College of Arts and Sciences

We can cool superfluid 3He to below 100 microkelvin where the number of unpaired 3He atoms is only of the order of 1 in 10^8. Here these quasiparticle excitations move ballistically as they are so tenuous that collisions are highly improbable. This dilute gas has very strange properties, since the Bardeen-Cooper-Schrieffer dispersion curve is quite unlike that for a classical gas. This makes the dynamics very unusual since even at the lowest temperatures and smallest quasiparticle energies the momentum they carry is very large. That means that we can detect this gas by its damping effect on a mechanical resonator even though by room temperature standards it would represent a reasonably good vacuum.

Continue reading… Ballistic Quasiparticles in Superfluid 3He: A Non-Newtonian Gas – George Pickett

Graphene, a two-dimensional network of carbon atoms, exhibits unique electronic properties because it supports low energy, massless, Dirac-like quasiparticles. The quantized Hall effect in this system has an unusual set of plateaus, whose locations may be interpreted in terms of a geometric “Berry’s phase” related to the chirality of the Dirac particles. The chiral nature of these states also leads to an unusual edge state structure, particularly near filling factor nu=0. We examine the transport behavior of the nu=0 graphene system in light of its unusual edge state structure. When electron-electrons interactions are included, we find a magnetic domain wall structure at the edge that is electrically conducting and behaves like a Luttinger liquid.

Continue reading… Chirality and Kondo Physics in Graphene – Herb Fertig

Graphene, a single atomic sheet of graphite, is a monolayer of carbon atoms arranged in a hexagonal lattice. The unique electronic band structure of graphene exhibits an unusual low-energy linear dispersion relation, radically different from the parabolic bands common to all previous two-dimensional systems. Most interestingly, the charge carriers in graphene mimic relativistic, massless Dirac particles, leading to intriguing new phenomena. In this talk, I focus on two projects related to graphene that complement each other: magneto- transport measurements in high magnetic fields, and infrared optical studies of graphene. In the transport experiments, we discovered a room temperature quantum Hall effect in graphene [1] and new quantum Hall phases in the extreme quantum limit [2,3].

Continue reading… Landau Level Spectroscopy of Graphene – Zhigang Jiang

Electrochromic matrials exchibit reversible and persistent change of the optical properties, hence the color, upon applying an electrical pulse that injects both electrons and compensating ions into the materials. Despite much research effort, a first-principles theory for the coloration mechanism in this material has not emerged. Although the connection between the appartent color of materrials and their optical properties is obvious, so far there has been no calculations of the color of materials from first-principles. In this talk, I will discuss first-principles investigations of the coloration of WO3 upon charge insertion, using sodium tungsten bronze (Na_xWO3) as a model system.

Continue reading… First-principles theory of coloration on WO3 upon charge insertion – Peihong Zhang

Surface plasmon polaritons (SPPs) are responsible for optical phenomena including negative refraction, surface enhanced Raman scattering, and nanoscale focusing of light. Although many materials support SPPs, the choice of metal for most applications has been based on traditional plasmonic materials such as Ag and Au because there have been no side-by-side comparisons of different materials on well- defined, nanostructured surfaces. This talk will describe a platform that not only enables rapid screening of a wide range of metals under different excitation conditions and dielectric environments but that also can identify unexpected materials for biosensing. Nanopyramidal gratings were used to generate SPP dispersion diagrams for Al,

Continue reading… Screening Plasmonic Materials using Nanopyramidal Arrays – Teri Odom

Polymer Electrolyte Fuel Cells are expected to replace internal combustion engines as power sources in transportation during our lifetime. The talk will discuss briefly main issues impeding commercialization of PEFC technology as well as the PEFC research at Kent State. Particular attention will be drawn to the need for high-temperature proton conducting membrane. The rest of the talk deals with our recent discovery of fast protonic conductivity in highly sulfonated arenes and its implications for the development of low-humidity high-temperature PEFC membranes.

