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After 86 Years, Physicists Have Finally Made an Electron Crystal

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In 1934, theoretical physicist Eugene Wigner proposed a new type of crystal.

If the density of negatively charged electrons could be maintained below a certain level, the subatomic particles could be held in a repeating pattern to create a crystal of electrons; this idea came to known as a Wigner crystal.

 

That’s a lot easier said than done, though. Electrons are fidgety, and it’s extremely difficult to get them to sit still. Nevertheless, a team of physicists has now achieved it – by trapping the wiggly little brats between a pair of two-dimensional semiconducting tungsten layers.

Conventional crystals – like diamonds or quartz – are formed from a lattice of atoms arranged in a fixed, three-dimensional repeating grid structure. According to Wigner’s idea, electrons could be arranged in a similar fashion to form a solid crystal phase, but only if the electrons were stationary.

If the density of the electrons is low enough, the Coulomb repulsion between electrons of the same charge produces potential energy that should dominate their kinetic energy, resulting in the electrons sitting still. Therein lies the difficulty.

“Electrons are quantum mechanical. Even if you don’t do anything to them, they’re spontaneously jiggling around all the time,” said physicist Kin Fai Mak of Cornell University.

“A crystal of electrons would actually have the tendency to just melt because it’s so hard to keep the electrons fixed at a periodic pattern.”

Attempts to create Wigner crystals therefore rely on some sort of electron trap, such as powerful magnetic fields or single-electron transistors, but complete crystallisation has still eluded physicists until now. In 2018, MIT scientists attempting to create a type of insulator may have instead produced a Wigner crystal, but their results left room for interpretation.

superlattice(UCSD Department of Physics)

MIT’s trap was a graphene structure known as a moiré superlattice, where two two-dimensional grids are superimposed at a slight twist and larger regular patterns emerge, as seen in the example image above.

Now the Cornell team, led by physicist Yang Xu, has used a more targeted approach with their own moiré superlattice. For their two semiconducting layers, they used tungsten disulfide (WS2) and tungsten diselenide (WSe2) specially grown at Columbia University.

 

When overlaid, these layers produced a hexagonal pattern, allowing the team to control the average electron occupancy at any specific moiré site.

The next step was to carefully place electrons in specific places in the lattice, using calculations to determine the occupancy ratio at which different arrangements of electrons will form crystals.

The final challenge was how to actually see if their predictions were correct, by observing the Wigner crystals or lack thereof.

“You need to hit just the right conditions to create an electron crystal, and at the same time, they’re also fragile,” Mak said.

“You need a good way to probe them. You don’t really want to perturb them significantly while probing them.”

This problem was solved with insulating layers of hexagonal boron nitride. An optical sensor was placed very close to (but not touching) the sample, at a distance of just one nanometre, separated by a boron nitride layer. This prevented electrical coupling between the sensor and the sample, while maintaining enough proximity for high detection sensitivity.

This arrangement allowed the team to probe the sample cleanly, and they made their detection. Within the moiré superlattice, electrons arranged into a variety of crystal configurations, including triangular Wigner crystals, stripe phases and dimers.

This achievement doesn’t just have implications for studying electron crystals. The findings demonstrate the untapped potential of moiré superlattices for quantum physics research.

“Our study,” the researchers wrote in their paper, “lays the groundwork for using moiré superlattices to simulate a wealth of quantum many-body problems that are described by the two-dimensional extended Hubbard model or spin models with long-range charge-charge and exchange interactions.”

The research has been published in Nature.

 



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Melting Time Crystals Could Help Us Model Complex Networks Like The Human Brain

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Passing electricity through a piece of quartz crystal generates a pulse you can literally set your watch by. Set a time crystal melting, on the other hand, and it just might pulse with the deepest secrets of the Universe.

 

A team of researchers from institutions across Japan has shown the quantum underpinnings of particles arranged as a time crystal could in theory be used to represent some fairly complex networks, from the human brain to the internet, as it breaks down.

“In the classical world, this would be impossible as it would require a huge amount of computing resources,” says Marta Estarellas, a quantum computing engineer from the National Institute of Informatics (NII) in Tokyo.

“We are not only bringing a new method to represent and understand quantum processes, but also a different way to look at quantum computers.”

Ever since they were first theorised in 2012 by Nobel Laureate Frank Wilczek, time crystals have challenged the very fundamentals of physics.

