College of Arts and Sciences

Antiferromagnetic resonance and in-gap terahertz continuum in Kitaev Honeycone magnet α−RuCl3

Spin-1/2 moments in the antiferromagnetic Mott insulator α-RuCl3 are coupled by strongly anisotropic bond-dependent exchange interactions on a honeycomb lattice. Intense study of α- RuCl3 by inelastic scattering has been driven by the proposal that its low energy excitations may be adiabatically connected to the Majorana quasiparticles that emerge in the exact solution of the Kitaev spin liquid model. In my talk, I will present optical absorption measurements using time- domain terahertz spectroscopy in the range 0.3 to 10 meV that reveal several new features of the low-energy spectrum of α-RuCl3 [1].

Continue reading… Liang Wu, UC Berkeley, MPPL3, Antiferromagnetic resonance and in-gap terahertz continuum in Kitaev Honeycomb magnet α−RuCl3

Future nanoscience and nanotechnologies, from quantum computation to light harvesting for energy and advanced medical therapies, will be based on new nanoscale materials and materials architectures that include quantum dots, photonic crystals, laterally confined inorganic and organic thin films and single molecules. In this talk, I will highlight recent advances at the Center for Nanoscale Materials at Argonne National Laboratory in the synthesis, self-assembly and characterization of nanostructured materials. I will emphasize how advanced x-ray techniques can address outstanding questions in nanoscale structure, dynamics and properties. Several recent examples include the x-ray visualization of the evolution of antiferromagnetic domain walls on the sub-micron scale in chromium,

Continue reading… Nanoscience with X-rays – Eric Isaacs

Particles on a flat surface usually pack into a simple triangular lattice. How does this change if curvature is switched on? The minimum energy configuration for repulsively interacting particles on curved surfaces is a challenging problem with applications to mathematical physics, computer science and a variety of biological, chemical and condensed matter systems. I will discuss the universal proliferation of novel defect arrays (“scars”) in the ground state of such spherical crystals for sufficiently large systems, including experimental results for self-assembled spherical colloidal crystals.

Continue reading… Order on Curved Surfaces: Scars in Sphereland – Mark Bowick

Nature appears to be inherently chiral. From the atomic scale with asymmetric carbon bonds, to much larger length scales like our hands or even spiral galaxies, all have the same common feature of lacking inversion symmetry, while not characterized by any vector (dipolar) property. In other words, many natural objects “know” the difference between right and left. This is the notion of chirality; since Pasteur and Kelvin in the mid-19 century it has always been a source of interest in various fields, from mathematics to medicine. Although stereo-specific intermolecular interactions are always very weak, there are many examples of macroscopic “phase chirality”

Continue reading… Molecular and Phase Chirality in Polymer Networks – Eugene Terentjev

At present the only means of carrying out nonperturbative calculations of the Strong Interactions from first principles is through large scale numerical simulations of Quantum Chromodynamics (QCD) on the lattice. These simulations promise to make possible stringent experimental tests of the Standard Model, as well as searches for new physics. Here, I discuss recent advances in Lattice QCD simulations that allow us to make computations in which all systematic errors are under control. With better algorithms and huge amounts of computer power, the effects of virtual quark-antiquark pairs — long neglected in the so called “quenched approximation” — can now be included.

Continue reading… Precision Results from Lattice QCD – Claude Bernard

Semiconductor quantum dots that contain a few hundred electrons have fascinating electronic properties shaped by the interplay of electron-electron interaction and randomness (due to chaotic scattering of electrons from device boundaries). Transport experiments that probe the electronic state and theoretical efforts to understand them will be reviewed. Our prediction of a new state of electronic matter in strongly interacting quantum dots will be discussed. In this novel electron liquid time-reversal symmetry is spontaneously broken and there is a persistent current in the electronic ground state even in the absence of superconductivity.

Continue reading… Do Quantum Dots Break Time-reversal Symmetry? – Harsh Mathur

In this talk, I shall begin by presenting some generalities about transparent conducting oxides (TCOs), including work at NREL, their typical properties and their relevance to solar cells. I shall demonstrate how a badly selected TCO can severely impact the performance of a new generation of high performance thin-film solar cells. I then demonstrate that the electron mobility of TCOs is the key property to which all investigations ought to focus. Only via high mobility can the dual requirements of excellent optical transmittance and electrical conductivity be achieved. Following this analysis, I apply the Drude theory to demonstrate that fundamental properties (such as the electron effective mass and relaxation time) of TCOs may be determined from their optical properties.

