Research in Physics at SNU
Physics department at SNU has an active research program in the broad areas of condensed matter physics and environmental physics. Details of the specific areas of research and the faculty members associated with them are given below
Condensed Matter Physics
The research in our group can be broadly classified as Theoretical Condensed Matter Physics. More specifically, our research focuses on the field of
strongly correlated electron systems, where electron-electron interactions cannot be treated as a perturbation to its motion in the crystal potential, resulting in the breakdown of conventional band-structure description for such systems, at least in the rigourous sense.
On one hand, this field helps us to better understand emergent phenomena that can arise out of strong, non-perturbative interactions between electrons in narrow-band solids, like compounds of transition metals, rare-earths and actinides. The hallmark of this is seen in exotic phenomena like colossal magnetoresistance in the Manganites, high-temperature superconductivity in the Cuprates, spin-charge separation and charge fractionalization in low-dimensional correlated systems, and the Kondo effect, to name a few. In such phenomena one simply cannot think of each electron independently, but must take into account the collective behaviour of a macroscopically large number (~ Avogadro's Number) of electrons, all acting in unison. On the other hand, a basic understanding of the physics of these materials helps in designing “smart materials” with advanced and energy-efficient functionalities.
Since treating the full correlation problem for an infinite solid is an unsolvable problem, the challenge for theory is to continuously develop newer and more efficient analytical approximations and numerical techniques to better understand the properties of these “quantum materials”, as constantly emerging from experiments. We have been working in this field for more than a decade, trying to model the ground state (low-energy) as well as the spectroscopic (high-energy) properties of correlated electron systems, in collaboration with leading experts in the field, both in India and abroad. We are interested both in model problems as well as in complex real materials. At present our research interests and efforts are directed towards the following broad areas :
We work in the field of electronic quantum transport in mesoscopic systems. Mesoscopic systems are intermediate to that of microscopic (atomic) and macroscopic systems where quantum coherence is observed. The goal of the research is towards building up of devices that finds use in quantum information processing (QIP). Two fundamental quantum phenomena are important to realize devices for QIP, they are non-locality and entanglement. Non-locality refers to the existence of quantum correlations in spatially separated parts of a quantum system. A fundamental route for the exploration of this phenomenon is the generation of Einstein-Podolsky-Rosen (EPR) pairs of quantum entangled objects. Such pairs of quantum entangled objects has already been tested for photons but not yet for massive particles, like electrons as it is extremely difficult to obtain entangled electrons because electrons are immersed in a macroscopic ground state- the Fermi Sea – which prevents the straightforward generation and splitting of entangled electron pairs. The challenge can be faced by, first using a superconducting material that consists of a Cooper pair spin-singlet state as its ground state and second, by using semiconductor quantum dots in Coulomb blockade regime connected to a superconductor that would force to split the spin-entangled electrons coming out of the superconductor, and thus we would have an on-demand generation of spin-entangled electrons. Such creation of non-local quantum-entangled states in solid state devices would be exploited for secure quantum communication, quantum teleportation and to perform Bell inequality tests- a direct proof of entanglement which has yet to be produced for fermionic particles. The non-locality and entanglement would be probed by a unique set-up that would measure noise cross-correlations, a technique that is very sensitive to measure quantum correlations. The devices would also be probed by conventional transport measurements where interesting physics would also be investigated at superconductor-quantum dot junctions, for example Andreev Bound States, Crossed Andreev Reflection and Elastic Cotunneling. A major part of the challenge involves careful preparation of samples which requires a cleanroom facility. Electron beam lithography, AFM, electron beam evaporator would be the commonly used instruments to fabricate the samples and make electrical contacts.Soft Matter & Biophysics
We work in the field of experimental soft matter physics including biophysics. Soft materials used in cosmetic industries are investigated to explore their underlying structures and corresponding viscoelastic properties. These structures are altered by tuning the electrostatic interaction among the self-assembled aggregates in amphiphilic systems. In turn, the materials show interesting physical properties which are important for industrial applications. We also work in the field of membrane biophysics to develop model systems to investigate the interaction of macromolecules (e.g. protein, DNA etc.) with model cellular membranes. We are now embarking on to develop devices for bio-medical applications using nano-technology. Different x-ray scattering (x-ray diffraction, x-ray reflectivity, grazing incidence x-ray diffraction etc.) and microscopy techniques are used at in-house and international synchrotron facilities to study the structures and properties of such soft materials and bio-systems.Statistical Physics of Complex Systems
Our research is concerned with the investigation of statistical properties of complex and/or chaotic systems. The study covers topics as varied as quantum conductance in mesoscopic devices, entanglement in random pure states, transmission properties in microwave resonators, and performance of multiple antenna communication systems. The mathematical tools used for this purpose include Random Matrix Theory and Supersymmetry, which are extremely rich subjects in themselves. Consequently, development of novel tools and techniques in these and related areas is also of interest.
