Superconductor Nanowires as Powerful Generators of THz Radiation
Lead Research Organisation:
University of Bristol
Department Name: Chemistry
Abstract
The so-called 'Terahertz gap' is rapidly closing. Originally perceived as a gap in the generation of electromagnetic radiation (it falls between two common methods of generating electromagnetic waves - infrared and microwave), in the last few years, research efforts have been geared towards exploiting this useful band between 0.5 THz and 2 THz. Terahertz devices are just starting to find use in spectroscopy, imaging and sensing particularly in the biological and physical sciences.
Superconductors are exceedingly sensitive detectors (known as bolometers) of THz radiation, owing to the cryogenic temperatures providing a low-noise environment. Cost however, is a severely limiting factor as low-temperature superconductors require expensive liquid helium cooling in order to attain the superconducting state. High-temperature superconductors (HTSC) are showing promise as bolometers as they require only cheap liquid nitrogen cooling and also exhibit fast quasi-particle relaxation times owing to their unique microstructure, yet it is this very microstructure that makes controlled crystal growth difficult.
The reason superconductors work so well in THz technology is that they can be used to create Josephson junctions (JJs) - two superconducting regions separated by an insulating layer. These junctions naturally convert dc voltages into electromagnetic radiation in the THz region. This means that a suitable array of JJs can be used both to detect impinging THz radiation, and also act as coherent emitters of THz radiation. It is this phenomenon that we propose to utilize here in this proposal, in order to create the most powerful and compact THz source to-date.
The current state of the art in HTSC bolometers attempt to exploit the fact that superconducting anisotropy in the crystal structure of these materials create intrinsic JJs. In the case of the superconductor 'bismuth-strontium-calcium-copper-oxide' (BSCCO), the unit cell can be thought of as consisting of layers of superconducting CuO2 planes separated by non-superconducting 'blocking' layers. This means that if the supercurrent could be made to flow along the c-axis of the unit cell, there would be JJs roughly every 15 Å, however herein lies the problem. Crystals of BSCCO can be grown naturally with any crystal axis expressed, but the supercurrent will always flow along the CuO2 planes in the ab axes, thereby avoiding crossing any intrinsic JJs. As HTSCs would be relatively cheap and powerful THz emitters if current could be made to flow across the JJs, efforts have been made to force the supercurrent along the c-axis by focussed-ion-beam (FIB) milling, but these devices containing BSCCO crystals have a very limited output, typically in the 20 - 50 micro-Watt region.
This proposal aims to improve significantly on this value, by using BSCCO nanowires grown via a biotemplated-inspired approach. Rather than have to use expensive and difficult techniques in order to produce nanostructured BSCCO, nanowires grown using this method can be produced spontaneously with the axis of elongation as the c-axis. This means that we can use them as the core of a compact, high-performance THz emitter. With lengths of up to 6 microns, these nanowires will therefore contain around 6,000 intrinsic JJs. As the radiative power increases as the square of the number of JJs, our nanowires should produce THz radiation in the thousands of mW range.
Superconductors are exceedingly sensitive detectors (known as bolometers) of THz radiation, owing to the cryogenic temperatures providing a low-noise environment. Cost however, is a severely limiting factor as low-temperature superconductors require expensive liquid helium cooling in order to attain the superconducting state. High-temperature superconductors (HTSC) are showing promise as bolometers as they require only cheap liquid nitrogen cooling and also exhibit fast quasi-particle relaxation times owing to their unique microstructure, yet it is this very microstructure that makes controlled crystal growth difficult.
The reason superconductors work so well in THz technology is that they can be used to create Josephson junctions (JJs) - two superconducting regions separated by an insulating layer. These junctions naturally convert dc voltages into electromagnetic radiation in the THz region. This means that a suitable array of JJs can be used both to detect impinging THz radiation, and also act as coherent emitters of THz radiation. It is this phenomenon that we propose to utilize here in this proposal, in order to create the most powerful and compact THz source to-date.
The current state of the art in HTSC bolometers attempt to exploit the fact that superconducting anisotropy in the crystal structure of these materials create intrinsic JJs. In the case of the superconductor 'bismuth-strontium-calcium-copper-oxide' (BSCCO), the unit cell can be thought of as consisting of layers of superconducting CuO2 planes separated by non-superconducting 'blocking' layers. This means that if the supercurrent could be made to flow along the c-axis of the unit cell, there would be JJs roughly every 15 Å, however herein lies the problem. Crystals of BSCCO can be grown naturally with any crystal axis expressed, but the supercurrent will always flow along the CuO2 planes in the ab axes, thereby avoiding crossing any intrinsic JJs. As HTSCs would be relatively cheap and powerful THz emitters if current could be made to flow across the JJs, efforts have been made to force the supercurrent along the c-axis by focussed-ion-beam (FIB) milling, but these devices containing BSCCO crystals have a very limited output, typically in the 20 - 50 micro-Watt region.
This proposal aims to improve significantly on this value, by using BSCCO nanowires grown via a biotemplated-inspired approach. Rather than have to use expensive and difficult techniques in order to produce nanostructured BSCCO, nanowires grown using this method can be produced spontaneously with the axis of elongation as the c-axis. This means that we can use them as the core of a compact, high-performance THz emitter. With lengths of up to 6 microns, these nanowires will therefore contain around 6,000 intrinsic JJs. As the radiative power increases as the square of the number of JJs, our nanowires should produce THz radiation in the thousands of mW range.
Organisations
People |
ORCID iD |
Simon Hall (Principal Investigator) | |
Jason Potticary (Researcher) |
Publications
Luke E
(2022)
Synthesis of porous high-temperature superconductors via a melamine formaldehyde sacrificial template
in Nanoscale Advances
Luke EJ
(2023)
Rapid sol-gel synthesis of honeycomb-layered Na3Ni2BiO6 and orthorhombic Na3Ca2BiO6.
in Dalton transactions (Cambridge, England : 2003)
Potticary J
(2023)
Template-Free Growth of High-Temperature Superconductor Nanowires
in Small Structures
Potticary J
(2023)
Template-Free Growth of High-Temperature Superconductor Nanowires
in Small Structures
Description | In 2014, we published in Science on the in-situ TEM observation of a microcrucible mechanism of nanowire growth [Science, 344, 636-626, 2014], where we identified this growth mechanism for the first time, using the synthesis of high-temperature superconductors in order to do so. What has been missing since this discovery though, is a synthetic approach to make these complex oxide nanowires reliably and in abundance, to facilitate their subsequent incorporation into the next generation of electronic devices, as the easy preparation of abundant quantities of complex functional materials as nanowires remains stubbornly challenging. This award relied on the fact that these complex superconductor nanowires could be produced reliably and in bulk. In this propject, we have now successfully demonstrated such an approach; using nanoparticles as quasi-catalytic morphological directors, we have created an extremely facile, template-free, flux-mediated growth of gargantuan quantities of three compositions of phase-pure, high-temperature superconductor nanowires, including for the first time, nanowires of the technologically important quinternary superconductor Bi2Sr2CaCu2O8+x (B2212). This has been submitted as a paper to Science Advances (as of 14th Feb. 2023). |
Exploitation Route | The results of this work will provide an opportunity to investigate the physics and chemistry of highly anisotropic superconductor nanowires and should open the door to their incorporation into new nanoelectronic and energy generation systems, including investigation of the THz generation by these materials. Now that we have a reliable method for producing BSCCO nanowires, once the paper is published, we hope that those who have the capability to undertake the THz emission experiments will be able to do so. |
Sectors | Aerospace, Defence and Marine,Energy |
Description | Global Advanced Materials & Surfaces International Conference, Paris |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | A talk was presented at the Global Advanced Materials & Surfaces International Conference, Paris. The discussion afterwards was on the growht of BSCCO nanowires which stimulated interest in the work. |
Year(s) Of Engagement Activity | 2022 |
Description | Inorganic & Materials section talks |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Postgraduate students |
Results and Impact | Emily Luke, a PhD student working on the growth of superconductor nanowires, gave a presentation to the Inorganic & Materials section in the School of Chemistry, Bristol. There were plenty of questions afterwards and it stimulated interest in the work across the Inorganic & Materials section. |
Year(s) Of Engagement Activity | 2022 |
Description | Presentation at the Annual Conference of the EPSRC Centre for Doctoral Training in Functional Materials: The BCFN |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Professional Practitioners |
Results and Impact | This was a talk on the progress of the BSCCO superconductor nanowire work, to the EPSRC Centre for Doctoral Training in Functional Materials: The BCFN. The talk stimulated debate on the role these materials may play in THz technologies and potential collaborations were suggested for the future. |
Year(s) Of Engagement Activity | 2021 |