His version of this novel state of matter sounds suspiciously like perpetual motion – particles rearranging periodically without consuming or shedding energy, repeating in patterns through time just as run-of-the-mill crystals do through space.

This is because the thermal energy shared by their constituent atoms can’t settle neatly into an equilibrium with their background.

It’s a little like having a hot cup of tea that remains a tiny bit hotter than room temperature no matter how long it’s been on your desk. Only, since the energy in these tick-tocking clumps of matter can’t be put to work elsewhere, time crystal theory safely avoids violating any physical laws.

 

Just a few years ago, experimental physicists successfully arranged a line of ytterbium ions in such a way that when struck with a laser, their entangled electron spins fell out of equilibrium in this very fashion.

Similar behaviours have been observed in other materials, providing novel insights into the way quantum interactions can evolve in systems of entangled particles.

Knowing time crystal-like behaviours exist is all well and good. The next question is whether we can harness their unique activity for anything practical.

In the new study, by using a set of tools found in graph theory to map potential changes in a time crystal’s arrangement (as seen in the clip below), researchers showed how a discrete unravelling of a time crystal’s arrangement – its melting, if you like – mimics a category of highly complex networks.

“This type of networks, far from being regular or random, contains nontrivial topological structures present in many biological, social, and technological systems,” the researchers write in their report.

Simulating such a highly complex system on a supercomputer could take impractically long periods and serious amounts of hardware and energy, and that’s if it could be achieved at all.

 

Quantum computing, however, relies on a completely different way to carry out computations – one that uses the mathematics of probability embedded in states of matter called ‘qubits’ prior to being measured.

The right combination of qubits arranged as time crystals swinging back and forth into oblivion could represent signals moving across vast webs of neurons, quantum relationships between molecules, or computers messaging one another around the globe.

“Using this method with several qubits, one could simulate a complex network the size of the entire worldwide internet,” says NII theoretical physicist Kae Nemoto.

Applying what we learn in time crystals to this emerging form of technology could give us a whole new way to map and model anything from new drugs to future communications.

As it is, we’re barely scratching the surface of the potential behind this new state of matter. Based on research like this, we can be confident time is on our side when it comes to the future of quantum computing.

This research was published in Science Advances.

 



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For The First Time, Physicists Have Controlled The Interaction of Time Crystals

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The existence of time crystals – a particularly fascinating state of matter – was only confirmed a few short years ago, but physicists have already made a pretty major breakthrough: they have induced and observed an interaction between two time crystals.

 

In a helium-3 superfluid, two time crystals exchanged quasiparticles without disrupting their coherence; an achievement that, the researchers say, opens up possibilities for emerging fields such as quantum information processing, where coherence is of vital importance.

“Controlling the interaction of two time crystals is a major achievement. Before this, nobody had observed two time crystals in the same system, let alone seen them interact,” said physicist and lead author Samuli Autti of Lancaster University in the UK.

“Controlled interactions are the number one item on the wish list of anyone looking to harness a time crystal for practical applications, such as quantum information processing.”

Time crystals are pretty fascinating. They look just like normal crystals, but they sport an additional, peculiar property.

In regular crystals, the atoms are arranged in a fixed, three-dimensional grid structure, like the atomic lattice of a diamond or quartz crystal. These repeating lattices can differ in configuration, but they don’t move around very much: they only repeat spatially.

In time crystals, the atoms behave a bit differently. They oscillate, spinning first in one direction, and then the other. These oscillations – referred to as ‘ticking’ – are locked to a regular and particular frequency. So, where the structure of regular crystals repeats in space, in time crystals it repeats in space and time.

 

Theoretically, time crystals tick at their lowest possible energy state – known as the ground state – and are therefore stable and coherent over long periods of time. This could be exploited, but only if their coherence could be preserved in a controlled interaction.

So, Autti and his colleagues from the UK and Finland set up a time crystal playdate. First, they cooled helium-3 – a stable isotope of helium with two protons but just one neutron – to within one ten thousandth of a degree of absolute zero, creating a B-phase superfluid, a zero-viscosity fluid with low pressure.

In this medium, the two time crystals emerged as spatially distinct Bose-Einstein condensates of magnon quasiparticles. Magnons are not true particles, but consist of a collective excitation of the spin of electrons – like a wave that propagates through a lattice of spins.

