Understanding Superconductivity at Low Temperatures and Room Temperature: A Comprehensive Guide

Material science presents a fascinating array of conducting properties, particularly with the phenomenon of superconductivity. Low temperatures can transform some materials into superconductors, enabling them to conduct electricity with zero resistance. However, why do these materials behave differently at different temperatures?

Electrical Conductivity and Molecular Structures

Depending on its molecular structure, all metals conduct electricity to varying extents. For instance, when the conductivity of all metals is measured with equal cross-sectional areas, and copper is taken as the reference (with a conductivity value of 1 at 20°C), silver has the highest conductivity (greater than 1), while the conductivities of other metals are generally lower. Additionally, the conductivity of any conductor drops as it is heated. Curiously, when cooled, the conductivity of metals tends to increase. Copper, for example, when cooled near absolute zero (-273°C), shows its resistance to electricity approaching zero, indicating an infinite flow of electricity. This phenomenon is utilized in the development of levitating trains, where superconducting materials are used in conjunction with magnetic fields to achieve high speeds.

Superconductivity of Specific Materials

While metals are the primary candidates for superconductivity, it is not exclusive to them. An alloy like NiChrome, known for its low conductivity, is used in heating coils due to its high resistance to the flow of electricity. Nonetheless, certain materials exhibit superconductivity even at high temperatures. For example, superconducting alloys discovered in 1986 by Bednorz and Müller, along with carbon nanotubes and graphene, can achieve superconductivity at temperatures above room temperature. These high-temperature superconductors revolutionize various industrial and scientific applications, reducing the need for supercooling to near absolute zero.

The Discovery and Theories of Superconductivity

The phenomenon of superconductivity was first discovered in 1911 by Kamerlingh Onnes, who observed it in metals at temperatures around a few degrees Kelvin. Over the years, scientists have proposed theories to explain this phenomenon, with the BCS (Bardeen, Cooper, and Schrieffer) theory being a significant milestone. According to BCS, an attractive interaction (U) between electrons with opposite spins is induced by lattice vibrations (phonons), which results in electron pairing at specific temperatures as described by the equation T1.14 Q exp-1/UD, where Q is the Debye temperature.

The Challenges of High-Temperature Superconductors

Although the BCS theory provides a framework for understanding superconductivity in certain metals, its applicability to high-temperature superconductors remains a topic of ongoing debate. This is because the interaction U is not universally attractive for all metals; minimal impurities or disorder can significantly impact the results. Therefore, it is still not definitively known if certain metals will achieve superconductivity at absolute zero, let alone at higher temperatures.

As a result, researchers continue to develop new materials, particularly composite metal oxides, aimed at achieving superconductivity at room temperature. This quest is crucial for widespread practical applications, reducing the energy costs associated with maintaining extremely low temperatures. The current journey into the realm of superconductivity demonstrates the intricate relationship between material properties, temperature, and electrical conductivity, offering immense potential for technological advancements and scientific discoveries.