Uranium Telluride...

Image source: link below

Topics: Atomic Physics, Magnetism, Superconductors

Superconductivity and magnetism don’t usually mix. When a superconductor is placed in a magnetic field, it expels the field from its bulk through the Meissner effect; a strong enough field destroys the superconducting state entirely. In the vast majority of superconductors, electrons form spin-singlet pairs, with s– or d-wave symmetry, that are twisted apart by the field. Even the rare p-wave, spin-triplet superconductors (such as strontium ruthenate; see Physics Today, December 2006, page 23) are limited in how strong a magnetic field they can tolerate.

Web Elements: Uranium Tritelluride

Last year the list of unusual superconductors grew by one, when Nicholas Butch and colleagues at NIST and the University of Maryland discovered spin-triplet superconductivity in uranium telluride, or UTe₂. (The paper reporting their results, although submitted in October 2018, wasn’t published until this August; in the intervening time, the discovery was confirmed by a team of researchers at Tohoku University in Japan and Grenoble Alps University in France.)

Exotic superconducting state lurks at an astonishingly high magnetic field
Johanna L. Miller, Physics Today

Boiling Superconductivity...

Under pressure: calculated structure of lithium magnesium hydride. Lithium atoms appear in green, magnesium in blue and hydrogen in red. (Courtesy: Ying Sun et al/Phys. Rev. Lett.)

Topics: Chemistry, Materials Science, Nanotechnology, Superconductors

A material that remains a superconductor when heated to the boiling point of water has been predicted by physicists in China. Hanyu Liu, Yanming Ma and colleagues at Jilin University have calculated that lithium magnesium hydride will superconduct at temperatures as high as 473 K (200 °C).

The catch is that the hydrogen-rich material must be crushed at 250 GPa, which is on par with pressures at the center of the Earth. While such a pressure could be achieved in the lab, it would be very difficult to perform an experiment to verify the prediction. The team’s research could, however, lead to the discovery of more practical high-temperature superconductors.

Superconductors are materials that, when cooled below a critical temperature, will conduct electricity with zero resistance. Most superconductors need to be chilled to very low temperatures, so the holy grail of superconductivity research is to find a substance that will superconduct at room temperature. This would result in lossless electricity transmission and boost technologies that rely on the generation or detection of magnetic fields.

Superconductivity at the boiling temperature of water is possible, say physicists
Hamish Johnston, Physics World

Strain, 2-D and Superconductivity...

Superconductors' never-ending flow of electrical current could provide new options for energy storage and superefficient electrical transmission and generation. But the signature zero electrical resistance of superconductors is reached only below a certain critical temperature and is very expensive to achieve. Physicists in Serbia believe they've found a way to manipulate superthin, waferlike monolayers of superconductors, thus changing the material's properties to create new artificial materials for future devices. This image shows a liquid phase graphene film deposited on PET substrate. Credit: Graphene Laboratory, University of Belgrade

Topics: Applied Physics, Superconductors, Thin Films

Superconductors' never-ending flow of electrical current could provide new options for energy storage and superefficient electrical transmission and generation, to name just a few benefits. But the signature zero electrical resistance of superconductors is reached only below a certain critical temperature, hundreds of degrees Celsius below freezing, and is very expensive to achieve.

Physicists from the University of Belgrade in Serbia believe they've found a way to manipulate superthin, waferlike monolayers of superconductors, such as graphene, a monolayer of carbon, thus changing the material's properties to create new artificial materials for future devices. The findings from the group's theoretical calculations and experimental approaches are published in the Journal of Applied Physics.

"The application of tensile biaxial strain leads to an increase of the critical temperature, implying that achieving high temperature superconductivity becomes easier under strain," said the study's first author from the University of Belgrade's LEX Laboratory, Vladan Celebonovic.

Strain enables new applications of 2-D materials, Phys.org

Room Tc...

The cage-like crystal structure (LaH₁₀) thought to be responsible for the high-temperature superconductivity observed in this study. Courtesy: R Hemley

Topics: Green Energy, Materials Science, Quantum Mechanics, Superconductors

Note: Room temperature is 300 K, which is 26.85 Celsius, 80.33 Fahrenheit.

A team of researchers from George Washington University in the US is saying that a hydride of lanthanum compressed to 200 GPa (2 Mbars) could be superconducting at temperatures near room temperature – a result that has been backed up with findings from another group in Germany. The results could be a major step towards realizing the long-sought goal of room-temperature superconductivity for energy applications.

