You know the states of matter that we encounter every day – such as solid, liquid and gas – but in more exotic and extreme conditions, new states can arise, and scientists from the United States and China have discovered some one earlier this year.
They call it the Bose-liquid chiral state and, as with every new arrangement of particles we discover, it can tell us more about the structure and mechanisms of the Universe around us – and in particular, at super-small quantum level. ladder.
States of matter describe how particles can interact with each other, giving rise to structures and various ways of behaving. Lock the atoms in place and you get a solid. Let them flow, you have a liquid or a gas. Force charged partnerships aside, you have plasma.
The quantum landscape offers particles even stranger ways to interact, enabling unique behaviors better described in terms of possibilities and energy.
The researchers discovered the new state through a frustrated quantum system. Simply put, it is a system with built-in constraints that prevent particles from interacting as they usually would (hence the frustration).
These constraints – and the resulting frustration – can lead to exciting results for scientists. Here, the researchers focused on electrons and used the analogy of a board game to explain what’s happening.
“It’s like a game of musical chairs, designed to frustrate the electrons,” said Tigran Sedrakyan, a theoretical condensed matter physicist at the University of Massachusetts Amherst.
“Instead of each electron having a chair to go to, it now has to move around and have many options for where it sits.”
The system the researchers developed was a two-layer semiconductor device: an upper layer rich in electrons and a lower layer with many available holes through which electrons can move naturally. The twist? There aren’t enough holes for all the electrons.
Although this type of system remains difficult to observe, the team used an ultra-strong magnetic field to measure the movement of electrons, revealing the first evidence of the new bose-liquid chiral state.
“At the edge of the semiconductor bilayer, electrons and holes move with the same speeds,” said physicist Lingjie Du of Nanjing University in China.
“This leads to helical-like transport, which can be further modulated by external magnetic fields as the electron and hole channels are gradually separated under higher fields.”
This new state revealed some rather interesting properties. For example, electrons will freeze in a predictable pattern and fixed spin direction at absolute zero and cannot be interfered with by other particles or magnetic fields. This stability could have applications in quantum-level digital storage systems.
Additionally, external particles affecting one electron can affect all electrons in the system, through relatively long-range quantum entanglement. It’s like hitting a cue ball against a bunch of billiard balls and all of those balls move in the same direction in response – another finding that could be useful.
Although all of this involves very high-level physics, each discovery like this – these oddities and edge cases that occur outside the bounds of common particle interactions – brings us closer to a complete understanding of our world.
“Quantum states of matter are found far beyond these limits, and they are much wilder than the three classical states we encounter in our daily lives,” Sedrakyan said.
The research was published in Nature.
A version of this article was first published in June 2023.