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Physical properties and Fermi surface studies of bulk crystal and nano device
Research expertise: (1) Nano device fabrications: exfoliation, stacking, and lithography, (2) nano-ARPES and u-ARPES: ARPES on bulk and nano device. (3) Single crystal growth: chemical handling, glass blowing expertise, and bulk crystal growth experiences. (4) Electrical transport and magnetization at low temperature: quantum transport phenomena.
Software: Mathematica, IGOR pro, Origin, Solidwork, blender
1. Nano device fabrications:
The reduced dimensionality of van der Waals materials exfoliated down to their two-dimensional limit (2D) generates a limitless space for engineering electronic environment. Additionally, a 2D stack of different materials multiplies the wide verities of individual properties, resulting in hybridized electronic behavior. Micron-sized devices are prepared to explore the charge carrier behavior in low-dimensional systems. Currently, we are working on graphene, TMDCs, and topological semimetals.
2. u-ARPES and nano-ARPES:
Angle-resolved photoemission spectroscopy (ARPES) study is a unique technique to investigate the electronic structure of materials directly. We performed nano-ARPES and u-ARPES experiments at state-of-the-art synchrotron-based beamlines. We focus on some key questions: (i) the behavior of the charge carrier in low dimensional systems, (ii) understanding the correlation physics using applied gate voltage, (iii) observation of hybridized states of different layer stack or twist angles, and (iv) evolution of band topology with the application of strain on a crystal using strain cell. We know that the interaction between two layers of carbon atoms in a hexagonal lattice leads to the electronic structure's flat band in twisted graphene at a magic angle.
For example, we observe a flat band in twisted double-bilayer graphene at near near-magic angle (Fig. 2). Using gate voltage we can tune the Fermi level and have ideas of many-body interaction.
3. Single crystal growth:
In my Ph.D. research, I have learned (a) flux growth technique, (b) Czochralski, (c) Bridgeman method, and (d) chemical vapor transport (CVT) crystal growth techniques. We have investigated the physical properties of many such bulk crystalline materials that possess strong spin-orbit coupling and show exotic properties. We have investigated some of the key questions: (i) the behavior of the complex crystal structure where 2D metallic layers are separated by insulating layers, (ii) the change in the transport properties while replacing the insulating layers with magnetic layers. Our observed unconventional behavior of transition metal - pnictides ternary compounds discloses some of the queries. Again, to investigate the charge transport in new quantum materials that host new fermions, we looked at some binary silicides. Furthermore, I studied a few-layered compounds, superconducting, and magnetic materials.
4. Electrical transport and magnetic study:
We performed low-temperature and high magnetic field electrical transport measurements on bulk single crystalline materials. Generally, I focus on temperature-dependent resistivities and low-temperature phenomena such as Shubnikov de Haas oscillation, weak antilocalization, quantum Hall effect, etc.
Recently, our experimental results on hexagonal layered crystal structures CaCuSb (111- compound) show negative magnetoconductance (weak antilocalization) where strong spin-orbit coupling (mainly originated transition metal and pnictides) results in interference between electron paths (shown in Fig. 4). Adding more transition metal and pnictides in 111- compound, we designed CaCu4As2, which has a more complex structure. The CaCu4As2 crystal structure has three septuple layers and metallic [Cu4As2] 2D networks are separated by insulating Ca layers. The charge carriers are more confined to 2D metallic layers with an increasing magnetic field. These layers play an important role in Hall resistance. Additionally, it reveals charge density transition at 51~K. Our results showed the coexistence of the quantum Hall effect and charge density wave (CDW) in CaCu4As2, indicating a strong correlation present in the compound (shown in Fig. 4).
SolidWorks design
Schematic of a chamber created in SolidWorks
Figure created in blender
Schematic diagram of a twisted double bilayer graphene device. The figure indicates the twisted double bilayer, hBN, graphite, and gold contact.
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