An ultrapure material taken to pressures greater than that in the depths of the ocean and chilled to temperatures colder than outer space has revealed an unexpected phase transition that crosses two different phase categories.
A Purdue University-led team of researchers observed electrons transition from a topologically ordered phase to a broken symmetry phase.
"To our knowledge, a transition across the two groups of phases had not been unambiguously demonstrated before, and existing theories cannot describe it," said Gábor Csáthy, an associate professor in Purdue's Department of Physics and Astronomy who led the research. "It is something like changing water from liquid to ice; except the two phases we saw were very different from one another."
A phase is a certain organization of matter. Most people know the ice, liquid and gas phases, and some are familiar with the different magnetic phases that store data in our electronic devices and the liquid crystalline phases that are used to create an image on certain electronic displays, but there are many other phases, Csáthy said.
In 1937 physicist Lev Landau established a theoretical framework that explained and classified all of the known phases, but in the late 1980s it was realized that there existed a second group of phases that occur at very low temperatures that do not fit in Landau's theory. The new phases were named topological phases, while the traditional phases described by Landau's theory are called broken symmetry phases.
[Wikipedia] topological order is a kind of order in zero-temperature phase of matter (also known as quantum matter). Macroscopically, topological order is defined/described by robust ground state degeneracy and quantized non-Abelian geometric phases of degenerate ground states (just like superfluid order is defined/described by vanishing viscosity and quantized vorticity). Microscopically, topological order corresponds to patterns of long-range quantum entanglement (just like superfluid order corresponds to boson condensation). States with different topological orders (or different patterns of long range entanglements) cannot change into each other without a phase transition.
Topologically ordered states have some scientifically interesting properties, such as ground state degeneracy that cannot be lifted by any local perturbations but depends on the topology of space, quasiparticle fractional statistics and fractional charges, perfect conducting edge states even in presence of magnetic impurities, topological entanglement entropy, etc. Topological order is important in the study of several physical systems such as spin liquids the quantum Hall effect, along with potential applications to fault-tolerant quantum computation.
Some suggest that topological order (or more precisely, string-net condensation) in local bosonic (spin) models have the potential to provide a unified origin for photons, electrons and other elementary particles in our universe
Purdue University professor Gábor Csáthy and graduate student Katherine Schreiber inspect equipment used to cool samples to near absolute zero. The equipment was used in Purdue-led research that led to the observation of an unexpected phase transition in an ultrapure material. (Purdue University photo/Mark Simons)
Nature Physics - Observation of a transition from a topologically ordered to a spontaneously broken symmetry phase
Read more »
