Skip to main content

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact customerservices@ioppublishing.org

Registration complete

Thank you for registering with Physics World
If you'd like to change your details at any time, please visit My account

Close
Home » Page 971

Quadrupole topological insulator created in mechanical metamaterial

The first “quadrupole topological insulator” has been created in a mechanical metamaterial by physicists in Switzerland. The experiment confirms a theoretical prediction made in 2017 that the concepts behind traditional dipole topological insulators can be extended to create higher multipole versions. The researchers believe the work could lead to one-way waveguides that are immune to scattering.

Unlike most topological insulators – which involve the conduction of electrical charge – the topological properties of the metamaterial arise from its vibrational modes. Work done recently by two other teams of physicists suggest that quadrupole topological insulators can also be made from systems based on electrons and photons.

In traditional electrical topological insulators, electric dipole moments sit head-to-tail in the bulk of the crystal, effectively cancelling each other. At the surfaces, however, electrical charges can build up, leading to edge modes that conduct charge in one direction with no scattering. In 2017, Taylor Hughes of the University of Illinois at Urbana Champaign and colleagues calculated that, if higher-order charge polarization occurred within a crystal, more complex phenomena could be seen at the edges. For example, if the bulk contained quadrupolar moments, each edge should become a 1D version of a traditional dipole topological insulator, giving rise to “corner modes” where they met.

Mathematical link

Topological insulators analogous to the electrical dipole type have been created in systems where electromagnetic radiation or mechanical oscillations play the role of electrical charge. “The link is really on the mathematical level,” explains Sebastian Huber of ETH Zurich. “The existence or absence of surface states is independent of these degrees of freedom being charged or not.” In the new research, Huber and colleagues produced a mechanical metamaterial that achieves the first experimental demonstration of a quadrupole topological insulator.

The team used the mathematical principles outlined by Hughes’ team to calculate the resonant frequencies of the various modes in a topological mechanical metamaterial made from 5 mm silicon plates connected together by beams. They then fabricated the metamaterial and measured its response to induced vibrations at various frequencies. “There is a whole frequency range where you can’t excite any vibrations in the system either in the bulk or in the edge,” says Huber. “However, at the four corners, right in the middle of this frequency band, you can excite vibrations: these are the four corner states.”

At present, the system is two dimensional, so the corner modes have nowhere to go. However, Huber and colleagues aim to develop a stacked, three-dimensional set-up. It should be possible, says Huber, to develop a cubic architecture in which some corners will only allow propagation in one direction and some will only allow it the opposite way. This, he says, would be “the dream” for producing things like topologically protected, scatter-proof waveguides.

“One of the significant things here is that I think this is the first example in which a concept from topological matter has been realized first in a mechanical system,” says Martin van Hecke of the Institute for Atomic and Molecular Physics in Amsterdam, who was not involved with the research.

Rapid realization

“We were excited to see that our predictions could be realized so quickly,” says Hughes, “It shows that the field of topological metamaterials is a very capable avenue for realizing these interesting topological phases in experiments.”

In pre-prints published recently, Hughes’ team describes an analogous system based on a microwave resonator, whereas Ronny Thomale of the University of Würzburg in Germany and colleagues describe a describe a similar system based on an electrical circuit.

Huber and colleagues described their metamaterial in Nature.

Chemists gear-up for 2019 International Year of the Periodic Table

Next year has been designated the International Year of the Periodic Table of Chemical Elements (IYPT) by the United Nations Educational, Scientific and Cultural Organization (UNESCO). The celebrations in 2019 will mark 150 years since the iconic chart – which contributed greatly to the development of modern chemistry and atomic and nuclear physics – was devised by the Russian chemist Dmitri Mendeleev. IYPT will also pay tribute to the recent discovery of four new elements: nihonium-113; moscovium-115; tennessine-117; and oganesson-118, which UNESCO says resulted from “close international scientific cooperation”.

The IYPT is supported by the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Pure and Applied Physics, the European Association for Chemical and Molecular Sciences, the International Astronomical Union and the International Union of History and Philosophy of Science and Technology.

Educational experiments

The IYPT will be used by UNESCO’s International Basic Sciences Programme to promote international co-operation in the basic sciences for sustainable development. A UNESCO Global Microscience Experiments Project will also be dedicated to the periodic table. Microscience is an educational initiative that provides low-cost experimental equipment to primary and secondary school pupils – and university students in some countries.

