{"id":82405,"date":"2025-02-04T14:04:44","date_gmt":"2025-02-04T13:04:44","guid":{"rendered":"https:\/\/aktuelles.uni-frankfurt.de\/?p=82405"},"modified":"2025-02-05T13:20:39","modified_gmt":"2025-02-05T12:20:39","slug":"quantum-leaps-in-materials-research","status":"publish","type":"post","link":"https:\/\/aktuelles.uni-frankfurt.de\/en\/english\/quantum-leaps-in-materials-research\/","title":{"rendered":"Quantum leaps in materials research"},"content":{"rendered":"

Quantum Research for new materials<\/strong><\/p>\n\n\n\n

100 years after the discovery of quantum mechanics, the International Quantum Year 2025 is being launched today in Paris. At the level of the smallest particles, conditions and laws prevail that seem to run counter to our intuitive understanding of physical processes. These include the phenomenon of superconductivity, where certain materials – cooled to very low temperatures – lose their electrical resistance. In the supraregional Collaborative Research Center ELASTO-Q-MAT, researchers are trying to produce materials with such \u201cquantum properties\u201d.  In \u201cForschung Frankfurt\u201d, Roser Valent\u00ed and Cornelius Krellner reveal how theory and experiment lead to quantum materials with surprising properties. (Research Frankfurt 1\/2023)<\/p>\n\n\n\n

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How crystals with surprising properties are produced in the laboratory and on the computer<\/h4>\n\n\n\n
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Protected by noble gases, crystals are formed in the heart of this apparatus by means of the Czochralski method (large picture p. 28 and detail above): a metal rod with a seed crystal is immersed in a melt and then slowly pulled out again so that the material can crystallize just below the melting point.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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That the microscopic world of atoms and molecules is governed by the laws of quantum physics has been known for a hundred years. For a long time, quantum phenomena were considered obscure and uncontrollable. Today, physicists are using quantum physical effects to develop materials with novel
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Cornelius Krellner, a physics professor originally from Dresden, is based at the Institute of Physics on Riedberg Campus in the north of Frankfurt. He swivels his chair round and opens the door of a mustard-colored cabinet, smiling mischievously at his hidden treasure. \u201cIn this cabinet, we have virtually all chemical elements in their purest form,\u201d says Krellner. It is a collection that you would tend to expect from a chemist. In this case, Krellner is using the chemical elements for his research in experimental physics. He produces crystals from them, that is, substances in which the atoms are arranged in a regular pattern. \u201cThanks to their ordered structure, crystals are particularly suitable for understanding the atomic structure of matter,\u201d says Krellner.<\/p>\n\n\n\n

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Superconducting quantum materials<\/strong><\/h3>\n\n\n\n

Cornelius Krellner is conducting research in the area of quantum materials. In a sense, every substance in the material world is a quantum one because every substance is made up of atoms, and their building blocks obey the laws of quantum physics. However, science defines \u201cquantum material\u201d more narrowly: here, the term refers to materials whose macroscopic properties are based on quantum effects. The most prominent example is superconductors. In these materials, electrical current flows without resistance \u2013 unlike in the copper conductors we are familiar with. Why this is the case can be explained by quantum physics: electrons move without resistance in superconductors because they join up to form agile pairs that are unstoppable.<\/p>\n\n\n\n

Superconductors have fascinating potential because they could in the future enable a power supply without transmission losses. It is therefore no surprise that researchers are looking for other quantum materials that have similarly useful properties. Cornelius Krellner has already produced several such materials. Krellner gives an example of a quantum material whose magnetic properties are puzzling: the substance loses its magnetic capability when it is compressed. To crystallize the material, Krellner used three elements from his mustard-colored cabinet: europium, palladium and silicon. These elements form a crystal, a regular lattice of unit cells. Each unit cell consists of one europium atom, two palladium atoms and two silicon atoms. The chemical formula EuPd2<\/sub>Si2<\/sub> is also the name of the quantum material: \u201ceuropium palladium two silicon two\u201d.<\/p>\n\n\n\n

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One electron makes all the difference<\/strong><\/h3>\n\n\n\n

\u201cThe interesting physics is in the europium,\u201d says Cornelius Krellner. To explain why this material loses its magnetism when compressed, he takes us on a journey into the microscopically small world of atoms. Europium is a rare earth metal. Sixty-three electrons orbit its atomic nucleus. They are distributed over six shells or 13 subshells. The subshell with one electron defines the distance to the atomic nucleus and its energy state. Of its 63 electrons, only one electron is responsible for the europium\u2019s magnetism, known as an 4f electron because it is usually located on the subshell 4f. However, when the crystal is compressed, the electron jumps from 4f to the subshell 5d.<\/p>\n\n\n\n

Although its energy state changes only imperceptibly, this quantum-physical process has two far-reaching consequences for the europium: it shrinks by about 20 percent \u2013 and it loses its magnetism. Through external pressure,the entire EuPd2<\/sub>Si2 <\/sub>crystal becomes non-magnetic. If the pressure is removed, the electrons from the subshell 5d return to their original position; the crystal becomes magnetic again. In the language of physics: through external manipulation, quantum materials perform a phase transition between two quantum states. For this effect to occur, the EuPd2<\/sub>Si2 <\/sub>crystal must be cooled to -100 \u00b0C.<\/p>\n\n\n\n

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IN A NUTSHELL<\/h5>\n\n\n\n