MZMichele Zacchigna

Michele Zacchigna

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Michele Zacchigna has a total of 262 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

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    Observation of charge dressing in Bi 4 Te 3 topological insulator thin films: A terahertz and infrared spectroscopic study

    by Veronica Stopponi, Johannes Schmidt, Andrea Perucchi, Gregor Mussler, Abdur Rehman Jalil, Alexander Grüneis, Michele Zacchigna, Stefano Lupi, Paola Di Pietro

    Bi 4 Te 3 has been first realized as an element of the adaptive series ( Bi 2 ) m ( Bi 2 Te 3 ) n —deriving from stacking metallic Bi and topological insulator Bi 2 Te 3 blocks—and studied for its promising thermoelectric properties. Recently, Bi 4 Te 3 has also been found as a topological insulator hosting a complex band structure with three Dirac cones in k space. Here we report measurements of the optical conductivity of five Bi 4 Te 3 thin films with thickness varying from 11 to 32 nm. This extensive study, based on terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy, provides a broadband optical conductivity. By employing a Kramers-Kronig constrained Drude-Lorentz model, the spectral contributions to the optical conductivity of each sample have been singled out. In contrast to an ideal topological insulator—with perfectly insulating bulk—in Bi 4 Te 3 far-infrared and mid-infrared bands indicate the presence of localized massive carriers, which dope the bulk system, as also observed in chemically compensated single crystals of other bismuth-based topological insulators. In addition, the localized bulk charges strongly renormalize the electronic mass. The charge dressing enhances as the thickness increases, indicating a trivial metallic behavior of Bi 4 Te 3 thin films. This study elucidates the inner relationship between the optical properties of a topological insulator like Bi 4 Te 3 and its complex band structure, since the detection of the topological massless carriers by optical measurements is prevented by the occurrence of novel and unusual conductive properties.

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    Room Temperature Evidence of PtTe 2 Topological Semimetal Character

    by Matteo Gardella, Chiara Massetti, Alessio Lamperti, Michele Zacchigna, Muthumalai Karuppasamy, Zdeněk Sofer, Zipporah Rini Behner, Polina M. Sheverdyaeva, Paolo Moras, Alessandro Molle

    Topological semimetals, being characterized by symmetry‐protected band crossings, represent a fascinating class of materials with extraordinary electronic properties. Type‐II Dirac semimetals, featuring highly tilted Dirac cones, offer unique opportunities for both fundamental research and technological advancements. Platinum ditelluride (PtTe 2 ) has emerged as a promising candidate for a type‐II Dirac semimetal, exhibiting relevant properties for future spintronic and optoelectronic devices. While the existence of type‐II Dirac cones in PtTe 2 has been confirmed by cryogenic temperature angle‐resolved photoemission spectroscopy (ARPES), practical applications necessitate their stability at ambient conditions. Here, we present a melt growth method for the synthesis of high‐quality PtTe 2 crystals and we perform ARPES characterization both at cryogenic and at room temperature, providing compelling evidence for the robust nature of its topological electronic structure under realistic operating conditions. This demonstration paves the way for the development of PtTe 2 ‐based devices leveraging its distinctive topological properties in practical settings.

    Cited by 2
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    Temperature dependent non-monotonic bands shift in ZrTe 5

    by G. Manzoni, A. Crepaldi, G. Autès, A. Sterzi, F. Cilento, A. Akrap, I. Vobornik, L. Gragnaniello, Ph. Bugnon, M. Fonin, et al.

    Cited by 31
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    Bulk diffusive relaxation mechanisms in optically excited topological insulators

    by A. Sterzi, G. Manzoni, L. Sbuelz, F. Cilento, M. Zacchigna, Ph. Bugnon, A. Magrez, H. Berger, A. Crepaldi, F. Parmigiani

    The possibility to inject spin currents in topological insulators (TIs) by ultrashort optical pulses has stimulated intense studies of their out-of-equilibrium electronic properties. However, a comprehensive description of the electronic relaxation dynamics has been elusive, so far. In order to reveal the role of the bulk and surface states in the microscopic scattering mechanisms, we have investigated, by means of time- and angle-resolved photoemission spectroscopy, a wide set of TIs. These have been selected in order to display different positions of the Fermi energy (EF) within the bulk band structure. When three-dimensional bulk states lie at EF, we observe a fast relaxation dynamics with a characteristic time scale of a few picoseconds (ps). On the contrary, a long lasting excited state is recorded when only the two-dimensional surface state crosses EF. These findings suggest the important role played by spatial diffusion in the direction orthogonal to the surface in governing the relaxation mechanisms. We propose that this electron diffusive mechanism is driven by the optically induced temperature gradient that is at play only for electrons residing in bulk states.

    Cited by 23
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    Persistence of a surface state arc in the topologically trivial phase of MoTe2

    by A. Crepaldi, G. Autès, A. Sterzi, G. Manzoni, M. Zacchigna, F. Cilento, I. Vobornik, J. Fujii, Ph. Bugnon, A. Magrez, et al.

