Seminar 2015
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Dr. Bidya Binay Karak NORDITA, Stockholm Modeling the solar global dynamo Wednesday 5 August 2015 1600-1700hrs FB 382 The origin of the 11-year sunspot cycle is not completely understood. A set of mean-field models which rely on parametrizations of the turbulent transport and the Babcock-Leighton process for the generation of poloidal field is successful in reproducing many observed features of the solar cycle. On the other hand, the global 3D simulations, in which we solve the full magnetohydrodynamical equations in spherical geometry, is struggling even to reproduce the basic features of the solar cycle. In my presentation, I shall discuss some of our recent results from both types of models to develop a coherent picture of the solar dynamo. |
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Dr. Borun Chowdhury The information paradox: Still alive and kicking 3rd August (Monday) 2015 4:00 PM FB 382 (Physics Seminar Room). It has been forty years since Hawking discovered that black holes violate the laws of quantum mechanics. This result was to be dubbed the Information Paradox. For various reasons the paradox received minimal interest and virtually lay dormant for the last twenty years. However, a lot of activity has been seen on the paradox in the last two years under the banner of "firewalls". I will review the information paradox, the reasons it lay dormant and the recent firewall paradox. I will also review the decade old fuzzball proposal which shares many of the features of firewalls and may be considered a top down approach to firewalls. Finally, I will discus some arguments against the firewalls and some of the ramifications of the firewall paradox for holography. |
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Dr. Surajit Saha National University of Singapore Novel phenomena at the interface of metal-oxides 3rd August (Monday) 2015 11:00 AM FB 382 (Physics Seminar Room). Inorganic metal-oxides have been known to the mankind for centuries. These oxides reveal a plethora of novel properties, such as, ferroelectricity, magnetism, superconductivity, and so on which have been intriguing the mankind for decades; some of which have already seen applications in our daily life. Further, confining these bulk oxides into two-dimensions, such as, ultra-thin films or heterostructures, may tailor their properties unraveling some whole new variety of emergent phenomena. One such recent discovery has been the observation of two-dimensional electron gas (2DEG) at the interface of two wide band-gap insulators, namely, LaAlO3 and SrTiO3. Further research on this 2DEG has unraveled the possible mechanisms involved and the various other interesting properties, e.g., magnetism and superconductivity exhibited at the interface. In this talk, I would first like to introduce the fascinating properties of the interface between LaAlO3 and SrTiO3 and then lead to our experiments on utilizing the magnetism of the interfacial 2DEG demonstrating a magnetic device having unusually long-range magnetic coupling. In addition to electrical transport and magnetic studies, Raman spectroscopy has been instrumental to understanding the possible mechanism behind this magnetic coupling. I would like to share the excitement of our experimental observations and discuss the possible mechanism and implications. |
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Prof. A. P. Baburaj IIT Madras The boundary layer velocity field in turbulent convection 25th April, 2015 (Saturday) 4 pm Old core lab 103E We measure the spatial velocity field in a horizontal plane within the velocity boundary layer over the horizontal hot plate in turbulent convection in water for 105<Ra<109 and Pr around 5. A new criterion is used to detect the coherent structures, namely line plumes, from this velocity field. The velocity field mostly shows four types of flow patterns, we present the PDF of velocities for each patterns to show their differences. The instantaneous velocity distributions match with that of laminar natural convection boundary layers, with the regions far away from plumes being affected by the external shear at the larger Ra. The mean velocity fields show no clear patterns and the fluctuating velocity fields show velocity field devoid of the mean shear, i.e. the pattern of flow driven by the plumes alone. The PDF of velocities of the plumes and the fluctuating components of the flow velocities coincide implying that plumes mostly contribute to the fluctuating velocity field. The joint PDF of horizontal and vertical instantaneous velocities show an 'arrow' type structure with the arms of the arrow head showing plume and boundary layers while the arrow shaft showing shear affected regions. The spectra of instantaneous velocities show a Bolgiano-Obukhov scaling at larger wave numbers while it shows a -1 scaling for lower wave numbers; we show that the -1 scaling is from regions affected by shear. |
