NYU Arts & Science
Condensed Matter Physics Seminars
November 20, 2017 Monday 3:00 PM  +
726 Broadway, room 871
Soft Condensed Matter Seminars (csmr)

Dave Philips
University of Exeter, UK

Hydrodynamic Micro-Manipulation

Optical tweezers have proven to be an extremely versatile tool to manipulate microscopic particles and investigate the mechanics of biological systems at the nanoscale. However, any object manipulated using optical tweezers is necessarily immersed in high intensity laser light, which places constraints on what materials can be manipulated, and can be potentially damaging to living cells. Here I will describe the development a new kind of micro-manipulation system based on locally generated fluid flow. The motion of optically trapped ‘actuator particles’ is orchestrated to engineer complex time-varying flow fields - enabling precise control of the trajectory of nearby free-floating particles (‘targets’). The actuator motion is driven using feedback based on measurement of the recent positions of target particles, combined with real-time multi-particle flowfield prediction. We demonstrate the suppression of Brownian motion and the targeted manipulation of multiple free-floating particles simultaneously, using only the indirect forces of the surrounding fluid. This technique removes material constraints over particles that can be ‘tweezed’, and may be useful for manipulation of delicate biological specimens and light sensitive cells.

November 21, 2017 Tuesday 11:00 AM  +
726 Broadway, Room 1067, CQP Conference Room
Condensed Matter Physics Seminars (cmp)

Meng Cheng
Yale University

Fractionalization and anomalies in two-dimensional topological phases

Topological phases of matter in two dimensions support fractionalized excitations. They exhibit a number of fascinating phenomena, such as anyonic exchange and braiding statistics and fractional quantum numbers, or symmetry fractionalization. A famous example is the fractionally charged quasiholes in quantum Hall systems while the electrons making up the system have charge one. In this talk I will discuss recent advances in the theory of symmetry fractionalization and global anomalies for 2D topological phases. I will describe how to systematically classify symmetry fractionalization in a topologically ordered phase, and how certain seemingly consistent patterns of symmetry fractionalization are in fact “anomalous”. This kind of anomaly is deeply connected to symmetry-protected topological phases in three dimensions via bulk-boundary correspondence. With these ideas, I will discuss a new perspective on the classic Lieb-Schultz-Mattis theorem and its higher-dimensional version by Oshikawa and Hastings, and possible refinements and generalizations.

December 5, 2017 Tuesday 11:00 AM  +
726 Broadway, Room 1067, CQP Conference Room
Condensed Matter Physics Seminars (cmp)

Pouyan Ghaemi
City College of New York

Light induced fractional Hall phases in Graphene

In this talk I present a new way to realize two-component fractional quantum Hall phases in monolayer graphene by optically driving the system. A laser is tuned into resonance between two Landau levels, giving rise to an effective tunneling between these two synthetic layers. Remarkably, because of this coupling, the interlayer interaction at non-zero relative angular momentum can become dominant, resembling a hollow-core pseudo-potential. In the weak tunneling regime, this interaction favors the formation of singlet states, as we explicitly show by numerical diagonalization, at filling = 1=2 and = 2=3. We discuss possible candidate phases, including the Haldane-Rezayi phase, the interlayer Pfa ffian phase, and a Fibonacci phase. This demonstrates that our method may pave the way towards the realization of non-Abelian phases, as well as the control of topological phase transitions, in graphene quantum Hall systems using optical fields and integrated photonic structures.

January 11, 2018 Thursday 11:00 AM  +
726 Broadway, Room 1067, CQP Conference Room
Condensed Matter Physics Seminars (cmp)

Nadya Mason
University of Illinois