Continue reading… Transparent Conducting Oxides – Timothy Coutts

Continue reading… Searching for dark matter with liquid xenon – Tom Schutt

With the exception of the Sun and Supernova 1987A, no astrophysical sources of neutrinos have been detected yet. However, emerging developments give us great confidence that “first light” on extragalactic neutrino sources will soon be attained by terrestrial neutrino detectors. I will highlight the prospects for what we may learn about what lies beyond the standard model of particle physics and about the dynamics of the invisible universe.

Continue reading… Towards First Glimpses of the Universe in Neutrinos – John Beacom

A number of recent experiments in mesoscopic physics have raised anew the question of what constitutes an “ideal” quantum detector, that is a detector which produces a minimal disturbance of the system being probed. I will discuss recent theoretical work addressing this issue, taking a point of view which stresses the physics of mesoscopic noise, and its connection to ideas from information theory. I will also discuss how these ideas apply to the quantum non-demolition measurement of a qubit, and to the study of nano-electromechanical systems.

Continue reading… Quantum-Limits in Mesoscopic Physics: From Quantum Noise to Qubits and Nanomechanics – Aashish Clerk

Single-walled carbon nanotubes, tubular crystals of sp2-bonded carbon atoms that are just one atom thick, come in different varieties, each with a subtle difference in structure and properties – some of them are metals and others are semiconductors. This talk will describe magneto-optical studies on carbon nanotubes in high magnetic fields, which confirm theoretical predictions that the band structure of a carbon nanotube is dependent on the magnetic flux threading the tube, in a truly unique manner. We observed significant field-induced optical anisotropy as well as red shifts and splittings of absorption and photoluminescence peaks. The amounts of shifts and splittings depend on the value of the magnetic flux and are quantitatively consistent with theories based on the Aharonov-Bohm effect.

Continue reading… Optical Signatures of the Aharonov-Bohm Phase in Carbon Nanotubes – Junichiro Kono

The universe is composed of normal matter, dark matter and a component that is causing cosmic acceleration. The existence of all three of these components poses a challenge to fundamental physics; the nature of dark matter remains unknown, dark energy or its equivalent is a complete mystery and even baryons, which we see all around us, should have annihilated with their antiparticles long before galaxies formed. In this colloquium I will briefly review the evidence for each of these components before discussing the associated problems and their possible resolutions. The focus will on the importance of connecting cosmic observations with both theoretical and experimental progress in fundamental physics.

Continue reading… Connecting the Dark Side and Fundamental Physics – Mark Trodden

Magnetic resonance imaging is an ever developing area that makes it possible to image the human body in vivo. The development of nuclear magnetic resonance in physics has led to multiple Nobel Prizes in various fields. The two most recent are in MR imaging for Paul Lauterbur and Peter Mansfield. That this should be so is evidenced by the amazing number of clinical and technical applications of this methodology. Today we can image down to resolutions of a few hundred microns in vivo, we can watch the brain at work and we can measure chemical processes in action. In this presentation,

Continue reading… Functional and Morphological Imaging of the Human Brain using Magnetic Resonance Imaging – E. Mark Haacke

We consider the quantum physics of correlated systems, with a focus on electron-phonon coupled systems. The static and dynamic formation properties of a polaron quasiparticle are calculated with surprising accuracy, and compared to experiment. The successes and failures of certain computational schemes force one reluctantly to confront fundamental issues in quantum mechanics.

Continue reading… Dynamics of electron-phonon systems – Stuart Trugman

Continue reading… Aerosil Nanoparticles in Liquid Crystals: Order, Disorder, Transitions and lots more – Dan Finotello

Continue reading… Surfactant and Geometric Effects on Interfacial Stability – David Rumschitzki

I will discuss the development and application of novel optical spectroscopic techniques to the study of ultrafast dynamics in complex materials. I will first describe all-optical pump probe and optical-pump far-infrared probe experiments on (a) colossal magnetoresistance manganites, (b) superconductors, and (c) heavy fermion materials. The experimental techniques are discussed followed by a brief review of ultrafast electron dynamics in conventional wide band metals that serves as a starting point in understanding dynamics in more complex systems. In. half-metallic manganites, the quasiparticle dynamics in the ferromagnetic metallic state can be understood in terms of a dynamic transfer of the spectral weight which is influenced by the lattice and spin degrees of freedom.

