Dr. Bhaskar Kaviraj completed his PhD from IIT Kharagpur in 2007. After his PhD degree, he worked as post-doctoral researcher during 2007 in the Laboratory of Electrical Engineering in Paris (LGEP), Paris under the organization SUPELEC. Then he moved to Georgia State University, Atlanta, USA in 2008 where he worked in electronic transport properties of low-dimensional systems as a Post-doctoral Research Associate. In 2009, he joined French Atomic Energy Commission (CEA) in Grenoble, France as a Research Engineer to work in mesoscopic systems and quantum shot noise and cross-correlations in superconducting hybrid nanostructures. In 2011, he moved to International Center for Materials Nanoarchitectonics (MANA) under the aegis of National Institute of Materials Science (NIMS), Tsukuba, Japan to carry out research in superconductor-quantum dot hybrid systems before joining as a Visiting Faculty at Indian Institute of Science Education and Research (IISER), Bhopal. His current research interests include fabrication of thin film heterostructures for investigations of charge and spin transport for use in spintronics based devices.
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).
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 course for first year students non-majoring 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)
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.