Sumiran Pujari
Associate Professor
Photograph: 
Phone: 
(+91) 22-2576-9376
Email: 
sumiran@phy.iitb.ac.in
sumiran.pujari@iitb.ac.in
Fax Number: 
Sometimes I may not reply within a reasonable time period due to wrong spam filing by the institute email server if it sees it coming from a new email address. If there is such a suspicion, please write to my gmail with handle "first name dot last name".
Office: 

221 Physics

Research Interests: 
  • Condensed matter theory, the physics of strong correlations, quantum magnetism and quantum spin liquids
  • Many-body topological order and quantum information processing, (century of) quantum engineering
  • Electronic, magnonic, etc. band structures and topologies and implications on physical transport
  • Algorithmic thinking and computational complexity, exact solvability techniques

Current group members:

  • Anoop Raj, Ph. D. candidate, 2022-now -- Coulomb correlations in classical dimer models and classical spin ices
  • Sankalp Kumar, Ph. D. candidate, 2021-now --  Entanglement entropies and quantum phase transitions in quantum antiferromagnets
  • Naba Prakash Nayak, Ph. D. candidate, 2019-now -- Disorder driven quantum phase transitions (primarily supervised by Soumya Bera) 
  • Arnav Pushkar, Institute post-doc, 2025-now --

  • Some photos with group members over the years here.

Past group members:

  • Vikas Vijigiri, Institute post-doc, 2021-2023  -- Deconfined criticality in S=1 Hamiltonians
  • Santanu Pal, Institute post-doc, 2019-2021 -- Colouring wavefunctions for quantum magnets
  • Saumitra Jain, Civil Engg., Ph.D., 2017-2022 -- Periodic Metamaterial based seismic isolation of structures (co-supervised with Arghadeep Laskar, Civil Engg.)
  • Tannistha Gupta, M. Phil exit, 2018-2022

Notable UG/PG collaborators:

  • Kilian Kuhlbrodt, M. Sc., 2022-2024 (ETH Zurich) and Adhyyan Mansukhani, B. Tech., 2021-2024 - Effect of magnetic fields on topological semimetals and superconductors
  • Vedant Motamarri, B.Tech+M.Tech, 2021-2022 -- Loop ensembles in Stochastic Series Expansion of Two-Dimensional Heisenberg Antiferromagnets
  • Abhishek Kejriwal, B.Tech+M.Tech, 2020-2023 -- Spin dynamics in Nitrogen vacancy centers in Diamond (co-supervised with Kasturi Saha, Elec. Engg.)
  • Sudipta Borah, M.Sc, 2020-2021 -- Study of edge modes in models with higher topological invariants
  • Vineet Punyamoorty, Elec. Engg., B.Tech+M.Tech, 2020-2021 -- Flux-flow Hall effect in superconductors using Time-Dependent Ginzburg-Landau Equations (co-supervised with Kasturi Saha, Elec. Engg.)

Extended past guest visitors:

  • Sept, 2024: Karlo Penc, Wigner Research Center, Budapest, Hungary.
    Lectures on spin-orbit coupling in Mott Insulators (available here).
    Some photos here.
  • Mar, 2019: Ribhu Kaul, Penn State University, USA (formerly University of Kentucky)
    Lectures on quantum spin chains. Some photos here.
Selected Publications: 

  • Most of my publications are listed on arxiv here. A selection of my publications follows below. A playlist of my talk videos is available here. A few papers resulting through collaborations in the engineering discipline are not in the arxiv list.

