A new type ofquasiparticle which has been named the quantum droplet or otherwise known as the “dropleton”, has been recently disovered by reserchers in the US and Germany. The dropleton was created within semiconductor quantum wells using ultra short laser pulses.
A new type of quasiparticle dubbed the quantum droplet, or “dropleton”, has been identified by researchers in the US and Germany. Created in semiconductor quantum wells using ultrashort laser pulses, the dropleton comprises a small number of electrons and holes that are bound together in a liquid-like drop.
Let’s get the basics down!
We need to understand that there are good and bad conductors of electric current and voltage, then there is silicon. Inside of these conductors (like in most solids) there is a lattice shell. (Shown in pic below)The picture above shows you what the lattice structure of Salt is.
In a material like copper there are millions of atoms arranged into this lattice structure, each atom has electrons around it (this is the valance shell) when enough energy is given to the electrons of these atoms they become unbound to them and can jump out of their points in the valence shell, releasing energy as they do this. The further away the electron is form the core of the atom, the less energy it needs to be realised, the closer it is to the core the harder it is to remove, this is due to electromagnetic force acting upon them.
In conductors it is easy to make an electron become unbound making it a good conductor! The opposite works for an insulator, where the electrons won’t move very well making it unable to carry current easily. Inside of silicon ( a semiconductor) there is a mixture of conductors and insulators, and adding impurities to the silicon will allow it to become a better current carrier.
So when you’re trying to mathematically describe this process it can get a little nasty, so what scientists have done is when they are describing a group dynamics particles together they can all them a quasiparticle.
What’s a quasiparticle?
Let’s say, when a photon comes into contact with a semiconductor e.g silicon. It gives the electrons within that semiconductor energy to move and break away from their valance shells. It leaves behind a positive hole to then be filled, this hole is a quasiparticle (called an electron hole). This electron hole is much like a bubble in a drink as it waits for another electron with a negative charge to fill it.
With electric charges you probably already know that opposites attract, and when an electron fills the hole this can give birth to a quasiparticle called an exciton. In quantum mechanics a hole has the similar properties to a proton. So because of this the new exciton acts much like a neutral hydrogen atom – where an electron and proton are bound together.
Moving onto greater things
A hydrogen atom is quite a stable atom and are very prominent within the universe, as the binding of electromagnetic forces that hold the electron and proton together are quite strong, in contrast to the binding electromagnetic force that keeps the electron and hole together is about 1000 times smaller.
Due to the fact it takes such little energy to break the bond of the hole and electron the team had to cool gallium-arsenide which is a semiconductor down to -263 degrees Celsius. The team then shot a laser into it ( the photons needed to break the electrons away from the holes) doing this for littlery a few trillionths of a second they were able to catch the creation of excitons.
The stronger the laser the more excitons where released, and due to the amount of excitons this then began to weaken the bonds of the other electrons around them. However at a certain laser intensity excitons can no longer be formed. Next the scientists changed the wavelength of the laser and shot it again at the gallium-arsenide, this created electron movement, holes and excitons but this timethe excitons came together to make quasiparticles called biexcitons.
In the same way the excitons are the same as hydrogen atom (in ways) the biexciton is much like the hydrogen molecule. So as before they increased the laser intensity expecting the binds between the biexcitons to weaken but this is where they found a very different response.
They began to become even more strongly bound with each other, and they began to create a whole new configuration of electrons and holes, with a configuration of 4 electrons and holes, they also created quasiparticles with 5 and 6 electrons and holes.
After checking some mathematical models, they recognised that they had created something totally new! As within the exciton the electrons and holes where forming things like hydrogen atoms, to the biexcitons where the excitons where spaced out like the atoms in e molecule. But inside this new quasiparticle the electrons and holes where no longer in a fixed state, instead they resembled the structure of that of a drop of liquid, that’s is why they decided to call it a dropletron.
To be sure the team performed a number of controlled experiments to make sure this truly was a new particle, and they where proved correct they had officially found a new state of matter! The benefits of finding this will help our understanding of how superconductors and semiconductors work!