Continue reading… Fast Protonic Conductivity in Crystalline Materials: Highly Sulfonated Aromatics – Yuriy Tolmachev

Place an atom in a nonuniform static external magnetic field and, because of the interaction between the atom’s magnetic moment and the magnetic field gradient, the atom will accelerate. This, of course, is what occurs in the classic Stern-Gerlach experiment. An important and fundamental question, which has been neglected in the literature, is whether or not the magnetic field is doing work on the atom. It is shown that, while the magnetic field does no work on the electron orbital contribution to the magnetic moment (the source of translational kinetic energy being the atom’s internal energy), whether or not it does work on the electron-spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin.

Continue reading… Dipole in a Magnetic Field, Work, and Quantum Spin – Robert Deissler

Novel approaches have been developed to engineer the microstructure of proton conducting membranes to enhance proton transport. Polymer composite and ceramic membranes were synthesized in which proton conducting pathways are aligned through the plane of the membrane. For polymer composite membranes, electric fields are applied during membrane synthesis to cause proton conducting domains aggregate into connected chains aligned through the membrane. For ceramic membranes, surfactant mediated crystallization is employed to direct crystal growth, resulting in aligned proton conducting paths. For both types of membranes, the engineered microstructure results in significantly enhanced proton conductivity through the membranes and improved performance of the membranes in fuel cells.

Continue reading… Synthesis of Novel Fuel Cell Membranes with Aligned Proton Conducting Pathways – Matt Yates

The subject of the presentation will be focused on molecular materials like liquid crystals, photochromic polymers or modified DNA-dye systems and their possible applications for lasing and dynamic optical information recording. Results on optical information processing were obtained in a typical degenerate two- or four-wave mixing experiments. For amplified spontaneous emission measurements, nano- or picosecond lasers of different wavelengths (355 nm and 532 nm) were used.

Continue reading… Molecular materials for dynamic holography and lasing applications – Jarek Mysliewiec

Continue reading… Bent-core nematic liquid crystals: Opportunities and mysteries – Jim Gleeson

Propagating basic acoustic pulses may behave as phonons. They can be characterized and utilized to evaluate channels through which they have travelled.

Continue reading… Phonon expansion and dispersion: Condensed matter channels: Material diagnosis – Dov Hazony

The terahertz (~ 100 GHz to 10 THz) electrical properties of nanomaterials are of relevance both to the fundamental science of low-dimensional systems and to the operation of next-generation smaller and faster electronics. I will describe the first terahertz time-domain electrical measurements of single-walled carbon nanotube transistors. A ballistic electron resonance is directly observed with a picosecond-scale period corresponding to the roundtrip transit of an electron along the nanotube. The electron velocity is found to be constant and equal to the Fermi velocity, showing that the high-frequency electron response is dominated by single-particle excitations rather than collective plasmon modes. These results demonstrate a powerful new tool for directly probing picosecond electron motion in nanostructures.

Continue reading… Terahertz Time-Domain Measurement of Ballistic Electron Resonance in a Single-walled Carbon Nanotube – Zhaohui Zhong

Diluted magnetic semiconductors are formed when magnetic transition metal ions are doped in small concentrations into a semiconductor host lattice. The first reports of ferromagnetism being observed at room temperature in a dilutely doped semiconducting oxide film attracted a great deal of attention, but were also met with considerable skepticism. These materials would have enormous potential for developing new classes of electronic devices, but there were concerns that the observed magnetism arose from impurity contributions, rather than any intrinsic property of the material. Although there has been some progress made in understanding these systems, in particular, the important role played by oxygen vacancies,

Continue reading… Room temperature ferromagnetism in semiconducting oxides – Chandran Sudakar

The intrinsic angular momentum of an electron (spin) – and its associated magnetic moment – can encode information: spin “up” or “down” can be interpreted as “0” or “1”, and potentially be used as the physical realization of a new paradigm of computing beyond electronics. However, this concept of spin-electronics (“spintronics”) needs to be built using a material where the electron spin orientation is preserved over long times (to enable many gate operations) and long distances (so that many devices can be integrated). Silicon, the materials basis for electronics, has been known for decades to have an extraordinarily long spin lifetime,

