In a macro-world we perceive transitions from one state to another as happening gradually. For example, a person travelling from town A to town B can make an infinite number of stops. In micro-world that is not always the case. Properties, such as energy, position, speed, and colour, can be quantised, i.e. they can occur only in discrete quantities. In other words, the traveller can be either in town A, or town B, but not somewhere in-between.
Since electron energy is quantised, electrons can occupy only specific energy levels. Quantum theory predicts that in a two-dimensional electron system, where moving electrons are confined to one plane, under a strong magnetic field electrons also will be restricted to climbing only one step of the energy level ladder at a time. however, the experiments show that electrons can jump to higher energy levels, skipping levels between. Prof. Konstantinov and his team are very excited about this discovery: "It is not everyday that we get a chance to observe the violation of quantum theory predictions!"
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In order to study abnormalities in electron state changes, the scientists applied a strong vertical magnetic field and then bombarded the system with microwave photons. Under these conditions selection rules seem to stop working. Prof. Konstantinov says that his group had theorised that such a phenomenon is possible and now they have proven it.
Selection rules describe a theoretical, absolutely pure, and homogenous system with no disorders. Real-life systems are more complex. In the case of electrons on helium, the system is pure and homogenous, but the surface of liquid helium is nonetheless disturbed by capillary waves -- ripples associated with the surface tension and similar to small, circular ripples in a pond when a pebble is tossed into the water. The height of these ripples is only the diameter of a hydrogen atom, but in combination with microwave radiation they create enough deviation from an ideal system for selection rules to change.
Conditions modelled in the Quantum Dynamics Unit's experiment are similar to those that led to observations of zero resistance in semiconductors. however, the electrons on helium system is relatively simple and can be described mathematically with great precision. Studying this system will further the development of quantum physics and will contribute to our understanding of electrons and various electrical phenomena. moreover, with some adjustments models, based on electrons on helium systems can be adapted to more complex systems, such as two-dimensional semiconductors.
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