Superconductivity is the ability of a material to conduct electricity without any resistance. It is observed in many materials when they are cooled to below their superconducting transition temperature (T_c). In the Bardeen-Cooper-Schrieffer (BCS) theory of (“conventional”) superconductivity, this occurs when electrons overcome their mutual electrical repulsion and form “Cooper pairs” that then travel unheeded through the material as a supercurrent.

Superconductivity was first observed in 1911 in solid mercury below a T_c of 4.2K (--268.95 Celsius, --452.11 Fahrenheit) and the search for room-temperature superconductors has been on ever since. Room-temperature superconductivity would help considerably improve the efficiency of electrical generators and transmission lines, as well simplify current applications of superconductivity, such as superconducting magnets in particle accelerators.

Researchers came a step closer to this holy grail with the high-temperature superconducting copper oxides, which were discovered in the 1990s and which have a Tc above liquid helium temperatures. It was only in 2015, however, that they discovered that hydrogen sulphide has a Tc of 203 K when compressed to pressures of 150 GPa. This result spurred a flurry of interest in the compressed hydrides – that is, solid materials containing hydrogen atoms bonded to other elements.

Dramatic resistance drop at 260 K

“We believe that a T_c at – or very near – room temperature has finally been realized,” says Russell Hemley, who led this latest research effort.

Thanks to quantum-mechanics-based calculations, Hemley’s group first predicted that lanthanum hydride (LaH₁₀) could be superconducting in July 2017. The researchers then synthesized the material, and reported direct measurements of its conductivity that indicated a T_c of 260 K (-13.15 Celsius, 8.33 Fahrenheit) at 180-200 GPa in May 2018, posting a paper on the arXiv in August 2018 that has now been published in Physical Review Letters. A team led by Mikhail Eremets at the Max Planck Institute for Chemistry in Germany reported on a T_c of 250 K (-23.15 Celsius, -9.67 Fahrenheit) for lanthanum hydride synthesized at pressures of around 170 GPa in independent work posted on the arXiv in December 2018.

Quantum-mechanics-based calculations for “materials by design”

The researchers say they have reproduced their result many times and also have preliminary magnetic susceptibility data that point to room-temperature superconductivity. To unequivocally prove, however, that this is indeed the case will require them to observe the Meissner effect (the expulsion of magnetic field from a material when it becomes superconducting) in LaH₁₀. This is challenging, they admit, but preliminary results from experiments on their samples at the Argonne National Laboratory in Illinoisare encouraging. Further work is also needed to characterize the superconducting properties of structures other than LaH₁₀ in their samples that they have predicted and observed using X-ray diffraction.

On the road to room-temperature superconductivity, Belle Dumé, Physics World

Strange Metals...

Topics: Condensed Matter Physics, Materials Science, Quantum Mechanics, Superconductors

A ubiquitous quantum phenomenon has been detected in a large class of superconducting materials, fueling a growing belief among physicists that an unknown organizing principle governs the collective behavior of particles and determines how they spread energy and information. Understanding this organizing principle could be a key into “quantum strangeness at its deepest level,” said Subir Sachdev, a theorist at Harvard University who was not involved with the new experiments.

The findings, reported today in Nature Physics by a team working at the University of Sherbrooke in Canada and the National Laboratory for Intense Magnetic Fields (LNCMI) in France, indicate that electrons inside a variety of ceramic crystals called “cuprates” seem to dissipate energy as quickly as possible, apparently bumping up against a fundamental quantum speed limit. And past studies, especially a 2013 paper in Science, found that other exotic superconducting compounds — strontium ruthenates, pnictides, tetramethyltetrathiafulvalenes and more — also burn energy at what appears to be a maximum allowed rate.

Universal Quantum Phenomenon Found in Strange Metals, Natalie Wolchover, Quanta Magazine

Superconducting Nanotech...

Illustration of the device structure: stanene is on top of the lead-tellurium film and bismuth-tellurium substrate. α-tin has a similar crystal structure to diamond.

Topics: Applied Physics, Materials Science, Nanotechnology, Superconductors

Almost a century after Heike Kamerlingh Onnes first discovered superconductivity, the factors that determine whether a system will be superconducting and at what temperature remain hard to pin down. However, advances in nanotechnology have given some good pointers where to look, as well as providing promising systems for exploiting superconductivity in real-world applications.

