Scientists from the Indian Institute of Sciences together with their colleagues from the Japanese National Institute of Material Engineering developed the ultra-pure graphene samples and for the first time registered a rare quantum state of matter – Dirac liquid. This discovery changes the perception of electrons’ behavior in non-standard conditions and opens the way to creating revolutionary quantum technologies.
Over many decades, physicists tried to find answer to the question: can electrons in a solid body form an ideal liquid flowing without friction and resistance? Theoreticians forecasted the possibility of such a state, but it was extremely difficult to confirm its existence. Even minor impurities or defects in the crystal lattice destroyed delicate quantum effects and thus bothered to observe this phenomenon.
To avoid this problem, Indian and Japanese researchers produced samples of ultra-pure graphene. Graphene is the material consisting of only one layer of carbon atoms, which long ago received the status of “wonder material” due to its mechanical and electronic properties. In ideal conditions it allows for viewing movement of electrons not just like a flow of particles, but as a collective quantum process.
The measurements demonstrated an unexpected picture: the higher the electrical conductivity of graphene is, the lower its thermal conductivity is, and vice versa. This completely contradicts to the Wiedemann-Franz law, which links two types of conductivity in regular metals and states that they should be changing concurrently. For graphene the deviation from this law is record-high – more than 200 times.
The analysis showed that heat transfer and charge transfer in graphene follow different routes, though both processes are subject to common quantum laws and are dependent on a fundamental constant – conductance quantum. This effect was especially bright in the so-called Dirac point – a special state, when graphene stops being a metal and an insulator simultaneously. This where electrons start behaving not like separate particles, but like a homogenous quantum liquid with extremely low viscosity. This Dirac liquid flows a hundred times lighter than water and its properties resemble quark-gluon plasma – the exotic state of material, which previously was received only at powerful particle accelerators.
The importance of this discovery can hardly be overestimated. For fundamental science graphene is turning into a convenient desk-top lab, where researchers can study the phenomena associated with high-energy physics. The applied sciences also have a good outlook: Dirac liquid may form the basis of the new generation of quantum sensors capable of capturing super-weak electrical and magnetic signals. Such appliances may also be applied in healthcare, when you need to register minor bio-electrical pulses, in telecommunications for high accuracy of data transfer, and also in computer engineering, where quantum technologies are becoming more and more important.
