Physics Department Highlights

Research Highlights 2005

Spin Injection from Ferromagnetic Contacts Into GaAs and InAs Based Structures

Athos Petrou's Group

Mr. Robert Mallory, a graduate student in Dr. Athos Petrou's group, has an invited talk at the 94th Topical Symposium of the New York State Section of the APS.  The title of his talk is "Electrical Spin Injection from Ferromagnetic Contacts Into GaAs and InAs Based Structures" .  The symposium title is "Physics and Technology of Microsystems" April 7 and 8, 2006, Finger Lakes Community College, Ganandaigua NY.
 

First Observation of the Protein "Glass" Transition at Terahertz Frequencies

Andrea Markelz's Group

Jing-Yin Chen of the Markelz group recently won a travel award to present her paper, "First Observation of the Protein "Glass" Transition at Terahertz Frequencies," at the annual Biophysical Society Conference in Salt Lake City, Utah, February 19-23, 2006. Ms. Chen was also first author on a paper that was recently featured in the Virtual Journal of Biological Physics, "Large oxidation dependence Observed in Terahertz Dielectric Response for Cytochrome C," J.-Y. Chen, J. R. Knab, J. Cerne and A. G. Markelz, Phys. Rev. E Rapid 72, 040901 (2005).

Electron spin decoherence via interaction with nuclear spins

Xuedong Hu's Group

Electron spins in semiconductor nanostructures are promising qubit candidates for a solid state quantum computer, and have seen truly impressive experimental progresses in the past two years. A central issue in spin-based quantum information processing is spin decoherence, which in a quantum dot is dominated by the hyperfine interaction with the surrounding nuclear spins. Recently we have analytically solved the single electron spin dynamics due to hyperfine interaction with surrounding nuclei in a quantum dot. We find that virtual nuclear spin flip-flops mediated by the electron contribute significantly to a complete decoherence of transverse electron spin correlation function. Our results show that a 90% nuclear polarization can enhance the electron spin T₂ time by almost two orders of magnitude. The work has been submitted and posted online: http://www.arxiv.org/abs/cond-m at/0510379.

Fundamental research at an energy frontier

Avto Kharchilava and Ia Iashvili

SUNY at Buffalo has recently become a member of the CMS experiment -- an international collaboration of High Energy Physicists that will conduct research at world's highest energy collider, LHC, being constructed at CERN, Geneva, Switzerland. Highest energies open up unprecedented opportunities to study properties of matter, fields, their interactions, address fundamental questions such as the origin of mass, dark matter, whether there are extra dimensions of space, etc. These are just a few tantalizing issues that LHC can shed light on. In the meantime, before startup of LHC at around 2007, physicists from SUNY at Buffalo are conducting research at Fermilab's Tevatron -- the world's highest energy collider currently in operation -- as members of the DZero Collaboration.

Higgs boson production with one bottom quark jet at hadron colliders

Doreen Wackeroth

One of the most pressing problems in particle physics is to uncover the mechanism that is responsible for the generation of W and Z boson masses. The Standard Model (SM) of particle physics predicts the existence of a Higgs boson as a consequence of mass generation via spontaneous electroweak symmetry breaking. Extensions of the SM often introduce more Higgs particles whose properties may drastically differ from the SM Higgs boson. Finding experimental evidence of one or more Higgs bosons and measuring their couplings to gauge bosons, leptons and quarks is a major goal of particle physics.

In a recent letter Phys. Rev. Lett. 94, 031802 (2005) we focus on Higgs boson production in association with bottom quarks at the Tevatron and the LHC in the supersymmetric extension of the SM. In the predictions for total rates and kinematic distributions we include next-to-leading order QCD corrections and compare the results obtained in two different calculational schemes. As a result of this study the theoretical uncertainties of the predictions are now well under control, which is crucial for experimental searches based on this process.

Dr. Wackeroth has recently received a prestigious NSF CAREER award in support of "Higher-Order Calculations for Precision and New Physics Studies at the Large Hadron Collider".

Phonon Self-energy in Metals

Peihong Zhang

We have recently developed a method for calculating the phonon self-energy in metals arising from the coupling between phonons and electrons near the Fermi surface. The essence of this scheme is the separation of the inter- and intra-band parts of the electron polarizability. Applications of this scheme to phonons in MgB₂ give excellent results when compared with experiments. In addition, both electron and hole dopings are found to reduce the renormalization effect of the E_2g phonon mode, which indicates a weakened electron-phonon coupling in the doped systems. [Phys. Rev. Lett. 94, 225502 (2005)]

Dr. Zhang's research is unified around the theme of understanding and predicting materials properties from first principles and involves large scale computation. We are in a process of acquiring a powerful linux cluster which will be shared among several groups within the department. The theoretical peak performance of the cluster exceeds 200 GFlops.

