Quantum effects at work in the world's smelliest superconductor

March 28, 2016
Ball-and-stick model of hydrogen sulfide. Credit: public domain

The quantum behaviour of hydrogen affects the structural properties of hydrogen-rich compounds, which are possible candidates for the elusive room temperature superconductor, according to new research co-authored at the University of Cambridge.

New theoretical results, published online in the journal Nature, suggest that the quantum nature of - meaning that it can behave like a particle or a wave - strongly affects the recently discovered hydrogen sulphur superconductor, a compound that when subjected to extremely high pressure, is the highest-temperature superconductor yet identified. This new step towards understanding the underlying physics of may aid in the search for a , which could be used for applications such as levitating trains, lossless electrical grids and next-generation supercomputers.

Superconductors are materials that carry electrical current with zero electrical resistance. Low-temperature, or conventional, superconductors were first identified in the early 20th century, but they need to be cooled close to absolute zero (zero degrees on the Kelvin scale, or -273 degrees Celsius) before they start to display superconductivity. For the past century, researchers have been searching for materials that behave as superconductors at higher temperatures, which would make them more suitable for practical applications. The ultimate goal is to identify a material which behaves as a superconductor at room temperature.

Last year, German researchers identified the highest temperature superconductor yet - hydrogen sulphide, the same compound that gives rotten eggs their distinctive odour. When subjected to extreme pressure - about one million times higher than the Earth's atmospheric pressure - this stinky compound displays superconducting behaviour at temperatures as high as 203 Kelvin (-70 degrees Celsius), which is far higher than any other high temperature superconductor yet discovered.

Since this discovery, researchers have attempted to understand what it is about hydrogen sulphide that makes it capable of superconducting at such . Now, new theoretical results suggest that the quantum behaviour of hydrogen may be the reason, as it changes the structure of the chemical bonds between atoms. The results were obtained by an international collaboration of researchers led by the University of the Basque Country and the Donostia International Physics Center, and including researchers from the University of Cambridge.

The behaviour of objects in our daily life is governed by classical, or Newtonian, physics. If an object is moving, we can measure both its position and momentum, to determine where an object is going and how long it will take to get there. The two properties are inherently linked.

However, in the strange world of quantum physics, things are different. According to a rule known as Heisenberg's uncertainty principle, in any situation in which a particle has two linked properties, only one can be measured and the other must be uncertain.

Hydrogen, being the lightest element of the periodic table, is the atom most strongly subjected to quantum behaviour. Its quantum nature affects structural and physical properties of many hydrogen compounds. An example is high-pressure ice, where quantum fluctuations of the proton lead to a change in the way that the molecules are held together, so that the chemical bonds between atoms become symmetrical.

The researchers behind the current study believe that a similar quantum hydrogen-bond symmetrisation occurs in the hydrogen sulphide superconductor.

Theoretical models that treat as classical particles predict that at extremely high pressures - even higher than those used by the German researchers for their record-breaking superconductor - the atoms sit exactly halfway between two sulphur atoms, making a fully symmetrical structure. However, at lower pressures, hydrogen atoms move to an off-centre position, forming one shorter and one longer bond.

The researchers have found that when considering the hydrogen atoms as quantum particles behaving like waves, they form symmetrical bonds at much lower pressures - around the same as those used for the German-led experiment, meaning that quantum physics, and symmetrical hydrogen bonds, were behind the record-breaking superconductivity.

"That we are able to make quantitative predictions with such a good agreement with the experiments is exciting and means that computation can be confidently used to accelerate the discovery of ," said study co-author Professor Chris Pickard of Cambridge's Department of Materials Science & Metallurgy.

According to the researcher's calculations, the quantum symmetrisation of the hydrogen bond has a tremendous impact on the vibrational and superconducting properties of . "In order to theoretically reproduce the observed pressure dependence of the superconducting critical temperature the quantum symmetrisation needs to be taken into account," said the study's first author, Ion Errea, from the University of the Basque Country and Donostia International Physics Center.

The discovery of such a high temperature superconductor suggests that room temperature superconductivity might be possible in other hydrogen-rich compounds. The current theoretical study shows that in all these compounds, the quantum motion of hydrogen can strongly affect the structural properties, even modifying the chemical bonding, and the electron-phonon interaction that drives the superconducting transition.