When the physicists allowed the two time crystals to touch, they exchanged magnons – which changed the oscillation to the opposite phase without sacrificing coherence.

The results were consistent with a superconductivity phenomenon known as the Josephson effect, in which a current flows between two pieces of superconducting material separated by a thin insulator known as the Josephson junction. These structures are one of several being explored for the construction of qubits, the base units of information in a quantum computer.

It’s only a very simple interaction, but it does open the door to trying to create and control much more sophisticated ones.

“Our results demonstrate that time crystals obey the general dynamics of quantum mechanics and offer a basis to further investigate the fundamental properties of these phases, opening pathways for possible applications in developing fields, such as quantum information processing,” the researchers wrote in their paper.

“Long-lived coherent quantum systems with tunable interactions, such as the robust time crystals studied here, provide a platform for building novel quantum devices based on spin-coherent phenomena.”

The research has been published in Nature Materials.

 



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Experiments Show Bacteria Grow More Lethal And Antibiotic-Resistant in Space

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China has launched its Tianwen-1 mission to Mars. A rocket holding an orbiter, lander and rover took flight from the country’s Hainan province earlier this week, with hopes to deploy the rover on Mars’s surface by early next year.

 

Similarly, the launch of the Emirates Mars Mission last Sunday marked the Arab world’s foray into interplanetary space travel. And on July 30, we expect to see NASA’s Mars Perseverance rover finally take off from Florida.

For many nations and their people, space is becoming the ultimate frontier. But although we’re gaining the ability to travel smarter and faster into space, much remains unknown about its effects on biological substances, including us.

While the possibilities of space exploration seem endless, so are its dangers. And one particular danger comes from the smallest life forms on Earth: bacteria.

Bacteria live within us and all around us. So whether we like it or not, these microscopic organisms tag along wherever we go – including into space. Just as space’s unique environment has an impact on us, so too does it impact bacteria.

We don’t yet know the gravity of the problem

All life on Earth evolved with gravity as an ever-present force. Thus, Earth’s life has not adapted to spend time in space. When gravity is removed or greatly reduced, processes influenced by gravity behave differently as well.

In space, where there is minimal gravity, sedimentation (when solids in a liquid settle to the bottom), convection (the transfer of heat energy) and buoyancy (the force that makes certain objects float) are minimised.

 

Similarly, forces such as liquid surface tension and capillary forces (when a liquid flows to fill a narrow space) become more intense.

It’s not yet fully understood how such changes impact lifeforms.

How bacteria become more deadly in space

Worryingly, research from space flight missions has shown bacteria become more deadly and resilient when exposed to microgravity (when only tiny gravitational forces are present).

In space, bacteria seem to become more resistant to antibiotics and more lethal. They also stay this way for a short time after returning to Earth, compared with bacteria that never left Earth.

Adding to that, bacteria also seem to mutate quicker in space. However, these mutations are predominately for the bacteria to adapt to the new environment – not to become super deadly.

More research is needed to examine whether such adaptations do, in fact, allow the bacteria to cause more disease.

Bacterial team work is bad news for space stations

Research has shown space’s microgravity promotes biofilm formation of bacteria.

Biofilms are densely-packed cell colonies that produce a matrix of polymeric substances allowing bacteria to stick to each other, and to stationary surfaces.

 

Biofilms increase bacteria’s resistance to antibiotics, promote their survival, and improve their ability to cause infection. We have seen biofilms grow and attach to equipment on space stations, causing it to biodegrade.

For example, biofilms have affected the Mir space station’s navigation window, air conditioning, oxygen electrolysis block, water recycling unit and thermal control system. The prolonged exposure of such equipment to biofilms can lead to malfunction, which can have devastating effects.

Another affect of microgravity on bacteria involves their structural distortion. Certain bacteria have shown reductions in cell size and increases in cell numbers when grown in microgravity.

In the case of the former, bacterial cells with smaller surface area have fewer molecule-cell interactions, and this reduces the effectiveness of antibiotics against them.

Moreover, the absence of effects produced by gravity, such as sedimentation and buoyancy, could alter the way bacteria take in nutrients or drugs intended to attack them. This could result in the increased drug resistance and infectiousness of bacteria in space.

All of this has serious implications, especially when it comes to long-haul space flights where gravity would not be present. Experiencing a bacterial infection that cannot be treated in these circumstances would be catastrophic.

