Profile

Research Interests

Currently, our reasearch focus is of two fold:

A. Optical, electronic and vibrational properties of two-dimensional layered materials

Two dimensional materials such as graphene and transition metal dichalcogenides TMDC such as MoS2, WSe2, MoSe2, MoTe2, etc) have emerged as brand new photonic materials due to their unique properties and multiple functions. TMDS's are atomical thin semiconductors of the type MX2 with a transition metal (M) atom and a chalcogen (X) atom (S, Se, Te). One layer of M atoms is sandwiched between two layers of X atoms. They are the part of the family of 2D materials,  a name to emphasize their thickness. The discovery of graphene shows different properties emerge when a bulk crystal of macroscopic dimensions is thinned down to atomic layers. Like graphite, TMD bulk crystals are formed of monolayers bound to each other by Van der Waals attraction. The following properties of TMDC's make it an interesting and a potential candidate, amongst others:

(i) TMD monolayers MoS2, WS2, MoSe2, WSe2, MoTe2 have a direct band gap, and can be used in electronics as transistors and in optics as emitters and detectors.

(ii) The TMD monolayer crystal structure has no inversion center, which allows to access a new degree of freedom of charge carriers, namely the k-valley index, and to open up a new field of physics: valleytronics

(iii) The strong spin-orbit coupling in TMD monolayers leads to a spin-orbit splitting of hundreds meV in the valence band and a few meV in the conduction band, which allows control of the electron spin by tuning the excitation laser photon energy and handedness. The work on TMD monolayers is an emerging research and development field since the discovery of the direct bandgap and the potential applications in electronics and valley physics. TMDs are often combined with other 2D materials like graphene and hexagonal boron nitride to make van der Waals heterostructure. These heterostructures need to be optimized to be possibly used as building blocks for many different devices such as transistors, solar cells, LEDs, photodetectors, fuel cells, photocatalytic and sensing devices. Some of these devices are already used in everyday life and can become smaller, cheaper and more efficient by using TMD monolayers.

B. Our current research also focusses on spintronics in thin film metal based magnetic nanostructures comprising of a ferromagnetic material and non-magnetic heavy metal (s) with high spin-orbit coupling. We are an experimental research group, chiefly concentrating on fundamental problems related to magnetism and spintronics under the purview of condensed matter physics.

Spintronics is a field that jointly utilizes spin and charge degrees of freedom to control equilibrium and non-equilibrium properties of materials and devices. The generation, manipulation and detection of spin currents is one of the key aspects of the field of spintronics. Among several possibilities to create and control spin currents, the Spin Hall effect (SHE) that has been first observed in 2004 stands out. In direct Spin Hall effect, an electrical current passing through a material can generate a transverse pure spin current polarized perpendicular to its plane defined by the charge and spin current. In its reciprocal effect, the inverse SHE (ISHE), a pure spin current through the material generates a transverse charge current. In both cases, the material must possess spin-orbit coupling. The initial challenge for SHE detection was primarily the lack of direct electrical signals; therefore initial experiments detected it by optical means. The ISHE was soon detected thereafter in 2006 by Saitoh, Valenzuela, Tinkham and Zhao.

There is another phenomenon occurring in ferromagnetic materials, the anomalous Hall effect (AHE), where relativistic spin-orbit coupling generates an asymmetric deflection of charge carriers depending on the spin direction. The AHE can be detected electrically in a ferromagnet via transverse voltage because of the difference in population of majority and minority carriers. Magnetic nanostructures have also been aimed to use spin currents injected from adjacent spin Hall NM for spin transfer torque (STT) switching of a ferromagnet. In addition to the SHE-induced torque, there is also a spin-orbit torque (SOT) which arises due to a process known as Inverse Spin Galvanic effect (ISGE), wherein a charge current can generate a non-equilibrium uniform spin polarization via spin orbit coupling.

Magnetic nanostructures thus allow us to investigate a wealth of relativistic quantum mechanical phenomena by properly designed lab based experiments. The experiments would involve careful deposition of thin films by dc magnetron sputtering or electron beam evaporation techniques. The systems would comprise of bilayers, trilayers and multilayers of FM/NM heterostructures (Pt/Co/Ta, Pt/Co/Pt, Ta/CoFeB/MgO, NiFe/Pt to name a few). The films would then be analyzed for thickness, uniformity and crystal orientation by techniques such as X-ray Reflectivity (XRR), Profilometer, X-ray diffraction (XRD). The devices would then be patterned into Hall bars by photlithography or electron beam lithography. Electrical detection of these effects would be carried out by DC and AC Hall effect measurements in a closed cycle refrigerator capable of reaching liquid Helium temperatures (4.2K).

Research Students

PhD Students Supervised

1. Dr. Dhirendra Sahoo (Defended Thesis on March 17, 2023)

Received post-doctoral fellowship to work in Royal KTH, Sweden.