  • A general theorem on extensive ground state entropy in spin-1/2 models
    arXiv:2407.06236 
    Recent seminar video here (and  here) that has some newer results on connections to Z2 Ising gauge and related theories ("happiest thought" during my recent stay at MPIPKS, Dresden!). Related older seminar video here or  here , and slides here (Part II). The two-dimensional models discussed here is likely a new beast in the zoo of strongly correlated phases and outside the string-net kind of correlated phases for gapped quantum spin liquids. This is as far as I can tell even though the related spin-1/2 or qubit Hamiltonians have quite a family resemblance to the Kitaev toric code which belong the more general class of Levin-Wen models.
  • A class of exactly solvable Hamiltonians for S=1/2 quantum magnets with spinless fermionic excitations in higher dimensions,
    arxiv:2406.17034 
    Part of the proceedings of the 67th DAE Solid State Physics Symposium. Related slides here (Part I). Material/Artificial realization for this class of models with bond-dependent couplings seems feasible. Could be relevant to both classical spin-based technologies and artificial quantum technologies (for more discussion on this, see the preprint). The "unfrustrated XX" case seems to be a genuinely new state of matter where a classical spin liquid coexists with a quantum spin liquid. (also see arXiv:2407.06236.)
  • Punctured-Chern topological invariants for semi-metallic bandstructures, 
    Phys. Rev. Lett. 130, 186202 (2023), arXiv:2205.07814
    Related slides here. These invariants could be useful for anyone interested in band topology in presence of gap-closing points.
  • Unusual spin dynamics in the low-temperature magnetically ordered state of Ag_3 Li Ir_2 O_6
    Phys. Rev. B 104, 115106 (2021), arXiv:2104.10057
    Related slides here that discuss the well-known (or perhaps little-known) issue about large muon relaxation rates in some ordered antiferromagnets (e.g. Gd_2 Sn_2 O_7 and also Ag_3 Li Ir_2 O_6) comparable to that of many spin liquid candidate materials.
  • Resummation-based quantum Monte Carlo for quantum paramagnetic phases
    Phys. Rev. B 104, L060406 (2021), arXiv:2104.06792
    Related seminar video here and slides here.
  • Bilayer Coulomb phase of two dimensional dimer models: Absence of power-law columnar order
    Phys. Rev. E 103, 042136 (2021), arXiv:2011.04506 
    Related seminar video here and slides here.
  • Gapless quantum spin liquid in the triangular system Sr_3 Cu Sb_ 2 O_9
    Phys. Rev. Lett. 125, 267202 (2020), arXiv:2012.01239 
    Related colloquium-style seminar video here and slides here.
  • Topological character of three-dimensional Nexus triple point degeneracies
    Phys. Rev. B 102, 235148 (2020),  arXiv:2006.00709 
    Related seminar video here and slides here.
    (a seminar video here and slides here on a previous work which was instrumental for this work.)
  • Resonating three-coloring wavefunctions for the kagome quantum antiferromagnet
    Phys. Rev. B 99, 104433 (2019), arXiv:1808.08633 
    Related seminar video here and slides here.
 
  • Interaction induced Dirac fermions in bilayer graphene
    Phys. Rev. Lett. 117, 086404 (2016), arXiv:1604.03876 
    Related slides here. (These slides contain unpublished results on SU(N>2) on-site Hubbard model on Bernal-stacked honeycomb bilayer, while the paper focused on SU(2). In short, for SU(4) there is a continuous quantum phase transition from a Dirac liquid to a Neél antiferromagnet similar to SU(2), while for SU(6) (and greater) there is a strong first-order transtion from the Dirac liquid to a valence bond solid.)
  • Sign-problem-free Monte Carlo simulation of certain frustrated quantum magnets
    Phys. Rev. Lett. 117, 197203 (2016), arXiv:1511.01586 
    Related slides here by F. Alet.
  • Transitions to valence-bond solid order in a honeycomb lattice antiferromagnet
    Phys. Rev. B 91, 104411 (2015), arXiv:1502.01035   
    Related slides here.
------------------------------------------- Puerile Ph.D. Phase ---------------------------------------------
 
  • Emergent spin excitations in a Bethe lattice at percolation
    Phys. Rev. Lett. 111, 157201 (2013), arXiv:1210.4621 
  • "Inversion" techniques for Scanning Tunneling Microscopy data analyses
    Ph. D. Thesis (2011)
    Related slides here and thesis document here.

Extended collaborations:

  • Sounak Biswas (2024-now, 2016-2017)
  • Fabien Alet (2024-now, 2011-2014 (as postdoc mentor))
  • Jonathan D'emedio (2023-now)
  • Nisheeta Desai (2016-now)
  • Ankur Das (2018-2024)
  • Avinash Majahan (2018-2024)
  • Kedar Damle (2019-2020, 2016-2017 (as postdoc mentor), 2011-2014 (as postdoc mentor))
    (introduced as the "fifth member of the spin quartet" by R. Moessner here though
    unfortunately not part of the video. For the spin quartet reference, see here 
    around the 17 minute mark.)
  • Hitesh Changlani (2017-2021, 2008-2011)
  • Christopher Henley (2012-2013, 2006-2011 (as Ph.D. guide))

Other intensive collaborators:

Extended physics interlocutors:

Old unpublished ideas:

  • Work on a Ladder representation for the Generalized Heisenberg Algebra [x̂, p̂] = i (1 + β(x̂ 2 + p̂ 2 )). An earlier version of this work has a section on "Unnatural Numbers" which may be of interest or amusement to some. 2015-16. Review exchange here.
  • Conjecture on an extension of the spontaneous symmetry breaking idea from ordering to fluctuations. 2010-13. One of the "happiest thoughts" of my life till now. This idea as it stands is wrong due to a wrong assumption on the microscopic classical dynamics that would be needed during equilibration. Such dynamics may be allowed in dissipative, non-equilibrium systems in steady steady state. I thank Veit Elser,  Jim Sethna, Deepak Dhar and Clement Sire for giving their time to me to discuss this work.

