Quantum 'pseudogap' mystery solved, could lead to superfast trains
A team of researchers has made significant progress in understanding the pseudogap state of materials, a long-standing puzzle in quantum physics. The term "pseudogap" refers to an unusual behavior observed in certain materials like cuprates (copper oxides), which act as superconductors at extremely low temperatures (below -140 degree Celsius). However, these same materials display characteristics of a semiconductor or regular metal at higher temperatures.
Pseudogap's existence: A mystery for decades
The existence of a pseudogap in these materials is due to an incomplete gap in electron energy levels. This occurs when some electron pairs begin forming at higher temperatures, but do not fully transition into the superconducting state. The reasons behind the appearance of a pseudogap have been unknown for decades, until now. The research team has successfully decoded this quantum conundrum using a unique algorithm.
Challenge in decoding pseudogap
The complexity of the pseudogap state is due to quantum entanglement, a phenomenon where electrons are interconnected. This means that the state of one electron instantly affects the state of another, regardless of their distance apart. "Computing the properties of these materials is extraordinarily challenging—you can't simulate them exactly on even the most powerful computer you can think of," said Antoine Georges, a physicist at the Polytechnic Institute of Paris and one of the study authors.
Hubbard model and Monte Carlo algorithm: Tools for decoding
To overcome this challenge, the researchers used the Hubbard model, a mathematical framework that describes how electrons move and interact in a material. This model views materials like cuprates as chessboards, with their electrons acting like pawns. To calculate electron behavior from the Hubbard model, they employed the diagrammatic Monte Carlo algorithm. It can analyze electron interactions occurring across the entire chess board at once.
Monte Carlo algorithm reveals new details
The use of the diagrammatic Monte Carlo algorithm proved successful, revealing previously unknown details. For example, as a material in the pseudogap state approaches absolute zero temperatures, "electrons organize into rows of matching spins separated by rows of empty squares." These formations are known as stripes. The researchers also discovered that the pseudogap state is actually due to checkerboard patches appearing in electron arrangements.
A step toward room-temperature superconductors
These findings could aid scientists in developing practical room-temperature superconductors, contribute to their understanding of quantum gas simulation, faster MRI machines, and superfast levitating trains. However, "further work involving controlled ground-state studies will be necessary to clarify the fate of the pseudogap at low temperatures," the study authors added. The research has been published in the journal Science.