"Theory and computation have played an important role in the hunt for superconducting hydrides under extreme compression," said Pickard. "The challenges for the future are twofold - increasing the temperature towards , but, more importantly, dramatically reducing the pressures required."

Explore further: New test of hydrogen sulfide backs up superconducting claim

More information: Ion Errea et al. Quantum hydrogen-bond symmetrization in the superconducting hydrogen sulfide system, Nature (2016). DOI: 10.1038/nature17175

Related Stories

New test of hydrogen sulfide backs up superconducting claim

July 2, 2015

(Phys.org)—A combined team of researchers from the Max Planck Institute and Johannes Gutenberg University, both in Germany has backed up the findings of prior research indicating hydrogen sulfide becomes a superconductor ...

Researchers set new temperature record for a superconductor

August 19, 2015

(Phys.org)—A combined team of researchers from the Max Planck Institute and Johannes Gutenberg-Universität Mainz has set a new warmth record for a superconductor. In their paper published in the journal Nature, the team ...

A quantum leap for the next generation of superconductors

February 26, 2016

Quantum materials – materials designed at the sub-atomic level – can be finely-tuned to achieve extremely useful properties that are often not found in nature. These include superconductivity, the ability to conduct electricity ...

Recommended for you

Theorists solve a long-standing fundamental problem

August 30, 2016

Trying to understand a system of atoms is like herding gnats - the individual atoms are never at rest and are constantly moving and interacting. When it comes to trying to model the properties and behavior of these kinds ...

Quest to find the 'missing physics' at play in landslides

August 30, 2016

During the 1990s, Charles S. Campbell, now a professor in the Department of Aerospace and Mechanical Engineering at the University of Southern California, began exploring why large landslides flow great distances with apparently ...

13 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Macksb
1 / 5 (2) Mar 28, 2016
"The quantum symmetrisation of the hydrogen bond has a tremendous impact on the vibrational and superconducting properties of hydrogen sulfide"

This research supports the hypothesis that I have advanced in many prior Physorg comments, many of which involve superconductivity. My hypothesis is based on Art Winfree's law of coupled oscillators (and Huygens' synchronized pendulum clocks). Winfree's law says that periodic oscillators have a tendency to couple their oscillations, and when they do, the coupling will be in certain simple synchronized patterns, which he specified.

I have applied Winfree's law to physics (Winfree did not), on the grounds that Planck's quantum of energy is a periodic oscillation. IMO, synchronized oscillations create superconductivity. My prior Physorg posts give many examples.

Quantum vibrations are a type of periodic oscillation. Here, they synchronize. The onset of such synchrony correlates well with the onset of superconductivity.
Macksb
1 / 5 (2) Mar 29, 2016
Per the Nature article, the onset of superconductivity occurs when the hydrogen atoms sit exactly halfway between two sulfur atoms (in a structure with Im3m symmetry). In the non-super state, the hydrogen atom sits off-center, so there is one short H-S bond and a longer H-S bond of a different type.

Under my hypothesis, set forth in my comment above, the "exactly halfway" position is critically important, because the phonons (vibrations) will be identical--rather than being of two types. The phonons will therefore synchronize their now identical oscillations in a simple Winfree pattern. So synchronized, they will interact uniformly with the periodic oscillations of the electrons.

This uniform beat of the phonons will cause the electrons to self-organize in Cooper pairs, as described in my next post.
antialias_physorg
3.7 / 5 (3) Mar 29, 2016
This research supports the hypothesis that I have advanced in many prior Physorg comments

I call BS on that statement.


I have applied Winfree's law to physics

No you have not. You were akekd many times to show your work and you didn't. Again: BS.

Writing physorg comments does not a scientist make.
Macksb
1 / 5 (2) Mar 29, 2016
IMO, Cooper pairs follow Winfree's law of coupled oscillators. Electrons have two primary periodic oscillations--orbit and spin. Cooper pairs are coupled by their orbits (each electron orbiting exactly anti-synchronous to its partner, 180 degrees opposed). Cooper pairs are also coupled by their spins (one electron spin up, the other spin down--again, exactly 180 degrees opposed). Integer spin and boson status are the results.

