In everyday scenarios, phase transitions can be abrupt, like water freezing into ice, resulting in an instant change in physical properties. On the other hand, some transitions are gradual. Consider an iron magnet heated to 760 degrees Celsius; it does not lose its ferromagnetic properties all at once but transitions slowly into a paramagnetic state. This transition exhibits a characteristic 'critical slowing down', where the change progressively slows as the energy difference between the two phases diminishes.
However, this typical behaviour is commonly associated with bosons, particles that mediate interactions such as magnetism. This does not pertain to fermions like electrons, the primary constituents of matter, due to a fundamental law of nature that prevents their destruction. Prof. Dr. Hans Kroha of the Bethe Center for Theoretical Physics at the University of Bonn states, "Fermions, however, cannot be destroyed due to fundamental laws of nature and therefore cannot disappear. That's why normally they are never involved in phase transitions."
But the team's groundbreaking research turns this conventional wisdom on its head when it comes to certain unique quantum materials. In these materials, some electrons can exist in a superposition state, forming what are known as quasiparticles. These quasiparticles are both mobile and immobile at the same time - a paradox only possible in the quantum world. Unlike ordinary electrons, these quasiparticles can be destroyed during a phase transition, enabling the observation of properties such as critical slowing down in these instances.
Previously, scientists could only infer this effect indirectly from experiments. However, this collaborative study led by theoretical physicist Hans Kroha, with Manfred Fiebig's experimental group at ETH Zurich, has pioneered a method that directly identifies the collapse of quasiparticles at a phase transition, specifically the associated critical slowing down.
In sharing their findings, Kroha, also a member of the Transdisciplinary Research Area "Matter" at the University of Bonn and the Cluster of Excellence "Matter and Light for Quantum Computing" of the German Research Foundation, said, "This has enabled us to show for the first time directly that such a slowdown can also occur in fermions."
This insight significantly enhances our understanding of phase transitions in the quantum realm. Furthermore, the implications of this research may extend beyond theoretical physics, potentially proving valuable in developing quantum information technology in the future.
Research Report:Critical slowing down near a magnetic quantum phase transition with fermionic breakdown
Related Links
University of Bonn
Understanding Time and Space
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