Physicists recently learned that special quantum partnerships of electrons – known as Cooper pairs – can also act as a brand new state of matter. Finding a new state for metals is the door not only to viable superconductors, but to new technology and a better understanding of the quantum world.
The Cooper Pairs and Their New State of Matter
To understand better the breakthrough achieved by physicists, we have to discuss in short about electrons, superconductors, and the Cooper Pairs.
Superconductivity is a phenomenon describing individual electrons carrying electrical charge through a material without resistance. In practice, we are talking about superconductors – materials through which electrical charges go from point A to point B with maximum efficiency (no heat loss).
To achieve such efficiency, electrons have to pair under specific circumstances. These quantum partnerships bear the name of Cooper Pairs. A collaboration of physicists from US and China found, however, that the Cooper Pairs can display a third – and brand new state of matter – in addition to the other two states science already knew about. The results are available in the Science journal.
Between the superconducting and insulating regimes, we detect a robust intervening anomalous metallic state characterized by saturating resistance and oscillation amplitude at low temperatures. Our measurements suggest that the anomalous metallic state is bosonic and that the saturation of phase coherence plays a prominent role in its formation.
A brand new state of matter when it comes to electrical efficiency, metals, and superconducting materials means opening the door towards new technology and a better understanding of bosons.
The Cooper Pairs and Their States of Matter: In-Between Worlds
Traditionally, scientists believed Cooper Pairs had only two states: they glide without an effort, roaming free and creating an electrical superconductivity state, or they jam up in material and become locked-up, letting no current pass at all.
The joint team of US and Chinese physicists wanted to know if these pairs had an in-between state and could act like normal individual electrons traveling at a leisure pace. They found the new state of matter – not superconducting current but not blocking it, either. One might say that such pairs lose their superpowers when found in this balanced, chill state, but evidence points to the contrary.
In fact, this particular state is something we have never seen before and it keeps scientists on the tip of their toes. One of the biggest challenges of modern physics is to understand how Cooper pairs work, why they sometimes behave like bosons, and how we could create them so we overcome the biggest challenges of achieving superconductivity.
Finding Metal Superconductivity at Reasonable Temperatures – A Celebration in the World of Physics
Let’s put it this way. Superconductivity – efficient energy without heat losses – is the poster child of particle physics for the obvious reasons. Imagine the technology and advancements humankind can achieve with the help of viable superconductor materials!
The current problem is that we can reach superconductivity in extremely difficult conditions: we either need extreme cold or extreme pressure for superconductors to work the way we want.
Until 2007, science knew that Cooper Pairs of electrons behaved more like bosons – they could run full steam ahead through a conductor acting like ghosts that could pass through one another. In 2007, scientists found a second state of the pairs – the insulation one. They managed to trap these little ghosts and hold them in their tracks.
Now, the same team experimented with a superconductor material to allow Cooper pairs to move at a leisurely pace and the findings require new theory and further experiments to allow scientists to understand how things work. According to Jim Valles, professor of physics at Brown University and the study’s corresponding author,
There had been evidence that this metallic state would arise in thin-film superconductors as they were cooled down toward their superconducting temperature, but whether or not that state involved Cooper pairs was an open question.
We’ve developed a technique that enables us to test that question and we showed that, indeed, Cooper pairs are responsible for transporting charges in this metallic state. What’s interesting is that no one is quite sure at a fundamental level how they do that, so this finding will require some more theoretical and experimental work to understand exactly what’s happening.
The New State of Matter Implications for Our Real Life
On one hand, this discovery contradicts some parts of the quantum theory, so further theoretical and experimental research is needed. On the other hand, to understand the importance of this finding we have to acknowledge the fact that if these boson-like Cooper pairs are responsible for this new metallic state, we can think about real-life applications. At some point in time, it might be possible for physicists and engineers to harness the bosonic metal state for new types of electronic devices.
The main advantage of the phenomenon is that it occurred in a high-temperature superconductor (yttrium barium copper oxide (YBCO) – pierced by an array of tiny holes). YBCO becomes operational as a superconducting material at a generous -181 degrees Celsius (which is way more comfortable than the absolute zero), leaving a lot of room for experimentation.
Moreover, the higher operational temperature also allows for the use of spectroscopy and other techniques science can use to get a grip of what really goes on in this mettalic state.
According to Valles,
The thing about the bosons is that they tend to be in more of a wavelike state than electrons, so we talk about them having a phase and creating interference in much the same way light does. So there might be new modalities for moving charges around in devices by playing with interference between bosons.
While there is a lot of research to do from now on – especially the adjustment of quantum theory and fine-tuning everything we know about superconductivity – the world of physics is thrilled to have found this new state of matter. It opens up possibilities experts are only now beginning to imagine.
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