Continue reading… Ultrafast Dynamics in Complex Materials – Antoinette J. Taylor

Cosmic Microwave Background (CMB) radiation observation is the most important and cleanest probe of the early universe. Currently, most of the information comes from the large-scale temperature spatial power spectrum which is directly coupled to early universe physics and largely uncontaminated by astrophysical foreground emission. Future CMB measurements promise to provide further tests of early universe conditions and evolution. Small-scale temperature anisotropy and polarization measurements will tell us about the formation and evolution of the earliest structures and possibly even detect evidence for horizon-scale gravity-waves left over from the inflationary epoch. However, these measurements pose very considerable new challenges both because of contamination from foreground emission which will no longer be unimportant,

Continue reading… Prospects for CMB observations – Stephan Meyer

Solar photovoltaic (PV) technology has advanced rapidly since the crystalline-silicon solar cell of a half-century ago. Have we arrived at our final destination? No, not yet. This presentation examines the current, near-term, and next-generation PV technologies-looking back to where we have been and forward to where we are going – and provides a critical evaluation of our needed research directions.

Continue reading… Solar photovoltaics – Larry Kazmerski

I will discuss our recent experiments where we have made the closest approach to the quantum limit for continuous position detection of a mechanical structure, a factor of ~5 from the uncertainty principle limit. We have developed a nano-electro-mechanical device with an integrated nanomechanical resonator and ultra-sensitive single electron transistor. The success of these experiments paves the way to the realization of truly quantum states of the mechanical device: squeezed states, number states, and most exciting, the formation of mechanical entangled states. I will also discuss the applications of this technology from advanced force microscopes to readout for quantum information devices.

Continue reading… Putting the Mechanics back into Quantum Mechanics – Keith Schwab

We report on the observation of non-classical rotational inertia behavior in solid He-4 confined to an annular channel in a sample cell under torsional motion, demonstrating superfluid behavior. The effect shows up as an abrupt drop in the resonant oscillation period as the sample cell is cooled below 230 mK. Measurement of 17 solid samples allows us to map out the boundary of this superfluid-like solid or supersolid phase from the melting line up to 66 bars. This experiment indicates that superfluid behavior is found in all three phases of matter, gas, liquid and solid. This work is done in collaboration with Eunseong Kim and is supported by the Condensed Matter Physics program of NSF.

Continue reading… Observation of Superflow in Solid Helium – Moses Chan

The three speakers will describe some of the contributions physicists are currently making to the well-being of the nation.

Continue reading… Physics and Society – Bill Fickinger, Cyrus Taylor, and Phil Taylor

Within the next few decades, we must find an energy source of at least 10 terawatts (TW) of cheap, clean power. In order for the billions of people in the developing world to achieve and sustain a modern lifestyle, we really need 50 TW. Who will make the necessary scientific and engineering breakthroughs? Can they be done soon enough to avoid the hard economic times, terrorism, war and human suffering that will otherwise occur?

Continue reading… Our energy challenge – Richard Smalley

Ferroelectric liquid crystals are of scientific interest and also have a variety of potential applications. I will review the various ways in which people have proposed to, claimed to, or succeeded in making ferroelectric liquid crystals, and suggest why it is “hard”. I will also suggest new possible ways to make such phases, and in particular ideas for and constraints on the formation of ferroelectric nematic phases.

Continue reading… Ferroelectric liquid crystals: Realities and possibilities – Rolfe Petschek

Continue reading… Reception to welcome new members of the department

A lecture given on the occasion of receiving the national 2004 AAPT Excellence in Undergraduate Teaching Award I describe the beginning of my fourth decade of undergraduate teaching, a story that has astonished me with how fast it is changing. In the first decade, frantic memories abound of realizing just how much I did not know about the class material I was slated to teach (sometimes the next day!). The second decade taught me how even very young undergraduates could contribute to even very theoretical research programs and could understand even very fancy nonlinear physics. The third decade found me using e-mail,

Continue reading… The Fourth Decade … and my introductory physics class this fall – Robert Brown

The world will start to run out of cheap, conventionally produced oil soon, possibly within this decade. This talk will discuss the reasoning that leads to this conclusion and the likely consequences if it is correct. It may be possible, with considerable difficulty, to substitute other fossil fuels for the missing oil. Even then, we will ultimately run out of all fossil fuels, probably within this century. Can civilization survive if this happens? We will consider the possibilities.

Continue reading… Out of gas: the end of the age of oil – David Goodstein