FeSe (Tetragonal Phase)

FeSe (Iron Selenide) is an iron-based superconductor that has attracted significant interest due to its fascinating electronic properties and potential applications in high-temperature superconductivity. The tetragonal phase of FeSe refers to its crystal structure, which exhibits different superconducting properties compared to other phases, such as the orthorhombic phase. The tetragonal phase of FeSe has been extensively studied, particularly for its relatively simple structure and potential for further research into the mechanisms of high-temperature superconductivity.

Physical Properties

• Appearance: FeSe typically appears as a dark-colored solid. In its tetragonal phase, it often forms small, crystalline grains.
• Crystal Structure: In the tetragonal phase, FeSe adopts a body-centered tetragonal (BCT) structure, with Fe atoms arranged in a square lattice and Se atoms positioned above and below this plane. This structure is characterized by strong covalent bonding between Fe and Se atoms.
• Superconductivity: FeSe (tetragonal phase) is a type-II superconductor, with a relatively high superconducting transition temperature (Tₛ) for an iron-based superconductor, around 8 K in bulk form. Under certain conditions, such as pressure, the superconducting transition temperature can increase significantly, with some studies showing a superconducting transition temperature up to 37 K when subjected to high pressure.
• Magnetic Properties: FeSe does not exhibit long-range magnetic ordering in its tetragonal phase, but it shows a strong correlation between superconductivity and magnetism, which is a characteristic of iron-based superconductors. The lack of magnetic ordering in the tetragonal phase makes it unique compared to other iron-based superconductors.
• Electronic Properties: The electronic structure of FeSe in its tetragonal phase is typically metallic, exhibiting strong electron correlation effects. It shows a significant Fermi surface, with both hole-like and electron-like pockets, which are important for understanding its superconducting behavior.

Applications

1. Superconducting Materials: FeSe is primarily studied for its superconducting properties, particularly in the search for high-temperature superconductors. Its relatively simple crystal structure compared to other iron-based superconductors makes it an ideal material for fundamental studies on superconductivity and pairing mechanisms.

2. Quantum Computing: FeSe's superconducting properties are of interest for potential applications in quantum computing, especially in the development of qubits based on superconducting circuits. Its superconductivity could enable the design of more efficient and stable quantum computers.

3. Energy Transmission: Due to its superconducting properties, FeSe could potentially be used in applications related to energy transmission, such as power cables, magnets, and transformers that require low-energy loss and high efficiency.

4. High-Pressure Research: The behavior of FeSe under high pressure has led to significant interest in understanding how pressure affects superconductivity. Studies of FeSe under extreme conditions may provide insights into the mechanism of high-temperature superconductivity in iron-based materials.