This self-organization is hard to achieve when the electrons are yoked to their protons--as they are in hydrogen sulfide. (In metals, the electrons enjoy greater freedom.) When their hydrogen protons have two sulfur dance partners at different distances, this means complex periodic oscillations.

Here, the "exactly halfway" position of hydrogen lets the hydrogen protons dance in a uniform manner. Simple, uniform phonons--not complex. So the electrons can and will form Cooper pairs, because they will couple per Winfree's law. Next: why high temp?
Macksb
1 / 5 (2) Mar 29, 2016
Finally, why does this hydrogen sulfide produce the highest temperature superconductivity? Can my "Winfree's Law" hypothesis shed light on that?

Yes, it can. It is precisely because the electrons are yoked to their protons that the hydrogen sulfide can remain stable in its superconducting state at higher temperatures than in any other case. At high pressure, the position of the hydrogen atom is supremely controlled--"exactly halfway," The electrons, yoked as they are, will thus find it easier to form Cooper partnerships with their mates.

Thanks for your fierce opposition, Antialias. . Open debate is the essence of science. Fire at will.
compose
Mar 29, 2016
This comment has been removed by a moderator.
compose
Mar 29, 2016
This comment has been removed by a moderator.
RealScience
5 / 5 (1) Mar 29, 2016
@ Compose - thanks for well-referenced comment with links to some interesting articles.

I found reference 4 to be of especially high interest because it specifically addresses distinguishing superconductivity from effects that could be masquerading as such, and also supported the findings with two independent measurements (lowering resistance as the alkanes were added, and also the persistent magnetic field disrupted by opening the loop).

#4 should also be easy to reproduce, and, if its finding hold up, to turn into a practical system.
Macksb
not rated yet Apr 03, 2016
Two very recent Physorg articles tie in nicely with my comments above.

See "Flat boron is a superconductor", March 31 on Physorg. The illustration shows two electrons paired: one spin up, the other spin down, with opposite momenta. And the caption says: "Electrons with opposite momenta and spins pair up via lattice vibrations..." This is the point I made above, primarily in my third post.

See also "Researchers prove Huygens was right about pendulum synchronization," March 29. The full article, to which the physorg article provides a link, is a wealth of information. I cited Huygens in my first comment above.

Both of these articles came out after I made my four comments above.

I have yet to receive an apology from Antialias, but I am sure one will arrive soon.

Returning to the "Flat boron" article, the precise, unified vibrations stemming from the precise 2D structure led to superconductivity. My "exactly halfway" comments above are on the same ground.

viko_mx
1 / 5 (1) Apr 03, 2016
Quantum efects can be observed more clearly in situations when small groups of atoms or individual atoms interact with the physical structure of the vacuum of space.
Macksb
not rated yet Apr 04, 2016
Art Winfree's law of coupled periodic oscillators also drives the symmetry to which the article refers at least five times. "Exactly halfway" describes the key symmetry.

Under great pressure, the hydrogen atoms sit exactly halfway between the two sulfur atoms. Why? Because the quantum oscillations on the "left" H-S bond have synchronized with the quantum oscillations on the "right" H-S bond. The "exactly halfway" position of the hydrogen bond is the inevitable result.

These synchronized oscillations are also why the vibrational characteristics change so dramatically.

compose
Apr 04, 2016
This comment has been removed by a moderator.
Macksb
not rated yet Apr 05, 2016
"The researchers have found that when considering the hydrogen atoms...behaving like waves they form symmetrical bonds at much lower pressures--around the same as those used for the ... experiment, meaning that quantum physics and symmetrical hydrogen bonds were behind the ... superconductivity."

Read that carefully, Compose. They attribute the superconductivity to quantum physics (the wave model, not the classical model) and symmetrical hydrogen bonds. These two factors fit my model perfectly, as I describe in my comments. Waves are periodic oscillations. When they synchronize in this setting they result in symmetrical hydrogen bonds.

They do not mention your "steric effect" detour, let alone credit any steric effect as having triggered superconductivity.

Given your success in developing practical high temp superconductors of an entirely different nature, at temperatures "high enough to melt solder," I wonder why you do not focus your energies there.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.