Exotic Quantum Crystal Discovered -

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Nature knows two opposite types of solids: one that emerges upon compression from a liquid and a second that appears if the pressure on a liquid is reduced.

While the former is typical for substances in our everyday life the latter occurs for example in a dense quantum liquid of electrons (such as in metals) or ions (in exotic white dwarf or neutron stars).

Now it has been shown that there exists yet a third form of matter that inherits both of these properties. This unusual behaviour has been predicted to exist in crystals of excitons - hydrogen atom-like bound states of electrons and holes - in a semiconductor quantum well placed in a strong electric field.

A team from Kiel University (Germany) consisting of Dr. Jens Bonning, Privatdozent Alexei Filinov and Prof. Michael Bonitz has performed extensive accurate computer simulations that shed light on the mysterious properties of this material.

The results appear in the current issue of Physical Review B. There the authors present a simple explanation for the coexistence of the two seemingly contradicting melting behaviours.

The secret lies in the character of the forces acting between two excitons: at low pressure excitons repel each other via a dipole force and form a quantum liquid.

Upon compression this fluid freezes into an exciton crystal. Further compression brings two excitons so close together that the quantum wave nature of their constituents (electrons and holes) starts to weaken the forces.
As a consequence, further compression leads to an increasing overlap of the exciton quantum waves that is no longer balanced by the inter-exciton repulsion, and the crystal melts again.

The researchers have made precise predictions where to search for this exotic crystal of excitons (particularly well suited are zinc selenide or gallium arsenide quantum wells) - it is now up to the experimentalists to find this new state of matter.

JUNO Mission: What Lies Inside Jupiter

Jupiter's swirling clouds can be seen through any department store telescope.

With no more effort than it takes to bend over an eyepiece, you can witness storm systems bigger than Earth navigating ruddy belts that stretch hundreds of thousands of kilometers around Jupiter's vast equator. It's fascinating.

It's also vexing. According to many researchers, the really interesting things--from the roots of monster storms to stores of exotic matter--are located at depth. The clouds themselves hide the greatest mysteries from view.

NASA's Juno probe, scheduled to launch on August 5th, could change all that. The goal of the mission is to answer the question, What lies inside Jupiter?

"Our knowledge of Jupiter is truly skin deep," says Juno's principal investigator, Scott Bolton of the SouthWest Research Institute in San Antonio, TX. "Even the Galileo probe, which dived into the clouds in 1995, penetrated no more than about 0.2% of Jupiter's radius."

There are many basic things researchers would like to know-like how far down does the Great Red Spot go? How much water does Jupiter hold? And what is the exotic material near the planet's core?

Juno will lift the veil without actually diving through the clouds. Bolton explains how: "Swooping as low as 5000 km above the cloudtops, Juno will spend a full year orbiting nearer to Jupiter than any previous spacecraft. The probe's flight path will cover all latitudes and longitudes, allowing us to fully map Jupiter's gravitational field and thus figure out how the interior is layered."

Jupiter is made primarily of hydrogen, but only the outer layers may be in gaseous form. Deep inside Jupiter, researchers believe, high temperatures and crushing pressures transform the gas into an exotic form of matter known as liquid metallic hydrogen--a liquid form of hydrogen akin to the slippery mercury in an old-fashioned thermometer. Jupiter's powerful magnetic field almost certainly springs from dynamo action inside this vast realm of electrically conducting fluid.

"Juno's magnetometers will precisely map Jupiter's magnetic field," says Bolton. "This will tell us a great deal about the planet's inner magnetic dynamo [and the role liquid metallic hydrogen plays in it]."

Juno will also probe Jupiter's atmosphere using a set of microwave radiometers.

"Our sensors can measure the temperature and water content at depths where the pressure is 50 times greater than what the Galileo probe experienced," says Bolton.

Jupiter's water content is of particular interest. There are two leading theories of Jupiter's origin: One holds that Jupiter formed more or less where it is today, while the other suggests Jupiter formed at greater distances from the sun, later migrating to its current location. (Imagine the havoc a giant planet migrating through the solar system could cause.) The two theories predict different amounts of water in Jupiter's interior, so Juno should be able to distinguish between them-or rule out both.

Finally, Juno will get a grand view of the most powerful Northern Lights in the Solar System.

New Anti-matter Exotic Particle Found

In a single collision of gold nuclei at the RHIC particle accelerator, many hundreds of particles are emitted.

The particles leave telltale tracks in the STAR detector (shown here from the end and side).

Scientists analysed about a hundred million collisions to spot the new antinuclei, identified via their characteristic decay into a light isotope of antihelium and a positive pi-meson. Altogether, 70 examples of the new antinucleus were found. Credit: BNL

Scientists have created a never-before seen type of exotic matter that is thought to have been present at the earliest stages of the universe, right after the Big Bang.

The new matter is a particularly weird form of antimatter, which is like a mirror-image of regular matter. Every normal particle is thought to have an antimatter partner, and if the two come into contact, they annihilate.

The recent feat of matter-tinkering was accomplished by smashing charged gold atoms at each other at super-high speeds in a particle accelerator called the Relativistic Heavy Ion Collider at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory in Upton, N.Y.

Among the many particles that resulted from this crash were bizarre objects called anti-hypertritons. Not only are these things antimatter, but they're also what's called strange matter. Where normal atomic nuclei are made of protons and neutrons (which are made of "up" quarks and "down" quarks), strange nuclei also have so-called Lambda particles that contain another flavour of quark called "strange" as well. These Lambda particles orbit around the protons and neutrons.

If all that is a little much to straighten out, just think of anti-hypertritons as several kinds of weird.

Though they normally don't exist on Earth, these particles may be hiding in the universe in very hot, dense places like the centers of some stars, and most likely were around when the universe was extremely young and energetic, and all the matter was packed into a very small, sweltering space.