We propose and analyze theoretically a class of energy-efficient magnetoelastic devices for analog signal processing. The signals are carried by transverse acoustic waves while the bias magnetic field controls their scattering from a magnetoelastic slab. By tuning the bias field, one can alter the resonant frequency at which the propagating acoustic waves hybridize with the magnetic modes, and thereby control transmission and reflection coefficients of the acoustic waves. The scattering coefficients exhibit Breit-Wigner/Fano resonant behavior akin to inelastic scattering in atomic and nuclear physics. Employing oblique incidence geometry, one can effectively enhance the strength of magnetoelastic coupling, and thus countermand the magnetic losses due to the Gilbert damping. We apply our theory to discuss potential benefits and issues in realistic systems and suggest routes to enhance the performance of the proposed devices.
The research leading to these results has received funding from the Engineering and Physical Sciences Research Council of the United Kingdom (Grant No. EP/L015331/1) and from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie Grant Agreement No. 644348 (MagIC).
From 11th to 14th August, fourth year PGR Carlota Ruiz De Galarreta attended the Complex Nanophotonic Science Camp, held in Cumberland Lodge (Windsor Park). The event is specifically oriented to early-career stage scientists working in different fields, such as imaging in turbid media, optical neural networks or disordered metasurfaces.CDT alumnus Ilya Starshynov contributed a talk on ‘Non-line-of-sight imaging using artificial neural networks’.
Here’s what Carlota said about her experience:
During the event, I had the opportunity to attend to various talks from a wide range of topics going from structural colour generators to biosensors, as well as to chair one of the sessions. In addition, I’ve been given the opportunity to present my work about all-dielectric phase-change metasurfaces in the poster session, which I found quite useful to get feedback from people working in different areas (hence to get new points of view and perspectives of my work!).
She is now working with David as a Postdoctoral Research Associate at University of Exeter, where she continues working in the field of reconfigurable phase-change metasurfaces and photonics, as well as helping new CDT students with their projects. She has been recently involved in the Fun-Comp European project, which aims to develop new electronic and photonic computing building blocks and computing networks based on phase-change materials.
This work looks at the properties of the tiny diamonds formed during the detonation of explosives. Particularly, we look at how light can be emitted from the diamonds due to the defects that occur within them as a result of their violent creation. The diamonds have applications in imaging, as the emission is both very bright and confined to a small area, amongst others. Such diamonds have, for example, previously been used to image inside cells as their small sizes mean they can easily move within biological samples. The key results from this paper are that the method used to produce the diamonds gives a high concentration of defects, and therefore brighter emission, and the demonstration that quantum effects allow us to switch the emission on or off by using a magnetic field.
The content of nitrogen-vacancy (NV−) colour centres in the nanodiamonds (DNDs) produced during the detonation of nitrogen-containing explosives was found to be 1.1 ± 0.3 ppm. This value is impressive for nanodiamonds of size < 10 nm with intentionally created NV− centres. The concentration was estimated from the electron paramagnetic resonance as determined from the integrated intensity of the g = 4.27 line. This line is related with “forbidden” ∆ms = 2 transitions between the Zeeman levels of a NV− centre’s ground triplet state. Confocal fluorescence microscopy enables detection of the red photoluminescence (PL) of the NV− colour centres in nanoscale DND aggregates formed from the 5-nm nanoparticles. Subwavelength emitters consisting of NV− with sizes a few times smaller than the diffraction-limited spot are clearly distinguished. We have further observed an abrupt drop in the PL intensity when mixing and anti-crossing of the ground and excited states spin levels in NV− occurs under an applied external magnetic field. This effect is a unique quantum feature of NV− centres, which cannot be observed for other visible domain light-emitting colour centres in a diamond lattice.
Congratulations to fourth year PGR Tom Collier, who has submitted his thesis, ‘Doubled-Gated Quantum Rings and Nanohelices: from Theory to Novel Applications’.
As well as his publications and conference presentations, in April 2018, Tom made an industry visit to De La Salle University, in the Phillipines, where he worked with Dr Richard Hartmann on theoretically solving non-simply connected systems with double quantum well potentials.
During his degree, Tom took part in Pint of Science 2017, giving a public talk in The Globe Inn to bring scientific research to the wider public.
Tom’s highlights of his time with the CDT include supervising an undergraduate summer student, with whom he will be submitting a paper. Looking back over his achievements during the CDT, Tom said the following:
I managed to finish with 5 first author publications in total: 3 journal articles, 1 book chapter, and 1 extended conference proceedings. I do have 3 further draft manuscripts to be submitted eventually.
I’ve managed to tutor Natural Science students taking physics or maths modules every year of my PhD, which I’ve thoroughly enjoyed. I’ve also managed to present at a fair few conferences. All in all, it’s been a blast.