The fundamental requirement for superconductivity is the coupling of fermionic electrons into Cooper pairs. Theory paints a neat picture of how the resulting bosonic behaviour allows occupation of the same energy levels and leads to a host of exotic behaviour - zero electrical resistance and the expulsion of magnetic flux lines so that superconducting objects levitate on magnets, to name a few. Where the picture grows fuzzy is extrapolating from there what specific aspects a material system needs to become superconducting at a given temperature. While design principles to fabricate a room-temperature superconductor remain elusive, a lot has been learnt in the chase, bringing applications of superconductors in a range of sectors from imaging, testing and quantum cryptography ever closer.

2D materials

Among the material systems where unusual electronic behaviour akin to Cooper pairing might be likely is the interface between perovskite oxides – in particular, LaAlO3 and SrTiO3 – where there is a discontinuity in the polarity of the crystalline lattice. Following the initial discovery of a highly mobile “2D electron gas” at the interface in 2004, Jochen Mannhart and colleagues then identified superconducting properties at the interface in a layer limited to just 20 nm in 2007. The transition temperature was a chilly 200 millikelvin, and the exact origins of the effect were unclear, but oxide interfaces remain a hotbed for exploring electronic and spintronic behaviour.

Since then several 2D structures have revealed superconducting behaviour where it does not exist in the bulk, an example being “grey” tin. The form of tin usually considered most useful is “white” tin, which has a conventional metal crystallographic structure, and was among the first superconducting materials to attract study. However, at low temperatures white tin will gradually transform into grey tin, which has a diamond cubic structure and is sometimes described as “tin pest”. To their surprise, Qi-Kun Xue, Ding Zhang and colleagues at Tsinghua University in China found that when they reduced the dimensions of tin to 2D stanene of just 2-20 layers, they could observe superconducting properties in grey tin too. Going even thinner to monolayers resulted in insulating properties.

"What we found is that the grey tin can be scientifically quite interesting," Zhang told nanotechweb.org. As well as the fundamental science the discovery opens up, it also poses the opportunity to produce circuits from all one material, with superconducting wires of few layer stanene separated by insulating monolayers.

Superconductivity - pairing up with nanotechnology, Anna Demming, Nanotechweb.org

10-Qubit Entanglement...

Illustration of the ten-qubit processor (Courtesy: Chao Song et al/ Physical Review Letters)

Topics: Nanotechnology, Quantum Computer, Quantum Mechanics, Superconductors

Physicists in China and the US have built a 10-qubit superconducting quantum processor that could be scaled up to tackle problems not solvable by classical computers. The performance of the device was verified using quantum tomography, which showed that the new approach can generate a true 10-partite Greenberger–Horne–Zeilinger (GHZ) state – the largest yet achieved in a solid-state system.

The field of quantum computing is in its infancy, and a genuinely useful, practical device that outperforms classical computers has not yet been built. At this stage of development, researchers do not even agree on the basics of implementation, but techniques employing superconducting circuits have an advantage over some other designs in that they are based on established and scalable microfabrication processes.

Superconducting quantum computer achieves 10-qubit entanglement
Marric Stephens, Physics World

Atoms and Josephson Junctions...

An electron microscope image of a quantum simulator made from a 1D array of Josephson junctions (light dots). (Courtesy: Philip Krantz, Krantz NanoArt, adapted by APS / Alan Stonebraker)

Topics: Modern Physics, Nanotechnology, Quantum Mechanics, Superconductors

A theory that describes how quantum particles interact with each other in 1D has been put to the test by two independent teams of physicists. In one experiment, aspects of the Tomonaga–Luttinger theory were verified using laser-trapped ultracold atoms. The other study made use of superconducting devices. Confirmation of the theory could lead to the development of new technologies based on nanowires and other 1D systems. Applications include electronics, sensing, energy harvesting and quantum information.

Tomonaga–Luttinger theory describes a 1D ensemble of interacting quantum particles in terms of a Tomonaga–Luttinger liquid (TLL). It predicts properties of 1D quantum systems such as how electrons behave in a nanowire. Testing these predictions in a systematic way has not been possible, however, because it is very difficult to control how particles interact in 1D systems such as nanowires.

Atoms and Josephson junctions simulate 1D quantum liquid, Hamish Johnston, Physics World

B-Doped Q-Carbon Superconductors...

