IIT Jodhpur | हिंदी संस्करण
Seminar by Dr. Bheema Linagm Chittari, Department of Physics, University of Seoul, Seoul, Korea on the 25th of October 2019

Dr. Bheema Linagm Chittari from the Department of Physics, University of Seoul, Seoul, Korea delivered a talk in the Department of Physics on 25th of October 2019.

Title:  Gate tunable Flatbands and Magnetism in two dimensional van der Waals (vdW) layered materials 
 
 Abstract: Following the discovery of graphene, research on two dimensional (2D) materials has been growing rapidly. Now, the 2D crystals have a large range of properties such as metals, semimetals, topological insulators, semiconductors, and insulators. However, the scope of correlation phenomena that includes superconductivity, Mott insulators, and Magnetism is still at
the budding stage in the 2D layered materials. Interestingly, the combination of two dimensional layers with diverse properties stacked together forms van der Waals (vdW) heterostructures, that allowed to investigate new physical effects, as well as the development of new devices. Misalignment and lattice mismatch between the heterostructures form moiré superlattice leads to exotic properties of van der Waals (vdW) heterostructures. Recent experiments have shown
resistance peaks as a function of carrier doping indicative of Mott-like phases in bilayer graphene with a twist between the layers and in ABC trilayer graphene (TLG) nearly aligned with hexagonal boron nitride (BN). Here, I present the tight-binding continuum model calculations on the flatbands that are engineered in twisted multilayer graphene and show how the experimental findings followed the theoretical prediction. In the twisted bilayer graphene (tBG), the flatband
minima angles are found to grow linearly with interlayer coupling and decrease with Fermi velocity. In tBG, the fltabands emerge as a function of twist angle, vertical pressure, and interlayer potential differences between the layers. Interestingly, in twisted double bilayer graphene (tDBG) the bandwidth is generally flatter than in tBG by roughly up to a factor of 2 in the same parameter
space of twist angle and interlayer coupling, making it in principle simpler to tailor narrow bandwidth, flat bands. A related system where flattening of the low-energy bands is facilitated by the presence of a vertical electric field is the ABC trilayer graphene (TG) on hexagonal boron nitride (hBN), TLG/BN, where Coulomb effects can lead to correlated gapped phases even without a specific twist angle. The other missing member of the family of 2D materials is 2D magnets. I will present the density functional study prediction on the possibility of single layered 2D magnetic materials, and the device application through carrier-density doping and strain dependence of magnetic order.

The manifestation of magnetic order through an applied electric field by presenting the magneto-electric response through anisotropic Heisenberg Monte-Carlo simulations.

References:
[1] BL Chittari, Y Park, D Lee, M Han, AH MacDonald, E Hwang, J Jung, Phys. Rev. B, 94, 184428 (2016);
arXiv:1709.09386; arXiv:1902.06418
[2] M Yankowitz, J Jung, E Laksono, N Leconte, BL. Chittari, K. Watanabe, T. Taniguchi, S Adam, D.
Graf & C. R. Dean, Nature, 557, 404 (2018).
[3] H Kim, N Leconte, BL Chittari, K Watanabe, T Taniguchi, A H MacDonald, J Jung, S Jung, Nano. Lett., 18,
7732 (2018)
[4] BL Chittari, N Leconte, S Javvaji and Jeil Jung, Electron. Struct. 1, 0150012 (2018).
[5] BL Chittari, G Chen, Y Zhang, F Wang, and J Jung, Phys. Rev Lett, 122, 016401 (2019).
[6] G Chen, L Jiang, S Wu, B Lv, H Li, BL Chittari, K Watanabe, T Taniguchi, Z Shi, J Jung, Y Zhang, and F
Wang, Nat. Phys, 15, 237 (2019).
[7] N R Chebrolu, BL Chittari, and J Jung, Phys. Rev. B, 99, 235417 (2019).