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Dr. Srimanta Middey Department of Physics, University of Arkansas, USA Heterointerface Engineering of Correlated Oxides 14-April-2015 (Tuesday) 4 pm FB-382 Periodic geometrical arrangement of the constituent atoms in a crystalline solid is the backbone of electronic and magnetic properties. The alternation of this atomic arrangement, by creating interface between two chemically, electronically and structurally dissimilar materials can be expected to result a set of many-body states, which are unattainable in the constituent bulk materials. As the strong intercoupling among spin, charge, orbital, lattice degrees of freedom in correlated oxides promote various fascinating collective phenomena (e.g. superconductivity, magnetism, ferrolectricity ...), the additional broken symmetries and frustrated couplings across interface may give rise to a new horizon to novel electronic, magnetic and topological states. However, microscopic understanding of such interfacial properties is a grand challenge and it requires various advanced techniques. In this talk, I will illustrate the success in creating `new’ electronic states by growing transition metal oxide superlattices with unit cell precision. The implementation of synchrotron diffraction, x-ray absorption spectroscopy, resonant x-ray scattering experiments to elucidate the response of the underlying structures, spins, orbitals and charges due to this heterostructuring will be also discussed. Additionally, I will present the prospect of such engineered heterointerfaces for energy harvesting and application as next generation materials for Mott electronics. |
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Auditya Sharma Tel Aviv University, Israel Landauer current and mutual information 14th April, 2015 2.30 pm FB-382We study quantum evolution of the density matrix of a quantum dot con- nected to left and right leads initially maintained at chemical potentials µL and µR respectively and temperature T, within the non-interacting resonant-level model. The full nonequilirbium mixed state density matrix of the whole system is written down exactly, and the mutual information of the dot with respect to the leads is computed. A strong and direct correlation is found between the Landauer current, and the mutual information at all times, the steady-state values in particular displaying a quadratic relationship at high temperatures. We argue that this relationship could potentially be exploited experimentally to ‘measure’ mutual information. I will try to give an elementary introduction and build up the technical details gradually. References: [1] Auditya Sharma and Eran Rabani. Phys.Rev.B 91, 085121 (2015). |
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Gagan Kumar IIT Guwahati Terahertz Plasmonic Waveguides 9-April-2015 (Thursday) 3 pm FB-382 Plasmonic metamaterials have the ability to facilitate the next generation miniaturized high speed communication devices and networks. In my talk, I will discuss about the design, fabrication and characterization of the terahertz guided wave devices on the planar surfaces using plasmonic metamaterials. Thin metal films when periodically corrugated with subwavelength scale structures forms a plasmonic waveguide, which can result in the propagation of terahertz modes confined in both the transverse directions. The degree of confinement and frequency of the resonant modes can be controlled with the geometrical parameters of the structures. In my talk, I will also discuss about the possibly of replacing metals substrates with semiconductors for such waveguide which can be advantageous in making active components. |
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Dr. R. Prabhu HRI, Allahabad Multipartite quantum correlations in many-body systems 8th April, 2015 (Wednesday) 4 pm FB-382 The cross-braiding between quantum information and condensed matter physics has recently stimulated excitation among researchers. Many-body systems are potential physical substrates to realize several quantum information protocols. The tools developed in quantum information have been put to use in analyzing collective phenomena in many-body systems. Many-body systems have been studied by observing, for example, their response to external perturbations, various order parameters, and excitation spectra. In this talk, I will characterize the behavior of several quantum correlation measures, including bipartite and multipartite ones, in spin models like Heisenberg spin system, XY-spin chain, etc. Also, I deal with the characterization of multipartite quantum correlation in spin models which can be both clean and disordered ones. |