FIG. 1.
SIMS profiles of (a) as-deposited boron and carbon layers with the inset showing a schematic of the alternating layers of amorphous carbon and boron deposited on c-sapphire using the pulsed laser deposition technique and (b) pulsed laser annealed (B-doped Q-carbon) thin films with the inset showing a schematic of B-doped amorphous Q-carbon formed on c-sapphire.

Topics: Condensed Matter Physics, Materials Science, Solid State Physics, Superconductors

ABSTRACT

Following a brief report on high-temperature superconductivity in B-doped Q-carbon [Bhaumik et al., ACS Nano 11(6), 5351–5357 (2017)], we present detailed structure-property correlations to understand the origin of superconductivity in strongly bonded lightweight materials and methods to further enhance the superconducting transition temperature (T_c). Nanosecond melting of carbon in a super undercooled state and rapid quenching result in a strongly bonded unique phase of B-doped Q-carbon. The temperature-dependent resistivity and magnetic susceptibility measurements demonstrate type II superconductivity in this material with a transition temperature of 36.0 ± 0.5 K and an upper critical field of 5.4 T at ∼0 K. It has also been shown that in B-doped Q-carbon, the upper critical magnetic field (H_c2(T)) follows H_c2(0) [1-(T/Tc)^2.1] temperature dependence and is consistent with the Bardeen–Cooper–Schrieffer formalism. In the present study, B-doped Q-carbon thin films are formed on sapphire substrates by employing pulsed laser annealing (PLA) using a nanosecond excimer laser. This process involves the rapid quenching of highly undercooled melt of homogenously mixed B and C. Through the structure-property correlation measurements in B-doped Q-carbon, we estimate a higher electronic density of states near the Fermi level. Higher density of states near the Fermi-level along with higher Debye temperature and phonon frequency are responsible for the enhanced T_c. As a result of rapid melting and quenching, we can achieve 17.0 ± 1.0 or higher atomic % of B in the electrically active sites of Q-carbon which leads to the formation of shallow electronic states near the valence band maximum. From the critical current density versus field moments, the value of critical current density (J_c (2T)) in B-doped Q-carbon at 21 K is calculated as 4.3 × 10⁷ A cm⁻², which indicates that this novel material can be used for the persistent mode of operation in MRI and nuclear magnetic resonance applications. This discovery of high-temperature superconductivity in B-doped amorphous Q-carbon shows that the non-equilibrium synthesis technique using the super undercooling process can be used to fabricate materials with greatly enhanced physical properties.

A novel high-temperature carbon-based superconductor: B-doped Q-carbon
Anagh Bhaumik¹, Ritesh Sachan^1,2, and Jagdish Narayan^1,a)
Journal of Applied Physics 122, 045301 (2017); doi: http://dx.doi.org/10.1063/1.4994787

HTS...

Image Source: Aventurine

Topics: Bose-Einstein Condensate, Condensed Matter Physics, Materials Science, Superconductors

The perfect performance of superconductors could revolutionize everything from grid-scale power infrastructure to consumer electronics, if only they could be coerced into operating above frigid temperatures. Even so-called high-temperature superconductors (HTS) must be chilled to hundreds of degrees Fahrenheit below zero.

Now, scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Yale University have discovered new, surprising behavior by electrons in a HTS material. The results, published July 27 in the journal Nature, describe the symmetry-breaking flow of electrons through copper-oxide (cuprate) superconductors. The behavior may be linked to the ever-elusive mechanism behind HTS.

"Our discovery challenges a cornerstone of condensed matter physics," said lead author and Brookhaven Lab physicist Jie Wu. "These electrons seem to spontaneously 'choose' their own paths through the material—a phenomenon in direct opposition to expectations."

Strange electrons break the crystal symmetry of high-temperature superconductors, Brookhaven National Laboratory, Phys.org

Selenide Vibrations...

In this illustration, an infrared laser beam (orange) triggers atomic vibrations in a thin layer of iron selenide, which are then recorded by ultrafast X-ray laser pulses (white) to create an ultrafast movie. The motion of the selenium atoms (red) changes the energy of the electron orbitals of the iron atoms (blue). (Courtesy: Greg Stewart/SLAC National Accelerator Laboratory)

Topics: Condensed Matter Physics, Materials Science, Solid State Physics, Superconductors

Two important breakthroughs in the understanding of iron-selenide superconductors have been made by two independent research groups. One team has shown that the electrons responsible for superconductivity in the material probably come from a specific atomic orbital. The other team, meanwhile, has measured the interaction between electrons and atomic vibrations in iron selenide, which is believed to be involved in its superconductivity.

