Sumiran Pujari

TIFR Residential Complex, 207 Jagadish, New Navy Nagar Colaba, Mumbai 400005 H +91-7506232723 B [email protected] Í pa.as.uky.edu/users/spu232

Education 09/05-09/11 M.S.,Ph.D., Dept. of Physics, Cornell University, 3.59/4.00. Thesis Title: Explorations in Scanning Tunneling Microscopy (STM) Phenomenology: Inversion Techniques for STM Data Analyses

07/01-05/05 B.Tech., Dept. of Physics, Indian Institute of Technology, Bombay, 8.41/10.00. Thesis Title: Dynamical Systems

Research Experience – Condensed Matter Theory 08/16-now Visiting Fellow, Department of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai, India. { Investigating the effect of SU (2) breaking exchange terms on a finite-temperature order-disorder phase transition in a frustrated quantum Heisenberg antiferromagnet on the square bilayer. { Building quantum Monte Carlo codes to numerically simulate the above physics based on previous work on sign-problem-free access to a class of frustrated quantum antiferromagnets. { Carrying out perturbative calculations in various limits to map out the analytically accessible corners of the phase diagram. { Studying classical dimer models with potential longitudinal correlations in spite of hard constraints on a bipartite lattice using classical Monte Carlo and effective field theory methods. { Collaborators: F. Alet, K. Damle, N. Desai, G. Murthy

08/14-08/16 Post-doctoral Scholar, Department of Physics, University of Kentucky, Lexington, USA. { Studied the effect of Hubbard Interactions on Bernal-stacked Honeycomb Bilayer motivated by Graphene bilayers which hosts a quadratic band touching semi-metal in the non-interacting limit. { Uncovered a stable gapless Dirac semi-metallic phase in weak-coupling that was previously believed to be a quantum Antiferromagnet with gapped single particle excitations. { Employed determinantal Quantum Monte Carlo code to perform large-scale computations to numerically characterize the various phases supported by the Bernal-stacked Honeycomb Bilayer. { Performed weak-coupling Renormalization Group and Hartree-Fock mean-field theory calculations to understand the phase diagram analytically. { Wrote down Ladder Representations for Generalized Heisenberg Algebras which have been invoked as possible routes to ultra-violet completions of physical theories. { Computed hopping vacuum expectation values for simple Bose/Fermi Hubbard models for all SU (N ) perturbatively in strong-coupling limit, and non-perturbatively using Exact Diagonalization, to compare with ADS-CFT type holographic models. { Collaborators: R. K. Kaul, T. C. Lang, G. Murthy, M. Fujita, R. Meyer, M. Tezuka

05/14-07/14 Visiting Scientist, Department of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai, India. { Characterized a classical phase transition between an ordered and a disordered phase (XY model in three dimensions) which hosts a dangerously irrelevant operator (anisotropy field) to contrast with our previously studied unconventional quantum phase transitions. { Applied the Wolff Algorithm to perform classical Monte Carlo computations. { Collaborators: F. Alet, K. Damle

1/5

11/11-03/14 Post-Doctoral Fellow, Indo-French Centre for the Promotion of Advanced Research, Laboratoire de Physique Théorique, IRSAMC, Université de Toulouse III, Toulouse, France. { Characterized unconventional phase transitions between quantum magnetic and non-magnetic phases described by the paradigm of Deconfined Quantum Criticality. { Employed computationally intensive approaches like the Stochastic Series Expansion Quantum Monte Carlo and Projector Quantum Monte Carlo techniques to study quantum spin models where analytical approaches cannot make substantial progress. { Extensive use of Statistical methods like Binning Analysis, Jack-knife procedure and Bootstrapping methods for quantifying uncertainties of observables in the Monte Carlo simulations. { Used the Algorithms and Libraries for Physics Simulations (ALPS) package to manage parallel runs on multiple CPUs for faster convergence of statistical errors. { Found a broad class of frustrated quantum antiferromagnets which admits sign-problem-free Quantum Monte Carlo simulation. { Collaborators: F. Alet, K. Damle