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Dr. Arijit Kundu IU Bloomington, IN, US Topology and Transport in Periodically Driven Systems 31st March, 2015 (Tuesday) 4 pm FB-382 One way to introduce topological phases in certain systems is periodic driving. For example, an 1D p-wave superconductor, driven periodically, can go through a Floquet transition to become topologically non-trivial. Such Floquet topological superconductor can host exotic steady states, which are called Floquet Majorana fermions. Whereas, graphene, under the application of circularly polarized laser is an example of Floquet topological insulator. Such topological insulators, like the quantum-hall systems, have non-trivial topology and chiral edge states. Such systems present potential applications to various fields from quantum computation to valleytronics. In this talk I'll present our recent works on topological classification and some novel transport characteristics of such driven systems. |
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Dr. Veeresh Singh University of KwaZulu-Natal Durban, South Africa Unveiling the population of distant radio galaxies and their environments 31st March, 2015 (Tuesday) 12 noon FB-382 Radio galaxies exhibit jet-lobe radio structures emanating from active nucleus and are found to be hosted in massive elliptical galaxies. Radio galaxies particularly at higher redshifts and in obscured environments can be used as beacon to identify active galaxies and understand their evolution. It has been shown that Ultra Steep Spectrum (USS) radio sources are one of the efficient tracers of powerful High-z Radio Galaxies (HzRGs). We study properties of a USS sample derived from deep 325 MHz and 1.4 GHz observations and find a substantial population of unexplored weaker radio galaxies potentially hosted in obscured environments along with the population powerful HzRGs. Furthermore, in general, powerful HzRGs tend to reside in (proto)cluster environments. |
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Dr. Debakanta Samal Max-Planck Institute, Munich, Germany Tailoring the electronic properties of cuprate layers on unit cell level: A boost towards designing artificial high Tc cuprates. 26th February, 2015 (Thussday) 4:30 pm FB-382 |
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Dr. Dinesh Narayana Naik Department of Physics, Mehsana Urban Institute of Sciences, Ganpat University Correlation holography: A marriage of holography with statistical optics 25th February, 2015 (Wednesday) 4 pm FB-382 With unconventional holographic techniques incoherent holography, coherence holography and photon correlation holography, it is possible to record and reconstruct 3-D objects as the second or fourth order correlation function of the optical fields. Unlike conventional holography, these techniques require only incoherent light for the illumination. The reconstructed object manifests itself in the spatial coherence function of the optical field. As a consequence, we can extend the holographic imaging to phenomena such as fluorescence with possible biomedical applications. Moreover, optical fields with a desired spatial coherence function can be synthesized using the technique of coherence holography with possible applications to microscopy and lithography. |
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Dr. Vishwanath Shukla IISc Particles And Fields In Superfluids: Insights From The Two-Dimensional Gross-Pitaevskii Equation. 23th February, 2015 (Monday) 4 pm FB-382 We study the dynamics of active particles in two-dimensional superfluids at temperature T = 0, for a variety of initial configurations, by carrying out extensive direct-numerical-simulations of the two-dimensional, Galerkin-truncated Gross-Pitaevskii equation. Our study elucidates the interplay of particles and fields, in both simple and turbulent flows. We show that particle collisions can be inelastic, if the repulsive interactions between particles is weak, and elastic otherwise. We show that assemblies of many particles and vortices yield turbulent spatiotemporal evolutions. |
| Speaker: | Hilal Ahmed |
| Affiliation: | AMU, Aligarh |
| Title: | Synthesis and Characterization of Nanocrystalline Colossal Magnetoresistive Manganites |
| Date: | 13th February 2015 (Friday) |
| Time: | 11 am |
| Venue: | FB-382 |
| Abstract: | In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO3. The parent material LaMnO3 is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications |
| Speaker: | Dr. Debi Prasad Datta |
| Affiliation: | Institute of Physics (IoP), Bhubaneshwar |
| Title: | Ion beam induced synthesis and modifications of nano structures: Fundamentals and some applications. |
| Date: | 14th January, 2015 (Wednesday) |
| Time: | 12 pm |
| Venue: | FB-382 |
