At normal temperatures, semiconducting perovskites display superfluorescence due to built-in thermal “shock absorbers” that insulate dipoles within the material from thermal interference. A recent study from North Carolina State University investigates the mechanism underlying this macroscopic quantum phase change and explains why materials such as perovskites exhibit macroscopic quantum coherence at high temperatures.
Consider a school of fish swimming in unison or fireflies flashing in unison—both are examples of collective activity in nature. When analogous collective behavior occurs in the quantum world—a phenomenon known as the macroscopic quantum phase transition—exotic processes such as superconductivity, superfluidity, or superfluorescence result. A set of quantum particles generates a macroscopically coherent system that operates like a big quantum particle in all of these operations.
Superfluorescence is a macroscopic quantum phase transition in which a population of tiny light-emitting dipoles forms a gigantic quantum dipole while simultaneously producing a burst of photons. Superfluorescence, like superconductivity and superfluidity, is generally found at cryogenic temperatures because the dipoles go out of phase too quickly to form a collectively coherent state.
“Our initial observations indicated that something was protecting these atoms from thermal disturbances at higher temperatures,”
Gundogdu says.
A team led by Kenan Gundogdu, professor of physics at NC State and corresponding author of a publication presenting the discovery, has detected superfluorescence in hybrid perovskites at room temperature.
“Our preliminary findings suggest that something is shielding these atoms from thermal disturbances at higher temperatures,” Gundogdu explains.
The researchers investigated the structure and optical characteristics of a commonly used lead-halide hybrid perovskite. In these materials, they observed the creation of polarons, which are quasiparticles composed of bound lattice motion and electrons. A set of atoms oscillating collectively is referred to as lattice motion. A polaron is formed when an electron attaches to these oscillating atoms.
“Our investigation revealed that the development of massive polarons results in the formation of a thermal vibrational noise filter mechanism that we named “Quantum Analog of Vibration Isolation,” or QAVI,” Gundogdu explains.
According to Franky So, NC State’s Walter and Ida Freeman Distinguished Professor of Materials Science and Engineering, “QAVI is a shock absorber in layman’s terms.” Once the shock absorbers protect the dipoles, they can synchronize and produce superfluorescence. ” So is the study’s co-author.
According to the researchers, QAVI is an inherent feature of certain materials, such as hybrid perovskites. On the other hand, understanding how this mechanism works could lead to quantum devices that can operate at a normal temperature.
Gundogdu says that understanding this method not only answers a big physics conundrum, but it may also help us find, select, and customize materials with features that allow extended quantum coherence and macroscopic quantum phase transitions.
The study was published in Nature Photonics and was funded by the National Science Foundation (grant 1729383) as well as NC State’s Research and Innovation Seed Funding. Melike Biliroglu and Gamze Findik, both graduate students at NC State, are co-first authors.