The research could shed light on the mystery of why some materials based on iron selenide are superconductors at relatively high temperatures, which has puzzled physicists for more than a decade. While bulk iron selenide is a superconductor below 8.5K, this transition temperature can reach as high as 75K when an ultrathin trilayer of the material is grown on certain substrates.

Experiments shed new light on iron superconductors, Hamish Johnston, Physics World

Ultra Cold and Fermi-Hubbard...

Raw fermionic microscope image (left) and processed image showing that spin-up atoms occupy alternating lattice sites as expected in an antiferromagnet. The spin-down atoms have been removed from the image. (Courtesy: A Mazurenko et al. / Nature)

Topics: Condensed Matter Physics, Optical Physics, Quantum Mechanics, Solid State Physics, Superconductors

New insights into a popular and potentially useful model of how electrons behave in solids have been provided by an experiment involving ultracold atoms. Markus Greiner and colleagues at Harvard University in the US studied the behaviour of lithium-6 atoms that are held in an optical lattice and interact according to rules set out by the Fermi-Hubbard model.

They found that the system becomes magnetic at low temperatures – and that the magnetism disappears when the density of atoms is reduced. The team can now use its atomic simulator to explore regimes of the Fermi-Hubbard model that could harbour very interesting physics including high-temperature superconductivity.

The electronic properties of solid materials arise from quantum-mechanical interactions between large numbers of electrons. It is notoriously difficult to calculate these properties, so physicists rely on simple models to simplify the mathematics – but even models have significant computational challenges. One such scheme is the Fermi-Hubbard model, which represents electrons as Fermi–Dirac particles (fermions) that hop between fixed sites on a lattice and only interact with each other when they occupy the same lattice site.

Physics World: Ultracold atoms shed light on the Fermi-Hubbard model
Hamish Johnston

Unconventional Superconductors...

A crystal sample of one of the iron-based unconventional superconductors studied by Ames Laboratory scientists. Their systematic investigation ofthis class of superconductors may lead to the creation of new materials with unique superconducting properties. Credit: U.S. Department of Energy, Ames Laboratory

Topics: Applied Physics, Condensed Matter Physics, Solid State Physics, Superconductors

Researchers at the U.S. Department of Energy's Ames Laboratory and partner institutions conducted a systematic investigation into the properties of the newest family of unconventional superconducting materials, iron-based compounds. The study may help the scientific community discover new superconducting materials with unique properties.

Researchers combined innovative crystal growth, highly sensitive magnetic measurements, and the controlled introduction of disorder through electron bombardment to create and study an entire range of compositions within a class of iron-based superconductors. They found that the key fundamental properties—transition temperature and magnetic field penetration depth—of these complex superconductors were dependent on composition and the degree of disorder in the material structure.

"This was a systematic approach to more fully understand the behavior of unconventional superconductors," said Ruslan Prozorov, Ames Laboratory faculty scientist and professor in the Department of Physics and Astronomy at Iowa State University. "We found that some proposed models of unconventional superconductivity in these iron-based compounds were compatible with our results, and this study further limited the possible theoretical mechanisms of superconductivity."Researchers combined innovative crystal growth, highly sensitive magnetic measurements, and the controlled introduction of disorder through electron bombardment to create and study an entire range of compositions within a class of iron-based superconductors. They found that the key fundamental properties—transition temperature and magnetic field penetration depth—of these complex superconductors were dependent on composition and the degree of disorder in the material structure.

Phys.org:
Scientists gain insight on mechanism of unconventional superconductivity
Ruslan Prozorov

Waves of Magnetism...

Magnetic order in (Sr,Na)Fe₂As₂: The crystal structure contains planes of iron atoms (shown as red spheres). Half the iron sites have a magnetization (shown as red arrows), which points either up or down, but the other half have zero magnetization. This shows that the magnetism results from the constructive and destructive interference of two magnetization waves, a clear sign that the magnetic electrons are itinerant, which means they are not confined to a single site. The same electrons are responsible for the superconductivity at lower temperature.

