College of Arts and Sciences

Plasmons in metal surfaces and clusters have been extensively studied due to their potential applications in sensing, imaging, light harvesting and optical metamaterials. Graphene is a semimetal with tunable conductivity and hence can support plasmons as well. In addition to the tunability, graphene plasmons have relatively weak damping due to the high carrier mobility. In this talk, I will present our recent progress on the plasmon excitations in graphene micro-structures and their behavior in an external high magnetic field. We demonstrated graphene plasmonic terahertz filters and polarizers with graphene/insulator stacks and revealed the unique properties of Dirac plasmons with and without a magnetic field.

Continue reading… Terahertz plasmons and magnetoplasmons in graphene – Hugen Yan

Quantum dots, semiconductor nanocrystals, have unique optical properties, including narrow emission bandwidths, broad excitation spectra, and remarkable photostability, which have made them excellent candidates for biological imaging. Since their introduction into the biological milieu in 1998, they have been applied for in vitro and in vivo imaging, diagnostic testing, and multiplexing. As researchers have appreciated the benefits of quantum dots for imaging, emphasis has shifted to fabricating nanocomposites containing quantum dots, and among these magnetic quantum dots have attracted significant attention. Here, we describe our efforts to fabricate quantum dots and magnetic quantum dots. Highlighting our most recent efforts in this area,

Continue reading… Quantum Dots and Magnetic Quantum Dots for Biomedical Imaging and Separations – Jessica Winter

How an interacting many-particle system which is initially out of equilibrium evolves in time, is a challenging question, especially for large system sizes where numerical simulations are difficult. The most puzzling issue is understanding the onset of thermalization, a process in which the system completely looses memory of its initial state, with the long time behavior characterized by only one or two parameters. Understanding this issue is important as ideal, thermally isolated systems, and their time-evolution can now be routinely studied in experiments. Using a novel time-dependent renormalization group approach I will show how a reduced part of a strongly interacting system can look effectively classical (or thermal) by being characterized by a dissipation and a noise,

Continue reading… Quench dynamics in one-dimensional systems – Aditi Mitra

Self-assembly within biological membranes controls structure, from the nano- to the microscale. The same physical processes also apply to synthetic systems. Here, I survey two different model systems for structure and dynamics within molecularly thin films.

Continue reading… Playing with monomolecular layers: model biological systems and liquid crystal alignment layers – Elizabeth Mann

I will discuss the mechanism behind the remarkable properties of double perovskites like Sr2FeMoO6 that show half-metallic ground states with 100% polarization and a ferromagnetic Tc above room temperature. I will conclude with a broad overview of other remarkable properties that can be achieved by changing the transition metal atoms. Reference: O. Erten, et. al Phys. Rev. Lett. 107, 257201 (2011).

Continue reading… Half Metallic Ferromagnetism in Complex Oxides and Implications for Spintronics – Nandini Trivedi

The presentation summarizes our recent efforts in developing new functional materials with a focus on operation in extreme environments. Discussion will include both fundamental aspects of behavior and the path to next generation of devices and applications. Two main topics will be discussed: (i) Oxide based heterointerfaces: Formation of a two dimensional conducting interface between two perovskite insulators (i.e., LaAlO3 on SrTiO3) was first reported in 2004. In 2006 it was reported for the first time that the conductivity of the hetero-interface could be switched between two states by application of an external field (analogous to gate voltage). This technologically significant but still infant discovery holds great potential for next-generation extreme environment electronics that can have both (i) higher information density and (ii) larger operation domain.

Continue reading… FUNCTIONAL FILMS AND CERAMICS – Alp Sehirlioglu

There is a rapidly growing effort to integrate quantum technologies with mechanical structures in order to manipulate and measure quantum states of mechanics for applications ranging from quantum computing to sensing of weak forces to fundamental explorations of quantum mechanics at massive scales. A central focus of this effort, informally dubbed quantum electromechanical systems, has been the integration of superconducting electronics as control and measurement elements in nano and microelectromechanical systems (NEMS and MEMS). In fact, in just the last few years, spectacular advancements have been made in this area, providing researchers with a suite of tools for preparing, manipulating and measuring NEMS and MEMS near and even in the quantum domain.

Continue reading… Qubit-Coupled Mechanics – Matt LaHaye

The problem of electrons in 2D is one of the most important topics in contemporary condensed matter physics. Coulomb interactions between charge carriers in 2D are dramatically enhanced with the much-reduced dielectric screening compared to their bulk counterpart. Recent advances in the development of atomically thin layers of materials have opened up new opportunities for the study of many-body effects in 2D. In the last talk, we will discuss the observations of strong excitonic effects in graphene and in a valley Hall semiconductor through optical spectroscopy. We will demonstrate the control of Coulomb interactions in such atomic membranes by tuning their dielectric screening through an electrostatic gate.

