Coming QuMat / CMT seminar in Utrecht
Dirac Fermions at the interfaces
Speaker: Semonti Bhattacharyya – Leiden Institute of Physics, Leiden University
Host: Machteld Kamminga
The low-energy electrons in graphene and topological insulators manifest themselves as Dirac fermions, by virtue of their linear band structures. These electrons are unique compared to ordinary semiconductors due to their gapless nature, and protection from scattering, resulting in superior electronic properties. In addition, by their very nature, these states appear at the surface, making them susceptible to external disturbances from their immediate surroundings. Our goal is to manipulate the electronic properties of these Dirac fermions through these perturbations. Deliberate manipulation of such interactions can give rise to novel emergent states and lead to novel functional devices.
In the first part of the talk, I will demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin Ga2O3 synthesized on the surface of liquid Ga metal . Electrical measurements of millimeter-scale passivated and bare CVD graphene on SiO2 substrate indicate that the passivated graphene maintains its high field effect mobility, desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in our passivated graphene over a range of temperatures below 230 K, due to the interplay of screening of the remote optical phonon modes of SiO2 by the high dielectric constant of Ga2O3, and the relatively high characteristic phonon frequencies of Ga2O3. Raman spectroscopy and electrical measurements indicate that Ga2O3 passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al2O3.
In the second part of the talk, I will talk about our previous work on topological insulators. In this work, we used universal conductance fluctuations to detect the crossover of symmetry classes under broken time-reversal symmetry . I will also give updates on our ongoing work on engineering topological phase transitions in van der Waals heterostructures of topological insulators , and briefly touch upon my future plans at my new research group at Leiden University.
 M. Gebert, S. Bhattacharyya et al., Nano Lett., 23, 363 (2023).  S. Islam, S. Bhattacharyya, et al. Phys. Rev. B, 97, 241412 (2018).  S. Bhattacharyya et al. 33, 2007795 (2021)