Other related anniversaries in 2019 include the discovery of phosphorus 350 years ago by the alchemist Hennig Brand. In 1789, Antione Lavoisier grouped 33 elements into gases, metals non-metals and earths. Next year is also the 190th anniversary of Johann Wolfgang Döbereiner’s work on “triads”, which was another attempt at making sense of the chemical elements. More recently, the element francium was discovered in 1939 by Marguerite Perey.

100th anniversary of IUPAC

The IYPT also coincides with the 100th anniversary of the founding of IUPAC – which along with IUPAP confirms the discovery of new elements and gives them their official names. Eager to start the festivities, IUPAC will be releasing monthly bulletins in 2018 that highlight the activities of the organization over the past century.

How to write a good CV for industry

Physics World: What do people in industry tell you they need to see on a CV?

Andrew Hirst: Writing a good CV for any job requires you to present strong evidence that you can do the job or – if you haven’t finished your degree yet – that you have the potential to do so. One mistake students often make is to believe their CV will land them the job they’ve applied for. A CV is the beginning and not the end of the recruitment process. It’s a door opener to the next step, be it a telephone interview, an assessment or a face-to-face interview. Your CV is a marketing tool that highlights to the recruiter your relevance to the job requirements, which will depend on the role, sector and seniority of the position.

So presumably it’s vital to tailor your CV to the role?

Yes, you need to emphasize the most relevant skills and experiences for the job. One common mistake that students make is to submit a generic CV to multiple employers. When your CV arrives at its destination, its content will either appeal or it won’t. Your job is to take the excellent work you’ve done and feature it in a way that opens the doors you want opened. Remember that companies have different needs depending on the sector they’re in – be it aerospace, food manufacturing, automotive or optics – and the type of role you are applying for.

If your degree’s purely academic, how can you show you’re suited to a job in industry?

Employers do want to see a track record of academic attainment but crucially they also want to see you can apply your physics knowledge beyond the lecture theatre, to solve real technical problems. They want evidence that you have a range of aptitudes that you’ll need in a business setting.

And what exactly are those aptitudes?

Having spoken to many employers about the skills they associate with excellent undergraduates and graduate students, they are after people who are commercially aware, who can provide solutions to business needs, and who enjoy applying knowledge to real and incomplete problems. They want people who can deliver results in different team environments and cultures, who understand themselves, and who are team players who can adapt to new situations.

So your CV shouldn’t just flag academic attainment?

Yes, employers are interested in a range of skills and behaviours beyond just the ability to solve equations or learn from a textbook. When writing your CV, think about examples from your time at university that show you’ve applied these competencies, whether it’s in the lab or in an extra-curricular activity – such as when you volunteered or worked in an office.

What practical advice do you have for writing a CV?

Only include information from your career that’s relevant to the job application. Concentrate on specific examples and write a maximum of two A4 pages – there’s no need to write a novel. Highlight what you’ve achieved – not just what you’ve done. Don’t just list the modules you’ve studied, people you’ve worked for or extra-curricular activities you’ve taken part in. They’re important, but also state what you did, how you did it and what were the results.

What’s the best way of marshalling all relevant information on a CV?

To make clear to employers how your academic knowledge, technical skills and extra-curricular activities are relevant to the job in hand, it’s useful to write a “competency-based” CV. This includes similar information to the more traditional “reverse-chronological” CV, where you list everything you’ve done starting from now and working backwards. A competency-based CV instead organizes the content into a sequence of competencies and skills that match the requirements in the job specification. This kind of CV lets employers see more easily how your experience and skills match the requirements of the job.

That sounds great, but how do you do that in practice?

A simple tactic is to use the “challenge-approach-results” (or CAR) method. First, think about a problem or obstacle you have faced (the challenge). Then consider the action you took to resolve the problem (the approach). Finally, note down what was the outcome (the result).

Can you can give some examples of this from someone who’s done a physics degree?

To show evidence for teamwork, you could say something like: “I worked in a group of five students to conduct a four-week project to investigate the linear expansion of metals through interferometry. My role was to assign and prioritize tasks to team members and to contribute to the data analysis and verbal presentation. This assignment gave me experience of project management, communicating results within a team and completing tasks to meet a set deadline.” Or, to give evidence of lab skills, you could say: “I have designed, implemented and run weekly experiments, with little supervisory guidance, in atomic physics, solid state and optics. For example, I conducted an experiment that investigated the moment of inertia of different bodies, making use of rotary motion and force sensors. I would calculate theoretical parameters and compare to experimental values found from manipulating data. This required me to problem-solve throughout the experiment in terms of fault-finding and error analysis.”