Topics: Condensed Matter Physics, Materials Science, Superconductors

A research team led by the U.S. Department of Energy's (DOE's) Argonne National Laboratory has discovered that only half the atoms in some iron-based superconductors are magnetic, providing a conclusive demonstration of the wave-like properties of metallic magnetism in these materials.

The discovery allows for a clearer understanding of the magnetism in some compounds of iron, the iron arsenides, and how it helps induce superconductivity, the resistance-free flow of electrical current through a solid-state material, which occurs at temperatures up to 138 degrees Kelvin, or minus -135 degrees Celsius.

"In order to be able to design novel superconducting materials, one must understand what causes superconductivity," said Argonne senior physicist Raymond Osborn, one of the project's lead researchers. "Understanding the origin of magnetism is a first vital step toward obtaining an understanding of what makes these materials superconducting. Given the similarity to other materials, such as the copper-based superconductors, our goal was to improve our understanding of high-temperature superconductivity."

Argonne National Laboratory:
New magnetism research brings high-temp superconductivity applications closer
Angela Hardin

For The Better...

Illustration: Takashi Takahashi/Tohoku University

Topics: Condensed Matter Physics, Graphene, Materials Science, Nanotechnology, Semiconductor Technology, Superconductors, Solid State Physics, Quantum Mechanics

Graphene is an amazing conductor. The transport of electrons through graphene nanoribbons has even surpassed what scientists thought were the theoretical limits for the material—so much so that electrons moving through it seem to behave almost like photons.

Graphene’s amazing properties as a conductor has inspired some researchers to explore whether the single-atom-thick sheets of carbon could also be made into superconductors. Last year, an international research team from Canada and Germany was able to demonstrate that graphene can be made to behave that way when it’s doped with lithium atoms.

Now researchers in Japan (from Tohoku University and the University of Tokyo) have developed a new method for coaxing graphene to behave as a superconductor that has some important and distinctive differences from the previous research by the Canadian and German researchers.

IEEE: Graphene's Role as a Superconductor Just Got Better, Dexter Johnson

Quantum Heat Transfer...

Image Source: Low Temperature Lab, Aalto University School of Science

Topics: Quantum Computer, Quantum Mechanics, Superconductors, Thermodynamics

Physicists in Finland have shown that it is possible to conduct heat over macroscopic distances at close to the maximum efficiency permitted by quantum mechanics. By directing photons along a superconducting waveguide, the researchers transferred heat between two resistors spaced up to a metre apart – some 10,000 times further than previously possible at the quantum limit. They say their technique could someday be used to cool chips inside quantum computers.

Quantum mechanics tells us that heat flow, like electric current, can be quantized. If a wire is so thin that an electron's cross-sectional wavefunction can only assume one possible configuration as it travels along the wire, there is an upper limit to the rate at which electrical energy can be transmitted for any given voltage. Likewise, there is a maximum rate at which heat energy can be transferred along a single channel connecting a hot bath to a cold one when the baths are at given temperatures. This is the quantum of thermal conductance, which is reached when the hot bath emits energy perfectly, the cold bath absorbs perfectly, and there is no heat loss along the way.

Physics World: Quantum-limited heat conduction smashes long-distance record
Edwin Cartlidge

MAGLEV @ Home...

Image Source: BBC - Leeds - K-T Picture Galleries

Topics: Materials Science, Quantum Mechanics, Semiconductor Technology, Superconductivity

I might do this at home, but I think this is already a neat demo done for many a high school or even college introductory physics class.

I disagree on one point in the video: we do use superconducting magnets specifically for levitation in the semiconductor industry in a few of our processes that require it. There are also several bullet trains that use this feature of super-cooled metal, thereby inducing superconductivity. You are welcome to invent other uses. Source: Scientific American, How to Do Quantum Magnetic Levitation at Home, November 17, 2015

Superconducting Uproar...

Image Source: Technology Review

Topics: Condensed Matter Physics, Materials Science, Solid State Physics, Superconductivity

TECHNOLOGY REVIEW: The world of superconductivity is in uproar. Last year, Mikhail Eremets and a couple of pals from the Max Planck Institute for Chemistry in Mainz, Germany, made the extraordinary claim that they had seen hydrogen sulphide superconducting at -70 °C. That’s some 20 degrees hotter than any other material—a huge increase over the current record.

Followers of this blog will have read about this work last December, when it was first posted to the arXiv. At the time, physicists were cautious about the work. The history of superconductivity is littered with dubious claims of high-temperature activity that later turn out to be impossible to reproduce.

