| UT-PRC, MRC 1st Floor North 10100 Burnet Road, Bldg 160 Mail Code R9900 Austin, TX 78758 |
phone: 512-471-1344 fax: 512-471-8575 email: brsahu@physics.utexas.edu |
Bhagawan Sahu is a research staff and PI in recently formed nano-electronics academy, SWAN, microelectronics research center at University of Texas, Austin. He received his Masters and Ph.D from the University of Pune in 1995 and 2000 respectively, all in Solid state and Materials Physics. In 2002, he joined Physics Department of UT-Austin, as a postdoctoral researcher with Prof. Leonard Kleinman. There he worked on the density functional electronic structure studies of bulk solids & nano-clusters and published large number of papers in peer-reviewed journals, all of which has a good number of citations. Since 2005, he has been a research associate with Dr. Sanjay Banerjee and a research staff & PI (2006- ) at SWAN. He has over 20 archival refereed publications and serves as a referee for prestigious Physics journals of American Physics Society and Institute of Physics (UK). He served in the NSF’s graduate fellowship committee and is a member of professional societies, APS, ACS, IEEE and MRS. He is currently co-supervising 3 graduate students of Physics at UT-Austin. He is currently active in the areas of graphene physics, complex oxides (multi-ferroics and strongly correlated quasi-two-dimensional electron gas) and nano-particles (of Si, GaN and transition metals) using density functional based electronic structure methods. He is also interested in the areas of methodological developments in realistic description of strongly correlated methods (non-perturbative), many-body corrections to density functional quasi-particles (perturbative methods such as GW & Bethe-Salpeter), and time-dependent density functional theory for excited state properties of finite systems (optical, electrical etc). He is using these methods in his research works.
These are 2-D carbon layers, stacked in a vertical direction by weak van der Waals forces in three-dimensional bulk graphite. The extraction of 2-d sheets from the graphite using plastic tapes and identifying the layers (mono- and multi-layers) by optical means, in 2004, started a new area in the physics of 2-d materials- chiral electron liquid. The chirality (left- and right-hand asymmetry), the electronic dispersions in momentum space (captured by single-particle theories as it results from its honey-comb lattice structure), the relativistic nature of charge-carriers and other physical properties made graphene a fertile ground for exploring single-particle as well as many-particle properties We, at SWAN, using a single particle picture of electron-electron interaction (in density functional formalism) explore the electronic properties of graphene [1,2,3] Many-body corrections to quasi-particles in graphene and hence the band gaps (at the time-dependent Hartree or RPA level) are now performed to get a realistic picture of confinement (along the width and the length) induced gaps in armchair or zigzag bilayer graphene nano-ribbons. Other interesting works, such as substrate (SiC, Si(111) etc) effect on the electronic properties of graphene, building blocks for all-graphene nano-device is in progress. More
1) Hongki Min, Jason Hill, Nicolai Sinistyin, Bhagawan Sahu , Leonard Kleinman and Allan MacDoanld, Intrinsic and Rashba spin-orbit interactions in graphene sheets, PHYSICAL REVIEW B 74, 165310 (2006). [abstract] [pdf]
2) Hongki Min, Bhagawan Sahu, Sanjay Banerjee and Allan H MacDoanld, ab-initio theory of gate induced gaps in graphene bilayers’, PHYSICAL REVIEW B 75, 155115 (2007). [abstract] [pdf]
3) Bhagawan Sahu, Hongki Min, Allan MacDonald and Sanjay Banerjee, Electronic properties of one and zero-dimensional bilayer graphene nano-ribbons: Electric field effects.[abstract] [preprint]
4) Bhagawan Sahu, Hongki Min, Allan MacDonald and Sanjay Banerjee, Quasi-particle corrections to the band-gaps of bilayer graphene nano-ribbons [preprint]
5) Bhagwan Sahu, Hongki Min, Allan MacDonald and Sanjay Banerjee, Graphene mono and bi-layers on 4H(0001)-SiC with ( 6√3*6√3)R30º surface reconstruction [preprint]
Complex Oxides
The complexity in oxides arises due to the interplay of orbital, spin and lattice degrees of freedom and they give rise to plethora of interesting physical effects from magneto-resistance to heavy-fermion behavior to multi-ferroic behavior (simultaneous existence of electric, magnetic and elastic order) including Mott-insulator transition. We explored the interplay of electric [1] and magnetic order [2] in a chalco-genide material and in class of oxide materials known as multi-ferroics [3, 4, 5] by using a single-particle approach. Creating an artificial multi-ferroic structure, by combining ferro-magnetic and ferro-electric materials and probing the existence of ferro-electricity in ultra-thin films of the only known magneto-electric material (where strong coupling between the electric and magnetic order is now established) are the recent works in progress. The hetero-structures of Mott insulators forming a quasi-2D strongly correlated electron gas at the interface with strong correlations probed by Hubbard U for localized orbitals [6] is in progress. A more sophisticated non-perturbative method, using dynamic screening and correlations which can treat the localized and delocalized orbitals on the same footing, with strong electron-electron interactions are now explored, with realistic material parameters from density functional theory. More
1) Adrian Ciucivara, Bhagawan Sahu and Leonard Kleinman, Density functional study of effect of pressure on ferroelectric GeTe, Phys. Rev. B 73, 214105 (2006) [abstract] [pdf]
2) Adriran Ciucivara, Bhagawan Sahu and Leonard Kleinman, Density functional study of Ge1-xMnxTe, PHYSICAL REVIEW B 75, 241201(R) (2007) [abstract] [pdf]
3) Adrian Ciucivara, Bhagawan Sahu and Leonard Kleinman, Density functional study of multi-ferroic Bi2NiMnO6, PHYSICAL REVIEW B 76, 064412 (2007) [abstract] [pdf]
4) Priya Gopal, Bhagawan Sahu and Leonard Kleinman, Critical thickness for ferro-electricity in BiFeO3 films with realistic electrodes [preprint]
5) Adrian Ciucivara, Bhagawan Sahu and Leonard Kleinman, Multi-ferroic properties of super-lattice of LaMnO3/BaTiO3 and YTiO3/BaTiO3 [preprint]
6) Joseph Cheng-Ching Wang, Bhagawan Sahu, Wei-cheng Lee and Allan MacDonald, Electronic properties of hetero-structure of Mott insulators- LSDA+U study. [preprint]
Magnetic Semiconductors
To introduce magnetic interactions in non-magnetic semiconductors such as Silicon and Germanium (in bulk as well as nano-crystals), we dope them with dilute concentrations of a magnetic species (in this case manganese atoms). The single particle picture of bulk silicon doped with holes (to mimic the experiments) and co-doped with Mn atoms (replacing Si atoms and located at the interstitials of the Si cubic lattice) show that the magnetic interactions, with and without strong local Coulomb correlations, are anti-ferromagnetic when Mn atoms are placed along [111] direction of the silicon crystal. We find that there is substantial wave-function amplitudes (through the projection of crystal wave-functions onto the atomic orbitals described by spherical harmonics) on the two Mn sites with a Si atom located in between them, meaning the magnetic interactions are mediated by Si delocalized states that helps in sustaining the magnetic order at low temperatures [1]. It would be interesting to put Mn atoms along [100] and [110] directions to explore the possibility of ferromagnetic interactions. In Si nano-crystals, where confinement effects on local magnetic states are predominant, especially for small diameter crystals, we find high-spin and low-spin states and their cross-over depending upon whether they are located in the central or sub-surface region [2]. We explain this interesting observation with the picture based on ligand field (produced by surrounding Si atoms on the doped Mn atom) effects and Pauli’s exclusion principle which guarantees the probability of two electrons with the same spin occupying the same orbital smaller. More .
1) Bhagawan Sahu, Sanjay Banerjee and Leonard Kleinman, Density functional study of Mn doped bulk Silicon, (Submitted) [abstract] [pdf]
2) Bhagawan Sahu, Sanjay Banerjee, Gustavo Dalpian and James Chelikowsky, Low spin to high spin transitions in Mn doped Si nano-crystals, (to be published) [abstract] [pdf]
© Microelectronic Research Center, UT-Austin
Please send comments or questions to Jean Toll.