Continue reading… Michelson Postdoc Prize talk 3:Many-body interactions in two-dimensional crystals – KinFai Mak

Optical spectroscopy provides an excellent means of understanding the distinctive properties of electrons in the two-dimensional system of graphene. Within the simplest picture, one has a zero-gap semiconductor with direct transitions between the well-known conical bands. This picture gives rise to a predicted frequency-independent absorption of \pi\alpha = 2.3%, where \alpha is the fine-structure constant. We will demonstrate that this relation is indeed satisfied in an appropriate spectral range in the near infrared, but that at higher photon energies electron-hole interactions significantly modify this result through the formation of saddle-point excitons. Optical spectroscopy also permits a detailed analysis of how the linear bands of graphene,

Continue reading… Michelson Postdoc Prize talk 2:Optics with Dirac electrons – KinFai Mak

The past few years have witnessed a surge of activities in the study of graphene, a stable sheet comprised of just a single atomic layer of carbon atoms in a honeycomb lattice structure. Indeed, 2010 Nobel Physics Prize recognized two researchers for their pioneering contributions to this field. In this talk we will describe the development of the field and some of the reasons for the intense interest in this new material system, highlighting its unusual electronic dispersion and its distinctive mechanical and chemical properties. We will also discuss recent advances in the fabrication and investigation of other 2D atomic membranes.

Continue reading… Michelson Postdoc Prize talk 1:Novel two-dimensional systems: graphene and beyond – KinFai Mak

Topological defects are pervasive in complex matter such as superfluids, liquid crystals, and early universe. They have been fruitful playgrounds for many emergent phenomena. Recently, vortex-like topological defects with six interlocked structural antiphase and ferroelectric domains merging into a vortex core were revealed in multiferroic hexagonal manganites. Numerous vortices are found to form an intriguing self-organized network, and may be used to test Kibble-Zurek model of early universe. Furthermore, emergent conduction and piezoelectric properties were observed in charged ferroelectric domain walls protected by topological defects. More excitingly, unprecedented alternating uncompensated magnetic moments were discovered at coupled antiferromagnetic-ferroelectric domain walls in hexagonal manganites,

Continue reading… Multiferroic vortices in hexagonal manganites – Weida Wu

Low temperature charge transport studies of high purity electron systems encompass fundamental subjects of disorder and electron-electron interaction. 50 years after Anderson’s theory of localization for non-interacting electrons, the question on whether and how electron-electron interaction qualitatively alters the picture is still unsettled. Fascinating subjects on interaction-driven phenomena such as Wigner crystallization of electrons (for the quantum scenario) have never been demonstrated. Experimentally, high-purity semiconductor bulk materials offer a desirable tunability of charge density down to ultra-dilute limits where both new frontiers of physics and important applications such as quantum information technologies can be explored. However, such a transition is often overshadowed by the substantial disorder which competes with or even dominates over interaction by rendering the system into an Anderson insulator.

Continue reading… Into the flat land: Transport studies of ultra-dilute GaAs two-dimensional hole systems in zero field – Jian Huang

In many crystals the Bloch bands have inequivalent and well separated energy extrema in the momentum space, known as valleys. The valley index constitutes a well-defined discrete degree of freedom for low-energy carriers that may be used to encode information. This has led to the concept of valleytronics, a new type of electronics based on manipulating the valley index of carriers. In the first part of the talk, I will describe a general scheme based on inversion symmetry breaking to control the valley index, using graphene and monolayers of MoS2 as an example. In particularly, the valley Hall effect and valley-dependent optical selection will be discussed.

Continue reading… Valley-Electronics in 2D Crystals – Di Xiao

The state-of-the-art polymer dielectrics have been limited to nonpolar polymers with relatively low energy density and ultra low dielectric losses for the past decades. With the fast development of power electronics in pulsed power and power conditioning applications, there is a need for next generation dielectric capacitors in areas of high energy density/low loss and/or high temperature/low loss polymer dielectrics. Given limitations in further enhancing atomic and electronic polarizations for polymers, this perspective article focuses on a fundamental question: Can orientational polarization in polar polymers be utilized for high energy density and low loss dielectrics? Existing experimental and theoretical results have suggested the following perspectives.

Continue reading… Novel Ferroelectric Polymers as High Energy Density and Low Loss Dielectrics – Lei Zhu

We purposefully design and study “molecular-like” interfacial interactions between the multidimensional nanometer-scale building blocks that compose larger-scale functional light harvesting devices. Using time-resolved optical spectroscopy, we aim to understand the nature of discrete interfacial electronic states and their role as crucial intermediates promoting efficient interactions between extended systems (e.g., charge transfer). Our research has suggested the importance of such intermediate interfacial states in both hard and soft nanomaterial heterostructures, including semiconductor quantum dots and organic semiconductors. We aim to understand the fundamental impact of “molecular-like” interfacial states on macroscopic material properties, such as charge transport and light harvesting. For example,

Continue reading… Interfacial Charge Transfer in Nanomaterial Based Light Harvesting Devices – Mat Sfire