Any practical tips about the style and appearance of the CV?

Don’t go mad. Don’t use fancy borders, fonts or background colours – no-one wants to read a CV in pink, 18-point Comic Sans. Just use clear, well-spaced text that can be read quickly and easily. It’s also vital to avoid clichés – I’ve lost count of the number of times I’ve read on a CV something like “I am an enthusiastic individual with excellent communication skills.” Clichés will not allow you to stand out from the crowd – instead give concrete examples of when you’ve learnt or enhanced these particular skills.

So what kind of things should you say?

If you want to flag your communications skills, you might write: “As part of my professional-skills module I have given several presentations, including one on the application of photomultiplier tubes. This gave me the experience to communicate ideas and results to both students and staff. I also wrote a formal report that investigated the temperature variation of electrical resistance within metals and semiconductors. I discussed the theory I applied to the experiments; mentioned the method I used to gather suitable data, for example, by calibrating a thermocouple and using data-acquisition interfaces; and analysed my results in terms of errors and the importance and implications of my results.”

Any final advice to help bag that top industry job?

Research the job and company you’re interested in before you start writing. Understand how your interests, academic knowledge and extra-curricular activities fit the role and the organization you hope to work for. Mirror the structure of the CV to the job’s specification or competencies and include relevant modules from your degree. Articulate relevant skills and experience – and give examples. And finally, proofread the document. There’s no excuse for spelling mistakes.

Ultramicroelectrodes deliver reliable neural recording

Implanted cortical microelectrode arrays can be used to record and stimulate neural activity, enabling studies of neural circuit function and treatment of many chronic diseases. The reliability of such arrays, however, is limited by insertion trauma and the foreign body response, which can lead to electrode encapsulation and neuron damage. Minimizing these tissue responses is vital for future development of brain-machine interfaces.

The impact of such tissue reactions depends upon factors including the electrode materials, and the size and geometry of the implanted microelectrodes. With this in mind, researchers from the University of Texas at Dallas and Boston University are developing microelectrode arrays based on amorphous silicon carbide (a-SiC). The arrays contain shanks (the parts that penetrate neural tissue) with a maximum transverse dimension of 10 µm and a cross-sectional area of below 60 µm2 (J. Neural. Eng. 15 016007).

“Recording and stimulation of neural activity is greatly influenced by the distance between the electrode site and the target neuron or neuronal network,” explained first author Felix Deku from UT Dallas’ Neural Interfaces Laboratory. “The small shank dimensions of our devices will reduce tissue damage during implantation and minimize the foreign body response, thereby increasing the possibility of our electrodes to be in close proximity to healthy neurons.”

Electrodes for recording neural activity work best with low impedance, while high charge-injection capacity is required for safe stimulation. The tiny shanks in these arrays have electrode sites with extremely small geometric surface areas (from 20–200 µm2). Consequently, they exhibit higher impedance and lower charge-injection capacity than typical silicon-based microelectrodes.

This small size does, however, confer a unique advantage. With one dimension smaller than 25 µm, the electrode sites meet the criteria to act as ultramicroelectrodes (UMEs). “Ultramicroelectrode behaviour allows for hemispherical migration of counterions to the neural interface and produces a substantial increase in the injectable charge per unit area compared to microelectrodes,” said Deku.

To improve stimulation and recording capabilities further, the team also investigated the use of low-impedance coatings – of titanium nitride (TiN) or sputtered iridium oxide (SIROF) – on the electrode sites.

Electrochemical characterization

The researchers chose a-SiC to create the implantable devices as is well-tolerated in the cortex and highly stable in saline. It is also amenable to standard thin-film fabrication processes. For this study, they used plasma enhanced chemical vapor deposition to deposit a-SiC films that completely encapsulate the metal interconnects, and created electrode sites by etching openings in the top of the a-SiC.

Deku and colleagues fabricated a-SiC microelectrode arrays with 16 penetrating shanks, each having a cross-sectional area less than 60 µm2. They characterized the electrochemical properties of gold and gold/platinum UMEs, as well as gold UMEs coated with SIROF or TiN. Cyclic voltammetry revealed cathodal charge storage capacities of 35 and 12 mC/cm2, for SIROF and TiN-coated UMEs respectively, compared with 10 and 2 mC/cm2 for uncoated platinum and gold UMEs, respectively.

