Ionic-Bond-Driven Atom-Bridged Room-Temperature Cooper Pairing in Cuprates and Nickelates: a Theoretical Framework Supported by 32 Experimental Evidences

This paper proposes a theoretical framework asserting that high-temperature superconductivity in cuprates and nickelates is driven by ionic-bond-mediated electron pairing bridged by oxygen or metal atoms, a mechanism supported by 32 experimental evidences and offering a potential path toward room-temperature superconductivity.

The Gist

Imagine electricity as a busy highway. In a normal car (a regular conductor), cars drive alone. In a superconductor, the cars decide to drive in tight, synchronized pairs called Cooper pairs. These pairs move without any friction, allowing electricity to flow perfectly.

For 40 years, scientists have been trying to solve a massive mystery: What acts as the "glue" that holds these electron pairs together in high-temperature superconductors (like cuprates and nickelates)?

Most theories suggested the glue was a weak, subtle force, like a gentle whisper between neighbors. This paper proposes a completely different, much louder, and stronger idea.

The New Idea: The "Ionic Bridge"

The authors suggest that the glue isn't a whisper; it's a massive, powerful handshake driven by the fundamental chemistry of the materials.

Here is the analogy:
Imagine two people (electrons) trying to hold hands across a wide gap.

• Old Theory: They try to reach out with a tiny, weak string.
• This Paper's Theory: They don't reach out directly. Instead, they both grab onto a giant, sturdy oxygen atom (or a metal atom) standing in the middle. This atom acts like a bridge.

Because oxygen atoms love electrons so much (a chemical trait called "affinity"), they act like a super-strong magnet. The paper argues that the electrons are actually "bridged" by these atoms, forming a chain like Electron — Oxygen — Electron. This is driven by ionic bonding, which is the same super-strong force that holds salt together.

Why This Changes Everything

1. The "Footprint" Clue: The authors say, "Let's trace the footprints." If you look at the chemical structure of these materials, the strongest force present is this ionic bond (the oxygen bridge). Therefore, the superconductivity must be built on this foundation, not on some weak, invisible force.
2. The "Room Temperature" Dream: Because this ionic glue is so incredibly strong (much stronger than the weak forces proposed by others), it can hold the electron pairs together even when things get hot. This explains why these materials work at "high" temperatures and suggests that room-temperature superconductivity (superconductors that work in your living room) might actually be possible.
3. The Evidence: The authors claim they have found 32 different pieces of experimental evidence (like puzzle pieces) that all fit this picture. One of the strongest pieces is a microscopic photo (STM image) showing the electrons huddled around the oxygen atoms exactly as predicted.

The Bottom Line

Think of this paper as finding the missing link in a 40-year-old treasure hunt.

• The Problem: We knew superconductors worked, but we didn't know how the electrons stayed paired.
• The Solution: The electrons aren't floating alone; they are being held together by a strong, chemical bridge made of oxygen and metal atoms.
• The Result: This explains why these materials are so special, validates why they work at high temperatures, and gives us a new roadmap to build superconductors that could one day power our world without any energy loss, even at room temperature.

In short: The secret to superconductivity isn't a whisper; it's a chemical handshake.

Technical Summary

Based on the abstract provided for the paper "Ionic-Bond-Driven Atom-Bridged Room-Temperature Cooper Pairing in Cuprates and Nickelates: a Theoretical Framework Supported by 32 Experimental Evidences" (arXiv:2503.13104v4), here is a detailed technical summary:

1. Problem Statement

Despite over four decades of intense research, the fundamental mechanism holding electrons together to form Cooper pairs in high-temperature superconductors (specifically cuprates and nickelates) remains unresolved. Conventional theories often rely on sub-eV interactions or covalent bonding models, which the authors argue are insufficient to explain the observed phenomena in these oxide materials. The core challenge is identifying the specific force that enables electron pairing at temperatures significantly higher than those predicted by standard BCS theory, potentially up to room temperature.

2. Methodology and Theoretical Framework

The authors propose a paradigm shift by grounding their theory in fundamental chemical principles rather than purely phenomenological models. Their methodology involves:

• Chemical-Bond-Driven Analysis: Adhering to the "chemical-bond $\rightarrow$ structure $\rightarrow$ property" relationship, the authors focus on the dominance of ionic bonding in these oxides.
• Energetic Considerations: They analyze specific energetic parameters, including:
  • The electron affinity of Oxygen ($O^-$: 1.46 eV; $O^{2-}$: -8.08 eV).
  • The large two-electron ionization energy of metal atoms (approx. 15–28 eV).
  • The scale of ionic bonding (eV range), contrasting it with weaker sub-eV mechanisms.
• Mechanism Proposal: They introduce the concept of atom-bridged itinerant Cooper pairing. Instead of direct electron-electron attraction mediated by phonons or spin fluctuations, they propose that electrons (or holes) are paired via a bridging atom:
  • Electron Pairing: $\mathbf{e^--O-e^-}$ (bridged by Oxygen).
  • Hole Pairing: $\mathbf{h^+-M-h^+}$ (bridged by Metal).
• Validation Strategy: The theory is tested against a comprehensive dataset of 32 diverse experimental evidences, with a specific emphasis on Scanning Tunneling Microscopy (STM) images of the $CuO_2$ plane and measurements of small pair sizes.

3. Key Contributions

• New Pairing Mechanism: The paper defines a novel mechanism where ionic bonding drives the formation of Cooper pairs at the pseudogap temperature ($T^*$), which is higher than the critical temperature ($T_c$).
• Universality: The framework is claimed to be applicable not only to cuprates but also to nickelates, iron-based superconductors, and other new ionic superconductors.
• Resolution of the "Missing Link": It establishes a direct theoretical connection between ionic bonding and superconductivity, resolving a 40-year puzzle regarding the pairing glue in high-$T_c$ materials.
• Exclusion of Competing Theories: The authors argue that any pairing mechanism relying solely on sub-eV energies or covalent binding is doubtful given the energetic landscape of these materials.

4. Results and Evidence

• Experimental Confirmation: The proposed $\mathbf{e^--O-e^-}$ and $\mathbf{h^+-M-h^+}$ models are supported by 32 distinct experimental observations.
• STM Correlation: A critical piece of evidence is the correlation between STM images in the $CuO_2$ plane and the calculated small size of the Cooper pairs, which aligns with the atom-bridged model.
• Bose-Einstein Condensation (BEC): The framework suggests that these pairs exhibit the strongest pairing strength, facilitating a transition to Bose-Einstein condensation, a key requirement for high-temperature superconductivity.
• Room-Temperature Feasibility: Theoretical calculations based on this framework validate the feasibility of achieving room-temperature carrier pairing in ionic superconductors.

5. Significance

• Theoretical Breakthrough: This work provides a definitive answer to the long-standing question of the pairing mechanism in high-$T_c$ superconductors, shifting the focus from weak coupling to strong ionic bonding.
• Technological Impact: By validating the feasibility of room-temperature superconductivity through ionic bonding, the paper opens a new avenue for designing materials that could operate without cryogenic cooling.
• Paradigm Shift: It challenges the prevailing sub-eV/covalent-centric views in condensed matter physics, proposing that the "footprints" of electrons in ionic lattices reveal a much stronger and more robust pairing interaction than previously assumed.

In summary, the paper argues that high-temperature superconductivity in oxides is driven by strong ionic interactions where oxygen or metal atoms act as bridges for electron/hole pairing, a mechanism supported by extensive experimental data and capable of explaining room-temperature superconductivity.