Research

My research interests focus on the electronic, optical, lattice and transport properties of two-dimensional atomic crystals (atomically thin materials like graphene or single or few-layer transition metal dichalcogenides) and their vertical and planar heterostructures. I am mainly interested in new phenomena which emerge in such heterostructures due to the interaction between two crystals and/or are driven by changes in the atomistic geometry at the interface between van der Waals-coupled materials. More recently, my activities expanded to include studies of structural and electronic low-symmetry phases in two-dimensional crystals. In my work, I use a variety of theoretical methods, including both analytical and computational approaches, maintaining close contact with experimental progress in the field.

My achievements to date include (numbers in square brackets refer to publications as listed in the complete list of publications):

• Describing electronic and optical properties of graphene/hBN [10,11,14,15,16,19,20,22,23,26,27]: I have developed a symmetry-based model for graphene electrons perturbed by underlying hexagonal boron nitride (hBN) substrate [10]. This model provides the most generic and widely adopted effective Hamiltonian for studies of the electronic properties of graphene/hBN moiré superlattice effects. I used this approach to support the first observation of fractal spectrum of electrons in two dimensions in periodic potential and perpendicular magnetic field [11], experiment listed as one of the top 10 physics breakthroughs of 2013 by Physics World. I applied the same framework to describe the angle-resolved photoemission spectra (ARPES) of graphene/hBN [22] and the appearance of an interfacial polaron in this heterostructure [27].
• Predicting impact of strain in suspended graphene on electron transport [9,12,18]: Because of their atomic thickness, strain can significantly influence the mechanical and electronic properties of two-dimensional atomic crystals. While the impact of strain on the electronic dispersion of graphene has been extensively studied, I have provided the first prediction of its influence on electron current in suspended flakes with experimentally-relevant geometry [12].
• Determining the impact of topology on electronic properties of bilayer graphene [6,7,8,17,21]: Bilayer graphene is possibly best known as a material with unusually tuneable electronic dispersion: applying transverse electric field induces an electronic band gap in an otherwise gapless spectrum. However, its low-energy electronic dispersion also features a Lifshitz transition - an energy point at which topology of constant-energy contours changes. In a series of works, I have studied the interplay between band topology, external perturbations and interaction effects and their impact on the electronic spectrum. In particular, I have discovered nematic phase of the electron liquid, a rare state in which electrons spontaneously break rotational symmetry, in ultra-clean suspended bilayer graphene [8]. I have also shown that presence of the Lifshitz transition leads to interaction-driven transitions between ferromagnetic phases in the quantum Hall regime [17].
• Predicting electronic Raman features in graphene systems [5,28,36]: Raman scattering is commonly associated with probing vibrational excitations of molecules (lattice excitations in solids). However, purely electronic excitations can also lead to a shift in the wavelength of the scattered photon. I have predicted the electronic Raman scattering features in bilayer graphene [5] as well as in monolayer graphene with induced superconducting order [28] and twistronic graphene [36]. In the last case, studying electronic Raman scattering could provide us with a quick and non-invasive method of measuring the twist angle.
• Describing evolution of the valence band structure of rhenium diselenide from the bulk to monolayer [25,29,34]: In contrast to most two-dimensional crystals, many properties of rhenium dichalcogenides ReSe₂ and ReS₂ show little change with decreasing thickness of the crystal. Based on angle-resolved photoemission spectroscopy measurements, I have showed that interlayer coupling in bulk ReSe₂ leads to k_z-dispersion of the order of 100 meV (as compared to ~1 eV in graphite) [25]. By studying few-layer crystals, I also showed that the weak thickness-dependence is due to the fact that the orbitals most sensitive to the presence of other layers (Re d_z² and chalcogen p_z orbitals) do not contribute significantly to the top valence band states [34].