Electrochemical impedance spectroscopy of UMEs
Electrochemical impedance spectroscopy of UMEs

Electrochemical impedance spectroscopy demonstrated that coating gold electrodes with SIROF reduced their average impedance at 1 kHz from 2.86 MΩ to 90.2 kΩ, while a TiN coating reduced the impedance to 31.1 kΩ. Finally, the team investigated the ability of the coated UMEs to deliver charge. The maximum charge injection capacity for SIROF-coated UMEs was 3.4 mC/cm2 at 0.0 V anodic bias and 15.3 mC/cm2 at 0.8 V bias; for TiN, these values were 3.2 and 6.2 mC/cm2 at 0.0 and 0.8 V. They point out that these values are notably larger than those reported for similar coatings on larger microelectrodes.

Electrical stimulation capabilities of UMEs
Electrical stimulation capabilities of UMEs

In vivo experiments

Finally, the researchers evaluated the ability of the a-SiC microelectrode arrays to provide neural recordings in vivo. For intracortical studies, they fabricated arrays with 16 penetrating shanks with one electrode per shank. Each shank was 4–5 mµ thick, 9 mµ m wide, 4 mm in length and terminated in a sharp point.

The researchers implanted a microelectrode array with 100 mµ m2 platinum UMEs in the basal ganglia nucleus of an anesthetized zebra finch. Immediately after implantation, they recorded neuronal spike waveforms demonstrating single unit spiking activity. The 16 recorded channels showed no strong coupling between contacts.

They also tested the feasibility of recording spontaneous activity in the motor cortex of an anesthetized rat, using a microelectrode array with SIROF-coated UMEs. They observed spontaneous neural activity recorded simultaneously on nine channels. Distinct spiking activity across multiple channels confirmed that the array recorded from spatially selective neuronal population. The spike shapes were similar to previously reported cortical single unit recordings.

The researchers concluded that the a-SiC microelectrodes have potential for decreased tissue damage and reduced foreign body response, as well as the potential for clinical translation. “While our a-SiC UME technology shows promising capabilities in the acute experiments, one of the drawbacks to existing technologies is the lack of chronic stability,” Deku told medicalphysicsweb. “We are therefore now evaluating our devices for chronic stability.”

PET tracer measures demyelination in mice

Demyelination – the loss or damage of the myelin that surrounds and insulates nerves – is the hallmark of the neurological disorder multiple sclerosis (MS). When segments of this protective membrane are damaged, nerve impulses can be disrupted, causing symptoms ranging from tingling and numbness to weakness, pain and paralysis. Quantitative imaging of demyelination would provide critical clinical insight, but currently there is no reliable way to achieve this.

At present, MRI is used to image demyelination, but it is not quantitative and cannot distinguish between demyelination and inflammation, which often coexist in MS. Now, a multi-institutional team in the USA has described early results of a novel minimally-invasive method to assess myelin damage using PET (Scientific Reports 8 607).

The PET scans employ a tracer designed to target voltage-gated potassium channels, which are found on demyelinated axons. “In healthy myelinated neurons, potassium channels are usually buried underneath the myelin sheath,” explained study author Brian Popko from the University of Chicago. “When there is loss of myelin, these channels become exposed. They migrate throughout the demyelinated segment and their levels increase.”

These exposed neurons leak intracellular potassium. This leaves them unable to propagate electrical impulses, which causes some of the neurological symptoms seen in MS. “So we developed a PET tracer that can target potassium channels,” Popko said.

The team started with an existing MS drug, 4-aminopyridine, which binds to exposed potassium channels. The drug can partially restore nerve conduction and alleviate neurological symptoms in MS patients. Using mouse models of MS, the researchers showed that the drug accumulated in demyelinated areas of the central nervous system.

They then examined fluorine-containing derivatives of 4-aminopyridine for binding to axonal potassium channels. They found that 3-fluoro-4-aminopyridine (3F4AP) had the desired properties and labelled it with fluorine-18 to enable PET imaging. “We were able to show, in rats, that the tracer accumulated to a higher degree in demyelinated areas than in control areas,” said Popko.

“All existing PET tracers used for imaging demyelination bind to myelin and, consequently, demyelinated lesions show as decreases in signal, which can be problematic for imaging small lesions,” explained first author Pedro Brugarolas, currently at MGH/Harvard Medical School. “3F4AP is the first tracer whose signal increases with demyelination, potentially solving some of the problems of its predecessors.”