Since the last two decades, technology is growing up with an unbelievable speed. Bulky-to-slimmer televisions, desktops-to-laptops, landlines-to-mobiles, gasoline-to-batteries, and then demand for further advancement of these devices in terms of reduced size, weight, cost, power, and enhanced utility show the power of “self-accelerated” technology. This has raised the demand to explore novel materials having multi-purpose utility and tunable properties. The potential of the conjugated polymers, organic molecules, layered materials, and two-dimensional crystals like “Graphene” and "MoS2" are being explored. Our group aims to use computational approach to explore such novel materials which hold promise in the field of opto-electronics, energy storage/generation, biomedical, defense, and space applications.Statistical Mechanics and Computational Physics
Our current research is focused on the understanding of the dynamics of non-equilibrium thermodynamic state leading to equilibrium state. We use various analytical and computational tools of statistical mechanics such as dynamical density functional theory, phase field theory Monte Carlo, and MD simulations. In particular, our group is interested in confined binary alloys and liquid crystals including the properties of their interfaces. Moreover, the efforts would be made to formulate various approaches to develop models requiring least computational budget.Low Dimensional Functional Materials
Our primary interest is focused on the functional materials at sub-500 nm thickness range, where fascinating science has manifested over the last decade. New materials with exotic properties and functions for the next generation electronic devices are being explored by growing thin epitaxial 2D/3D films, nano-materials, and hetero-structures using pulsed laser deposition and ion implantation of surfaces. Our group is currently interested in transparent oxide layers, homo/hetero junction, bandgap engineering, 2D layer-oxide interactions, strain engineering at sharp atomic interfaces, defect induced ferromagnetism and resistive switching. We are equally enthusiastic to apply energetic ion beam for material characterizations and modifications via impurity doping, atomic mixing, alloying, nano-structuring, and solid state catalysis processes.Nano-carbon and Nano-Tribology
We aim to understand the structure and properties of functionalized nano-materials, nano-structured surfaces and develop new concepts suitable for sensor, microfluidic and energy applications. Our group is involved in producing variety of nanoscale structures (such as ultrathin carbon films and nanotubes, graphene as well as zinc oxide) using chemical and physical vapour deposition techniques. Carbon based nano-materials have remarkable thermal, electrical, optical, surface and mechanical properties. Moreover, it is essential to study surface and tribological properties for their efficient use in sensor, energy and electronic devices.Semiconductor Materials and Devices
Current research in our group aims to innovate advanced electronic and optical materials and devices through fundamental understanding of their charge and energy transports processes. We develop and apply variety of new characterization tools appropriate for organic and inorganic semiconducting hetero-junction devices like light emitting diodes, transistors, solar cell, lasers and sensors. Also we are interested in fabricating new class of nano-electronic devices. Moreover, the in-depth understanding of structure-property-performance correlation is essential to devise the strategy in developing new class of electronic materials leading to diverse applications in next generation devices.Dielectric Materials
Our research interests are related to the synthesis and understanding of the basic properties of novel piezoelectric, ferroelectric and multiferroic materials. The tuning of their properties opens up the possibilities of various technological applications. They have capacity to hold electrostatic field for a longer duration because each atom in these materials has tendency to become an electric dipole and are known as “electret”, an electrical analogue of magnet. Dielectric materials have been broadly classified into two categories viz. active and passive dielectrics. Our research is focused on the active dielectrics having mainly three field responsive directions which are known as electric axis, optic axis and mechanical axis. For example, such materials generate electric polarization in a particular direction if a stress or optical field is applied along another direction and vice-versa. Such interesting features are being exploited for making piezo, magnetic, and optical sensors, memory, transducers and actuators.Surface and Nano Science
Our research interest is interdisciplinary in nature, covering a variety of outstanding problems in science and technology of condensed matter physics. It involves ideas, techniques and conundrums from a wide range of fields including materials science, thin film science and technology, surface and interface, nanoscience, ion beam physics, optoelectronics and spintronics. We will initially focus on the synthesis of surface nanopatterns by low energy ion beams, and study of their fundamental properties using varieties of surface sensitive techniques. The growth of nanostructures embedded in thin films and at surfaces will also be carried out. Structural, electronic, chemical and physical properties will be studied for fabrication of novel semiconductor device structures. The tunable properties of the group IV semiconductors will be investigated and will be extended to other compound semiconductors, alloys and carbon based materials.Environmental Physics
The Atmospheric and Environmental Science (AES) group seeks for studies in solar spectral radiation, in aerosol optical, physical properties and climate implications, in synoptic and dynamic meteorology and its association with atmospheric pollution, in climatology and in remote sensing of the atmosphere through satellite sensors. Furthermore, natural hazards phenomena, like tropical cyclones, intense dust storms and severe smoke plumes from biomass burning constitute research topics of the group. During the last decades, atmospheric aerosols and pollutants have been tremendously increasing over India due to growth of population, urbanization, industrialization and increased energy demands. The mixture of anthropogenic aerosols rich in carbonaceous components with desert and mineral dust, cause a thick aerosol layer over India, the so-called atmospheric brownish clouds, with significant effects on radiation budget, monsoon system, rainfall re-distribution and atmospheric warming.