PhD Students Supervising

1. Shivam Tyagi (PhD)

2. Srishti Agarwal (PhD)

3. Sheikh Najeeb ul Haq (Project JRF, DST-SERB)

PhD students co-supervising

1. Abhishek Panghal (jointly with Prof. Susanta Sinha Roy)

Former UG Students supervised

1. Varchasv Chotani (Thesis: Micromagnetic simulations of agnetic thin films using MuMax3)

 2. Kailash MN (Thesis: Exploring and applying models used in physics to financial markets)

Courses Taught(Selected) 

Review of Classical Electrodynamics (PHY509- a graduate course for PhD students majoring in Physics)

Characterization of Materials-II (PHY575- a graduate course for PhD students majoring in Physics)

Exploration in research (PHY599- a graduate course for PhD students majoring in Physics)

Classical Electrodynamics (PHY303- an undergraduate course for third year students majoring in Physics)

Introduction to Physics II (PHY102- an undergraduate Core Course for first year students non-majoring in Physics)

Introduction to Physics I (PHY101- an undergraduate Core Course for first year students non-majoring in Physics)

Abridged Course for Minor in Physics ((PHY207)- an undergraduate Core Course for students doing their Minors in Physics)

Fundamentals of Physics II (PHY104- an undergraduate course for first year students majoring in Physics)

Classical Mechanics (PHY301- an undergraduate course for first year students majoring in Physics)

Projects being undertaken/completed under OUR (Opportunities of Undergraduate Research)

1. Vibhooti Shekhawat (1710110384):  

Constructing different types of circuit elements by using graphite pencils and paper. 

OUR Project Code:  OUR20180046  

2. Akshat Jain  (1710110038) 

Faraday’s law in the presence of extended conductors.

OUR Project Code: OUR20180040

3.  Ashwin Deepa (1710110079)  

Response analysis of earphones under various conditions for snag detection. 

OUR Project Code: OUR20180008 

Recent Publications (Recent)

B. Kaviraj, and J. Sinha; Magnetic skyrmions in chiral ferromagnets: electrical transport properties and device applications ECS J. Solid State Sci. Technol. 2022 11 115003    https://doi.org/10.1149/2162-8777/ac9eda    

Sahoo, D. ; Shakya, J.; Choudhury, S.; Roy, S. S.; Devi, L.; Singh, B.; Ghosh, S.; Kaviraj, B. High-Performance MnO2 Nanowire/MoS2 Nanosheets Composite for a Symmetrical Solid-State Supercapacitor. ACS Omega 2022, 7, 20, 16895–16905. https://doi.org/10.1021/acsomega.1c06852.

A simple two-step strategy to synthesize defect-rich MoS2 nanocrystals for enhanced electrochemical hydrogen evolution- Dhirendra Sahoo, Jyoti Shakya, Sudipto Choudhry, Budhi Singh, and Bhaskar Kaviraj  AIP Advances 12, 035119 (2022) https://doi.org/10.1063/5.0083934

Edge Rich Ultrathin Layered MoS2 Nanostructures for Superior Visible Light Photocatalytic Activity- Dhirendra Sahoo, Jyoti Shakya, Nasir Ali, Won Jong Yoo, Bhaskar Kaviraj  Langmuir 2022, 38, 4, 1578–1588 (https://doi.org/10.1021/acs.langmuir.1c03013)

Cost-effective synthesis of 2D molybdenum disulfide (MoS2) nanocrystals: An exploration of the influence on cellular uptake, cytotoxicity, and bio-imaging- Dhirendra Sahoo, Sushreesangita P Behera, Jyoti Shakya, Bhaskar Kaviraj PLoS One 17 e0260955 (2022)

Cost effective liquid phase exfoliation of MoS 2 nanosheets and photocatalytic activity for wastewater treatment enforced by visible light- Dhirendra Sahoo, Birendra Kumar, Jaivardhan Sinha, Subhasis Ghosh, Susanta Sinha Roy, Bhaskar Kaviraj Scientific Reports 10 10759 (2020)

Relativistic torques induced by currents in magnetic materials: physics and experiments- Bhaskar Kaviraj and Jaivardhan Sinha RSC Advances (2018) 8, 25079

Magnetic properties of microwave-plasma (thermal) chemical vapour deposited co-filled (Fe-filled) multiwall carbon nanotubes: Comparative study for magnetic device applications- Ashish Mathur, Tuhin Maity, Shikha Wadhwa, Barun Ghosh, Sweety Sarma, Sekhar Chandra Ray, Bhaskar Kaviraj, Susanta S. Roy and Saibal Roy Material Research Express (2018) 5, 076101

SQUIDs based set-up for probing current noise and correlations in three-terminal devices – A. Pfeffer, B. Kaviraj, O. Coupiac and F. Lefloch Review of Scientific Instruments 83 115107 (2012)

Noise Correlations in Three-Terminal Diffusive Superconductor-NormalMetal-Superconductor Nanostructures- B. Kaviraj, O. Coupiac, H. Courtois and F. Lefloch  Physical  Review Letters 107 (2011) 077005.