Finally, in collaboration with scientists at the National Institutes of Health, the researchers conducted a study in healthy monkeys. They confirmed that radiolabelled 3F4AP entered the brain of primates and localized to areas where there was little myelin.

“We think that this PET approach can provide complementary information to MRI, which can help us follow MS lesions over time,” said Popko. “It has the potential to track responses to remyelinating therapies, an unmet need. This approach should also help determine how much disruption of the myelin sheath contributes to other central nervous system disorders.”

Archaeology may help climate-change adaptation

Ancient cultures were able to farm in regions that are now uncultivated. But what is the potential of using their sophisticated techniques to adapt to today’s climate-change-related aridification? A recent publication by Eva Kaptjin of the Royal Belgian Institute of Natural Sciences investigates.

Archaeological finds show how past societies adapted to variable environmental conditions and which techniques succeeded or failed. The water-management techniques of ancient peoples often worked on a local level. Unlike many modern-day water-management projects that include large dams and the rerouting of river water, these local methods are cheaper, more sustainable and don’t need as much oversight from distant authorities.

Complications arise from the many aspects of human societies that do not leave traces in the archaeological record, for example religion or social organization. Such aspects can have a large impact on human behaviour and don’t always lead to rational responses to external threats. So to implement ancient techniques successfully today, it’s important to understand ancient methods in their sociocultural context.

With that in mind, Kaptjin cites the example of the Mexican province of Tabasco, where the government tried to reinstate an old agricultural technique that used raised fields in swamps and lakes. These Chinampas were favoured by Aztec and Mayan societies across the region. The first modern attempt saw Chinampas built using bulldozers and without the involvement of archaeologists and local farmers. This led to failed harvests and a mismatch between the crops produced and market demands. After strict regulations were dropped, local indigenous peoples were able to build and farm the Chinampas more successfully.

A second example are the Cochas in Peru – natural depressions used by Inca societies to store rain and run-off. A modern-day implementation recruited local people as community messengers to advocate for the practice. These messengers informed local communities about the necessity of adaptation to climate change and functioned as contacts locals could turn to when problems arose.

The main lessons learned from this study, which appeared in Wiley Interdisciplinary Reviews: Water, are that modern-day planners need a detailed understanding of the ancient techniques. This includes the geological and geomorphological environment and details of the technical execution, as well as the socio-cultural context in which the method was developed and whether it’s translatable to the modern situation. And the involvement of local communities and inclusion of their environmental knowledge from an early stage is fundamental to success today. But if these lessons are accounted for, the past has great potential for the future.

Neutrons fly left or right depending on size of colliding nuclei

Researchers at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab (BNL) in the US have discovered that when spinning protons collide with nuclei they produce neutrons that fly-off in different directions that depend on the size of the target nucleus. The physicists say that this unexpected observation suggests that the neutrons-producing mechanism is different for large and small nuclei. They add that this could have important implications for interpreting other high-energy particle collisions, including the interactions of ultra-high-energy cosmic rays with the Earth’s atmosphere.

RHIC has been operating since 2000 and is the only collider in the world with the ability to precisely control the spin polarization of colliding protons. During its first polarized proton run in 2001–2002 researchers discovered that when a proton with upward spin collides with another proton, the neutron produced in the collision prefers to emerge to the right.

Almost a decade later, in 2011, theoretical physicists published a paper explaining this result. But then in 2015 a PhD student at Seoul National University in South Korea and BNL, Minjung Kim, made a surprise discovery. She observed that when protons collided with gold nuclei – which are much larger than protons – they produce a neutron with a strong preference to travel in the other direction: to the left.

Completely unexpected

This change in directional preference was not predicted by the 2011 theory. “What we found from the collisions with gold nuclei in 2015 was not only that the asymmetry magnitude increased by a factor of around three, but also its sign flipped, with the preferred scattering direction changing from the right to the left,” Alexander Bazilevsky, a physicist at BNL and deputy spokesperson for the PHENIXcollaboration at RHIC, tells Physics World. “It was completely unexpected.”

To confirm Kim’s finding, PHENIX physicists worked on data analysis and detector simulations, and repeated the measurements under more precisely controlled conditions. These new experiments also included collisions between protons and aluminium nuclei, which sit between protons and gold nuclei in size.