Phase-Sensitive Tests of the Pairing State Symmetry in Sr₂RuO₄

Igor Zutic

Exotic superconducting properties of strontium ruthenate have provided strong support for symmetry of paired electrons different from conventional superconductors such as aluminum, lead, or mercury. While recent phase-sensitive experiments in Josephson junctions consisting of strontium ruthenate and a conventional superconductor [K. D. Nelson et al. Science 306, 1151 (2004)] have been interpreted as conclusive evidence for a spin-triplet pairing [T. M. Rice, Science 306 (2004)] we propose an alternative interpretation and suggest further experiments to resolve this controversy [I. Zutic and I. Mazin, [Phys. Rev. Lett. 95, 217004 (2005)].

For his research in spintronics Dr. Zutic has been awarded a three year grant from the US Office of Naval Research and his National Science Foundation CAREER proposal has been recommended for funding.

Baby Solitary Waves

Surajit Sen

I work on nonlinear dynamical systems. A part of this work concerns how impulses propagate through granular materials. The latest work centers on how a combination of discreteness of space and nonlinearity of interactions can give rise to energy propagation in the form of "tight bundles" or "solitary waves." We have even managed to control the breaking and making of these waves. With our collaborator Francisco Melo at University of Santiago, Chile, the first experiments on breaking of solitary waves have now been published (Phys. Rev. Lett. 94, 178002 (2005)). For more news tune in to http://www.physics.buffalo.edu/~sen

Quantum fluids and phase transitions: 32 years of research in Gasparini's group

Frank Gasparini

The behavior of liquid ⁴He and ³He and mixtures are unusual for several reasons: they remain liquids to the absolute zeros, a mainfestation of the role of quantum mechanical zero point motion; they have low temperature phases which are superfluids, a manifestation of quantum statistics; and, the transitions themselves, from normal liquid to a superfluid, are a paradigm for phase transitions in other systems. In the case of ⁴He the characteristic behavior at its superfluid onset is that of a ferromagnet with two easy axes of magnetization. Gasparini has been studying quantum fluids for many years. He has received $2.2M of funding from the National Science Foundation spanning a period of 29 years. The most recent work addresses the issue of universality and finite-size scaling in mixtures of ³He and ⁴He. This appeared in Phys. Rev. Lett. 95, 165701 (2005).

Quantum Hall Effect and Shubnikov-de Haas Oscillations

Shigeji Fujita

Shigeji Fujita gave two plenary lectures, (1) "On the Radiation - Induced Quantum Hall effect" at the international workshop Similarity in Diversity 10, Tokyo, Japan, September 7-9, 2005. (2) "Theory of the Shubnikov-de Haas Oscillations in GaAs/AlGaAs", at the Condensed Matter Theory 29, Kyoto, Japan, September 13-17, 2005. Both will be published in the Proceedings, Nova Science, New York.

W Bosons at the CERN Large Hadron Collider

Richard J. Gonsalves

W bosons are carriers of the weak force. They mediate the decay of free neutrons to protons, electrons and anti-neutrinos, for example. A W boson is almost a hundred times as massive as a proton, so it takes a high energy particle accelerator to create Ws. The LHC at CERN is expected to begin producing Ws at a rate of a hundred million a year starting in 2007. Precise predictions for production cross sections as a function of the transverse momentum of the W were published in Phys. Rev. Lett. 95, 222001 (2005). For more information on these predictions see http://www.physics.buffal o.edu/gonsalves/ewbqt/.

Relativistic Quantum Mechanics of Few-Particle Systems

Michael Fuda

Recent research has focused on constructing a relativistic, quantum mechanical model for the pion-nucleon system. This system is of particular interest as it is the source for much of the information on the excited states of the nucleon, i.e., the baryon resonances. These resonances are excited in pion-nucleon reactions, so it is important to have an accurate model for these reactions. Information on these resonances provides important tests of Quantum Chromodynamics in the non-perturbative region. The model that has been constructed has a finite number of degrees of freedom, and satisfies exactly the requirements of special relativity and quantum mechanics. With this model the probability of any particular process does not depend on the inertial frame used to describe it. Since the model has a finite number of degrees of freedom it is amenable to exact numerical solutions. Most recently it has been possible to extend the model of the pion-nucleon system to allow for three-particle final states. This extension of the model is quite remarkable in that the final equations that have to be solved to obtain the various scattering and reaction amplitudes are coupled integral equations in one continuous variable. Essentially it has been possible to reduce a relativistic three-body problem to an effective one-body problem. The method for doing this has been presented in Phys. Rev. C 72, 064001 (2005).