Research Interests
Waves in Dynamical Matter
The propagation of waves in matter has fascinated humanity over much of its history. Today, spinning out of the discipline of condensed matter physics, the field of metamaterials provides a unified framework for the study of waves, ranging from electromagnetics to acoustics, water and matter (i.e. probability) waves in arbitrarily structured media.
But what happens when a material is not only structured in space, but also in time? What new physics does dynamical matter have to offer?
Focusing on new materials which enable ultrafast temporal modulation of their electromagnetic properties, my current research focuses on exploring the new range of wave phenomena which arise from the temporal modulation of matter.
This includes new schemes for wave amplification and localisation, as well as novel wave-coupling techniques to reduce losses and improve tunability in near-field photonic platforms, based on the breaking of time-translation symmetry.
You can find out more about this line of my research, on publications [5], [6] and [10] below.
Transformation Optics and Plasmonic Singularities in Graphene and Noble Metals
Close to a metallic surface, electromagnetic excitations called surface plasmons enable us to capture radiation and manipulate it in the nanoscale by conveniently structuring the surface. Graphene, a 2D sheet of carbon atoms, has the remarkable properties that its conductivity may be spatially designed by altering the local density of charge carriers, so that its metallic behaviour may be widely tuned, enabling spatial design of its optical response.
During the first stage of my PhD I used the powerful analytical tool of Transformation Optics to investigate the plasmonic properties of singular surfaces, namely structured metallic surfaces featuring extremely subwavelength thickness, and sharp points. Focusing on the case of graphene, I showed how periodically suppressing the doping level- and hence the conductivity- of a graphene sheet along its surface leads to nano-scale focusing of terahertz waves, beating the so-called diffraction limit by more than 4 orders of magnitude.
In this extreme focusing regime, light is squeezed down to length-scales which are comparable to the wavelength of a free electron in a metal. This allows us to study the quantum, non-local behavior of electrons in condensed matter systems.
In graphene, these effects may find applications in the development of THz technology, such as broadband absorbers, as well as for the enhancement of spectroscopic signals in molecular characterisation and nonlinear effects in the terahertz frequency regime.
You can find out more about this line of my research on publications [2-4], [7-9] below.
Quantum Reflection
Casimir/Van-der-Waals-type forces result from the polarisation induced by vacuum fluctuations on charge-neutral objects, such as atoms, nanoparticles and surfaces. The long-range character of these interactions challenges density functional approaches, which become especially expensive for the case of nano-structures, and low-energy scattering experiments are often used to verify the calculated Casimir potentials. During my Master's, I worked on numerical studies of quantum mechanical scattering of neutral atoms subject to Casimir-Polder forces near a metallic surface.
You can find you more about my MSci research work on publication [1] below.
Publications
[10] Galiffi, E., Wang, Y. T., Lim, Z., Pendry, J. B., Alù, A., & Huidobro, P. A. (2020). Wood Anomalies and Surface-Wave Excitation with a Time Grating. Physical Review Letters, 125(12), 127403.
[9] Lu, L., Galiffi, E., Ding, K., Dong, T., Ma, X., & Pendry, J. B. (2020). Plasmon Localization Assisted by Conformal Symmetry. ACS Photonics, 7(4), 951-958.
[8] Yang, F., Galiffi, E., Huidobro, P. A., & Pendry, J. B. (2020). Nonlocal effects in plasmonic metasurfaces with almost touching surfaces. Physical Review B, 101(7), 075434.
[7] Galiffi, E., Huidobro, P. A., Gonçalves, P. A. D., Mortensen, N. A., & Pendry, J. B. (2020). Probing graphene’s nonlocality with singular metasurfaces. Nanophotonics, 9(2), 309-316.
[6] Galiffi, E., Huidobro, P. A., & Pendry, J. B. (2019). Broadband nonreciprocal amplification in luminal metamaterials. Physical Review Letters, 123(20), 206101.
[5] Huidobro, P. A., Galiffi, E., Guenneau, S., Craster, R. V., & Pendry, J. B. (2019). Fresnel drag in space–time-modulated metamaterials. Proceedings of the National Academy of Sciences.
[4] Galiffi, E., Pendry, J., & Huidobro, P. A. (2019). Singular graphene metasurfaces. EPJ Applied Metamaterials, 6, 10.
[3] Galiffi, E., Pendry, J. B., & Huidobro, P. A. (2018). Broadband Tunable THz Absorption with Singular Graphene Metasurfaces. ACS nano.
[2] Pendry, J. B., Huidobro, P. A., Luo, Y., & Galiffi, E. (2017). Compacted dimensions and singular plasmonic surfaces. Science, 358(6365), 915-917.
[1] Galiffi, E., Sünderhauf, C., DeKieviet, M., & Wimberger, S. (2017). Two-dimensional simulation of quantum reflection. Journal of Physics B: Atomic, Molecular and Optical Physics, 50(9), 095001.