The results confirmed that proton-proton collisions produce a directional asymmetry with more neutrons scattering to the right, while proton-gold collisions produce a stronger asymmetry with neutrons scattering to the left. And, collisions with the intermediate-sized aluminium ions produced neutrons with near zero asymmetry – a roughly equal number scattered in each direction.

Charged collisions

To explain their findings the physicists looked closely at the processes and forces affecting the scattering particles. They concluded that in proton–proton collisions the asymmetry is driven by interactions governed by the strong nuclear force, as described in the 2011 theory. In large nuclei with more positive electric charge, however, electromagnetic interactions play a much more important role in particle production than in collisions between two equally charged protons.

“We believe due to much larger electric charge of gold nucleus compared to proton, the electromagnetic interactions take on a larger role for neutron production in competition with strong nuclear interactions, with generated asymmetry of opposite sign to the one produced by strong nuclear interactions,” explains Bazilevsky. He adds that in medium sized aluminium nuclei the asymmetries generated by nuclear and electromagnetic interactions cancel each other out, and the result is no directional asymmetry in the resulting neutrons. “As our paper shows, the asymmetry sign flip happens around the aluminium nucleus, hence we would expect all nucleus lighter than aluminium would generate negative asymmetry (right preference), and all heavier nucleus would produce positive asymmetry (left preference),” he explains.

The study is described in Physical Review Letters.

Optical ‘astrocomb’ could boost searches for Earth-like planets

A new type of laser frequency comb (LFC) has been developed by scientists in Europe. The prototype device could lead to improvements in how scientists search for Earth-like exoplanets, measure the expansion of the Universe and test the fundamental constants of nature.

LFCs produce spectral lines of light with evenly spaced frequencies and have a wide range of applications in metrology and spectroscopy. The new LFC was developed by Tobias Herr of the Swiss Centre for Electronics and Microtechnology, Francesco Pepeof the Geneva Observatory and colleagues. It uses a laser-driven microresonator on a silicon-nitride chip that produces 24 GHz pulses for use in calibrating near-infrared spectrometers. This gives it an advantage over traditional LFCs, which operate at frequencies below 10 GHz and create a line spacing that is too small for astronomical spectroscopy.

The pulses are produced by way of a phenomenon known as temporal dissipative Kerr-cavity solitons (DKSs), which involves trapping ultra-short pulses of light in a circular, micron-sized microresonator. Each time the DKS pulse passes the microresonator’s input-output coupler, some of the pulse is siphoned away and directed towards the spectrometer, producing a series of spectral lines that, in the prototype, are each precisely 24 GHz apart. These lines form a spectral comb and act as a precise calibration tool for the spectrometer.

One popular method of detecting exoplanets is the radial velocity technique. This involves measuring a star’s subtle motion that is caused by the gravitational tug of an orbiting planet. These motions are often no faster than walking pace and require highly accurate spectroscopic measurements of the Doppler shift in the star’s light as it moves. The size of the Doppler shift and the period at which it occurs can tell astronomers both the mass and the distance from the star of the planet. The greater the mass of the star, or the less massive or more distant the planet, the smaller the Doppler shift.

Increasing accuracy

Currently, astronomical spectrometers use hollow-cathode lamps that produce a limited number of noisy calibration lines, or standard, low frequency LFCs that pass through Fabry–Pérot etalons to increase their spectral range at the expense of accuracy. For example, the HARPS instrument on the 3.6 m telescope at the European Southern Observatory in Chile can measure a Doppler shift caused by velocities as low as 30 cm/s. Meanwhile, the ESPRESSO, which saw first light on ESO’s Very Large Telescope in December 2017 can achieve an overall spectral resolution of 10 cm/s. Both use thorium-argon lamps as well as LFCs passed through Fabry–Pérot etalons.

Although the success of the DKS frequency comb also depends on the stability of the spectrometer, it has the potential to measure Doppler shifts of just a few centimetres per second. This means that it could, in principle, be used to discover potentially habitable worlds orbiting Sun-like stars.

“In the future we hope to increase the number of LFC lines to reach the 1 cm/s level,” says Herr. “However, before the technology can be used routinely there are number of technological challenges to overcome,” Herr adds. Among these obstacles is the need to increase the span of the LFC to cover the entire near-infrared and optical bands, and also the need to make the technology less complex and more user-friendly for routine use.