 

The benefits of performing research in space

On the other hand, the effects of space also result in a unique environment that can be positive for life on Earth.

For example, molecular crystals in space’s microgravity grow much larger and more symmetrically than on Earth. Having more uniform crystals allows the formulation of more effective drugs and treatments to combat various diseases including cancers and Parkinson’s disease.

Also, the crystallisation of molecules helps determine their precise structures. Many molecules that cannot be crystallised on Earth can be in space.

So, the structure of such molecules could be determined with the help of space research. This, too, would aid the development of higher quality drugs.

Optical fibre cables can also be made to a much better standard in space, due to the optimal formation of crystals. This greatly increases data transmission capacity, making networking and telecommunications faster.

As humans spend more time in space, an environment riddled with known and unknown dangers, further research will help us thoroughly examine the risks – and the potential benefits – of space’s unique environment.

Vikrant Minhas, PhD candidate, University of Adelaide.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 



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Scientists Think Cockroach Milk Could Be a New Superfood, And We Wish We Were Kidding

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An international team of scientists sequenced a protein crystal located in the midgut of cockroaches back in 2016. The reason?

It’s more than four times as nutritious as cow’s milk and the researchers think it could be the key to feeding our growing population in the future.

 

Although most cockroaches don’t actually produce milk, Diploptera punctate, which is the only known cockroach to give birth to live young, has been shown to pump out a type of ‘milk’ containing protein crystals to feed its babies.

The fact that an insect produces milk is pretty fascinating – but what fascinated researchers is the fact that a single one of these protein crystals contains more than three times the amount of energy found in an equivalent amount of buffalo milk (which is also higher in calories than regular cow’s milk).

Clearly milking a cockroach isn’t the most feasible option, so an international team of scientists headed by researchers from the Institute of Stem Cell Biology and Regenerative Medicine in India decided to sequence the genes responsible for producing the milk protein crystals to see if they could somehow replicate them in the lab.

“The crystals are like a complete food – they have proteins, fats and sugars. If you look into the protein sequences, they have all the essential amino acids,” said Sanchari Banerjee, one of the team, in an interview with the Times of India back in 2016.

 

Not only is the milk a dense source of calories and nutrients, it’s also time released.

As the protein in the milk is digested, the crystal releases more protein at an equivalent rate to continue the digestion.

“It’s time-released food,” said Subramanian Ramaswamy, who led the project.

“If you need food that is calorifically high, that is time released and food that is complete. This is it.”

It’s important to point out that this dense protein source is definitely never going to be for those trying to lose weight, and probably isn’t even required for most western diets, where we are already eating too many calories per day.

But for those who struggle to get the amount of calories required per day, this could be a quick and easy way to get calories and nutrients.

“They’re very stable. They can be a fantastic protein supplement,” said Ramaswamy.

Now the researchers have the sequence, they are hoping to get yeast to produce the crystal in much larger quantities – making it slightly more efficient (and less gross) than extracting crystals from cockroach’s guts. 

Who needs kale and quinoa when you have cockroach milk supplements?

…Yeah, we aren’t 100 percent convinced either. But if it helps alleviate the food shortages we’ll have to deal with this generation, we’ll take it.

The research was published in IUCrJ, the journal of the International Union of Crystallography. 

A version of this article was first published in July 2016.

 



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An Ancient Meteorite Is The First Chemical Evidence of Volcanic Convection on Mars

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For many years, we thought Mars was dead. A dusty, dry, barren planet, where nothing moves but the howling wind. Recently, however, pieces of evidence have started to emerge, hinting that Mars is both volcanically and geologically active.

 

Well, the idea of a volcanically active Mars just got a little more real. A meteorite that formed deep within the belly of Mars has just provided the first solid chemical proof of magma convection within the Martian mantle, scientists say. 

Crystals of olivine in the Tissint meteorite that fell to Earth in 2011 could only have formed in changing temperatures as it was rapidly swirled about in magma convection currents – showing that the planet was volcanically active when the crystals formed around 574 to 582 million years ago – and it could still be intermittently so today.

“There was no previous evidence of convection on Mars, but the question ‘Is Mars a still volcanically active planet?’ was previously investigated using different methods,” explained planetary geologist Nicola Mari of the University of Glasgow to ScienceAlert.

“However, this is the first study that proves activity in the Mars interior from a purely chemical point of view, on real Martian samples.”