    (I especially thank Jim who engaged with this idea perhaps more than necessary for a busy, professional scientist. Generally, they are trying to balance engaging with good ideas and ignore crackpot ideas. His intuition was in fact correct about something not being right somewhere in the argument. It took some amount of time for me to realize the underlying wrong assumption on the microscopic dynamics. Such dynamics is likely impossible for energy conserving Hamiltonian dynamics as a matter of principle, i.e. for generic initial conditions or start points in the phase space, the trajectories end up exploring a fraction of the phase space that is *not* measure zero in the full phase space. In fact at a many-body level, this is the underlying (ergodicity) hypothesis of classical statistical mechanics including spontaneous symmetry breaking of the standard ordering kind where there is an effective loss of ergodicity breaking, however at the macroscopic level and which is still measure one in the accessible phase space volume. In the above idea , a drastic "measure zero ergodicity breaking"  was assumed at the microscopic or few-body level which is very likely impossible in Newtonian mechanics or any dynamical situation with at most a few integrals of motion except for perhaps the (not very relevant) case of completely free and non-interacting particles.)

Teaching history:

  • 2023-24/1 PH 251 - Classical Mechanics (minor)
  • 2023, Tutor for summer school on the physics of quantum matter
  • 2021-22/2 PH 554 : Computational Many-body Physics
  • 2021-22/1 PH 217 : Classical Mechanics
  • 2021-22/2 PH 554 : Computational Many-body Physics
  • 2021-22/1 PH 401 : Classical Mechanics
  • 2020-21/2 PH 410 : Statistical Physics
  • 2020-21/1 PH 401 : Classical Mechanics
  • 2019-20/2 PH 438 : Statistical Physics
  • 2019-20/1 PH 217 : Classical Mechanics
  • 2018-19/2 PH 310 : Introduction to Condensed Matter Physics
  • 2018-19/1 PH 409 : Introduction to Condensed Matter Physics
  • 2017-18/2 EP 320 (now PH 438) Statistical Physics
  • 2017-18/1 PH 409 : Introduction to Condensed Matter Physics 

Miscellaneous:

  • a general talk video here given to IIT Bombay community on convocation-2020 speaker F. D. M. Haldane's Nobel prize winning work
  • slides on an outreach talk here on "Differential Equations in Science and Engineering" given at Sharad Chandra ACS College, Naigaon, Nanded, Maharashtra on Feb, 2020
  • my only published poem! The forgotten chapbook is available here. Even received a cheque of ~15$ for the reading! which is now misplaced :( I would change a few things here and there in the published version, but that's how it goes ...
    Original version here. A video of the reading here; please excuse the cringe.
  • Some other non-work stuff can be accessed through my LinkedIn page.

"Happiest thoughts" (reverse chronological):

  • Jan-Apr 2025: Emergence of Xu-Moore model after one-time block decimation in the 4-spin «anticommuting» quantum spin liquid. (there are a few inaccuracies in the document since this is the first time I was working out fair notes for this idea.)
  • April 2023: The gedanken described in pg. 1 of the one-dimensional of Jordan-Wigner embedding paper here.
  • Mar end-Apr start 2021: Emergence of the quantum Dimer model Hilbert space in the resummed uncoloured SSE-QMC algorithm. See the main text discussion relating to Fig. 3 of resummed algorithm paper and the last section of the supplementary here.
  • March-April 2020 (Covid pandemic wave 1!): a local discrete path resummation idea for SSE-QMC of frustrated quantum spin-1/2 Hamiltonians (notes made later in 2022 here). The idea is not effective to reduce sign problem though :(
  • May-July 2015: Rediscovery of generalized harmonic oscillators and "discovery" of unnatural numbers. See here.
  • sometime in 2009 in front of the physics office of Clark Hall: Conjecture on an extension of the spontaneous symmetry breaking idea from ordering to fluctuations. The implementation of the idea as described is wrong or inapplicable due to invalid microscopic dynamics or equations of motion.  some other writings here

Worldline:

  • 1983: Sambalpur, Odisha (birth, Prasanta Kumar Pujari (retired executive metallurgical engineer, RSP), Arundhati Pati (retired senior reader in Home Science)) 
  • 1983-2001: Rourkela, Odisha (childhood and schooling with Saswati Pujari)
  • 2001-2005: Mumbai (undergraduate)
  • 2005-2011: Ithaca, NY, USA (Ph.D. training)
  • 2011-2014: Toulouse, France (postdoc)
  • 2014-2016: Lexington, KY, USA (postdoc)
  • 2016-now: Mumbai
  • Summers of 2018,2019: Lexington, KY, USA (science + personal)
  • October of 2022: Bordeaux, France (science)
  • Winter of 2023: Trieste, Italy (science + visit)
  • June of 2024: Toulouse, France (science)
  • August of 2024: Bhubaneshwar, Odisha (science + personal)
  • Oct-Nov of 2024: Toulouse, France (science + travel)
  • Jan-Mar of 2025: Dresden, Germany (science + travel)
Research Category: 
Condensed Matter Theory