Monthly Archives: July 2017

July 12, 2017 The different spatial layout of the atoms in the iron lattice and in the nickel lattice is responsible for their different physical behaviour under extreme conditions. The coloured graphic shows the electronic dispersion of nickel in the region which is responsible for this behaviour. Credit: Michael Karolak

Without a magnetic field life on Earth would be rather uncomfortable: Cosmic particles would pass through our atmosphere in large quantities and damage the cells of all living beings. Technical systems would malfunction frequently and electronic components could be destroyed completely in some cases.

Despite its huge significance for life on our planet, it is still not fully known what creates the Earth's magnetic field. There are various theories regarding its origin, but a lot of experts consider them to be insufficient or flawed. A discovery made by scientists from Wrzburg might provide a new explanatory angle. Their findings were published in the current issue of the journal Nature Communications. Accordingly, the key to the effect could be hidden in the special structure of the element nickel.

Contradiction between theory and reality

"The standard models for Earth's magnetic field use values for the electric and thermal conductivity of the metals inside our planet's core that cannot square with reality," Giorgio Sangiovanni says; he is a professor at the Institute for Theoretical Physics and Astrophysics at the University of Wrzburg. Together with PhD student Andreas Hausoel and postdoc Michael Karolak, he is in charge of the international collaboration that was published recently. Among the participants are Alessandro Toschi and Karsten Held of TU Wien, who are long-term cooperation partners of Giorgio Sangiovanni, and scientists from Hamburg, Halle (Saale) and Yekaterinburg in Russia.

At Earth's centre at a depth of about 6,400 km, there is a temperature of 6,300 degrees Celsius and a pressure of about 3.5 million bars. The predominant elements, iron and nickel, form a solid metal ball under these conditions which makes up the inner core of the Earth. This inner core is surrounded by the outer core, a fluid layer composed mostly of iron and nickel. Flowing of liquid metal in the outer core can intensify electric currents and create Earth's magnetic field at least according to the common geodynamo theory. "But the theory is somewhat contradictory," Giorgio Sangiovanni says.

Band-structure induced correlation effects

"This is because at room temperature iron differs significantly from common metals such as copper or gold due to its strong effective electron-electron interaction. It is strongly correlated," he declares. But the effects of electron correlation are attenuated considerably at the extreme temperatures prevailing in Earth's core so that conventional theories are applicable. These theories then predict a much too high thermal conductivity for iron which is at odds with the geodynamo theory.

With nickel things are different. "We found nickel to exhibit a distinct anomaly at very high temperatures," the physicist explains. "Nickel is also a strongly correlated metal. Unlike iron, this is not due to the electron-electron interaction alone, but is mainly caused by the special band structure of nickel. We baptised the effect 'band-structure induced correlation'." The band structure of a solid is only determined by the geometric layout of the atoms in the lattice and by the atom type.

Iron and nickel in Earth's core

"At room temperature, iron atoms will arrange in a way that the corresponding atoms are located at the corners of an imaginary cube with one central atom at the centre of the cube, forming a so-called bcc lattice structure," Andreas Hausoel adds. But as temperature and pressure increase, this structure changes: The atoms move together more closely and form a hexagonal lattice, which physicists refer to as an hcp lattice. As a result, iron looses most of its correlated properties.

But not so with nickel: "In this metal, the atoms are as densely packed as possible in the cube structure already in the normal state. They keep this layout even when temperature and pressure become very large," Hausoel explains. The unusual physical behaviour of nickel under extreme conditions can only be explained by the interaction of this geometric stability and the electron correlations originating from this geometry. Despite the fact that scientists have neglected nickel so far, it seems to play a major role in Earth's magnetic field.

Decisive hint from geophysics

The goings-on inside Earth's core are not the actual focus of research at the Departments of Theoretical Solid-state Physics of the University of Wrzburg. Rather Sangiovanni, Hausoel and their colleagues concentrate on the properties of strongly correlated electrons at low temperatures. They study quantum effects and so-called multi-particle effects which are interesting for the next generation of data processing and energy storage devices. Superconductors and quantum computers are the keywords in this context.

Data from experiments are not used in this kind of research. "We take the known properties of atoms as input, include the insights from quantum mechanics and try to calculate the behaviour of large clusters of atoms with this," Hausoel says. Because such calculations are highly complex, the scientists have to rely on external support such as the SUPERMUC supercomputer at the Leibniz Supercomputing Centre (LRZ) in Garching.

And what's the Earth's core got to do with this? "We wanted to see how stable the novel magnetic properties of nickel are and found them to survive even very high temperatures," Hausoel says. Discussions with geophysicists and further studies of iron-nickel alloys have shown that these discoveries could be relevant for what is happening inside Earth's core.

Explore further: Splitting water for the cost of a nickel

More information: A. Hausoel et al. Local magnetic moments in iron and nickel at ambient and Earth's core conditions, Nature Communications (2017). DOI: 10.1038/ncomms16062

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Quantum mechanics inside Earth's core - Phys.org - Phys.Org

Every time physicists find a new particle, the Standard Model gets one step closer to becoming a Super Model.

