Dr Dharmalingam Prabhakaran

Abstract:

Three-dimensional (3D) topological Dirac semimetals (TDSs) represent an unusual state of quantum matter that can be viewed as "3D graphene." In contrast to 2D Dirac fermions in graphene or on the surface of 3D topological insulators, TDSs possess 3D Dirac fermions in the bulk. By investigating the electronic structure of Na3Bi with angle-resolved photoemission spectroscopy, we detected 3D Dirac fermions with linear dispersions along all momentum directions. Furthermore, we demonstrated the robustness of 3D Dirac fermions in Na3Bi against in situ surface doping. Our results establish Na3Bi as a model system for 3D TDSs, which can serve as an ideal platform for the systematic study of quantum phase transitions between rich topological quantum states.

Abstract:

Condensed matter in the low-temperature limit reveals exotic physics associated with unusual orders and excitations, with examples ranging from helium superfluidity to magnetic monopoles in spin ice. The far-from-equilibrium physics of such low-temperature states may be even more exotic, yet to access it in the laboratory remains a challenge. Here we demonstrate a simple and robust technique - the 'magnetothermal avalanche quench' - and its use in the controlled creation of non-equilibrium populations of magnetic monopoles in spin ice at millikelvin temperatures. These populations are found to exhibit spontaneous dynamical effects that typify far-from-equilibrium systems and yet are captured by simple models. Our method thus opens new directions in the study of far-from-equilibrium states in spin ice and other exotic magnets. © 2014 Macmillan Publishers Limited.

Abstract:

Social networks are believed to affect health-related behaviors and health. Data to examine the links between social relationships and health in low- and middle-income country settings are limited. We provide guidance for introducing an instrument to collect social network data as part of epidemiological surveys, drawing on experience in urban India. We describe development and fielding of an instrument to collect social network information relevant to health behaviors among adults participating in a large, population-based study of non-communicable diseases in Delhi, India. We discuss basic characteristics of social networks relevant to health including network size, health behaviors of network partners (i.e., network exposures), network homogeneity, network diversity, strength of ties, and multiplexity. Data on these characteristics can be collected using a short instrument of 11 items asked about up to 5 network members and 3 items about the network generally, administered in approximately 20 minutes. We found high willingness to respond to questions about social networks (97% response). Respondents identified an average of 3.8 network members, most often relatives (80% of network ties), particularly blood relationships. Ninety-one percent of respondents reported that their primary contacts for discussing health concerns were relatives. Among all listed ties, 91% of most frequent snack partners and 64% of exercise partners in the last two weeks were relatives. These results demonstrate that family relationships are the crux of social networks in some settings, including among adults in urban India. Collecting basic information about social networks can be feasibly and effectively done within ongoing epidemiological studies.

Abstract:

We present a study of the magnetic and crystallographic structure of TbMnO3 in the presence of crossed electric and magnetic fields using circularly polarized x-ray nonresonant scattering. A comprehensive account is presented of the scattering theory and data analysis methods used in our earlier studies, and in addition we present interesting high magnetic field data and its analysis. We discuss in detail how polarization analysis was used to reveal structural information, including the arrangement of Tb moments which we proposed for H=0 T, and how the diffraction data for HHC as for H

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