From September, Tom will be working as a patent attorney in Brighton. He cites the CDT training on Intellectual Property awareness as the inspiration for his career choice.
Tom’s publications include:
T. P. Collier, “Eigenvalues and eigenfunctions for angular double-well potential”, Wolfram Demonstrations Project, published: June 13, 2019
“Double-gated nanohelix as a novel tunable binary superlattice” accepted in Nanoscale Research Letters 29/6/19 (authors T.P. Collier and M.E. Portnoi)“Terahertz applications of non-simply-connected and helical nanostructures” Chapter 11, in Fundamental and Applied Nano-Electromagnetics II. THz Circuits, Materials, Devices, edited by A. Maffucci and S. A. Maksimenko (Springer) 2019 (authors:T. P. Collier, V. A. Saroka, C. A. Downing, A. M. Alexeev, R. R. Hartmann, and M. E. Portnoi)
During his PhD, Henry also participated in many different events. He joined in the Startup Weekend Exeter in October 2018, where his team Dot_IT was the winner of the competition. He also participated in many outreach events as part of the Exeter University Optics and Photonics Society. He was the president of this society from February 2018 to February 2019. He was also the chair of the IONS Exeter conference, recently held from 9 to 12th July 2019. IONS Exeter was a student-led conference that brought together esteemed keynote and invited speakers, as well as normal contributions from different countries.
Hybrid light-matter states are quantum states that result from an efficient combination of light and matter. This combination is efficient when the two constituents exchange their energy faster than the overall energy dissipation.
For such efficiency, devices have to be designed and structured to maximise the energy exchange. When an efficient energy exchange between light and matter is achieved, new quasiparticles are formed.
One type of these particles are the exciton-polaritons, which result from an efficient energy exchange between excitons and a confined light field.
Over the past 40 years, exciton-polaritons have been extensively studied in conventional semiconductors integrated with devices that confine a light field.
However, only in the last five years, exciton-polaritons have been realised in semiconductors with a thickness at the monolayer limit, which was first observed at low temperatures, and later extended to observations at room temperature. These devices performing at room temperature and at the nanoscale are promising for future technologies, where exciton-polaritons may play an important role, due to their combined light and matter properties that provide them with the strong non-linearities necessary for quantum communications among other applications.
However, one crucial step for the use of exciton-polaritons in real applications is the control over their formation. Recent reports elucidate ways to control the excitation of exciton-polaritons at room temperature, using semiconductor transistors integrated with light confinement devices. This control over the excitation of exciton-polaritons is the main focus of the work presented in this thesis.
Previous reports have focused their research in controlling either the light confinement or the excitonic properties of the semiconductor material in separate ways. In this work, however, both have been carefully controlled, allowing for an extended manipulation of exciton-polariton states. The results presented here set a substantial advance on the manipulation of exciton-polaritons in devices operating at room temperature and using 2-dimensional semiconductor materials in tuneable optical microcavities.
These results may lead to application in future quantum technologies through switchable quantum states.
Congratulations to Miguel Camacho Aguilar, who graduated from the CDT last month, for the recent publication of his tenth journal article. This is an extraordinary research output for a PGR. Miguel is in a postdoctoral role in the prestigious group of Prof. Nader Engheta at the University of Pennsylvania.
Miguel’s journal publications are:
“Extraordinary transmission and radiation from finite by infinite arrays of slots in IEEE Transactions on Antennas and Propagation (in press) (authors: Miguel Camacho, R.R. Boix, F. Medina, A. P. Hibbins, and J. R. Sambles)
“Far-Field and Near-Field Physics of Extraordinary THz Transmitting Antennas” in IEEE Transactions on Antennas and Propagation (in press) (authors: Miguel Camacho, R.R. Boix, S.A. Kuznetsov, M. Beruete, and M. Navarro-Cia)
“NUFFT for the efficient spectral domain MoM analysis of a wide variety of multilayered periodic structures” in IEEE Transactions on Antennas and Propagation (in press) (authors: Miguel Camacho, R.R. Boix, and F. Medina )
By using new and unique methods developed at the University of Exeter, we have produced thin films of different two-dimensional (2D) materials. These thin films can then be transferred easily to almost any other surface. In this work we have then investigated the properties of the different 2D materials in the terahertz frequency range. The results show that the tested 2D materials are suitable for applications in terahertz modulation devices. Ultimately, this work, with further improvement, could lead to cheaper and improved terahertz systems with applications ranging from non-destructive materials testing, to biomedical imaging, and security and communications technologies.
