The quantum dance of oxygen

July 07, 2014

Perhaps not everyone knows that oxygen has - quite unusually for such a simple molecule - magnetic properties. The phase diagram of solid oxygen at low temperatures and high pressures shows, however, several irregularities (for example, proper "information gaps" with regard to these magnetic properties) that are still poorly understood. A team of researchers from the International School for Advanced Studies (SISSA) and International Centre for Theoretical Physics Abdus Salam (ICTP) of Trieste, while trying to understand the origin of these phenomena, have identified a new phase, in which oxygen exhibits previously unknown characteristics.

The magnetism of oxygen is related to the spin of its electrons. "In each molecule two electrons align their intrinsic spin and magnetic moment, spin 1/2, giving rise to a spin 1 magnetic moment", explains Erio Tosatti, professor at SISSA and among the authors of the paper just published in PNAS. "At very high pressures, however, the world goes upside down", he jokes, "insulators become superconductors, magnetic materials lose their properties and so on. Like oxygen, for example: while exhibiting magnetic properties at intermediate pressures, oxygen molecules lose their magnetism at pressures above 80,000 atmospheres. Or at least that's what we used to think, because our studies suggest that the situation is more complex than that".

The first non-magnetic phase, called epsilon, has been studied for years. "Scientists didn't understand what was going on", continues Tosatti. "A few years ago, it became clear, first experimentally and then theoretically, that this loss of magnetism is caused by the sudden grouping of molecules into 'quartets', in turn related to some sort of 'reluctance' of oxygen to become metallic". At even higher pressures (one million atmospheres) oxygen takes on a metallic form and becomes a superconductor. "The formation of quartets with loss of magnetism could be defined as a gimmick used by oxygen to delay becoming metallic. An interesting explanation, but some inconsistencies in the epsilon-phase data at 'lower' pressures, just above 80,000 atmospheres, prompted our group to delve deeper into the matter", explains Tosatti. Tosatti, together with Michele Fabrizio from SISSA, Yanier Crespo from ICTP and Sandro Scandolo, also from ICTP, performed very delicate and extensive calculations and developed quantum models specifically to understand this corner of the phase diagram".

More in detail...

"Our study demonstrated that the epsilon phase is actually divided into two phases and that in the first, from 80,000 to 200,000 atmospheres, which we called epsilon 1, the quartet molecules engage in a real 'quantum dance'".

The four scientists observed, in fact, that the four oxygen molecules in each group constantly exchanged magnetic moments. "It's as if the molecules were playing ball with their spins, the direction in which the electrons rotate around their axis, continuously passing the ball to one another, so that the mean value of each molecule's moment and magnetism is zero. In the epsilon 1 phase of oxygen, the molecules retain their spins, but these fluctuate coherently within and across quartets like a chorus of cicadas", explains Tosatti.

Based on these observations, it isn't true that oxygen in epsilon 1 phase has no magnetic properties, it's just that they hadn't been calculated or measured clearly. "Following our results we checked the literature on the subject and found experimental findings consistent with our model, but which had so far been regarded as anomalies" specifies Tosatti.

This study therefore divided the epsilon phase into two, epsilon 1 (from 80,000 to 200,000 atmospheres), with fluctuating magnetic properties, and epsilon 0 (from 200,000 to 1,000,000 atmospheres), without magnetic properties. "We considered a new transition line between the two phases, perhaps with a critical point, which would be unprecedented in this context. There are also other implications, for example as regards the magnetic response and dissipation present in epsilon 1 but not in epsilon 0", explains Tosatti. "Now we hope to prompt the experimental physicists to verify all these new data".

International School of Advanced Studies (SISSA)

Related Electrons Articles from Brightsurf:

One-way street for electrons
An international team of physicists, led by researchers of the Universities of Oldenburg and Bremen, Germany, has recorded an ultrafast film of the directed energy transport between neighbouring molecules in a nanomaterial.

Mystery solved: a 'New Kind of Electrons'
Why do certain materials emit electrons with a very specific energy?

Sticky electrons: When repulsion turns into attraction
Scientists in Vienna explain what happens at a strange 'border line' in materials science: Under certain conditions, materials change from well-known behaviour to different, partly unexplained phenomena.

Self-imaging of a molecule by its own electrons
Researchers at the Max Born Institute (MBI) have shown that high-resolution movies of molecular dynamics can be recorded using electrons ejected from the molecule by an intense laser field.

Electrons in the fast lane
Microscopic structures could further improve perovskite solar cells

Laser takes pictures of electrons in crystals
Microscopes of visible light allow to see tiny objects as living cells and their interior.

Plasma electrons can be used to produce metallic films
Computers, mobile phones and all other electronic devices contain thousands of transistors, linked together by thin films of metal.

Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.

Researchers develop one-way street for electrons
The work has shown that these electron ratchets create geometric diodes that operate at room temperature and may unlock unprecedented abilities in the illusive terahertz regime.

Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.

Read More: Electrons News and Electrons Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to