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Quantum phase transitions in metals

In the realm of , certain substances undergo phase transitions with fascinating properties that differ from macroscopic examples like water freezing. Researchers at the University of Bonn and ETH Zurich have made groundbreaking discoveries, revealing that near these exotic phase transitions, the conventional concept of electrons as carriers of quantized electric charge might not hold true.

Their findings, published in Nature Physics, shed light on the mysterious world of . Unlike typical phase transitions, where substances like water solidify into ice with abrupt changes in properties, these exotic transitions involve gradual shifts in characteristic features. For instance, when iron is heated to 760 degrees Celsius, it transitions from ferromagnetic to paramagnetic state, with its atoms acting as tiny magnets.

At lower temperatures, the iron atoms align parallel to each other, exhibiting some degree of ferromagnetism. As the temperature rises, they fluctuate around this alignment until they become randomly oriented, causing the material to lose its magnetism entirely. This unique behavior opens up exciting new insights into the captivating world of quantum physics.

Matter particles cannot be destroyed

In the fascinating world of continuous phase transitions, like the one observed in iron's shift from ferromagnetic to paramagnetic states, the process occurs gradually, with the transition slowing down as it progresses. This , known as “critical slowing down,” is a result of the two phases getting energetically closer and closer together.

To understand this, think of a ball on a ramp—it rolls downhill, but as the height difference decreases, its speed slows down. Similarly, when iron is heated, the energy difference between its magnetic phases decreases gradually, causing the magnetization to vanish during the transition.

Continuous phase transitions are driven by the excitation of bosons, particles responsible for interactions like magnetism. In contrast, matter consists of fermions, such as electrons, which do not generate interactions and cannot be destroyed due to fundamental laws of nature.

Typically, fermions are not involved in phase transitions because they cannot vanish like bosons. However, the exotic phase transitions near quantum mechanics' smallest building blocks challenge this norm, revealing intriguing insights into the interactions and behaviors of these .

Electrons turn into quasi-particles

Electrons in atoms are bound to fixed positions, while in metals, some electrons are freely mobile, allowing the metal to conduct electricity. However, in exotic quantum materials, both types of electrons can combine to form quasiparticles—a remarkable state where they are simultaneously immobile and mobile, a unique feature only possible in the quantum realm.

These quasiparticles, unlike regular electrons, can be destroyed during a phase transition, exhibiting critical slowing down—a behavior characteristic of continuous phase transitions. Until now, this effect was observed indirectly, but a team of researchers led by theoretical physicist Hans Kroha and Manfred Fiebig's experimental group at ETH Zurich has developed a new method for direct identification of quasiparticle collapse and associated critical slowing down.

By using this method, they showed for the first time that fermions, like electrons, can also experience critical slowing down during phase transitions. This discovery enhances our understanding of phase transitions in the quantum world and holds potential implications for applications in quantum information technology in the long run.

Source: University of Bonn

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