Job Offers

“High frequency vortex dynamics and ratchet phenomena”

Promoters: Prof. V.V. Moshchalkov, Prof. A. Stesmans and Dr. J. Van de Vondel
This PhD research will be funded by the Methusalem NANO Programme.

Dynamic vortex control (including ratchet effects) will be extended to high frequency range, up to a few GHz. This control is a key factor for potential use of fluxonics devices for the removal of unwanted trapped vortices from SQUIDs, which will dramatically reduce the noise in these ultra-sensitive devices. The “tracks” for vortex removal will be provided by specially designed “vortex routers”. The flux lensing will be achieved by using the so called “vortex lenses”, which take care of increasing flux density at specific locations. Secondly, we are aiming at innovative approach of projecting on large nanoarrays the results achieved up to now on individual asymmetric superconducting microstructures, which have been successfully used to show the presence of a reversible vortex diode effect. As a result, a new condensed-matter quantum device can be used to produce a tunable diode effect important for realization of the guided motion of large vortex ensembles.

“Vortex matter in two-component nano-superconductors”

Promoters: Prof. V.V. Moshchalkov, Prof. L. Chibotaru and Dr. A. Silhanek
This PhD research will be funded by the Methusalem NANO Programme.

We shall investigate nanostructured single-component (reference system, low-Tc superconductors) and two-component superconductors with antidot lattices of different geometries and sizes. Moreover, the two-component superconductivity will be modeled by using the S₁/S₂ bi-layers where S1 and S2 are two superconductors with different coherence lengths and the London penetration depths. For that purpose Al/Pb, Al/Nb bi-layers will be used. The recent theoretical predictions of the non-composite vortex state will be experimentally verified. We shall fabricate antidot lattices by using modern techniques (e-beam lithography, in collaboration with IMEC, self-assembly, self-organized templates). Integrated response techniques, advanced local techniques with nanoscale resolution and state-of-the-art simulation and modeling of confined condensate and flux as well as their dynamics in different artificially nanoengineered confined geometries will be used to reveal novel phenomena appearing in nanostructured two-component superconductors.

“Magnetic nanophotonics”

Promoters: Prof. V.V. Moshchalkov and Prof. K. Clays
This PhD research will be funded by the Methusalem NANO Programme.

In quantum dots the photoluminescence (PL) is governed by the electron-hole recombination of excited charge carriers. This process will be probed and fine tuned by using external magnetic field, which “changes the colour” of the emission (blue shift of the PL line). We shall investigate confinement effects on magneto PL in quantum dots of different shape and sizes made from different materials. To enhance the optical output, we shall use nanomodulated metallic films placed on top of the planar structures containing quantum dots. One of the key experiments will be time-resolved magneto-photoluminescence and application of non-linear optical techniques. Enhanced PL using metallic nanostructures (“optical nanoantennas”) in close vicinity with nanostructures will also be investigated, including metal nanoparticles coated by polythiophene. Selective enhancement of the optical radiation at specific locations of plasmonic metallic nanoparticles will be probed by the photonic STM. This enhancement will be used for developing bright markers for bioimaging and bio- and chemical sensing as well as for boosting the efficiency of photovoltaic systems through plasmonics effects in incorporated metallic nanograins.

“Nanoscale metamaterials and plasmonics”

Promoters: Prof. V.V. Moshchalkov and Prof. G. Vandenbosch
This PhD research will be funded by the Methusalem NANO Programme.

Different topologies used for the development of new metamaterials will be analyzed in order to give a “computational electromagnetics” feedback to the experimental data. This will provide valuable information in order to optimize the design of new metamaterials. In order to investigate low absorption limit at the frequencies below the superconducting gap, metamaterials will be also made from superconducting materials. The perfect conductor limit is a very important case for the finite-difference time domain simulations and the comparison between the theory and experiment is a very valuable asset in that respect. Typical nanoengineered systems will be fabricated from both normal metallic and superconducting materials and their electromagnetic response will be compared. Transmission and reflection will be recorded, providing the means of extracting optical properties, i.e. magnetic permeability and electric permittivity, using Kramers-Kronig relations. The electromagnetic intensity response of these systems will be simulatedand compared with the intensity map measured with photonic STM. This research will be carried out in the framework of the METHUSALEM NANO Programme.