Time-resolved terahertz spectroscopy has become a common method both for fundamental and applied studies focused on improving the quality of human life. However, the issue of finding materials applicable in these systems is still relevant. One of the appropriate solution is 2D materials. Here, we demonstrate the transmission properties of unique graphene-based structures with iron trichloride FeCl3 dopant on glass, sapphire and Kapton polyimide film substrates that previously were not investigated in the framework of the above-described problems in near infrared and THz ranges. We also show properties of a thin tungsten disulfide WS2 film fabricated from liquid crystal solutions transferred to a polyimide and polyethylene terephthalate substrates. The introduction of impurities, the selection of structural dimensions and the use of an appropriate substrate for modified 2D layered materials allow to control the transmission of samples for both the terahertz and infrared ranges, which can be used for creation of effective modulators and components for THz spectroscopy systems.
On Saturday 13th July we held the first ever CDT Summer Ball. The ball was a formal black tie event for all students and staff associated with the CDT. This was a great opportunity for everyone to socalise outside of the office enviroment and build lasting relationships. The night consisted of a drinks reception, followed by a delightful 3 course dinner. Students and staff worked together to solve quiz questions and take pictures using the fun props at the photography corner. It was a wonderful evening, celebrating the many sucesses of the CDT this year. We hope that this was the first of many such events!
A huge thank you to the organisers of this event- our PGRs Conor Murphy, Hannah Barnard and Katie Lewis- for their hard work and making it such a success.
The experience in Pisa has been definitely valuable.
From the organization perspective, nothing has been left unplanned or uncared for. The venue was the main hall of the University of S.Anna, Pisa, built on the pre-existing 15th-century monastery, which does not add scientific value but is indeed pleasant. The buffet lunches, the organized visit to the historical city center, and the gala dinner have been spotless, laying the foundation for an efficient network building with researchers and academics from all Europe and beyond.
From the content perspective, the initial focus was on the provision of a needed background on the fundamentals of silicon photonics, to allow the audience to make the most out of the information-packed following lectures. These spanned through a wide range of fields, such as fabrication techniques, plasmonics, non-linear phenomena, conventional and quantum device and applications, with the course program being tailored to follow a natural and logical sequence (i.e. from light sources to passive devices, then to active devices, detectors, integration, and eventually innovative approaches). The visit to the CNIT labs has also been extremely interesting and provided a deeper insight into the hands-on research carried out in Pisa.
Most of the courses were very well delivered. I would have preferred a tighter focus on the fundamentals, but I also acknowledge how the panoramics onto the many fields has been of great value, providing a wider and yet precise picture of the concepts of silicon photonics research and applications.
His two-week placement, made possible by the EPSRC’s funding award, was with Shouhang European S.L., which develops energy resources saving technologies such as air cooling systems, water treatment technologies, waste heat utilization, heating supply and Concentrated Solar Power (CSP) Stations. In China, the company has been awarded for many pioneering achievements on these topics and was the first company in that country to produce the largest amount of kilowatts from its projects based on those technologies.
David was assigned the task of developing an interactive GUI (Graphic User Interface) through Matlab to let the user perform the following actions:
• After introducing the technical parameters and physical dimensions of the station, show a simulated sunspot on the target of the solar tower (where rays are collected) with a frontal view (a piece of code with the mathematics of the ray optics was provided)
• Import a real image of that sunspot provided by an IR camera
• Draw an isometric schematic of the system (tower+plane of incidence+sun rays) to give an idea to the user of how the orientation changes as parameters are modified in real time
• A difference image to spot differences more easily. The purpose of this program is to infer from simulations a parameter called the ‘slope sigma error’, an error related to the aiming of the heliostats (mirrors) to the solar tower. The real sunspot must have the same ‘sigma error’ that the one in simulations when both sunspots look similar, which helps to modify the aiming settings of the heliostat in real time, compensate the error and get a more efficient aiming to the collection target. This can be checked by taking orthogonal cuts to both spots, simulated and real and comparing the width of the Gaussian distributions of normalized power intensity.
David talks about his experience:
The Matlab code I implemented was mainly based on ‘call-back’ functions linked to buttons and toggles that can be pressed on the main window. The imported data also needed image processing and geometrical transformations (trigonometry, perspectives and projections on cylindrical planes… etc.) to make it suitable for comparison with simulations. In summary, I learned how to implement interactive GUI’s in Matlab and more specifically for image processing. This is very helpful for developing a user-friendly and clean GUI for any other scientific, control or data processing purpose in my research project. It will also make so much easier for new students/users to use for the first time any Matlab program that incorporates such an interface. Objectives were accomplished within the two weeks and the Matlab code was given to the company for further improvement and future use.
I also attended a few meetings where the team discussed about the state-of-the-art of some of their projects and about a visit to an international congress, which was very insightful and I could hear about the latest news on solar technology and the company’s plans moving forward.