Olivine, a magnesium iron silicate, isn’t rare. It crystallises from cooling magma, and it’s very common in Earth’s mantle; in fact, the olivine group dominates Earth’s mantle, usually as part of a rock mass. On Earth’s surface, it’s found in igneous rock.

 

It’s fairly common in meteorites. And olivine is also fairly common on Mars. In fact, the presence of olivine on the surface of Mars has previously been taken as evidence of the planet’s dryness, since the mineral weathers rapidly in the presence of water.

But when Mari and his team started studying the olivine crystals in the Tissint meteorite to try to understand the magma chamber where it formed, they noticed something strange. The crystals had irregularly spaced phosphorus-rich bands.

We know of this phenomenon on Earth – it’s a process called solute trapping. But it was a surprise to find it on Mars.

magma olivine(Mari et al., Meteoritics & Planetary Science, 2020)

“This occurs when the rate of crystal growth exceeds the rate at which phosphorus can diffuse through the melt, thus the phosphorus is obliged to enter the crystal structure instead of ‘swimming’ in the liquid magma,” Mari said.

“In the magma chamber that generated the lava that I studied, the convection was so vigorous that the olivines were moved from the bottom of the chamber (hotter) to the top (cooler) very rapidly – to be precise, this likely generated cooling rates of 15-30 degrees Celsius per hour for the olivines.”

 

The larger of the olivine crystals were also revealing. Traces of nickel and cobalt are in agreement with previous findings that they originated from deep under the Martian crust, a depth of 40 to 80 kilometres (25 to 50 miles).

This supplied the pressure at which they formed; along with the equilibration temperature of olivine, the team could now perform thermodynamic calculations to discover the temperature in the mantle at which the crystals formed.

They found that the Martian mantle probably had a temperature of around 1,560 degrees Celsius in the Martian Late Amazonian period when the olivine formed. This is very close to the ambient mantle temperature of Earth of 1,650 degrees Celsius during the Archean Eon, 4 to 2.5 billion years ago.

That doesn’t mean Mars is just like an early Earth. But it does mean that Mars could have retained quite a bit of heat under its mantle; it’s thought that, because it lacks the plate tectonics that help to dissipate heat on Earth, Mars may cool more slowly.

“I really think that Mars could be a still volcanically active world today, and these new results point toward this,” Mari told ScienceAlert.

“We may not see a volcanic eruption on Mars for the next 5 million years, but this doesn’t mean that the planet is inactive. It could just mean that the timing between eruptions between Mars and Earth is different, and instead of seeing one or more eruptions per day (as on Earth) we could see a Martian eruption every n-millions of years.”

We’ll need more research to confidently say this hypothesis checks out. But these results also mean that previous interpretations of the planet’s dryness based on surface olivine may need to be revisited. (Although let us be clear, Mars is still extremely dry.)

The ongoing NASA InSight mission that recently found evidence of Marsquakes, measures – among other things – the heat flux from the Martian crust. If Mars is still volcanically active, we may know more about it really soon.

The research has been published in Meteoritics & Planetary Science.

 



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The Latest Breakthrough in Time Crystals Is a Structure That Needs No External Input

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A newly theorised type of time crystal could revolutionise the potential of these fascinating structures. Unlike the time crystals that have been created to date, it would not require the application of an external stimulus to keep the atoms ticking.

 

The method hinges on inducing entangled particles to affect each other’s ‘spin’ (a property like angular momentum) over a distance. But to understand the details of this latest approach, first we need to step back a little.

Time crystals may sound like some wacky sci-fi concept, but they’re a real phenomenon, first theorised in 2012. From the outside, they look just like normal crystals. But inside, the atoms – arranged in an otherwise normal repeating lattice structure – are behaving quite peculiarly.

They oscillate, spinning first in one direction, and then the other. These oscillations – what is referred to as “ticking” – are locked to a very regular and particular frequency. So, where the structure of regular crystals repeats in space, in time crystals it repeats in space and time – hence, time crystals.

To date, time crystals produced experimentally have required an external stimulus (such as a pulse of electromagnetic radiation) at ground state, or lowest-energy state, to induce their ticking. This was achieved in 2016, but since then, there has been debate over whether this fits what we imagine a real time crystal to be like.

 

In fact, it has seemed very much that time crystals without an energy input to its ground state are simply physically impossible, according to a 2015 paper. In physics this is known as a no-go theorem.

