My research, done with students, postdoctoral associates and colleagues at TIFR, has focused on cooperative effects in interacting systems, both in and out of equilibrium. In recent years, and in particular after moving to TCIS, I have been working primarily on nonequilibrium statistical physics. The theme has been to work on new phases that involve a balance between fluctuations and order, and arise from external driving and interactions between particles.

Fluctuation-Dominated Phase Ordering (FDPO) refers to a state in which giant fluctuations coexist with long range order. Its signatures have been found in several systems, ranging from models of the cell membrane and active nematics, to experiments on shaken rods. Challenges include understanding the origin of singular scaling functions for correlations in space and time, and investigating the interrelationships and scaling properties of the infinite set of order parameters required to characterize FDPO.

The area of Coupled Driven Systems with several interacting species has seen important progress in recent times, and systems have recently been grouped into universality classes, with distinct dynamical exponents for different propagating modes. We are interested in the outcome of instabilities of these modes, which often herald macroscopic phase separation. The classification of the resulting ordered states is an important goal, towards which we are working.

Entropy-induced Ordering is important in crowded environments. In earlier work, we showed that density gradients induce long-range ordering in an assembly of needles in two dimensions. The dynamics of approach to crowded ordered states, involving coarsening and persistence, has surprising aspects which we are investigating within models of hard objects with different shapes.

Aggregation-Fragmentation Dynamics can lead to a phase transition with macroscopically large aggregates forming. Interestingly, we found that the large-aggregate state shows strong intermittency or burst-like behaviour in an open system with influx and outflux. These studies were motivated by aspects of protein transport through the Golgi organelle within the cell, for which a more realistic model which incorporates more features of the biological system has been developed.

In Disordered Driven Systems, the impediments brought in by quenched disorder can change the qualitative aspects of transport. These effects can be studied in depth within lattice models of particle transport as well as interface motion through a disordered medium. We are interested in quasi-arrested states arising from large barriers, and spurts of motion between such states.

Fluctuation-Dominated Phase Ordering (FDPO)

  1. “Order-parameter scaling in fluctuation-dominated phase ordering” R. Kapri, M. Bandyopadhyay and M. Barma
    Phys. Rev. E 93, 012117 (2016)

  2. “Singular Scaling Functions in Clustering Phenomena” M. Barma
    European Physical Journal B 64, 387 (2008)

  3. “Dynamics of fluctuation-dominated phase ordering: Hard-core passive sliders on a fluctuating surface” Sakuntala Chatterjee and M. Barma
    Phys. Rev. E 73, 011107 (2006)

  4. “Strong clustering of non-interacting, passive sliders driven by a Kardar-Parisi-Zhang surface” A. Nagar, S.N. Majumdar and M. Barma
    Phys. Rev. E 74, 021124 (2006)

  5. “Phase separation driven by a fluctuating two-dimensional self-affine potential field” G. Manoj and M. Barma
    J. Stat. Phys. 110, 1305 (2003)

  6. “Fluctuation-dominated phase ordering driven by stochastically evolving surfaces” D. Das, M. Barma and S. N. Majumdar
    Phys. Rev. E 64, 046126 (2001)

Entropy-induced Ordering

  1. “ Orientational correlations and the effect of spatial gradients in the equilibrium steady state of hard rods in two dimensions: A study using deposition-evaporation kinetics” M.D. Khandkar and M. Barma
    Phys. Rev. E 72, 051717 (2005)

Coupled Driven Systems

  1. “Phase diagram of a two-species lattice model with a linear instability” S. Ramaswamy, M. Barma, D. Das and A. Basu
    Phase Transitions, 75, 363 (2002)

  2. “Weak and strong dynamic scaling in a one-dimensional coupled field model: Effects of kinematic waves” D. Das, A. Basu, M. Barma and S. Ramaswamy
    Phys. Rev. E 64, 021402 (2001)

  3. “Strong phase separation in a model of sedimenting lattices” R. Lahiri, M. Barma and S. Ramaswamy
    Phys. Rev. E 61, 1648 (2000)

Aggregation-Fragmentation Dynamics

  1. “Analytical Study of Giant Fluctuations and Temporal Intermittency” H. Sachdeva and M. Barma
    J. Stat. Phys. 154, 950 (2014)

  2. “Condensation and Intermittency in an Open-Boundary Aggregation-Fragmentation Model” H . Sachdeva, M. Barma and Madan Rao
    Phys. Rev. Lett. 110, 150601 (2013).

  3. “Multispecies model with interconversion, chipping, and injection” H. Sachdeva, M. Barma and Madan Rao
    Phys. Rev. E 84, 031106 (2011).

  4. “Phases of a conserved model of aggregation with fragmentation at fixed sites” K. Jain and M. Barma
    Phys. Rev. E 64, 016107 (2001)

  5. “Nonequilibrium phase transition in a model of diffusion, aggregation and fragmentation” S. N. Majumdar, S. Krishnamurthy and M. Barma
    J. Stat. Phys. 99, 1 (2000)

  6. “Phase transition in the Takayasu model with desorption” S. N. Majumdar, S. Krishnamurthy and M. Barma
    Phys. Rev. E 61, 6337 (2000)

Driven Disordered Systems

  1. “Condensate formation in a zero-range process with random site capacities ” Shamik Gupta and Mustansir Barma
    J. Stat. Mech. P07018 (2015)

  2. “Driven diffusive systems with disorder ” M. Barma
    Physica A 372, 22 (2006)

  3. “Dynamics of the disordered, one-dimensional zero range process” K. Jain and M. Barma
    Phys. Rev. Lett. 91, 135701 (2003)

  4. “Driven lattice gases with quenched disorder: exact results and different macroscopic regimes” G. Tripathy and M. Barma
    Phys. Rev. E 58, 1911 (1998)

  5. “Pattern formation in interface depinning and other models: erratically moving spatial structures” S. Krishnamurthy and M. Barma
    Phys. Rev. E 57, 2949 (1998).

Other Publications

  1. “Tagged particle correlations in the asymmetric simple exclusion process: finite size effects ” S. Gupta, S.N. Majumdar, C. Godreche and M. Barma
    Phys. Rev. E 76, 021112 (2007)

  2. “Directed diffusion of reconstituting dimers ” M. Barma, M.D. Grynberg and R. B. Stinchcombe
    J. Phys. Condens. Matter 19, 065112 (2007)

  3. “Asymptotic distributions of periodically driven stochastic systems ” S. Dutta and M. Barma
    Phys. Rev. E 67, 061111 (2003)