A versatile experimental platform for studying the complex phases of quantum systems characterized by two order parameters
As a physical system undergoes a phase transition, it typically becomes more --- or, less --- ordered. For instance, when a piece of iron is heated to above the Curie temperature, the strong ferromagnetic alignment of the elementary magnetic dipole moments gives way to much weaker paramagnetic alignment.
Phase diagrams showing the four different regions observed in the experiment: white -- superfluid without photons; red and yellow -- photons in only one of the cavities; blue -- photons in both cavities simultaneously (mixed phase). As the coupling between the orders is increased, the mixed-phase regime (blue) becomes increasingly favourable.
Credit: Esslinger group, ETH Zurich (adapted from doi: 10.1038/s41563-018-0118-1)
Such changes are well described in the general framework of order parameters, provided by the Landau theory of phase transitions. However, many materials of current fundamental and technological interest are characterised by more than one order parameter. And here the situation can become extraordinarily complex rather quickly, in particular when the different orders interact with one another.
The traditional route to gaining an understanding of such complex quantum systems is, simply speaking, to carefully explore the response to changes in external conditions and to various probes, and thus to map out the phase diagram of the system. A complementary approach is now presented by Tobias Donner and his team in the group of Tilman Esslinger in the Department of Physics of ETH Zurich.
They control all relevant microscopic parameters of a quantum system governed by two coupled order parameters and therefore can essentially construct, and modify, the phase diagram from bottom up, as they report in a paper published today in the journal Nature Materials.
Phenomenological models that reproduce the experimentally determined phase diagrams of materials with one or more ordering tendencies have provided deep insight into the behaviour of a variety of systems, such as multiferroics --- where a material exhibits simultaneously ferromagnetism and ferroelectrism, opening the door to new functionality --- or certain families of superconductors.
However, the microscopic processes underlying the formation of macroscopic order in these systems remain often unknown. This gap in understanding limits the predictive power of phenomenological models and at the same time makes it difficult to know just how a given material should be modified to obtain desired properties.
Hence the appeal of the approach taken by Donner and his colleagues, who started not with a specific system and its phenomenological description, but with a flexible quantum system whose relevant microscopic parameters can be controlled with high accuracy, and be tuned across a broad range of values, enabling the realization of diverse scenarios.
To create such a versatile platform, the team optically trapped a Bose-Einstein condensate (BEC) at the intersection of two optical cavity modes (see the figure). In this configuration, the BEC can crystallise in two different patterns, each of which is associated with a different order parameter.
Depending on the experimental setting, the two orders either competed with one another --- forcing the system into one of the two patterns (red and yellow) --- or to coexists, leading to a new coupled phase (blue), where the two orders do not simply add, but give rise to a more complex spatial arrangement. The extent of this mixed-order phase can be controlled as well, to favour regimes of mutual exclusion or of mutual enhancement.
Whereas these particular phases have no known direct role in practical materials, the approach established with these experiments can be modified to simulate in the future properties of materials that are technologically highly relevant indeed.
In particular, in cuprate high-temperature superconductors coupled spin and charge order are know to have an important, yet not fully understood role. The sort of experiments now pioneered by the ETH physicists should offer a unique tool to explore such phases --- and various others --- starting from a 'clean' quantum system with well-controlled and widely tunable interactions.
Andreas Trabesinger | EurekAlert!
Hubble finds tiny 'electric soccer balls' in space, helps solve interstellar mystery
26.06.2019 | NASA/Goddard Space Flight Center
Cyanide compounds discovered in meteorites may hold clues to the origin of life
26.06.2019 | NASA/Goddard Space Flight Center
From June 25th to 27th 2019, the Fraunhofer Institute for Digital Media Technology IDMT in Ilmenau (Germany) will be presenting a new solution for acoustic quality inspection allowing contact-free, non-destructive testing of manufactured parts and components. The method which has reached Technology Readiness Level 6 already, is currently being successfully tested in practical use together with a number of industrial partners.
Reducing machine downtime, manufacturing defects, and excessive scrap
The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.
Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...
The well-known representation of chemical elements is just one example of how objects can be arranged and classified
The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...
Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.
Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...
Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.
The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...
24.06.2019 | Event News
29.04.2019 | Event News
17.04.2019 | Event News
26.06.2019 | Materials Sciences
26.06.2019 | Physics and Astronomy
26.06.2019 | Health and Medicine