseudogap phenomenon, the electronic phase of cuprate compounds is regarded as exotic and non-Fermi Liquid, resulting in a peculiar and unknown coupling mechanism for Cooper pairs. However, novel experimental results obtained within TheONE ERC project are entirely reshaping our understanding of these remarkable compounds, with the cornerstone being the discovery of universal conductance, unveiling the existence of two electronic subsystems.
The overall electronic system comprises 1+p charges, where p represents doping. At low dopings, precisely ONE hole is localized per planar CuO2 unit. As doping and temperature increase, the ONE hole gradually transitions from localized to itinerant. Remarkably, the itinerant holes exhibit an identical Fermi liquid character across the cuprate phase diagram, enabling a straightforward count of carrier density, thereby providing a comprehensive understanding of key features in the normal and superconducting states. These features include the pseudogap phenomenon, the linear temperature dependence of planar resistivity in the strange-metal state, as well as the doping dependence of the superfluid density.
By carefully addressing compound-specific properties, a key parameter tuning Tc among different compounds was identified—the degree of degeneracy of planar oxygens, which tunes the distribution of the ONE localized charge within the CuO2 unit. A proposed superconducting mechanism aligns with key experimental facts. The base of this mechanism is the interaction of fast Fermi liquid carriers with TheONE per CuO2 unit localized hole. The shift in the microscopic nature of chemical bonding in the copper oxide planes, from ionic to covalent, is considered pivotal in explaining the phase diagram of these captivating compounds.
The obtained results have been successfully published in papers featured in the highest-rated journals and presented at several dozen international conferences. Special emphasis has been placed on outreach efforts, including interviews with the Principal Investigator (PI) on radio and television, along with newspaper articles that articulate the significance of these discoveries for a broad audience.
The overall electronic system comprises 1+p charges, where p represents doping. At low dopings, precisely ONE hole is localized per planar CuO2 unit. As doping and temperature increase, the ONE hole gradually transitions from localized to itinerant. Remarkably, the itinerant holes exhibit an identical Fermi liquid character across the cuprate phase diagram, enabling a straightforward count of carrier density, thereby providing a comprehensive understanding of key features in the normal and superconducting states. These features include the pseudogap phenomenon, the linear temperature dependence of planar resistivity in the strange-metal state, as well as the doping dependence of the superfluid density.
By carefully addressing compound-specific properties, a key parameter tuning Tc among different compounds was identified—the degree of degeneracy of planar oxygens, which tunes the distribution of the ONE localized charge within the CuO2 unit. A proposed superconducting mechanism aligns with key experimental facts. The base of this mechanism is the interaction of fast Fermi liquid carriers with TheONE per CuO2 unit localized hole. The shift in the microscopic nature of chemical bonding in the copper oxide planes, from ionic to covalent, is considered pivotal in explaining the phase diagram of these captivating compounds.
The obtained results have been successfully published in papers featured in the highest-rated journals and presented at several dozen international conferences. Special emphasis has been placed on outreach efforts, including interviews with the Principal Investigator (PI) on radio and television, along with newspaper articles that articulate the significance of these discoveries for a broad audience.
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 PI's 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