Publications

2021

• Exciton band structure of Molybdenum Disulfide: from monolayer to bulk
  
  • Fugallo Giorgia
  • Cudazzo Pierluigi
  • Gatti Matteo
  • Sottile Francesco
  Electronic Structure, IOPScience, 2021, 3 (1), pp.014005. Exciton band structures analysis provides a powerful tool to identify the exciton character of materials, from bulk to isolated systems, and goes beyond the mere analysis of the optical spectra. In this work, we focus on the exciton properties of Molibdenum Disulfide (MoS2) by solving the ab initio many-body Bethe-Salpeter equation, as a function of momentum, to obtain the excitation spectra of both monolayer and bulk MoS2. We analyse the spectrum and the exciton dispersion on the basis of a model excitonic Hamiltonian capable of providing an efficient description of the excitations in the bulk crystal, starting from the knowledge of the excitons of a single layer. In this way, we obtain a general characterization of both bright and darks excitons in terms of the interplay between the electronic band dispersion (i.e. interlayer hopping) and the electron-hole exchange interaction. We identify for both the 2D and the 3D limiting cases the character of the lowestenergy excitons in MoS2, we explain the effects and relative weights of both band dispersion and electron-hole exchange interaction and finally we interpret the differences observed when changing the dimensionality of the system. (10.1088/2516-1075/abdb3c)
  DOI : 10.1088/2516-1075/abdb3c
• Systemic consequences of disorder in magnetically self-organized topological MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$n$ superlattices
  
  • Sitnicka Joanna
  • Park Kyungwha
  • Skupiński Paweł
  • Grasza Krzysztof
  • Reszka Anna
  • Sobczak Kamil
  • Borysiuk Jolanta
  • Adamus Zbigniew
  • Tokarczyk Mateusz
  • Avdonin Andrei
  • Fedorchenko Irina
  • Abaloszewa Irina
  • Turczyniak-Surdacka Sylwia
  • Olszowska Natalia
  • Kołodziej Jacek
  • Kowalski Bogdan J
  • Deng Haiming
  • Konczykowski Marcin
  • Krusin-Elbaum Lia
  • Wołoś Agnieszka
  2D Materials, IOP Publishing, 2021, 9 (1), pp.015026. MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$n$ materials system has recently generated strong interest as a natural platform for the realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic (FM) MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$n$ it is found that migration of Mn between MnBi$_2$Te$_4$ septuple layers (SLs) and otherwise non-magnetic Bi$_2$Te$_3$ quintuple layers (QLs) has systemic consequences—it induces FM coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation ( n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies show that Mn disorder within an SL causes delocalization of electron wave functions and a change of the surface band structure as compared to the ideal MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$n$. These findings highlight the critical importance of inter- and intra-SL disorder towards achieving new QAH platforms as well as exploring novel axion physics in intrinsic topological magnets. (10.1088/2053-1583/ac3cc6)
  DOI : 10.1088/2053-1583/ac3cc6
• Hyperbolic plasmonics with anisotropic gain–loss metasurfaces
  
  • Kuzmin Dmitry
  • Bychkov Igor
  • Shavrov Vladimir
  • Temnov Vasily
  Optics Letters, Optical Society of America - OSA Publishing, 2021, 46 (2), pp.420. In this Letter, a fundamentally new concept of realization of hyperbolic plasmonic metasurfaces by anisotropic gain–loss competition is proposed, and the possibility of highly directional propagation and amplification of surface plasmon polaritons is predicted. A simple realistic configuration of such a metasurface represents the periodic array of lossy metallic slabs embedded in the gain matrix. Our results may pave the way for numerous applications ranging from integrated and highly directional quantum light emitters to nonlinear-optical frequency converters. (10.1364/OL.413511)
  DOI : 10.1364/OL.413511