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

Condensation-driven phase transitions in perturbed string nets

Physical Review B 96 (2017)

M Mariën, J Haegeman, P Fendley, F Verstraete

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.

Spinon decay in the spin-1/2 Heisenberg chain with weak next nearest neighbour exchange


S Groha, FHL Essler

Long coherence times for edge spins

Journal of Statistical Mechanics: Theory and Experiment 2017 (2017) 063105-063105

J Kemp, NY Yao, CR Laumann, P Fendley

Variation of the Contact Time of Droplets Bouncing on Cylindrical Ridges with Ridge Size.

Langmuir : the ACS journal of surfaces and colloids 33 (2017) 7583-7587

M Andrew, Y Liu, JM Yeomans

Reducing the contact time between bouncing droplets and an underlying solid surface is relevant to a broad range of industrial applications, such as anti-icing and self-cleaning. Previous work has found that placing cylindrical obstacles on the substrate leads to a reduction in contact time. For obstacles large compared to the drop, this is a result of hydrodynamic coupling between the azimuthal and axial spreading directions. For obstacles small compared to the drop, the reduction in contact time is interpreted as being due to fast retraction along the cylindrical ridge, followed by drop breakup. Here we use simulations to discuss in greater detail the effect of varying the obstacle size on the dynamics of the drop bouncing. We investigate the crossover between the two regimes and explain why the contact time is minimized when the radii of the drop and the cylindrical obstacle are comparable.

On truncated generalized Gibbs ensembles in the Ising field theory


FHL Essler, G Mussardo, M Panfil

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.

Nature’s engines: active matter

Europhysics News 48 (2017) 21-25

JM Yeomans

Multi-scale statistics of turbulence motorized by active matter


J Urzay, A Doostmohammadi, JM Yeomans

Strong peak in Tc of Sr2RuO4 under uniaxial pressure.

Science (New York, N.Y.) 355 (2017)

A Steppke, L Zhao, ME Barber, T Scaffidi, F Jerzembeck, H Rosner, AS Gibbs, Y Maeno, SH Simon, AP Mackenzie, CW Hicks

Sr2RuO4 is an unconventional superconductor that has attracted widespread study because of its high purity and the possibility that its superconducting order parameter has odd parity. We study the dependence of its superconductivity on anisotropic strain. Applying uniaxial pressures of up to ~1 gigapascals along a 〈100〉 direction (a axis) of the crystal lattice results in the transition temperature (Tc) increasing from 1.5 kelvin in the unstrained material to 3.4 kelvin at compression by ≈0.6%, and then falling steeply. Calculations give evidence that the observed maximum Tc occurs at or near a Lifshitz transition when the Fermi level passes through a Van Hove singularity, and open the possibility that the highly strained, Tc = 3.4 K Sr2RuO4 has an even-parity, rather than an odd-parity, order parameter.

Electric-field-induced shape transition of nematic tactoids.

Physical review. E 96 (2017) 022706-

L Metselaar, I Dozov, K Antonova, E Belamie, P Davidson, JM Yeomans, A Doostmohammadi

The occurrence of new textures of liquid crystals is an important factor in tuning their optical and photonics properties. Here, we show, both experimentally and by numerical computation, that under an electric field chitin tactoids (i.e., nematic droplets) can stretch to aspect ratios of more than 15, leading to a transition from a spindlelike to a cigarlike shape. We argue that the large extensions occur because the elastic contribution to the free energy is dominated by the anchoring. We demonstrate that the elongation involves hydrodynamic flow and is reversible: the tactoids return to their original shapes upon removing the field.

Focusing and Sorting of Ellipsoidal Magnetic Particles in Microchannels


D Matsunaga, F Meng, A Zottl, R Golestanian, JM Yeomans

Entrainment and scattering in microswimmer-colloid interactions


H Shum, JM Yeomans

Biopolymer dynamics driven by helical flagella


AK Balin, A Zottl, JM Yeomans, TN Shendruk

Valley-selective Landau-Zener oscillations in semi-Dirac p-n junctions

Physical Review B 96 (2017)

K Saha, R Nandkishore, SA Parameswaran

© 2017 American Physical Society. We study transport across p-n junctions of gapped two-dimensional semi-Dirac materials: nodal semimetals whose energy bands disperse quadratically and linearly along distinct crystal axes. The resulting electronic properties - relevant to materials such as TiO2/VO2 multilayers and α-(BEDT-TTF)2I3 salts - continuously interpolate between those of mono- and bilayer graphene as a function of propagation angle. We demonstrate that tunneling across the junction depends on the orientation of the tunnel barrier relative to the crystalline axes, leading to strongly nonmonotonic current-voltage characteristics, including negative differential conductance in some regimes. In multivalley systems, these features provide a natural route to engineering valley-selective transport.

Disorder-driven destruction of a non-Fermi liquid semimetal studied by renormalization group analysis

Physical Review B 95 (2017)

RM Nandkishore, SA Parameswaran

© 2017 American Physical Society. We investigate the interplay of Coulomb interactions and short-range-correlated disorder in three-dimensional systems where absent disorder the noninteracting band structure hosts a quadratic band crossing. Though the clean Coulomb problem is believed to host a non-Fermi liquid phase, disorder and Coulomb interactions have the same scaling dimension in a renormalization group (RG) sense, and thus should be treated on an equal footing. We therefore implement a controlled expansion and apply it at leading order to derive RG flow equations valid when disorder and interactions are both weak. We find that the non-Fermi liquid fixed point is unstable to disorder, and demonstrate that the problem inevitably flows to strong coupling, outside the regime of applicability of the perturbative RG. An examination of the flow to strong coupling suggests that disorder is asymptotically more important than interactions, so that the low-energy behavior of the system can be described by a noninteracting sigma model in the appropriate symmetry class (which depends on whether exact particle-hole symmetry is imposed on the problem). We close with a discussion of general principles unveiled by our analysis that dictate the interplay of disorder and Coulomb interactions in gapless semiconductors, and of connections to many-body localized systems with long-range interactions.

Deconfinement transitions in a generalised XY model


P Serna, JT Chalker, P Fendley

Spin-catalyzed hopping conductivity in disordered strongly interacting quantum wires

Physical Review B 95 (2017)

SA Parameswaran, S Gopalakrishnan

© 2017 American Physical Society. In one-dimensional electronic systems with strong repulsive interactions, charge excitations propagate much faster than spin excitations. Such systems therefore have an intermediate temperature range [termed the "spin-incoherent Luttinger liquid" (SILL) regime] where charge excitations are "cold" (i.e., have low entropy) whereas spin excitations are "hot." We explore the effects of charge-sector disorder in the SILL regime in the absence of external sources of equilibration. We argue that the disorder localizes all charge-sector excitations; however, spin excitations are protected against full localization, and act as a heat bath facilitating charge and energy transport on asymptotically long time scales. The charge, spin, and energy conductivities are widely separated from one another. The dominant carriers of energy in much of the SILL regime are neither charge nor spin excitations, but neutral "phonon" modes, which undergo an unconventional form of hopping transport that we discuss. We comment on the applicability of these ideas to experiments and numerical simulations.

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.).