Abstract-Terahertz tuning of Dirac plasmons in Bi 2 Se 3 topological insulator

P. Di Pietro, N. Adhlakha, F. Piccirilli, A. Di Gaspare, J. Moon, S. Oh, S. Di Mitri, S. Spampinati, A. Perucchi, and S. Lupi

https://journals.aps.org/prl/accepted/4a070KdfY0f1530f14789af239849412267149091

Light can be strongly confined in sub-wavelength spatial regions through the interaction with plasmons, the collective electronic modes appearing in metals and semiconductors. This confinement, which is particularly important in the terahertz spectral region, amplifies light-matter interaction and provides a powerful mechanism for efficiently generating non-linear optical phenomena. These effects are particularly relevant in graphene and Topological Insulators, where massless Dirac fermions show a naturally non-linear optical behavior in the terahertz range. The strong interaction scenario has been considered so far from the point of view of light. In this paper, we investigate instead the effect of strong interaction on the plasmon itself. In particular, we will show that Dirac plasmons in Bi${}_2$Se${}_3$ Topological Insulator are strongly renormalized when excited by high-intensity terahertz radiation by displaying a huge red-shift down to 60% of its characteristic frequency. This opens the road towards tunable terahertz non-linear optical devices based on Topological Insulators.

Abstract-Terahertz-based retrieval of the spectral phase and amplitude of ultrashort laser pulses

A. Curcio, V. Dolci, S. Lupi, and M. Petrarca

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-4-783

Terahertz (THz) radiation is of great interest for a variety of applications, e.g., particle accelerations, spectroscopy investigations of quantum systems, and high-field study of materials. One of the most common laser-based processes to produce THz pulses is optical rectification, which transduces an infrared pump laser to the THz domain (0.1–20 THz). In this work, we propose and theoretically describe a method to characterize the amplitude and phase of the electric field of the pump laser pulse relying on THz generation and detection. We demonstrate with a numerical example how THz radiation can be used as diagnostics to characterize laser pulses with temporal length at the femtosecond level.

© 2018 Optical Society of America

Abstract-Photoinduced terahertz dynamics in BizSes topological insulator

 F. Giorgianni, M. Shalaby,   C. Vicario,  C. P. Hauri,  S. Lupi

http://ieeexplore.ieee.org/document/8087694/

Plasmons are collective charge density waves in a conductive material, which show remarkable electromagnetic properties and have great potential for photonics from terahertz to the ultraviolet. Besides the conventional plasmonic excitations in metals and in semiconductors, 2-dimensional (2D) plasmons of massless Dirac electrons have been observed in graphene and at the surface of topological insulators (TIs). TIs are quantum electronic materials with an insulating gap in the bulk originated by a strong spin-orbit coupling and Dirac metallic states at their interfaces. Among the various TIs, Bi2Se3 is one of the most promising material due to its large band gap Eg~300 meV. Recently, it has been shown that the low energy single particle and collective (plasmons) electrodynamics response are dominated by surface Dirac electrons in Bi2Se3 in steady state regime [1]. The relaxation dynamics show that an excess of electrons are continuously injected from bulk to the surface through surface states-bulk phonon scattering channel [2,3]. In this work we study the time resolved photoinduced THz dynamics of plasmonic response in micro-ribbons patterned Bi2Se3 thin film by means of optical-pump/THz-probe spectroscopy.

Abstract-Possible light-induced superconductivity in K3C60 at high temperature

• M. Mitrano,
• A. Cantaluppi,
• D. Nicoletti,
• S. Kaiser,
• A. Perucchi,
• S. Lupi,
• P. Di Pietro,
• D. Pontiroli,
• M. Riccò,
• S. R. Clark,
• D. Jaksch
• & A. Cavalleri

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature16522.html

The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity¹. Nonlinear excitation^2, 3 of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc(refs 4, 5, 6). This effect was accompanied by the disruption of competing charge-density-wave correlations^7, 8, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results.