Gotham-Metro Condensed Matter Meeting (1)

Agenda

*Presentation times are subject to change.

Speaker Abstracts

Keynote Presentations

When and How To Walk on Water: A New Perspective on Shear Thickening in Suspensions

Heinrich Jaeger, PhD, University of Chicago

Suspensions of solid particles in simple liquids can exhibit remarkably counter-intuitive behavior. A prototypical example is a mixture of cornstarch in water which appears like a thin liquid when stirred slowly but, when forced more strongly, turns solid-like to the point where it can support a person's weight for a short time, enough to walk across without sinking in. This shear thickening is a form of extreme non-Newtonian response with a viscosity that tends to diverge at a critical shear rate. Traditionally, shear thickening has been interpreted as being driven by hydrodynamic interactions between the particles inside the suspension. This talk will review some recent experimental findings which add up to a new perspective whereby shear thickening can be understood as arising from the interplay between dilation and confinement of the particle arrangement near jamming. This "granular" perspective is independent of any underlying hydrodynamic model and can predict in simple terms the scaling of the stress range over which shear thickening is observable. In particular, it argues that strong shear thickening is a generic property of all suspensions and that it can be recovered even in systems dominated by a large yield stress once this yield stress is reduced sufficiently.

Computational Design of New Multifunctional Materials: From Magnetoelectronics To a Theory of Everything

Nicola Spaldin, PhD, University of California Santa Barbara

Modern computational methods are proving to be invaluable in the first-principles design of new materials with specific targeted functionalities. I will illustrate their utility with two examples from the field of multiferroics: First, the design of new materials for electric-field control of magnetism, and second, testing extensions to the Standard Model by searching for the electric dipole moment of the electron.

Short Talks

Electron transport in graphene on BN

C. R. Dean^1,2, A. F. Young ³, P. Kim³, J. Hone², K. Shepard^1
1Department of Electrical Engineering, Columbia University, New York, NY
²Department of Mechanical Engineering, Columbia University, New York, NY
³Department of Physics, Columbia University, New York, New York

Hexagonal BN (h-BN) represents the insulator analogue of graphene, sharing identical crystal structure but with B and N atoms each comprising the two sublattices. Owing to its large bandgap, chemical inertness, hexagonal lattice structure (with only 2% lattice mismatch to graphene), planar (i.e. atomically flat) surface structure and good dielectric properties, single crystal h-BN is an ideal supporting substrate in graphene FET devices. We discuss our investigation of graphene-BN hybrid devices, realized by precision transfer of mechanically exfoliated graphene and single crystal h-BN flakes. We compare device performance of graphene-over-BN with the more conventional graphene-over-SiO2 geometry.  Recent magnetoresistance measurements in ultraclean graphene-on-BN devices are discussed.

Quasiparticle Scattering From Vortices in d-wave Superconductors: Superflow and Berry Phase Contributions

Sriram Ganeshan, SUNY Stony Brook

In the vortex state of a d-wave superconductor, massless Dirac quasiparticles are scattered from magnetic vortices via a combination of two basic mechanisms: effective potential scattering due to the superflow swirling about the vortices and Aharonov-Bohm scattering due to the Berry phase acquired by a quasiparticle upon circling a vortex. In this talk, we present scattering contribution of each of these mechanisms in the absence of the other. First [1], we consider the superflow contribution by calculating the differential cross section for a quasiparticle scattering from the effective non-central potential of a single vortex. Next [2], we consider the Berry phase contribution, which results in branch cuts between neighboring vortices across which the
quasiparticle wave function changes sign. Here, the simplest problem that captures the physics is that of scattering from a single finite branch cut that stretches between two vortices. Elliptical coordinates are natural for this two-center problem and we proceed by separating the massless Dirac equation in elliptical coordinates. Using the method of partial wave analysis, we construct the exact scattering cross section for this case. We summarize the scattering effect of each mechanism, superflow and Berry phase, as a future motivation to study the effect of interference between these two mechanisms in the double vortex setup.
[1] M. Kulkarni, S. Ganeshan, and A. C. Durst, arXiv:1006.2818
[2] S. Ganeshan, M. Kulkarni and A. C. Durst, arXiv:1010.2213

Randomly Packing Spheres

Yuliang Jin, CUNY City College

Randomly packing spheres of equal size into a container consistently results in a static configuration with a density of ~ 64%.  The ubiquity of random close packing (RCP) rather than the optimal crystalline array at 74% begs the question of the physical law behind this empirically deduced state. Indeed, there is no signature of any macroscopic quantity with a discontinuity associated with the observed packing limit. Here we show that RCP can be interpreted as a manifestation of a thermodynamic singularity, which defines it as the ''freezing point'' in a first-order phase transition between ordered and disordered packing phases. Despite the athermal nature of granular matter, we show the thermodynamic character of the transition in that it is accompanied by sharp discontinuities in volume and entropy. This occurs at a critical compactivity, which is the intensive variable that plays the role of temperature in granular matter.  Our results predict the experimental conditions necessary for the formation of a jammed crystal bycalculating an analogue of the ''entropy of fusion''. This approach is useful since it maps out-of-equilibrium
problems in complex systems onto simpler established frameworks in statistical mechanics.