“Fast spin reversal in molecular magnets and magnetic clusters”

Promoters: Prof. V.V. Moshchalkov and Prof. J. Vanacken
This PhD research will be funded by the Methusalem NANO Programme.

Molecular magnets (Mn₁₂, Fe₈) have recently been found to emit electromagnetic radiation, which possibly can be of superradiance origin. The main objective of this research is to study the possibilities to obtain superradiance in the GHz-THz range, by using molecular magnets as well as semiconducting heterostructures The Mn₁₂-Ac molecular magnet samples will be obtained via a longstanding collaboration with Prof. J. Tejada (Barcelona, Spain). The fast external field reversal will be generated in our existing pulsed field faciliy which is equipped with the necessary cryostats operational at temperatures down to 600mK. The mechanisms responsible for optical properties, especially Dicke superradiance, in self-assembled quantum dots, will be revealed. The Si, A²B⁵ and A²B⁶ quantum dots and magnetic clusters of different sizes and inter-distances will be used. The size of the excitons and the coupling between the dots will be determined via photoluminesce in high pulsed magnetic fields (=60 T).

“Mapping confinement effects in superconductors on photonic nanomaterials”

Promoters: Prof. V.V. Moshchalkov and Dr. A. Silhanek
This PhD research will be funded by the Methusalem NANO Programme.

Nanopatterns developed for solving fluxon confinement problem in superconductors are practically identical to the ones used by others to develop negative refraction index (NRI) and plasmonics materials: arrays of antidots – isotropic and anisotropic (fishnet), arrays of semiconducting and metallic dots, multilayers, arrays of rings, periodic arrays of molecular magnets, quantum dots, etc. Not only nanostructuring patterns, but also confinement physics can be mapped from fluxon to plasmon problem. Using these remarkable similarities, arrays of metallic nanocells of different shape and size will be made on an insulating substrate. Complimentary arrays of antidots of the same shape and size made in a metallic film on an insulating substrate will be used to induce NRI. According to the Babinet principle, such arrays should exhibit similar electro-magnetic properties. By varying the composition of the cells, their shape and size as well as the thickness of these nanocells and films we shall optimize the range of frequencies where the NRI is observed. Downscaling of the developed patterns will be used for stretching the NRI range up to a visible range. Numerous nanoscale topologies, needed also for superlensing, will be designed and implemented.

“Fluxon behavior in superconductor/ferromagnet hybrid nanosystems: Reality of novel field-resistance superconductors”

Promoters: Prof. V.V. Moshchalkov and Dr. W. Gillijns
This PhD research will be funded by the Methusalem NANO Programme.

We shall combine a superconductor with a lattice of magnetic nanodots. The dots create local magnetic fields which form the so called dipole loops: field emanates from the dots and then it comes back in the space between the dots. These field loops can be used to compensate the applied field between the dots. By sacrificing the small areas under the dots, where the magnetic fields will be enhanced through the presence of magnetic dots, we shall protect superconductivity in a substantially larger area between the dots where field lines from the dots eliminate the applied field lines. As a result, the whole superconductor, except a minor area under the dots, becomes magnetic-field resistant and can sustain much higher applied magnetic field. Coupled to the re-entrant Tc(H) behavior, is the new phenomenon of the current-induced superconductivity. Therefore, we are proposing an innovative approach how to make magnetic-field resistant superconductors through nanoengineering. We shall also compare this effect with the Jaccarino-Peter compensation effect for the exchange interaction and investigate the possibility of the field compensation with the paramagnetic ions. Recently discovered Fe-based new superconductors will be also used in these studies.