Astronomical applications

However, Pepe says, “instruments such as the upcoming NIRPSspectrograph, which will join HARPs on ESO’s 3.6 metre telescope in 2019, will possibly be equipped with LFCs based on this new technology”. Ultimately, the compact nature of the technology could even see it employed in spectrometers on space-based missions.

Beyond planet-finding, the new technology could improve measurements of the redshifts of galaxies, thereby assisting in providing a more accurate measure of dark energy or the Hubble constant. Meanwhile, by observing galaxies at varying distances and measuring shifts in specific emission lines that are directly dependent upon the properties of the fundamental constants of nature, cosmologists are seeking to discover whether these constants are really variables. Because the shifts related to varying constants, such as the fine structure constant, are so tiny, a DKS laser frequency comb is likely to be the best way of making these measurements.

The new laser frequency comb is described in a preprint on arXiv.

Engineers reinvent the inductor after two centuries

Could the inductor be redesigned in a fundamentally new way? Yes, according to new work by researchers in the US, Japan and China who have made the first high-performance inductors from intercalated graphene that work in the 10-50 GHz range thanks to the mechanism of kinetic inductance – rather than magnetic inductance as in conventional devices. The new inductors, which have both small form-factors and high inductance values, of around 1-2 nanoHenry (a combination that has been difficult to obtain so far), are a third smaller in terms of surface area than conventional devices but with the same performance. They might thus be used in ultra-compact wireless communication systems for applications in the Internet of Things (IoT), sensing and energy storage/transfer.

“The inductor was invented nearly 200 years ago, but this is the first time since then that a completely new mechanism (kinetic inductance) is being exploited (using intercalated graphene) to re-invent this fundamental passive device,” team leader Kaustav Banerjee of the University of California, Santa Barbara, tells nanotechweb.org. “This could have significant implications for wireless communications, sensing and energy storage/transfer applications for the IoT era. It also highlights a practical application for graphene beyond circuit interconnects.”

The IoT promises to connect us with as many as 50 billion objects by 2020, with a potential impact of $2.7 to 6.2 trillion per year by 2025. This revolution will require an enormous number of miniaturized, high-performance and scalable wireless connections that are driven by radio-frequency (RF) integrated circuits (RF-ICs). Another important area, that of radio-frequency identification (RF-ID), which relies on electromagnetic fields to automatically identify and track tags attached to objects, is predicted to increase to nearly $19 billion by 2026.

Planar on-chip metal inductors are the main types of device employed in RF-ICs and can take up as much as half of the chip area space. They are also responsible for the major part of the form factor of RF-IDs.

Scaling down difficult for on-chip inductors

However, the problem is that, unlike transistors and interconnects in IC technology that have been successfully scaled down, the same cannot be said for on-chip inductors. This is because inductors have been traditionally designed to work using magnetic fields alone, so a certain amount of inductor area is needed to capture these fields. What is more, conventional metals only have a small kinetic inductance because of their low momentum relaxation time (which is the average time for a carrier – an electron or hole – to lose its original momentum because of a scattering event).

To scale down inductors, we need to improve their inductance density. This is defined by the inductance per unit area = total inductance (Ltotal)/inductor area, where Ltotal is the sum of the magnetic inductance (LM) and the kinetic inductance (LK).

Kinetic inductance is a purely material property

Magnetic inductance is the property of an electrical conductor by which a change in current through it induces an electromotive force in both the conductor itself (self-inductance) and in any nearby conductors (mutual inductance) that opposes the change. Kinetic inductance, for its part, is the inertial mass of mobile charge carriers in alternating electric fields and so does not rely on the magnetic field.

All this means that the magnetic inductance depends on the geometrical design of the inductor itself, while the kinetic inductance is a purely material property, says Banerjee. Improving both the LM and LK should thus improve the overall inductance density, which is our goal.

Carbon nanomaterials to the rescue

Banerjee and colleagues recently found that carbon materials, including carbon nanotube bundles and multilayer graphene, are attractive materials for on-chip inductors thanks to their high magnetic inductance and high LK, which can be equal or even greater than the magnetic inductance. “We can thus use these materials to now scale down the on-chip inductor size without compromising their inductance values.”

In this work, the researchers started out with millimeter-sized multi-layer graphene sample transferred to isolating substrates that they intercalation doped with bromine.

Layer separation increases the kinetic inductance

“Intercalation involves inserting ‘guest’ molecules between the two other ‘host’ molecules in multilayered structures, which in this case are bromine and MLG respectively,” explains Banerjee. “This intercalation introduces two important properties in the MLG. First, and perhaps most crucially, it increases the separation between the adjacent graphene layers. This increase has the effect of ‘decoupling’ these layers and thereby increases the kinetic inductance by increasing the momentum relaxation time.”

Thanks to its linear electronic band structure, monolayer graphene typically has a significantly larger momentum relaxation time compared to its multi-layer counterpart. In fact, interlayer coupling in MLG transforms the linear band structure of the monolayers to hyperbolic, which leads to lower momentum relaxation times and thus lower kinetic inductance.

A new working mechanism for inductors

“Secondly, intercalation dopes the MLG and increases its electrical conductivity, which helps in improving its performance (or Q-factor).”

The work could revolutionize the way we make on chip inductors employed in analogue/RF ICs for wireless communications, and highlights a new working mechanism for these devices, he says. “Such inductors are set to become crucial in the near future where billions of connected IoT devices will send and receive huge quantities of information to each other in applications such as continuous monitoring of vital health signs and security, and also provide unprecedented connectivity for living a smarter life.”

The team, which includes researchers from the Shibaura Institute of Technology in Tokyo and Shanghai Jiao Tong University, is now busy looking into ways to further improve the efficiency of the intercalation process so that the kinetic inductance can be further increased. “This would in turn increase the inductance density and could help further downscale on-chip inductors and thus improve the area-efficiency of the chip as well as its Q-factor,” explains Banerjee. “We are also trying to make the entire inductor fabrication process compatible with back-end-of-line CMOS technology.”

Full details of the research are reported in Nature Electronics doi:10.1038/s41928-017-0010-z.

Arctic reaches a ‘new normal’

The Arctic environment has reached a “new normal”, characterized by thinner sea ice covering less of the surface area, shorter and less extensive winter snow cover, less ice mass in Greenland and Arctic glaciers, and warmer sea surface and permafrost temperatures. That conclusion represents the work of 85 scientists from 12 countries who prepared the 12th annual Arctic Report Card for the US National Oceanic and Atmospheric Administration (NOAA). It was released at the annual meeting of the American Geophysical Union (AGU) in New Orleans in December.

Jeremy Mathis of NOAA told reporters at AGU that changes in the Arctic affect not only that region, but “will impact all of our lives”. They will result in more extreme weather events, higher food prices and climate refugees. Although there were fewer weather anomalies in the Arctic in 2017, compared with the record-breaking warming of 2016, he said, “the Arctic shows no signs of returning to the reliably frozen state it was in just a decade ago”.

Arctic temperatures continue to rise at double the rate of the rest of the planet, NOAA reports. For the year ending September 2017, the average Arctic surface air temperature was the second warmest since 1900, after 2016.

Specifically, reported NOAA’s Emily Osborne at AGU, the average Arctic air temperature was 1.6o C above the long-term average from 1981 to 2010. The record summer temperatures of 2016 were followed by the lowest recorded winter sea ice maximum since satellite observations began in 1979, she said. The cooler summer of 2017 resulted in the minimum sea ice cover being ranked eighth lowest on record, she explained, adding that 10 of the lowest observed sea ice minima occurred in the past 11 years.

The remaining sea ice is much younger, more fragile and more prone to melting than in the past, Osborne noted. The report card says that only 21% of the 2017 ice cover was older than one year, and so thicker. In 1985 this figure was 45%. More exposed seawater means more absorption of radiant energy from the Sun, leading to warmer water, and additional melting of the remaining ice.

The August 2017 sea surface temperatures in the Barents and Chukchi Seas were as much as 4o C warmer than average, NOAA reported. The higher temperatures contributed to a delayed freeze-up in those regions in the autumn.

Turning to land, Vladimir Romanovsky of the University of Alaska Fairbanks reported at AGU that the Eurasian Arctic experienced above-average snow cover in 2017, while North America’s Arctic had less than average snow cover and earlier snow melt, continuing a trend of 11 of the past 12 years. The Greenland ice sheet has been measured since 2002, he said. It experienced less melting than average in 2017, compared with the previous nine years, but remains nevertheless a major contributor to sea level rise.

The Arctic Report Card covers many additional topics, including fisheries, wildfires, greening of the tundra and primary productivity (at the base of the marine food web).

Copyright © 2026 by IOP Publishing Ltd and individual contributors