Nav: Home

Superconductivity: After the scenario, the staging

August 18, 2016

Superconductivity with a high critical temperature (high Tc) continues to present a theoretical mystery. While this phenomenon is experimentally well established, no scientist has managed to explain its mechanism. In the late 90's, the British physicist Anthony Leggett proposed a scenario based on the Coulomb energy. Today, researchers at the University of Geneva (UNIGE), Switzerland, in collaboration with Leggett and his group, committed to test this scenario. Their findings challenge Leggett's conjecture, opening new avenues for the explanation of high Tc superconductivity. These results are available in the journal Physical Review X.

Superconductivity is at the heart of intensive research in physics, in particular because of its remarkable electronic properties, such as the absence of electrical resistance. Its properties make it an indispensable element for applications in medicine, as well as in transportation and energy storage.

In the late 90's, Prof. Leggett of the University of Illinois presented a scenario for high Tc superconductivity in the cuprates, materials consisting primarily of copper and oxygen. In his scenario, the transition of the material into the superconducting state is a direct consequence of a decrease of that part of the Coulomb energy which is associated with long wavelengths and «midinfrared» frequencies. It remained to be tested experimentally; optical spectroscopy proves to be a suitable technique for probing this part of the Coulomb energy.

The team of Dirk van der Marel, professor at the Department of physics of quantum matter of UNIGE Faculty of Science, has addressed this issue and the many challenges associated to it. 'We have set up an experimental device and a protocol for measuring the long range Coulomb energy. By varying the temperature and the light frequency applied to several superconducting samples, we observed the subtle influence of superconductivity on the Coulomb energy', explains Dirk van der Marel.

The importance of chemical doping

Based on cuprate superconductors, UNIGE physicists have observed that the behavior of the Coulomb energy at the superconducting transition depends on the doping -i.e. the lack (or excess) of electrons: for some values of the doping it decreases, but for others it stagnates or even increases. Changes in temperature of the Coulomb energy appear linked to the doping of the sample: 'there is a critical doping below which the observed behaviour is opposite to Leggett's scenario', says the physicist.

These experimental advances still do not explain high Tc superconductivity in the cuprates, however, they permit to make progress in the understanding and to adapt existing theories having foundations in common with Leggett's scenario. They can be extended to the measurement of the Coulomb energy in other superconducting materials, to other phenomena such as magnetism, to other methods, and provide directions for the development of experiments which will further advance the understanding of superconductivity and other quantum phenomena.
-end-


Université de Genève

Related Superconductivity Articles:

Looking at light to explore superconductivity in boron-diamond films
More than a decade ago, researchers discovered that when they added boron to the carbon structure of diamond, the combination was superconductive.
Discovery in new material raises questions about theoretical models of superconductivity
The US Department of Energy's Ames Laboratory has successfully created the first pure, single-crystal sample of a new iron arsenide superconductor, CaKFe4As4, and studies of this material have called into question some long-standing theoretical models of superconductivity.
Superconductivity with two-fold symmetry -- new evidence for topological superconductor SrxBi2Se3
Topological superconductivity is the quantum condensate of paired electrons with an odd parity of the pairing function.
Portable superconductivity systems for small motors
Superconductivity is one of modern physics' most intriguing scientific discoveries.
Graphene's sleeping superconductivity awakens
The intrinsic ability of graphene to superconduct (or carry an electrical current with no resistance) has been activated for the first time.
More Superconductivity News and Superconductivity Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...