But in the months since then, Eremets and co have worked hard to conjure up the final pieces of conclusive evidence. A few weeks ago, their paper was finally published in the peer reviewed journal Nature, giving it the rubber stamp of respectability that mainstream physics requires. Suddenly, superconductivity is back in the headlines.

Physics arXiv:
Superconductivity above the lowest Earth temperature in pressurized sulfur hydride
Antonio Bianconi, Thomas Jarlborg

Schrödinger's Bacterium...

Electron microscope image of the bacterium Mycoplasma mycoides, which could someday be put in a quantum superposition. (Courtesy: Thomas Deerinck, NCMIR/Science Photo Library)

Topics: Biology, Quantum Mechanics, Schrödinger's cat, Superconductivity, Research

A proposal for putting a living bacterium into a superposition of quantum states has been unveiled by physicists in the US and China. If successful, the experiment would be the first realization – albeit microscopic – of Schrödinger's famous thought experiment involving a cat in a box that is simultaneously alive and dead until an observer makes a measurement by peering into the box. As well as improving our understanding of the foundations of quantum mechanics, the researchers say that their proposed experiment could also yield a new technique for monitoring defects in biological molecules.

Superposition is a quirky property of the quantum world that allows a physical system such as an atom or photon to exist in two or more quantum states, until a measurement is made on it. In recent years, physicists have created superposition states using inanimate objects of increasing size, from electrons and photons to atoms, molecules and even tiny mechanical systems. Now, Tongcang Li* of Purdue University and Zhang-Qi Yin of Tsinghua University propose doing the same thing with a living object – a tiny bacterium – to realize a version of Schrödinger's cat.

The proposal involves a tiny mechanical oscillator built by John Teufel and colleagues at the National Institute of Standards and Technology in Colorado. That oscillator is an aluminium disc 15 μm across and 100 nm thick that forms the upper plate of a capacitor within a superconducting inductor-capacitor (LC) circuit. In 2011 Teufel's group was able to put the mechanical oscillator in its quantum ground state. This was done by first cooling the apparatus in a cryostat and then subjecting the oscillator to "sideband cooling", which involves coupling its mechanical vibrations to microwave radiation.

* Dr. Tongcang Li was Dr. Mark G. Raizen's former PhD student, University of Texas, Austin; my distinct honor to know both gentlemen.

Physics World:
Could 'Schrödinger's bacterium' be placed in a quantum superposition?
Edwin Cartlidge

Graphene Superconductor...

Graphene turns into a superconductor when decorated with lithium atoms. (Courtesy: Shutterstock/Inozemtsev Konstantin)

Topics: Condensed Matter Physics, Graphene, Materials Science, Nanotechnology, Phonons, Semiconductor Technology, Superconductors, Solid State Physics, Quantum Mechanics

THIS changes the game! The application to longer life batteries is the first thought that comes to mind. Within semiconductors, we could supplement the physical limitations we're butting up to at the Moore's Law limit with a neat change in the material chemistry used to build the circuitry. A step before and enhancement of carbon nanotubes when they eventually replace them. Exciting times!

The "wonder material" graphene has another significant quality to add to its impressive list of electrical and mechanical properties: superconductivity. Physicists in Canada and Germany have shown that graphene turns into a superconductor when doped with lithium atoms – a result that could lead to a new generation of superconducting nanoscale devices.

Graphene exhibits a range of remarkable properties, thanks to its special structure – a one-atom-thick hexagonal lattice of carbon atoms. It is far stronger than steel while also flexible, and is an excellent conductor of both electricity and heat. In its pristine form, however, it is not a superconductor.

Neither is pure graphite, but in 2005 physicists showed that graphite could be made to superconduct when chemically treated, so as to create bulk materials consisting of graphene alternated with one-atom-thick layers of another element. The best performing material thus created, calcium graphite (CaC₆), has a superconducting transition temperature of 11.5 K. Theorists identified the underlying mechanism for that superconductivity as electron–phonon coupling. Phonons are vibrations in a material's crystal lattice that bind electrons together into "Cooper pairs" that can travel through the lattice without resistance – one of the hallmarks of superconductivity. It was then realized that such electron–phonon coupling might occur not just in bulk graphite compounds but also by depositing atoms of a suitable element on to single layers of graphene.

Physics World: 'Decorated' graphene is a superconductor, Edwin Cartlidge