Correlation function diagnostics for type-I fracton phases

PHYSICAL REVIEW B 97 (2018) ARTN 041110

T Devakul, SA Parameswaran, SL Sondhi

Trial wave functions for a composite Fermi liquid on a torus

PHYSICAL REVIEW B 97 (2018) ARTN 035149

M Fremling, N Moran, JK Slingerland, SH Simon

Special issue on complex fluids at structured surfaces.

Journal of physics. Condensed matter : an Institute of Physics journal 29 (2017) 180301-

P Teixeira, JM Yeomans

Non-Fermi Glasses: Localized Descendants of Fractionalized Metals.

Physical review letters 119 (2017) 146601-

SA Parameswaran, S Gopalakrishnan

Non-Fermi liquids are metals that cannot be adiabatically deformed into free fermion states. We argue for the existence of "non-Fermi glasses," phases of interacting disordered fermions that are fully many-body localized (MBL), yet cannot be deformed into an Anderson insulator without an eigenstate phase transition. We explore the properties of such non-Fermi glasses, focusing on a specific solvable example. At high temperature, non-Fermi glasses have qualitatively similar spectral features to Anderson insulators. We identify a diagnostic based on ratios of correlators that sharply distinguishes between the two phases even at infinite temperature. Our results and diagnostic should generically apply to the high-temperature behavior of MBL descendants of fractionalized phases.

The macroscopic pancake bounce


JA Bro, KSB Jensen, AN Larsen, JM Yeomans, T Hecksher

The hydrodynamics of active systems(*)


JM Yeomans

Onset of meso-scale turbulence in active nematics.

Nature communications 8 (2017) 15326-

A Doostmohammadi, TN Shendruk, K Thijssen, JM Yeomans

Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at low Reynolds number in fluidized biological systems. This spatiotemporal disordered flow radically changes nutrient and molecular transport in living fluids and can strongly affect the collective behaviour in prominent biological processes, including biofilm formation, morphogenesis and cancer invasion. Despite its crucial role in such physiological processes, understanding meso-scale turbulence and any relation to classical inertial turbulence remains obscure. Here we show how the motion of active matter along a micro-channel transitions to meso-scale turbulence through the evolution of locally disordered patches (active puffs) from an ordered vortex-lattice flow state. We demonstrate that the stationary critical exponents of this transition to meso-scale turbulence in a channel coincide with the directed percolation universality class. This finding bridges our understanding of the onset of low-Reynolds-number meso-scale turbulence and traditional scale-invariant turbulence in confinement.

Quantum Hall physics: Hierarchies and conformal field theory techniques


TH Hansson, M Hermanns, SH Simon, SF Viefers

Using evaporation to control capillary instabilities in micro-systems.

Soft matter 13 (2017) 8947-8956

R Ledesma-Aguilar, G Laghezza, JM Yeomans, D Vella

The instabilities of fluid interfaces represent both a limitation and an opportunity for the fabrication of small-scale devices. Just as non-uniform capillary pressures can destroy micro-electrical mechanical systems (MEMS), so they can guide the assembly of novel solid and fluid structures. In many such applications the interface appears during an evaporation process and is therefore only present temporarily. It is commonly assumed that this evaporation simply guides the interface through a sequence of equilibrium configurations, and that the rate of evaporation only sets the timescale of this sequence. Here, we use Lattice-Boltzmann simulations and a theoretical analysis to show that, in fact, the rate of evaporation can be a factor in determining the onset and form of dynamical capillary instabilities. Our results shed light on the role of evaporation in previous experiments, and open the possibility of exploiting diffusive mass transfer to directly control capillary flows in MEMS applications.

Efficient Representation of Fully Many-Body Localized Systems Using Tensor Networks

PHYSICAL REVIEW X 7 (2017) ARTN 021018

TB Wahl, A Pal, SH Simon

Quantum Hall edges with hard confinement: Exact solution beyond Luttinger liquid

PHYSICAL REVIEW B 95 (2017) ARTN 201108

R Fern, SH Simon

A solvable model of axisymmetric and non-axisymmetric droplet bouncing.

Soft matter 13 (2017) 985-994

M Andrew, JM Yeomans, DO Pushkin

We introduce a solvable Lagrangian model for droplet bouncing. The model predicts that, for an axisymmetric drop, the contact time decreases to a constant value with increasing Weber number, in qualitative agreement with experiments, because the system is well approximated as a simple harmonic oscillator. We introduce asymmetries in the velocity, initial droplet shape, and contact line drag acting on the droplet and show that asymmetry can often lead to a reduced contact time and lift-off in an elongated shape. The model allows us to explain the mechanisms behind non-axisymmetric bouncing in terms of surface tension forces. Once the drop has an elliptical footprint the surface tension force acting on the longer sides is greater. Therefore the shorter axis retracts faster and, due to the incompressibility constraints, pumps fluid along the more extended droplet axis. This leads to a positive feedback, allowing the drop to jump in an elongated configuration, and more quickly.