| Abstract: | Ion bombardment of solids is an efficient route towards processing of nano-scale surface patterns as well as synthesis and modification of nanostructures. Ion-beam-patterned surfaces are receiving increasing interest due to their promising applications, e.g., as templates for growing thin films with tailored properties. In this talk, I shall present our experimental investigations on the evolution of surfaces under off-normally incident medium energy ion bombardment. In fact, I shall show that ripple pattern evolution on Si[1], Ge[2], or SiO2 can be understood in a common theoretical framework, viz. as a result of ion erosion and ion induced mass redistribution. Irradiation-induced transition of such sinusoidal ripple patterns to a saw-toothed one will be demonstrated, which will be correlated to slope-dependent non-linear effect and shadowing of the incident ion beam. On the other hand, similar off-normal ion bombardment will be shown to result in no surface patterning but development of a porous structure containing nanofibers in case of GaSb and InSb [3], owing to growth of voids during bombardment. Some properties of such ion-induced structures, like photoluminescence, antireflection and hydrophobicity, will be discussed. In the last part of the talk, I shall describe studies on synthesis and modification of embedded Au nanoparticles in SiO2 by MeV Au2+-ion bombardment [4]. 1. D. P. Datta et al., Phys. ReV. B 69, 235313 (2004); Phys. Rev. B 71, 235308 (2005); Phys. Rev. B 76, 075323 (2007), S. K. Garg and D. P. Datta et al., Appl. Surf. Sci. 310, 147 (2014); Appl. Surf. Sci. 317, 476 (2014). 2. D. P. Datta et al., (to be communicated to Phys. Rev. B). 3. D. P. Datta et al., J. Appl. Phys. 115, 123515 (2014); Applied Surface Science 310, 189 (2014); J. Appl. Phys, 116, 033514 (2014); J. Appl. Phys. 116, 143502 (2014). 4. D. P Datta et al., Appl. Surf. Sci. 310, 164 (2014). |
| Speaker: | Faraz Ahmed Inam |
| Affiliation: | Dept. of Physics, Aligarh Muslim Universiuty |
| Title: | Fundamental characterisation of nanodiamond nitrogen-vacancy (NV) centres spontaneous emission as a single photon source. |
| Date: | 06 January 2015 (Tuesday) |
| Time: | 3 pm |
| Venue: | FB - 382 |
| Abstract: | With its inbuilt, unique spin and optical properties, negatively charged nitrogen-vacancy (NV) centres in diamond have attracted wide interest in interdisciplinary research fields, ranging from quantum technologies, high-resolution magnetometry to biomedical imaging and tracking. Most of the highly sensitive applications of diamond-NV centers in the above fields rely on bright, controllable and photo-stable NV luminescence from very small diamond nanocrystals. Nanodiamond NV centre has been widely studied in the past decade and significant enhancements in its emission rate and capture factors were achieved. Nevertheless a complete picture of its spontaneous emission under the influence of the local electromagnetic nano-environment was non-existent at the beginning of my research study. In my research, I sought to improve the understanding of NV emission by systematically isolating the various individual mechanisms influencing its emission. In this talk, I will shows how the systematic approach of our study of nano diamond NV emission under a range of conditions and environments elped us to develop and contribute towards the evolved understanding of its spontaneous emission. |
| Speaker: | Dr. Swapnil Patil |
| Affiliation: | Tata Institute of Fundamental Research (TIFR) |
| Title: | Photoemission insight into exotic low temperature physics of rare-earth intermetallics: heavy-fermion behaviour, mixed valency, Kondo physics etc. |
| Date: | 6th January, 2015 (Tuesday) |
| Time: | 12 pm |
| Venue: | FB - 382 |
| Abstract: | In this talk, I shall present the results of photoemission studies of remarkable Ce- and Yb- based materials, exhibiting unique properties like Kondo physics, heavy-fermion behaviour, and mixed valency. One of the important problems in correlated electron systems concerns the observation of "large-small" Fermi surface transition in Kondo systems with temperature. It is believed that the Fermi surface of a Kondo system expands at lower temperatures due to the formation of many-body Kondo singlet states. Our photoemission results however demonstrate temperature invariant Fermi surface in a prototypical Kondo system, YbRh2Si2. Additionally our results on Ce-Kondo systems demonstrate electronic spectral evolution which deviates from the predictions of Anderson model, a theoretical model normally used to interpret photoemission spectra from Kondo systems. Potential candidates to explain these discrepancies will be briefly discussed. Finally Fermi surface studies on YbCo2Si2, a stable valent Kondo lattice, will be discussed which serves as a reference compound for YbRh2Si2, which happens to be close to quantum criticality. |