But there is a notable exception to this theorem as it pertains to time crystals, and it’s what Valerii Kozin of the University of Iceland in Reykjavík and Oleksandr Kyriienko of the University of Exeter in the UK used to approach the problem.

That 2015 paper assumes that interactions between particles grow weaker over distance. This is actually a pretty fair assumption to make – think of magnetic or gravitational forces weakening over distance, for example.

But there’s a handy exception. Particles that are entangled have a relationship that doesn’t grow weaker with distance. Measuring the spin of one particle will immediately determine the spin of its entangled partner, no matter how far away it is.

According to the physicists, in time crystals such interaction-at-a-distance could theoretically produce a time crystal ground state that needs no energy injection.

In their new paper, they propose a system of particles within the time crystal, each of which has a spin. They demonstrate that there is a way to describe the entangled particles’ spins using a string theory model that meets the 2015 paper’s definition of a time crystal.

Even if the particles were spinning out of sync, the interactions between the particles would produce the ticking of a time crystal, according to the researchers.

Now, this system would be incredibly complicated, with each particle able to spin in superposition – that is, in an undetermined state of both up and down at the same time.

In fact, the whole thing might not be feasible to create in a lab setting. Entangling particles in this manner is an idea that works well on paper, but is unlikely to be easily doable practically.

But time crystals themselves were a pretty wild idea when first proposed. The future could surprise us yet.

The research has been published in Physical Review Letters.

 



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Scientists Might Have Finally Found The Origin of This Surreal Jagged Crystal Cave

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If you travel to the outskirts of a town called Pulpí in Spain, you’ll find an abandoned silver mine. Descend about 50 metres (164 feet) into it, and you’ll enter a strange, shimmering room quite unlike anywhere else on Earth.

 

This incredible natural space is the Geode of Pulpí, the closest thing in real life to Superman’s Fortress of Solitude: an amazing egg-shaped cavern where jagged shards of brilliant, clear crystal jut from the walls like teeth in a dragon’s mouth.

As far as geodes go, Pulpí’s is a giant – one of the largest known geodes in the world in fact.

In terms of cavernous chambers, though, it’s actually tiny, but is large enough that multiple people can fit inside it at once, which isn’t something you can say about most geode cavities.

012 geode pulpi 2(Hector Garrido)

Just make sure you’re careful and trust whoever you go inside with: the hollow space at the heart of the geode only measures about 11 metres cubed in total, and with all those pointy crystalline deposits protruding from the walls, there’s definitely no room for pushing.

Other spectacular crystal caves are known to exist around the world – most notably the famous, towering Naica crystals of Mexico – but how do these remarkable formations come to be?

In the case of Pulpí – which was only discovered 20 years ago – the geochemical origins of the geode’s crystals have remained largely unknown, with a background seemingly even more mysterious than its cavernous counterparts.

“To reveal their formation has been a very tough task because unlike in the case of Naica, where the hydrothermal system is still active, the large geode of Pulpí is a fossilised environment,” explains geologist and crystallography expert Juan Manuel García-Ruiz from the University of Granada, the senior author of a new study on the geode.

012 geode pulpi 2(Canals et al., Geology, 2019)

In the new research, García-Ruiz and his team sought to reconstruct the geological history of the Geode of Pulpí, analysing samples from the mineral and geochemical environment, as well as mapping in detail the geological structures of the mine that surrounds the crystal chamber.

According to the researchers, the geode’s gypsum (selenite) crystals grew through a “self-feeding mechanism”, due to a continuous supply of salt, provided from the dissolution of anhydrite (the anhydrous form of calcium sulphate).

 

This process, occurring at a temperature of about 20°C (68°F), was amplified by a thermodynamic phenomenon called Ostwald maturation (or Ostwald ripening), along with temperature oscillations that the geode was exposed to at its relatively shallow depth in the mine.

One remaining mystery, though, is exactly when all this crystal formation took place.

Due to the extreme purity of the crystals inside the geode – which are so perfectly clear you can see straight through them – it’s difficult to date the shards, although the team has a few ideas.

“They grew for sure after the desiccation of the Mediterranean Sea that occurred 5.6 million years ago,” García-Ruiz says.

“They are most probably younger than 2 million years but older than 60,000 years, because this is the age of the carbonate crust coating one of the large gypsum [crystals].”