Separating Stretching From Folding in Fluid Mixing

Douglas H. Kelley, Yale University

Efficient large-scale mixing of an impurity in a fluid depends on stretching and folding--together they expand the periphery of material volumes, allowing diffusion to mix at small scales. Yet stretching and folding are difficult to decouple in real flows with complex spatiotempora structure. To separate the two processes, we divide the local fluid deformation into affine and non-affine parts; similar techniques have been used previously to identify shear transformation zones in glassy solids and colloids. We study stretching and folding in a quasi-two-dimensional laboratory flow, measuring its velocity by tracking about 30 000 particles per frame. At short times stretching dominates, but once fluid elements have elongated, folding becomes suddenly stronger and dominates thereafter. The relative strength of the two processes also varies strongly in space. This work is supported by the National Science Foundation.

Dynamical Mean-Field Theory for Quantum Chemistry

Nan Lin, C. A. Marianetti, Andrew J. Millis, and David R. Reichman

The dynamical mean-field concept of approximating an unsolvable many-body problem in terms of the solution of an auxiliary quantum impurity problem, introduced to study bulk materials with a continuous energy spectrum, is here extended to molecules, i.e. finite systems with a discrete energy spectrum. Application to chains and small clusters of hydrogen atoms yields ground state energies which are competitive with leading quantum chemical approaches at intermediate and large interatomic distances, and provides good approximations to the excitation spectrum. The method is a promising approach to the strong correlation problems of quantum chemistry.

Microfluidic Devices Fabricated by Soft-Lithographic Replication of Adhesive Tape for Patterning Biological Cells

Anil Shrirao, Raquel Perez-Castillejos, New Jersey Institute of Technology

We describe a method to fabricate microfluidic devices using only bench-top materials and tools (adhesive tape, scalpel, 65°C oven, glass slides, and PDMS¹). We base our developments on soft lithography², which replicates a master (typically: micropatterned photoresist) in PDMS. But access to photolithography is often limited in non-engineering-focused settings—e.g., medical schools and biology-oriented research centers. Non-photolithographic techniques exist³ and compared to those techniques, ours is the very simplest way to fabricate PDMS devices, as it uses bench-top materials and tools only. First we attach one (or more) tape layer to a glass slide (Fig. 1a) and pattern the tape with a blade following the lines of the design (b,c), removed the extra tape (d), and replicated the master in PDMS (e,f). The tape thickness (~60 µm⁴) sets the height of the microchannels. Larger heights result from stacking several tape layers. For maximum simplicity, we used a scalpel to pattern the tape with features larger than 0.25 mm—laser cutters or robotic blades could be used for higher precision. We have replicated the same tape master up to 50 times and did not show signs of wearing out.

We used these tape-replicated microfluidic devices to pattern biological cells—in particular, Micro Vascular Endothelial Cells or MVEC. Our results show the viability of the patterned MVE cells for times of culture of up to seven days. After patterning, we released the cells from any spatial constraints and monitored for seven days their migration and proliferation on the surface of the culturing dish.

We believe benchtop fabrication of microdevices will favor the development of microlabs in settings lacking cleanroom facilities, such as biologically-oriented research institutions or teaching-intensive colleges and high schools. Even for those with access to a cleanroom, our method offers rapidity (~1h to fabricate a device), low cost (<$1/device), and safety (no harmful chemicals or UV required).
[1] Information about Dow Corning® brand Silicone Encapsulants, Dow Corning Product Information.
[2] Y. Xia and G. M. Whitesides, Annu. Rev. Sci., 1998, 28: 153-184.
[3] M.S. Thomas, B. Millare, J.M. Clift, D. Bao, C. Hong, and V.I. Vullev. 2010. “Print-and-peel fabrication for microfluidics: what’s in it for biomedical applications?” Ann. Biomed. Eng., 38: 21.
[4] 3M Scotch® Transparent Tape 600; www.3m.com.

Travel & Lodging

Our Location

The New York Academy of Sciences

7 World Trade Center
250 Greenwich Street, 40th floor
New York, NY 10007-2157
212.298.8600

Click here for directions.

Hotels Near 7 World Trade Center

Recommended partner hotel:

The New York Academy of Sciences is a part of the Club Quarters network . Please feel free to make accommodations with Club Quarters on-line to save significantly on hotel costs.

Club Quarters Reservation Password: NYAS

Club Quarters, World Trade Center
140 Washington Street
New York, NY 10006
Phone: (212) 577-1133

Located on the south side of the World Trade Center, opposite Memorial Plaza, Club Quarters, 140 Washington Street, is just a short walk to our location.

Other hotels located near 7 WTC: