Research

During my PhD and postdoctoral research, I have had the opportunity to work on several distinct areas of materials physics research. I group my research experience below according to the material platform:

• Topological insulators:

I worked on understanding the origin of conductance fluctuations in topological insulators (TIs) which is not only an important parameter for device performance, but also provides information about the underlying disorder dynamics. Conductance fluctuations can also be used to probe the underlying symmetries of a system, which are key to understanding topological phases. Through 1/f noise measurements in topological insulators, we identified bulk disorder as the main source of noise these materials, irrespective of thickness and method of synthesis, unlike other two-dimensional materials, where noise originates either at the channel-substrate interface or at the contacts. I also investigated the dephasing mechanism in Tis, where intriguingly I observed the saturation of the phase breaking length at low temperatures. While the origin of the saturation remains unknown, I was able to exclude several possibilities such as electron heating, spin-orbit coupling length, magnetic impurities, and surface-bulk coupling, leading me to conclude that internal disorder and temperature-dependent screening play a crucial role in the saturation. I have also co-written a review article on 1/f noise in van der Waals materials. The following are the peer-reviewed publications under this topic:

8. Review article on noise and dephasing in quantum materials, accepted in Advanced Materials

7. Phys. Rev. Research, 2, 033019 (2020)

6. Phys. Rev. B 99, 245407 (2019)

5. Phys. Rev. B 97 (24), 241412 (Rapid)) (2018)

4. Appl. Phys. Lett. 111 (6), 062107 (2017)

3. Appl. Phys. Lett. 108 082101 (2017)

2. Adv. Phys. X, 2 (2), 428-449 (2017)

1. ACS Nano 9,12 (2015)

• Graphene

• Infra-red photodetectors with graphene-based hybrids

To address the absence of infra-red photo-response in single layer graphene, we employed hybrids of dichalcogenides (Bi2Te3 nanowires and SnSe2 nanoplatelets). These devices showed ultra-sensitive infra-red response from 920 nm to 1720 nm incident illumination, including communication frequencies, even upto room temperature. The specific detectivity of 10^10 Jones is comparable to the best devices in reported in the literature. The noise equivalent power indicates that the devices can be used to detect ~10 photons. These devices have several practical applications such as in military technologies, imaging, and communications. These results have been published in:

2. Nanoscale, 11, 1579-1586 (2019)

1. Nanoscale, 11, 870-877 (2019)

• Graphene-based biosensors

We developed biomolecule sensing using graphene, which proved to be an excellent platform for detecting various diseases such as human immunodeficiency virus, cardiac muscle damage, and arthritis. This was achieved by immobilizing anti-bodies on the graphene-FET, and detecting a change in conductivity, due to binding of the antibody with the corresponding antigen. The limit of detection is comparable to state-of-the-art detectors.

3. Sci. Rep., 10, 14546 (2020)

2. Sci. Rep., 9, 276 (2019)

1. Bios. Bioelectron, 126, 1, 792-799 (2019)

• Bimetallic nanostructures:

I worked on understanding Ag/Au nanostructures, whose properties fascinated me. Some of the date can be found in the manuscripts on arxiv we uploaded. Hopefully, I can update this space soon.

• accepted manuscript, Supercond. Sci. Technol.

• arXiv:1807.08572v3

• arXiv:1906.02291v2

• arXiv:1912.05428

• Other projects

We also demonstrated a method to control hysteresis and stable memory effect with a floating gate in ultra-thin 2D channels, including graphene, MoS2, and topological insulators. This was published in Materials Research Express (contributed equally first author). I also worked on linear magnetoresistance in thermally evaporated thin films of bismuth, which showed a low crossover field at room temperature. This work was published in the Journal of Applied Physics (second author). Electrical and optical properties of the n-doped molecular semiconductor were investigated by temperature-dependent conductivity, electron paramagnetic resonance (EPR), and flash-photolysis time-resolved microwave conductivity (FPTRMC) measurements. The results provide a significant step towards building optoelectronic devices from organic semiconductors. I contributed to understating the electrical characteristics of films made from these materials. These results were published in ACS Applied Electronic Materials.

1. Mater. Res. Express 7 014004 (2020)

2. J. Phys. D: Appl. Phys. 53 425102 (2020)

3. Nanotechnol. 30, 395704 (7pp) (2019)

4. ACS Appl. Electron. Mater, 2, 1, 66–73 (2020)

• For fabrication of mesoscopic devices, I have used scotch-tape exfoliation technique from bulk single crystals, followed by electron-beam lithography and deposition techniques (thermal/sputtering). Most of the measurements were done in a He-3 system (Janis), or dilution refrigerator (wet system from Leiden). In many cases, a home-built variable temperature cryostat was used.