Continue reading… Spin injection, transport, and control in Silicon – Ian Appelbaum

The miniaturization of mechanical devices opens new opportunities for investigating and exploiting novel phenomena that occur for components in close proximity. The Casimir force, for example, originates from the zero-point quantum fluctuations of the electromagnetic fields. I will describe experiments that investigate the Casimir effect in micromechanical devices. In particular, we demonstrate the strong boundary dependence of the Casimir force on silicon surfaces with an array of nanoscale trenches. In another effort, subwavelength structures are fabricated on the surface of metal films to strongly modify their interaction with light. The evanescent fields channel the optical energy to specific locations, resulting in strong and localized field enhancement.

Continue reading… Coupling nanomechanical motion to electromagnetic fields through the Casimir effect and surface evanescent waves – HoBun Chan

The Cryogenic Dark Matter Search (CDMS) seeks to detect putative weakly-interacting massive particles (WIMPS), which could explain the dark matter problem in cosmology and particle physics. By simultaneously measuring the number of charge carriers and the energy in non-thermalized phonons created by particle interactions in intrinsic Ge and Si crystals at a temperature of 40 mK, a signature response for each event is produced. This response, combined with phonon pulse-shape information, allows CDMS to actively discriminate candidate WIMP interactions with nuclei apart from electromagnetic radioactive background which interacts with electrons. The challenges associated with these techniques are unique. Carrier drift-fields are maintained at only a few V/cm,

Continue reading… Charge Transport Phenomena in MilliKelvin Germanium and Detectors of the Cryogenic Dark Matter Search – Kyle Sundqvist

The single particle spectrum of an electronic system is a measure of the ease of inserting a single, whole electron into the system at a particular energy. A peak in this spectrum indicates that there is a long-lived state available for electrons at that particular energy — in essence, that it is possible to form a quasiparticle at that energy. By revealing the energies of the quasiparticles, these spectra teach us about the many-body ground state of the system. However, experimental difficulties have prevented the measurement of this spectrum in two dimensional electron systems until recently. I will present tunneling measurements of the single particle spectrum of a 2D system in a Gallium Arsenide quantum well performed using a novel pulsed technique called timed domain capacitance spectroscopy.

Continue reading… High Resolution Spectroscopy of the Quantum Hall Liquid – Oliver Dial

I will review some key concepts and computations in statistical genetics and discuss some analogies with the calculations on disordered spin systems. No prior knowledge of genetics is assumed.

Continue reading… Pedigrees and Partition Functions – Joseph Abraham

This talk will report on studies of the properties of carbon nanotubes of known chiral index, as determined by Rayleigh scattering spectroscopy. These properties include the mechanical stiffness, the electromechanical response, and basic electrical transport properties. The behavior of heterojunctions between nanotubes of different chiral indices will also be described. We have measured the mechanical properties of suspended graphene sheets, which show ultrahigh stiffness and the highest tensile strength ever measured. Finally, I will describe recent work on the use of graphene for high-frequency resonators.

Continue reading… Electrical, Mechanical, and Electromechanical Studies of Carbon Nanotubes and Graphene – James Hone

Quantum dots (QDs) have been receiving considerable attention lately due to the unique properties, which arise due to the confinement of the electron and holes in a lower band gap material. The InAs on GaAs material system is one of the most studied combinations in which quantum dots form during epitaxy. These QDs form in a Stranski Krastanov manner via a self-assembly process in which the dots nucleate at a critical adatom coverage on a wetting layer of InAs. QDs may be vertically aligned by using the residual strain above a buried dot layer to enhance the nucleation of the second layer of dots.

Continue reading… Heterostructured quantum dots: growth and characterization – Kurt Eyink

Continue reading… Collective molecular motor using chiral liquid crystalline thin films – Hiroshi Yokoyama