That’s a pretty long gap in time, raising the possibility that other researchers in the future might try to narrow the gap further.

 

Until they do, you can check out the Geode of Pulpí yourself, with Spanish authorities opening the site to visitors earlier this year – giving anyone now the chance to enter this very strange and special sanctuary of sorts.

“Bending your body between the huge crystals is an incredible sensation,” researcher Javier Garcia-Guinea, who discovered the formation, explained to the BBC in 2000.

“When I was young I dreamt of flying, but never to go into a geode internally covered with transparent crystals.”

The findings are reported in Geology.

 





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Newly Found Structures in Tooth Enamel Might Finally Explain Its Bizarre Strength

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A new, first-of-its-kind glimpse at the nanostructure of tooth enamel helps to explain why the hardest substance in the human body is so incredibly resilient.

Tooth enamel looks like bone, but it’s not actually living tissue. This outer layer of the tooth – which encases and protects other tissue inside the tooth – forms when we are young, and once teeth are developed, it has no natural ability to self-repair or regrow.

 

Luckily, the mineralisation process that produces tooth enamel creates an incredibly tough substance that is harder than steel, and new research reveals a never-before-seen mechanism that helps make its exceptional resilience possible.

“We apply huge pressure on tooth enamel every time we chew, hundreds of times a day,” says biophysicist Pupa Gilbert from the University of Wisconsin-Madison.

“Tooth enamel is unique in that it has to last our entire lifetime. How does it prevent catastrophic failure?”

The answer lies in what the researchers call the “hidden structure” of tooth enamel: an infinitesimal structural arrangement of the nanocrystals that make up our outer layer of teeth.

012 tooth enamel crystals 1PIC mapping of tooth enamel, with colours representing degrees of nanocrystal mis-orientation. (Pupa Gilbert)

These extremely tiny crystals are made of a kind of calcium apatite called hydroxyapatite. The same mineral substance is found in the teeth of other creatures too, and the crystals really are small, measuring less than one thousandth the thickness of a human hair.

They’re so small in fact, it’s been difficult to get a good look at them before now.

 

“Prior to this study, we just didn’t have the methods to look at the structure of enamel,” Gilbert says.

“But with a technique that I previously invented, called polarisation-dependent imaging contrast (PIC) mapping, you can measure and visualise in colour the orientation of individual nanocrystals and see many millions of them at once.”

This electron microscopy method, Gilbert says, makes the architecture of complex biominerals “immediately visible to the naked eye”, and in doing so, revealed something scientists had never seen before.

When using the PIC mapping technique on human teeth, the researchers observed that the hydroxyapatite nanocrystals were not oriented in the way that researchers had previously assumed.

In enamel, the crystals are bundled into formations called rods and interrods, but the team detected a gradual change in the crystal orientations between adjacent nanocrystals that wasn’t expected, with mis-orientations ranging between 1 and 30 degrees in adjacent crystals.

As for why such non-alignment exists, Gilbert and colleagues think they have an answer.

“We propose that mis-orientation of adjacent enamel nanocrystals provides a toughening mechanism,” the authors write in their paper.

 

“If all crystals are co-oriented, a transverse crack can propagate across crystal interfaces, whereas if the crystals are mis-oriented a crack primarily propagates along the crystal interfaces.”

Of course, it would be difficult or impossible to test this hypothesis in human teeth in real life, but molecular dynamics simulations performed by the team support the idea.

In a computer model (see video above) designed to simulate how cracking could spread through enamel’s crystal structure through pressure, the cracking propagated more quickly through crystal networks that didn’t resemble human teeth mis-orientations (of 1 to 30 degrees).

The researchers therefore suggest that this range of nanocrystal mis-orientation may represent a sweet spot in crack deflection, and one which “enamel’s long evolutionary history” may have selected for, the team says.

“This may therefore be the sweet spot  crystals 1–30° apart may maximise energy release and toughening,” the paper explains.

“Crack deflection is a well-established toughening [mechanism], we therefore conclude that in enamel the observed mis-orientations play a key mechanical role: they increase the toughness of enamel at the nanoscale, which is fundamentally important to withstand the powerful masticatory forces, approaching 1,000 newtons, repeated thousands of times per day.”

The findings are reported in Nature Communications.

