Substances undergo phase transitions when cooled below critical temperatures, altering their properties. Such changes are evident in familiar cases like water freezing into ice. However, certain metals exhibit unique phase transitions at the quantum level, where classical laws may not apply.
Researchers from the University of Bonn and ETH Zurich have made significant strides in understanding these exotic quantum phase transitions. They have discovered that the traditional concept of electrons as carriers of quantized electric charge might not hold near these transitions.
While freezing water causes a sudden change in density, some phase transitions in metals occur gradually. For instance, when heating an iron magnet to 760 degrees Celsius, it shifts from being ferromagnetic to paramagnetic. During this process, the alignment of iron atoms gradually changes until they lose their magnetism entirely.
These findings, published in Nature Physics, offer intriguing insights into the fascinating world of quantum physics, unveiling new possibilities for understanding the behavior of matter at its smallest scale.
Matter particles cannot be destroyed
In the realm of continuous phase transitions, like the shift from ferromagnetic to paramagnetic in iron, the transformation occurs gradually. This phenomenon, known as “critical slowing down,” is due to the two phases getting energetically closer as the transition progresses. Picture a ball on a ramp—it rolls downhill, but the smaller the difference in altitude, the slower it moves. Similarly, as iron is heated, the energy difference between the phases decreases, causing the transition to decelerate, especially as the magnetization diminishes.
Continuous phase transitions typically involve bosons, particles responsible for interactions like magnetism. In contrast, matter is composed of fermions, such as electrons, which don’t generate interactions and don’t usually play a role in phase transitions. The uniqueness of the iron phase transition lies in the fact that particles or their related phenomena are gradually disappearing. As fewer atoms align in parallel, the magnetism diminishes, but fermions cannot be destroyed due to fundamental laws of nature, making them typically uninvolved in phase transitions. This new understanding provides valuable insights into the fascinating world of quantum physics.
Electrons turn into quasi-particles
In atoms, electrons are bound and confined to specific positions, while in metals, some electrons are free to move, allowing the metal to conduct electricity. In exotic quantum materials, a fascinating phenomenon occurs where both types of electrons can combine to form quasiparticles. These quasiparticles possess a unique property of being simultaneously immobile and mobile, a characteristic exclusive to the quantum realm.
Unlike “normal” electrons, quasiparticles can be destroyed during a phase transition, leading to properties resembling critical slowing down in continuous phase transitions. While this effect was previously observed indirectly in experiments, researchers, led by theoretical physicist Hans Kroha and Manfred Fiebig’s experimental group at ETH Zurich, have developed a new method to directly identify the collapse of quasiparticles during phase transitions.
Through this breakthrough, they have demonstrated that such slowdowns can also occur in fermions, which are particles like electrons. This discovery provides valuable insights into phase transitions in the quantum world and may have future applications in quantum information technology. Understanding these exotic phenomena unlocks exciting possibilities for exploring quantum physics and its potential technological implications.