College of Arts and Sciences

Magnetic impurities in conductors alter the Fermi sea: A many-body state (A Kondo singlet) is formed that entangles itinerant carriers and the impurity site. This causes a sharp rearrangement of the density of states near the Fermi surface into a hierarchical set governed by a single energy parameter Tk, the Kondo temperature. Equilibrium physics of such electronic “knots” scales with Tk and is highly universal: impurities that differ microscopically from one another yet have similar Kondo temperatures produce Kondo states with similar properties. Recent studies of Kondo physics with voltage-controllable spin traps known as Single-Electron Transistors (SETs) have focused on nonequiibrium Kondo phenomena,

Continue reading… Non-adiabatic Transport in Single-Electron Transistors in the Kondo Regime – Andrei Kogan

Chip-integrated nanophotonics investigates the interaction of light with nanostructures integrated on a chip. Lying at the intersection of condensed matter physics, optics, nanotechnology, and materials science, nanophotonics draws upon expertise from broad areas of physics and engineering, while presenting major opportunities to advance fundamental physics and transformative photonic technologies. In this talk, I will focus on our experimental research in two areas of nanophotonics. First, I will show that nanostructured semiconductors, such as quantum dot heterostructures coupled to photonic crystal nanocavities, can now offer

First, I will show that nanostructured semiconductors, such as quantum dot heterostructures coupled to photonic crystal nanocavities,

Continue reading… Chip-integrated Nanophotonic Structures for Classical and Quantum Devices – Antonio Badolato

Continue reading… Michelson Postdoc Lecture – Michael Hatridge

Symmetry breaking is ubiquitous in nature and represents the key mechanism behind rich diversity of patterns exhibited by nature. One commonly introduces an order parameter field to describe onset of qualitatively new ordering in a system on varying a relevant control parameter driving a symmetry breaking transition. In case of continuous symmetry breaking an order parameter consists of two qualitatively different components: an amplitude and gauge field. The latter component enables energy degeneracy and reveals how symmetry is broken. Inherent degeneracy could in general lead to nearby regions exhibiting significantly different gauge fields. Resulting frustrations can nucleate topological defects (TDs) [1].

Continue reading… Supercooling-Driven Glass Behaviour in Systems Exhibiting Continuous Symmetry Breaking – Sami Kralj

Organic semiconductors (OSCs) are emerging candidates for the applications in electronic and photonic devices due to material’s low cost and ease of processing. Many materials have been studied to understand the charge generation and transport physics, as well as to develop techniques for facile processing into light emitting diodes, thin film transistors, photovoltaics, and host of other devices. A recurring theme in this effort is the role of disorder in determining critical material parameters, such as mobility and photogeneration efficiency. A particularly useful class of materials in this quest is that of liquid crystalline (LC) OSCs. LCOSCs offer many advantages including facile alignment and the opportunity to study the effects of differing intermolecular geometries on transfer integrals,

Continue reading… Photogeneration and Charge Transport in Liquid Crystalline Organic Semiconductors – Sanjoy Paul

Two-dimensional crystals such as graphene and monolayer transition metal dichalcogenides (TMD) possess unique properties not found in bulk materials. These materials are atomically-thin, yet are strong enough to remain intact as free standing membranes. Because these materials are “all surface”, they tend to be highly surface sensitive and amenable to inducing proximity effects. In this talk, I will discuss our progress of investigating spin-dependent phenomena in graphene and TMD monolayers. We investigate spin transport in graphene utilizing ferromagnetic electrodes to inject and detect

In this talk, I will discuss our progress of investigating spin-dependent phenomena in graphene and TMD monolayers.

Continue reading… Spins in 2D Materials – Roland Kawakami

The coupling of geometrical and electronic properties is a promising venue to engineer conduction properties in graphene. In particular, different regimes can be achieved by manipulating confinement and strain fields, as shown in recent experiments on nanobubbles, drumheads oscillating membranes, and narrow strips deposited on patterned SiC substrates [1].

To investigate strain signatures on graphene systems, we focus on a simple model with a circularly symmetric out-of-plane deformation. Results from numerical tight-binding and Dirac-continuum models for a static deformation reveal intriguing flower-shaped structures in the local density of states with profound consequences for charge transport through the structure [2].

Continue reading… Static and Dynamic Flowers in Strained Graphene – Nancy Sandler

Organic-inorganic methylammounium lead halide perovskites, CH3NH3PbX3 (X= Cl, Br, I), have revolutionized the field of thin-film solar cells. Within five years, the efficiency of lead halide perovskite-based thin-film solar cells have increased rapidly from 3.8% in 2009 to 20.1% for a planar CH3NH3PbI3-based thin-film solar cell in 2014. Such rapid progress has never been seen before in the history of solar cell development. In this talk, I will review the history and status of lead halide perovskite thin films solar cells. I will explain why lead halide perovskites exhibit superior photovoltaic properties that conventional solar cell materials such as Si,

Continue reading… The Status and Challenges of Lead Halide Perovskite Solar Cells – Yanfa Yan

LED-lighting is at the verge of replacing conventional incandescent light sources. These white LEDs are based on nitride technology which produces the blue emission, that is subsequently converted in a separate phosphorescent layer to provide the additional required colors. The latter often consists of an insulating material doped with rare earth ions. In order to facilitate further integration, the possibility of introducing rare earth ions directly into the nitride material has been explored, with considerable success. Doping with europium ions (Eu) is of particular interest since they can produce the red color, which remains a challenge for nitride based materials.

Continue reading… Device-compatible Defect Engineering of Rare Earth Doped Nitrides – Volkmar Dierolf

Magnetism is an important problem in many areas of science including biology, physics and material science. For example, many migratory animals (birds, whales and sea turtles) use magnetism to sense direction for their migrations; computer hard drives store information via magnetism; and so forth. Quantum magnetism in low-dimensional systems plays a particularly important role in biophysical systems within which magnetic moments of different sizes might be useful for different purposes. In this perspective, the role of magnetism with higher magnetic moments is relatively less understood. To gain a better understanding for magnetism encompassing low and high moments, we studied a quantum mechanical spin lattice system consisting of one-dimensional anti-ferromagnetic Heisenberg chain of spin s embedded in a three dimensional lattice.

Continue reading… Quantum Magnetism in Low Dimensions: An Intriguing Phenomenon Connecting Biology with Physics – Yi-Kuo Yu