09/05-09/11 Graduate Research, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA. { Dissertation Research: - Devised techniques to analyze data collected in an STM experiment to extract unbiased information about the microscopic quantum interactions (e.g. impurity strength and location, charge carrier’s lifetime, greater-than-gap bosonic feature properties in Cuprates) of the sample without making any stronger assumption than quasiparticle interference. - Implemented the Recursion Method (developed by R. Haydock) for inhomogeneous metals and Superconductors to simulate artificial STM data for testing the techniques. The Recursion Method avoids the (expensive) Diagonalization for the system’s Eigenstates, and instead calculates the density of states as a continued fraction expansion of tri-diagonalized coefficients. - Developed a Mathematica module to solve an interesting phase-reconstruction problem encountered during lifetime extraction, by taking advantage of the smoothness of Green’s functions’ phase as a function of space. { Calculated Photoemission Spectroscopy signatures for Herbertsmithite using Algebraic Spin Liquid ansatz and field-theoretic Renormalization Group methods. { Modeled the low-energy spectrum of Quantum Heisenberg Magnet on a diluted Bethe Lattice at percolation threshold. { Built minimal Toy Models for Spontaneous Orbital Currents for fermions on lattices. { Collaborators: C. L. Henley, M. J. Lawler, H. J. Changlani, S. Ghosh

08/04-04/05 Undergraduate Research, Dept. of Physics, Indian Institute of Technology, Bombay, India. { Surveyed Dynamical systems, including linear and non-linear ordinary multivariate differential equations. { Analyzed the local stability properties of the various critical points and trajectories using techniques of Linear Algebra, thereby arriving at the global behavior of various dynamical systems in presence or absence of perturbations. { Advisors: G. K. Srinivasan, S. Umasankar

05/04-07/04 Visiting Summer Research Program, Dept. of Theoretical Physics, Tata Institute of Fundamental Research, Bombay. { Investigated the properties of trapped Fermi gases in one dimension in the context of Ultra-cold Atomic experiments. { Computed observables (e.g. density profiles) as functions of various parameters (e.g. temperature, magnetic field strength) using techniques from statistical physics. { Advisor: N. Trivedi

2/5

Publications and Preprints { Effect of SU (2) breaking exchange terms on a finite-temperature order-disorder phase transition in a frustrated bilayer quantum Heisenberg antiferromagnet, SP, F. Alet and K. Damle, in preparation (2016). { Effective hopping in a holographic Bose-Hubbard model, M. Fujita, R. Meyer, SP and M. Tezuka, to be submitted (2016). { Interaction induced Dirac fermions from quadratic band touching in bilayer Graphene, SP, T. C. Lang, G. Murthy and R. K. Kaul, Phys. Rev. Lett. 117, 086404 (2016). { Sign-problem-free Monte Carlo simulation of certain frustrated quantum magnets, F. Alet, K. Damle and SP, accepted at Phys. Rev. Lett., preprint at http://arxiv.org/abs/1511.01586 (2015). { Quantum Oscillator spectra for some Generalized Heisenberg Algebras, SP, unpublished, preprint at https://pa.as.uky.edu/users/spu232 (2015). { Transitions to valence-bond solid order in a honeycomb lattice antiferromagnet, SP, K. Damle and F. Alet, Phys. Rev. B 91, 104411 (2015). { Boson features in STM spectra of Cuprate superconductors: Weak-coupling Phenomenology, SP and C. L. Henley, Phys. Rev. B 90, 085129 (2014). { Néel to Columnar Valence-bond Solid Transition on the Honeycomb Lattice: Evidence for Deconfined Criticality, SP, K. Damle and F. Alet, Phys. Rev. Lett. 111, 087203 (2013). { Emergent spin excitations in a Bethe lattice at percolation, H. J. Changlani, S. Ghosh, SP and C. L. Henley, Phys. Rev. Lett. 111, 157201 (2013). { Effect of Dirac Spinons on ARPES signatures of Herbertsmithite, SP and M. J. Lawler, Phys. Rev. B 87, 104415 (2013). { Extracting Quasiparticle Lifetimes from Scanning Tunneling Microscopy Data, SP, unpublished, preprint at http://arxiv.org/abs/1104.1749 (2011). { Quasiparticle Echoes in Scanning Tunneling Microscopy, SP and C. L. Henley, Phys. Rev. B 82, 035109 (2010). { Spontaneous currents in Fermion Lattice Models at the Strong Coupling Limit, SP and C. L. Henley, Phys. Rev. B 80, 085116 (2009). { Spatio-temporal Pattern Formation of a Sedentary Plant Species, that propagates in a Dispersal Limited Scenario, SP and S. Pujari, Proceedings of National Conference on Nonlinear Systems and Dynamics (2003).

Presentations ’16 Effect of Hubbard Interactions on the quadratic band touching semi-metal on BernalStacked Honeycomb Bilayer, APS March Meeting, Baltimore. ’16 Effect of Hubbard Interactions on the quadratic band touching semi-metal on BernalStacked Honeycomb Bilayer, TIFR, Mumbai. ’14 ’14 ’14 ’14 ’14 ’14

Inversion Techniques for Scanning Tunneling Microscopy, University of Kentucky, Lexington. Deconfined Criticality on Honeycomb Lattice, IMSc, Chennai. Deconfined Criticality on Honeycomb Lattice, IISc, Bengaluru. Deconfined Criticality on Honeycomb Lattice, HRI, Allahabad. Deconfined Criticality on Honeycomb Lattice, IISER, Pune. Deconfined Criticality on Honeycomb Lattice, NISER, Bhubhaneswar. 3/5

’13 Néel to Valence-bond Solid Quantum Phase Transition on Honeycomb Lattice, IIT, Mumbai. ’13 Quantum Phase Transition from Néel to Valence-bond Solid on Honeycomb Lattice: Evidence for Deconfined Criticality, APS March Meeting, Baltimore. ’11 ARPES spectral function of Kagome Antiferromagnetic Insulators, APS March Meeting, Dallas. ’10 Extracting Quasiparticle Lifetimes from STM (poster), Gotham Metro Meeting, New York. ’10 Hole in a Kagome Antiferromagnet (poster), International Conference on Highly Frustrated Magnetism, Baltimore. ’10 ’09 ’10,’06 ’04

Single Hole in a Kagome Antiferromagnet, APS March Meeting, Portland. Echolocation of Impurities by Quasiparticles, APS March Meeting, Pittsburgh. LASSP Summer Seminars, Cornell University, Ithaca. VSRP Research Seminar, Tata Institute of Fundamental Research, Mumbai.

’03 Spatio-temporal Pattern Formation of a Sedentary Plant Species, that Propagates in a Dispersal Limited Scenario (poster), National Conference on Nonlinear Systems and Dynamics, IIT Kharagpur, India.

Teaching Experience ’05 Teaching Assistant : Electricity and Magnetism for Engineering sophomores ’09,’07,’06 Laboratory Assistant : Electronic Circuits for Physics juniors and seniors

Technical Skills { Green’s function methods { Hartree-Fock Mean-field Theory and Degenerate Perturbation Theory { Weak-coupling Renormalization Group for Interacting Fermions { Familiar with Gauge field theoretic approaches { Quantum Monte Carlo approaches : { Stochastic Series Expansion for quantum spin systems { T=0 Projector Monte Carlo algorithm for quantum spin systems { Stochastic Green’s Function algorithm for quantum spin systems { Worked with Determinantal QMC code for interacting fermions { Cluster algorithms for classical spin models

Computer Skills { Algorithms and Libraries for Physics Simulations (ALPS) { Programming Languages: { proficient in C++, Mathematica { familiar with Python, Fortran, Matlab { Data Processing Tools: Sed, Awk, Gnuplot { Shell Scripting (bash, tcsh) in Linux Environment

Awards and Achievements ’15-’17 A grant (DMR150037) of 3,200,000 CPU hours worth ∼ $130,000, Extreme Science and Engineering Discovery Environment (XSEDE)

4/5

’11-’14 Post-doctoral Fellowship, Indo-French Centre for Promotion of Advanced Research (CEPIFRA/IFCPAR) ’05-’10 Graduate Research Fellowship for four semesters, Cornell University ’04 Visiting Students Research Scholarship, Tata Institute of Fundamental Research ’04 Jawaharlal National Centre for Advanced Research award for Summer Research ’01 163rd among ∼ 200, 000 examinees in the Joint Entrance examination conducted by Indian Institutes of Technology ’00, ’99 Top 1 % in Indian National Physics, Chemistry and Mathematics Olympiads ’99-’01 Jawahar Scholarship for academic excellence by Steel Authority of India Ltd. ’99 2nd in the state of Orissa, Indian Certificate of Secondary Education (ICSE) ’98-’05 National Talent Search Examination Scholarship by Govt. of India

References { Prof. F. Alet Laboratoire de Physique Théorique, IRSAMC, Université de Toulouse III Toulouse, France. [email protected] { Prof. K. Damle Dept. of Theoretical Physics, Tata Institute of Fundamental Research Mumbai, India. [email protected] { Prof. Christopher L. Henley (deceased) Laboratory of Atomic and Solid State Physics, Dept. of Physics, Cornell University Ithaca, NY, USA. [email protected] { Prof. Ribhu K. Kaul Dept. of Physics, University of Kentucky Lexington, KY, USA. [email protected] { Prof. Michael J. Lawler Dept. of Physics, Applied Physics and Astronomy, Binghamton University Binghamton, NY, USA. [email protected] { Prof. G. Murthy Dept. of Physics, University of Kentucky Lexington, KY, USA. [email protected]

5/5