 



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Scientists Just Created a Bizarre Form of Ice That’s Half as Hot as The Sun

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It has taken one of the most powerful lasers on the planet, but scientists have done it. They’ve confirmed the existence of ‘superionic’ hot ice – frozen water that can remain solid at thousands of degrees of heat.

 

This bizarre form of ice is possible because of tremendous pressure, and the findings of the experiment could shed light on the interior structure of giant ice planets such as Uranus and Neptune.

On Earth’s surface, the boiling and freezing points of water vary only a little – generally boiling when it’s very hot, and freezing when it’s cold. But both these state changes are at the whim of pressure (that’s why the boiling point of water is lower at higher altitudes).

In the vacuum of space, water can’t exist in its liquid form. It immediately boils and vaporises even at -270 degrees Celsius – the average temperature of the Universe – before desublimating into ice crystals.

But it’s been theorised that in extremely high-pressure environments, the opposite occurs: the water solidifies, even at extremely high temperatures. Scientists at Lawrence Livermore National Laboratory directly observed this for the first time just recently, detailed in a paper last year.

They created Ice VII, which is the crystalline form of ice above 30,000 times Earth’s atmospheric pressure, or 3 gigapascals, and blasted it with lasers. The resulting ice had a conductive flow of ions, rather than electrons, which is why it’s called superionic ice.

 

Now they’ve confirmed it with follow-up experiments. They have proposed the new form be named Ice XVIII.

In the previous experiment, the team had only been able to observe general properties, such as energy and temperature; the finer details of the internal structure remained elusive. So they designed an experiment using laser pulses and X-ray diffraction to reveal the ice’s crystalline structure.

“We wanted to determine the atomic structure of superionic water,” said physicist Federica Coppari of the LLNL.

“But given the extreme conditions at which this elusive state of matter is predicted to be stable, compressing water to such pressures and temperatures and simultaneously taking snapshots of the atomic structure was an extremely difficult task, which required an innovative experimental design.”

Here’s that design. First, a thin layer of water is placed between two diamond anvils. Then six giant lasers are used to generate a series of shockwaves at progressively increasing intensity to compress the water at pressures up to 100-400 gigapascals, or 1 to 4 million times Earth’s atmospheric pressure.

At the same time, they produce temperatures between 1,650 and 2,760 degrees Celsius (the surface of the Sun is 5,505 degrees Celsius).

 

This experiment was designed so that the water would freeze when compressed, but since the pressure and temperature conditions could only be maintained for a fraction of a second, the physicists were uncertain that the ice crystals would form and grow.

So they used lasers to blast a tiny piece of iron foil with 16 additional pulses, creating a wave of plasma that generated an X-ray flash at precisely the right time. These flashes diffracted off the crystals inside, showing the compressed water was indeed frozen and stable.

“The X-ray diffraction patterns we measured are an unambiguous signature for dense ice crystals forming during the ultrafast shockwave compression demonstrating that nucleation of solid ice from liquid water is fast enough to be observed in the nanosecond timescale of the experiment,” Coppari said.

These X-rays showed a never-before-seen structure – cubic crystals with oxygen atoms at each corner, and an oxygen atom in the centre of each face.

“Finding direct evidence for the existence of crystalline lattice of oxygen brings the last missing piece to the puzzle regarding the existence of superionic water ice,” said physicist Marius Millot of the LLNL.

“This gives additional strength to the evidence for the existence of superionic ice we collected last year.”

The result reveals a clue to how ice giants such as Neptune and Uranus could have such strange magnetic fields, tilted at bizarre angles, and with equators that don’t circle the planet.

Previously, it was thought that these planets had a fluid ocean of ionic water and ammonia in place of a mantle.

But the team’s research shows that these planets could have a solid mantle, like Earth, but made of hot superionic ice instead of hot rock. Because superionic ice is highly conductive, this could be influencing the planets’ magnetic fields.

“Because water ice at Uranus and Neptune’s interior conditions has a crystalline lattice, we argue that superionic ice should not flow like a liquid such as the fluid iron outer core of the Earth. Rather, it’s probably better to picture that superionic ice would flow similarly to the Earth’s mantle, which is made of solid rock, yet flows and supports large-scale convective motions on the very long geological timescales,” Millot said.

“This can dramatically affect our understanding of the internal structure and the evolution of the icy giant planets, as well as all their numerous extrasolar cousins.”

The research has been published in Nature.

 



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