There's always talk of whether the new arrival fits in, or stands out, or matches the model's predictions. Everything gets related back to this "Bible of quantum physics".

The Standard Model isn't mystical, however. It's purely, beautifully mathematical.

Yet for all its predictive power, it's not perfect it can't explain gravity, dark matter or dark energy. The real goal of particle-smashing physicists is to break it.

Only by finding new particles that weren't predicted by the Standard Model, and can't fit inside it, will we move to a new and improved model one that doesn't have big gaps where gravity and the dark parts of physics should be.

Forty years ago scientists pulled everything they knew about quantum physics into one massive equation the Standard Model of particle physics.

If you can follow the maths, the Standard Model is a stunning piece of work. It's like a how-to guide for the particles and forces that operate at the tiny quantum scale including all the atoms that makes up people, plants, planets and stars.

(Luckily for the non-physicists among us, it also comes in handy table form and our handy video above.)

The really big deal with the Standard Model is that it didn't just describe particles that were already known, like the electron and quarks that make up atoms.

It did something much more important it predicted some new particles too, including the Higgs boson.

Testing predictions is at the heart of science, and every one of the particles that the Standard Model predicted has since been discovered. The Higgs was the last to be found, in 2012.

That ability to predict and explain every aspect of the quantum world makes the Standard Model a bit of a superstar.

But while it's undeniably brilliant, no one has ever pretended the Standard Model is perfect.

The most obvious flaw in the Standard Model was there from the beginning it could never account for gravity, the force that rules at the macro scale. That's not the Standard Model's fault; quantum theory and Einstein's gravitational theory just don't work together.

But gravity's not the only thing missing from the model.

The Standard Model can't account for the dark matter and dark energy that make up a cool 95 per cent of the universe either.

And most bizarre of all, it comes right out and says that universe shouldn't exist at least not the way it is. The Model predicts that matter and antimatter should have been produced in equal amounts at the birth of the universe and annihilated immediately thereafter, leaving one enormous sea of light.

Thankfully that hasn't exactly gone to plan either; there's matter all over the place, including little old you and me.

Some of the Standard Model's other shortcomings are on a much less grand and galactic scale.

One of the best-known problems is that it predicts that one family of particles neutrinos should have zero mass. But as the recipients of the 2015 Nobel Prize in Physics can attest, these ridiculously small particles that travel at near light speed have very tiny, but not zero, masses.

Far from being considered a failure for its shortcomings, the Standard Model has always been appreciated by physicists for what it is: a great start to understanding and possibly unifying all of physics.

And in the decades since it appeared, theoretical physicists have thrown up a pile of possible additions to the Model, trying to account for the things it can't explain.

These mostly involve new particles that are much heavier than the known quarks, leptons and bosons. In supersymmetry, the best known 'upgrade' to the model, every particle has a much heavier partner, called a sparticle, which helps patch the current gaps.

Theories are great, but if we want to find out which, if any, of the various upgrades to the Standard Model are right, we really need to find new particles. And that's where particle accelerators come in.

The Higgs boson was found at the Large Hadron Collider in 2012. With higher energy collisions heavier particles could also be discovered.

(www.cern.ch)

The Higgs boson was found at the Large Hadron Collider in 2012. With higher energy collisions heavier particles could also be discovered.

Particle accelerators smash together tiny bits of matter everything from electrons to whole atoms at almost light speed. When that happens, the energy of the collision can be converted into matter. (Einstein's E=mc2 tells us that mass and energy are two sides of the same deal).

And if there's enough energy it can form a heavier particle than we've ever observed.

Heavy particles made in colliders are generally unstable they only exist for an incredibly short time before breaking down into lighter, more stable bits. But those telltale leftovers are exactly the thing physicists look for in particle accelerator experiments all over the world.

So far, new particles haven't been able to 'break' the Standard Model; they just keep opening new chapters of it.

Knowing the mass and energy of these particles will favour some of the new theoretical additions, and knock others out of contention.

The more new particles we find, the narrower the field for refinements to the model.

Any new, heavy particles that are found will result in some new characters in the Standard Model equation, and the beginnings of an extra row or column in the accompanying table. This 'Standard Model Plus' could account for the mass of neutrinos, the antimatter/matter issue, dark matter and dark energy.

But accounting for gravity won't happen without shifting to a new theory altogether one that accounts for all known particles and phenomena as well as the current model does, but that can work with gravity as well.

And theories of quantum gravity won't be validated by particle accelerators any time soon. The energies required to test them are well beyond the range of even the very biggest atom smashers.

For now, a grand unified theory of the universe that ties in quantum and gravitational scales appears to be out of reach. If we ever find it, we'll be in serious Super Model territory.

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The Standard Model of particle physics is brilliant and completely flawed - ABC Online