    The prediction of Weyl fermions in the low-temperature noncentrosymmetric 1T′ phase of MoTe2 still awaits clear experimental confirmation. Here, we report angle-resolved photoemission (ARPES) data and ab initio calculations that reveal a surface state arc dispersing between the valence and the conduction band, as expected for a Weyl semimetal. However, we find that the arc survives in the high-temperature centrosymmetric 1T′′ phase. Therefore, a surface Fermi arc is not an unambiguous fingerprint of a topologically nontrivial phase. We have also investigated the surface state spin texture of the 1T′ phase by spin-resolved ARPES, and identified additional topologically trivial spin-split states within the projected band gap at higher binding energies.

    Cited by 28
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    Evidence for a Strong Topological Insulator Phase in ZrTe5

    by G. Manzoni, L. Gragnaniello, G. Autès, T. Kuhn, A. Sterzi, F. Cilento, M. Zacchigna, V. Enenkel, I. Vobornik, L. Barba, et al.

    The complex electronic properties of ZrTe5 have recently stimulated in-depth investigations that assigned this material to either a topological insulator or a 3D Dirac semimetal phase. Here we report a comprehensive experimental and theoretical study of both electronic and structural properties of ZrTe5, revealing that the bulk material is a strong topological insulator (STI). By means of angle-resolved photoelectron spectroscopy, we identify at the top of the valence band both a surface and a bulk state. The dispersion of these bands is well captured by ab initio calculations for the STI case, for the specific interlayer distance measured in our x-ray diffraction study. Furthermore, these findings are supported by scanning tunneling spectroscopy revealing the metallic character of the sample surface, thus confirming the strong topological nature of ZrTe5.

    Cited by 209
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    SmB6electron-phonon coupling constant from time- and angle-resolved photoelectron spectroscopy

    by A. Sterzi, A. Crepaldi, F. Cilento, G. Manzoni, E. Frantzeskakis, M. Zacchigna, E. van Heumen, Y. K. Huang, M. S. Golden, F. Parmigiani

    SmB6 is a mixed valence Kondo system resulting from the hybridization between localized f electrons and delocalized d electrons. We have investigated its out-of-equilibrium electron dynamics by means of time- and angle-resolved photoelectron spectroscopy. The transient electronic population above the Fermi level can be described by a time-dependent Fermi-Dirac distribution. By solving a two-temperature model that well reproduces the relaxation dynamics of the effective electronic temperature, we estimate the electron-phonon coupling constant λ to range from 0.13±0.03 to 0.04±0.01. These extremes are obtained assuming a coupling of the electrons with either a phonon mode at 10 or 19 meV. A realistic value of the average phonon energy will give an actual value of λ within this range. Our results provide an experimental report on the material electron-phonon coupling, contributing to both the electronic transport and the macroscopic thermodynamic properties of SmB6.

    Cited by 15
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    Advancing non-equilibrium ARPES experiments by a 9.3eV coherent ultrafast photon source

    by F. Cilento, A. Crepaldi, G. Manzoni, A. Sterzi, M. Zacchigna, Ph. Bugnon, H. Berger, F. Parmigiani

    Cited by 31
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    Ultrafast Optical Control of the Electronic Properties ofZrTe5

    by G. Manzoni, A. Sterzi, A. Crepaldi, M. Diego, F. Cilento, M. Zacchigna, Ph. Bugnon, H. Berger, A. Magrez, M. Grioni, et al.

    We report on the temperature dependence of the ZrTe5 electronic properties, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoelectron spectroscopy. Our results unveil the dependence of the electronic band structure across the Fermi energy on the sample temperature. This finding is regarded as the dominant mechanism responsible for the anomalous resistivity observed at T*∼160  K along with the change of the charge carrier character from holelike to electronlike. Having addressed these long-lasting questions, we prove the possibility to control, at the ultrashort time scale, both the binding energy and the quasiparticle lifetime of the valence band. These experimental evidences pave the way for optically controlling the thermoelectric and magnetoelectric transport properties of ZrTe5.

    Cited by 101
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    Engineering the topological surface states in the(Sb2)m−Sb2Te3(m=0–3)superlattice series

    by J. C. Johannsen, G. Autès, A. Crepaldi, S. Moser, B. Casarin, F. Cilento, M. Zacchigna, H. Berger, A. Magrez, Ph. Bugnon, et al.

    We investigate the evolution of both the occupied and unoccupied electronic structure in representative compounds of the infinitely adaptive superlattice series (Sb2)m−Sb2Te3 (m=0–3) by means of angle-resolved photoemission spectroscopy and time-delayed two-photon photoemission, combined with first-principles band-structure calculations. We discover that the topological nature of the surface states and their spin texture are robust, with dispersions evolving from linear (Dirac-like) to parabolic (Rashba-like) along the series, as the materials evolve from semiconductors to semimetals. Our findings provide a promising strategy for engineering the topological states with the desired flexibility needed for realizing different quantum phenomena and spintronics applications.

    Cited by 24
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