Fermions in flatland pair up at very high temperatures: Heidelberg physicists find evidence of an exotic state of matter
Using ultracold atoms, researchers at Heidelberg University have found an exotic state of matter where the constituent particles pair up when limited to two dimensions. The findings from the field of quantum physics may hold important clues to intriguing phenomena of superconductivity. The results were published in Science magazine.
In a known and well-understood scenario, pairing is caused solely by the attraction between two fermions (green lines). However, Heidelberg scientists found that with strong interactions between the fermions, a different type of pairing takes place, which strongly depends on the density of the surrounding medium (gray shaded regions). This suggests that in this state, each particle is not only paired with one other particle, but that there are additional correlations with other particles in its surroundings.
Figure: Puneet Murthy
Superconductors are materials through which electricity can flow without any resistance once they are cooled below a certain critical temperature. The technologically most relevant class of materials, with exceptionally high critical temperatures for superconductivity, is poorly understood so far. There is evidence, however, that in order for superconductivity to occur, a certain type of particles – the fermions – must pair up.
Moreover, research has shown that materials which become superconducting at relatively high temperatures have layered structures. “This means that electrons in these systems can only move in two-dimensional planes”, explains Prof. Dr Selim Jochim of Heidelberg University’s Institute for Physics, who heads the project. “What we did not understand until now was how the interplay of pairing and dimensionality can lead to higher critical temperatures.”
To explore this question, researchers at the Center for Quantum Dynamics performed experiments in which they confined a gas of ultracold atoms in two-dimensional traps which they created using focused laser beams. “In solid-state materials like copper oxides, there are many different effects and impurities that make these materials difficult to study.
That is why we use ultracold atoms to simulate the behaviour of electrons in solids. This allows us to create very clean samples and gives us full control over the essential system parameters”, says Puneet Murthy, a PhD student at the Center for Quantum Dynamics at Heidelberg University and one of the lead authors of this publication.
Using a technique known as radio-frequency spectroscopy, the researchers measured the response of the atoms to a radio-wave pulse. From this response, they could tell exactly whether or not the particles were paired and in what way. These measurements were also performed for different strengths of interaction between fermions.
In the course of the experiments, the researchers discovered an exotic state of matter. Theory states that fermions with a weak interaction should pair up at the temperature at which they become superconductive. However, when the scientists increased the interaction between fermions, they found that pairing occurred at temperatures several times higher than the critical temperature.
“To achieve our ultimate goal of better understanding these phenomena, we will start with small systems that we put together atom by atom”, says Prof. Jochim. The research project also involved scientists from Heidelberg University’s Institute for Theoretical Physics and from Simon Fraser University in Vancouver (Canada).
P. A. Murthy, M. Neidig, R. Klemt, L. Bayha, I. Boettcher, T. Enss, M. Holten, G. Zuern, P. Preiss, S. Jochim: High Temperature Pairing in a strongly interacting two-dimensional Fermi gas. Science (published online on 21 December 2017), doi: 10.1126/science.aan5950
Prof. Dr Selim Jochim
Institute for Physics
Center for Quantum Dynamics
Phone +49 6221 54-19472
Communications and Marketing
Phone +49 6221 54-2311
Marietta Fuhrmann-Koch | idw - Informationsdienst Wissenschaft
Structured light and nanomaterials open new ways to tailor light at the nanoscale
23.04.2018 | Academy of Finland
On the shape of the 'petal' for the dissipation curve
23.04.2018 | Lobachevsky University
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
24.04.2018 | Information Technology
24.04.2018 | Earth Sciences
24.04.2018 | Life Sciences