cupraatit

Cupraatit, known in English as cuprates, are a family of copper-oxide materials that have played a central role in the study of high-temperature superconductivity. They are layered compounds characterized by copper-oxide (CuO2) planes, which are crucial for their electronic properties. The superconducting behavior arises when the parent insulating compound is doped with charge carriers, typically holes, by chemical substitution or oxygen content adjustment.

Structure and composition

Cuprates typically feature CuO2 planes separated by charge-reservoir layers that control the doping level. The copper ions in these planes are coordinated by oxygen in a square-planar environment. The layering and ionic substitutions create complex, highly anisotropic structures that influence their electronic, magnetic, and superconducting properties. The general chemistry allows a wide range of compositions and structural families, including single-, bi-, and trilayer variants.

Electronic properties and phase diagram

Undoped cuprates are Mott insulators with antiferromagnetic order. Upon doping, they undergo a transition to a superconducting state within a dome-shaped region of the temperature-doping phase diagram. Cuprates also display a pseudogap phase and other unconventional electronic phenomena, making their behavior a subject of ongoing research. The mechanism behind their high critical temperatures remains a topic of debate, with theories emphasizing spin fluctuations, electron correlations, and, to a lesser extent, lattice interactions.

Notable members and record temperatures

Prominent cuprates include La2−xSrxCuO4 (LSCO), YBa2Cu3O7−δ (YBCO), Bi2Sr2CaCu2O8+δ (BSCCO), and HgBa2Ca2Cu3O8+δ (HBCCO). Tc values vary widely but some members exhibit superconductivity above the boiling point of liquid nitrogen, with records around 133–138 K at ambient pressure and higher under pressure.

Discovery and significance

Cuprates were discovered to superconduct around 1986 by Johannes Georg Bednorz and Karl Alexander Müller, leading to the 1987 Nobel Prize in Physics. They remain central to condensed-matter physics due to their unusual properties, potential applications in energy and electronics, and the ongoing challenge of understanding their underlying superconducting mechanism.