Because their critical temperatures exceed the boiling point of liquid nitrogen (77 K), these materials are classified as high-temperature superconductors.

Figure 1. New Tunneling Technique Reveals Hidden Traits of High-Temperature Superconductors.

A fundamental feature of superconductivity is the superconducting gap—a crucial property that indicates how electrons pair to form the superconducting state. Detecting this gap is vital for distinguishing the superconducting phase from normal metallic behavior. Figure 1 shows New Tunneling Technique Reveals Hidden Traits of High-Temperature Superconductors.

However, measuring the superconducting gap in hydrogen-rich materials such as H₃S has been extremely difficult. These compounds must be synthesized under ultra-high pressures—over one million times atmospheric pressure—using diamond anvil cells. Under these extreme conditions, conventional measurement techniques like scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) are not practical.

About Superconductivity

Superconductivity is a remarkable property of certain materials that allows them to conduct electrical current with zero resistance. It was first discovered in pure mercury by Heike Kamerlingh Onnes in 1911. For many years, this phenomenon was believed to occur only at extremely low temperatures, close to absolute zero (–273 °C). This view changed in the late 1980s when Georg Bednorz and Karl Alexander Müller discovered a new family of copper-oxide (cuprate) superconductors that exhibited high-temperature superconductivity at atmospheric pressure.

This breakthrough sparked intense global research, leading to materials with critical temperatures (Tc)—the temperature below which a material becomes superconducting—reaching about 133 K at ambient pressure and 164 K under high pressure. Yet, no superconductor with a higher Tc had been found—until the emergence of hydrogen-rich compounds.

The discovery of superconductivity in H₃S at megabar pressures, with a Tc of 203 K by the research group led by Dr. Mikhail Eremets, marked a revolutionary step toward superconductivity near room temperature. This breakthrough was soon followed by hydrogen-rich metal hydrides exhibiting even higher Tc values, such as YH₉ (Tc ≈ 244 K) and LaH₁₀ (Tc ≈ 250 K). Today, theoretical models predict superconductivity above room temperature in several hydrogen-dominated systems under extreme pressures.

About Cooper Pairs and the Superconducting Gap

In ordinary metals, electrons with energy levels near the Fermi level can move freely. The Fermi level represents the highest energy level that electrons occupy in a solid at absolute zero. However, when a material transitions into a superconducting state, electrons pair up to form so-called Cooper pairs, entering a collective quantum state. This highly correlated state allows the Cooper pairs to move through the crystal lattice as a single entity without scattering off phonons or impurities, resulting in zero electrical resistance.

This electron pairing is marked by an energy gap near the Fermi level—the superconducting gap—which is the minimum energy required to break a Cooper pair apart. The presence of this gap protects the superconducting state from disturbances such as scattering.

The superconducting gap is the defining characteristic of a superconductor’s quantum state. Its magnitude and symmetry provide crucial insights into how electrons interact and pair, acting as a unique fingerprint of the underlying superconducting mechanism.

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2025), Innovative Tunneling Method Uncovers Hidden Characteristics of High-Temperature Superconductors, AnaTechMaz, pp. 283