Breakdown of ergodicity in quantum systems: from solids to synthetic matter.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 375 (2017)

M Pepper, A Pal, Z Papic, U Schneider, S Simon

Filling-enforced nonsymmorphic Kondo semimetals in two dimensions

Physical Review B 96 (2017)

JH Pixley, S Lee, B Brandom, SA Parameswaran

© 2017 American Physical Society. We study the competition between Kondo screening and frustrated magnetism on the nonsymmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. This model is known to host a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i) both the paramagnet and the heavy Fermi liquid are semimetals protected by a glide symmetry; and (ii) partial Kondo screening breaks the symmetry, removing this protection and allowing the partially Kondo screened phase to be deformed into a Kondo insulator via a Lifshitz transition. We confirm these results using large-N mean-field theory and then use nonperturbative arguments to derive a generalized Luttinger sum rule constraining the phase structure of two-dimensional nonsymmorphic Kondo lattices beyond the mean-field limit.

Biopolymer dynamics driven by helical flagella


AK Balin, A Zottl, JM Yeomans, TN Shendruk

Eigenstate phase transitions and the emergence of universal dynamics in highly excited states

Annalen der Physik 529 (2017)

SA Parameswaran, AC Potter, R Vasseur

© 2017 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We review recent advances in understanding the universal scaling properties of non-equilibrium phase transitions in non-ergodic disordered systems. We discuss dynamical critical points (also known as eigenstate phase transitions) between different many-body localized (MBL) phases, and between MBL and thermal phases. (Figure presented.).

Viewpoint: Topological Insulators Turn a Corner

Physics American Physical Society 10 (2017) 132

SA Parameswaran, Y Wan

Dancing disclinations in confined active nematics.

Soft matter 13 (2017) 3853-3862

TN Shendruk, A Doostmohammadi, K Thijssen, JM Yeomans

The spontaneous emergence of collective flows is a generic property of active fluids and often leads to chaotic flow patterns characterised by swirls, jets, and topological disclinations in their orientation field. However, the ability to achieve structured flows and ordered disclinations is of particular importance in the design and control of active systems. By confining an active nematic fluid within a channel, we find a regular motion of disclinations, in conjunction with a well defined and dynamic vortex lattice. As pairs of moving disclinations travel through the channel, they continually exchange partners producing a dynamic ordered state, reminiscent of Ceilidh dancing. We anticipate that this biomimetic ability to self-assemble organised topological disclinations and dynamically structured flow fields in engineered geometries will pave the road towards establishing new active topological microfluidic devices.

Topological defects in epithelia govern cell death and extrusion.

Nature 544 (2017) 212-216

TB Saw, A Doostmohammadi, V Nier, L Kocgozlu, S Thampi, Y Toyama, P Marcq, CT Lim, JM Yeomans, B Ladoux

Epithelial tissues (epithelia) remove excess cells through extrusion, preventing the accumulation of unnecessary or pathological cells. The extrusion process can be triggered by apoptotic signalling, oncogenic transformation and overcrowding of cells. Despite the important linkage of cell extrusion to developmental, homeostatic and pathological processes such as cancer metastasis, its underlying mechanism and connections to the intrinsic mechanics of the epithelium are largely unexplored. We approach this problem by modelling the epithelium as an active nematic liquid crystal (that has a long range directional order), and comparing numerical simulations to strain rate and stress measurements within monolayers of MDCK (Madin Darby canine kidney) cells. Here we show that apoptotic cell extrusion is provoked by singularities in cell alignments in the form of comet-shaped topological defects. We find a universal correlation between extrusion sites and positions of nematic defects in the cell orientation field in different epithelium types. The results confirm the active nematic nature of epithelia, and demonstrate that defect-induced isotropic stresses are the primary precursors of mechanotransductive responses in cells, including YAP (Yes-associated protein) transcription factor activity, caspase-3-mediated cell death, and extrusions. Importantly, the defect-driven extrusion mechanism depends on intercellular junctions, because the weakening of cell-cell interactions in an α-catenin knockdown monolayer reduces the defect size and increases both the number of defects and extrusion rates, as is also predicted by our model. We further demonstrate the ability to control extrusion hotspots by geometrically inducing defects through microcontact printing of patterned monolayers. On the basis of these results, we propose a mechanism for apoptotic cell extrusion: spontaneously formed topological defects in epithelia govern cell fate. This will be important in predicting extrusion hotspots and dynamics in vivo, with potential applications to tissue regeneration and the suppression of metastasis. Moreover, we anticipate that the analogy between the epithelium and active nematic liquid crystals will trigger further investigations of the link between cellular processes and the material properties of epithelia.

Topological defects in epithelia govern cell death and extrusion


A Doostmohammadi, TB Saw, V Nier, L Kocgozlu, SP Thampi, Y Toyama, P Marcq, CT Lim, JM Yeomans, B Ladoux