Most of us are familiar with the existing states of matter. Under normal conditions, matter can either be solid, liquid, or gas. Going beyond the normal situations, however, things can look very different as the temperatures approach absolute zero. At this point, objects that are smaller than a fraction of an atom or those with low states of energy behave in a way that are more extreme than those of the three classical states.
New State of Matter Revealed
A group of experts headed by assistant professor Tigran Sedrakyan of University of Massachusetts performed an experiment that led them to the discovery of a new state of matter. They developed a frustration machine in the form of a bilayer semiconducting device. It contains an electron-rich top layer where the elections can freely move, while the bottom layer are full of holes that can be occupied by roving electrons. These two layers are positioned extremely close to each other in a degree known as interatomic close.
The particles are expected to act in a correlated manner if there is an equal number of electrons in the top layer and holes in the bottom layer. In this experiment, Sedrakyan and his team decided to design the bottom layer in such a way that the number of electrons and the holes in the bottom layer achieve a local imbalance. This is intended to frustrate the electrons as they scramble to look for holes to pass through.
The resulting frustration level triggers the novel chiral edge state which was found to have unusual properties. For instance, cooling quantum matter in a chiral state up to absolute zero degree will freeze the electrons in a predictable way. The arising charge-neutral particles in this state will spin either in a clockwise or a counterclockwise direction. Breaking another particle into one of these electrons or introducing a magnetic field cannot change this spin.
The chiral bose-liquid state has remained hidden for so long because it is difficult to be observed. To address this challenge, another study was conducted by a group of experts from Nanjing University and Peking University which includes theoretical physicists Rui Wang and Baigeng Wang as well as experimental physicists Lingjie Du and Rui-Ruir Du. Their research involves designing a theory and an experiment which uses an extremely strong magnetic field that has the ability to measure the movements of the electrons while looking for their respective holes.
It was found out that both the electrons and the holes are moving with the same velocities on the edge of the semiconductor bilayer. This creates a spiral-like transport which can be controlled by external magnetic fields where the electron and holes are detached under higher fields. The result of their experiment has revealed the first piece of evidence of the existence of chiral bose-liquid which the researchers called the excitonic topological order.
What is a Frustrated Quantum System?
In the quantum world, two or more interaction terms that are having conflict with each other in some physical system are said to be frustrated. In frustrated systems, new degrees of freedom are usually formed as a result of minimization of local conflict.
In condensed matter physics, electrons can undergo a quantum fluid state carrying electricity without losses. This property known as superconductivity occurs at relatively high temperatures in some materials.
Interacting quantum systems demonstrate geometric frustration as their spin degree of freedom can be compared to little compass needles. In an antiferromagnet, the spins are placed next to each other pointing in opposite directions with the goal of lowering their energy.
Studying frustrated quantum systems is one of the most challenging elements in quantum magnetism due to the fact that they can hold quantum spin liquids whose properties are quite vague.
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