Events

• Physics of the Cosmos: NASA's program to understand the Universe's origin and fate

  Tue, 09/09/08 03:30PM   Michael Salamon, NASA
  Hosted by Steve Ahlen.
  

  This event is part of the Department Colloquia Series. Colloquia are at 3:30 in the Metcalf Science Center (SCI 107) Refreshments will be served at 3:15 in the 1st Floor Lounge

  Abstract:

  “A number of missions are being planned by NASA’s Astrophysics Division that will be dedicated to understanding the evolution of our Universe. In this colloquium we will describe the dramatic role of these space missions in furthering our knowledge of cosmology, the inflationary epoch and dark energy. We will focus on the cosmic microwave background missions (WMAP and Planck), the measurement of gravitational radiation by LISA to test strong field gravity and “hear” the coalescence of supermassive black holes, and the measurement of the equation of state of dark energy by JDEM.”

• Superconducting gaps and Pseudogaps: spectroscopic evidence for two competing, coexisting phases below Tc

  Fri, 09/19/08 12:00PM   Vidya Madhavan, Boston College
  

  This event is part of the Condensed Matter Seminar Series. All seminars will take place in the Metcalf Science Center, Room 352 at noon, unless otherwise noted

  Abstract:

  The origin of the pseudogap (PG) phase is one of the most important unsolved mysteries of high temperature superconductivity. Explanations for the PG range from fluctuating superconducting (precursor) pairs to a competing phase. A huge hindrance to progress is that in most of the extensively studied superconductors, the PG and superconducting energy scales coincide. In optimally doped Bi2Sr2-xLaxCuO6+δ (La-Bi2201) however, these two energy scales are well separated. Through a comparison study of scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES) on La-Bi2201, we report the observation of two distinct gaps that coexist both in real space and in the anti-nodal region of momentum space. The smaller gap can be identified as the superconducting gap while the large gap persists above Tc and can be identified as the PG in these samples. These data provide tantalizing evidence for a competing phase description of the PG in this material. Intriguingly, we find that the pervasive charge ordering in these samples disappears in the overdoped samples concomitant with a suppressed large-gap and a weakened nesting condition, suggesting a causal relationship between them.

News

• Graduate Student Silvia Kusminskiy Models Heavy Fermion Effect

  August 07, 2008

  Heavy fermions are materials which, at low temperatures, behave like metals with unusually high specific heat and magnetic susceptibility coefficients. These materials can be modeled as a lattice of magnetic impurities embedded in a metallic host. The magnetic interaction between the impurities and the conduction electrons gives rise to new collective entities, called quasi-particles, which behave as very massive electrons.

  It is known that an applied magnetic field will eventually destroy the heavy fermion state, however the exact mechanism for this has been debated. In a recent paper published in Physical Review B, graduate student Silvia Viola Kusminskiy and collaborators have proposed a model for the evolution of the Fermi surface of heavy fermion materials in the presence of a magnetic field. Opposite to what is generally argued, they find that the Fermi surface fully polarizes well before the heavy fermion state is destroyed. This manifests itself as a crossover to a phase that they call the “locked state,” which can be confused with the collapse of the heavy fermion state.

  Kusminskiy et al. claim that this model can explain the metamagnetic behavior of the heavy fermion compound YbRh2Si2 that has previously been attributed to the aforementioned collapse. Recent experimental results have provided strong evidence for this prediction. You can read more about those results here.

• Professor Polkovnikov Published in Nature Physics

  June 05, 2008

  In thermodynamics, it is generally believed that a system will behave adiabatically – that is, no heat will be produced – if the parameters of the system are changed sufficiently slowly. This is often justified using the adiabatic theorem of quantum mechanics, which states that the transitions between different energy levels in a quantum system are suppressed if the system changes sufficiently slowly. Though these two ideas have long been connected, their exact relationship has remained elusive.

  In a recent paper published in Nature Physics, Professor Anatoli Polkovnikov and his colleague have elucidated this relationship. They have identified three response regimes for slowly changing thermodynamic systems, and as a result, have shown that adiabaticity can break down for low-dimensional, gapless systems.

  Click here to read the full paper in Nature Physics.

• Professor Averitt receives DARPA Young Faculty Award

  March 20, 2008

  Professor Richard Averitt has received a DARPA Young Faculty Award for his proposal “Metamaterial Enhanced MEMS for Terahertz Technology”. The Young Faculty Award program is designed to seek out ideas from non-tenured faculty with an emphasis on ideas that are innovative, speculative, and high-risk. DARPA’s Microsystems Technology Office sponsors the program. Read more about this award here.

• GIMS Travel Grant awarded to graduate student Utku Kemiktarak

  March 14, 2008

  Utku Kemiktarak, graduate student and recent author of a Nature-published paper, won a travel grant from the APS Topical Group on Instrument and Measurement Science.

  GIMS awarded travel grants of up to $800 each to students as the first author of contributed papers in sessions sponsored by GIMS at the March Meeting. Applicants were chosen on the basis of the quality of their work as evidenced by the abstract of the paper, a letter of support from their thesis advisor and the travel distances.

• Physics Today book review authored by Professor Stanley

  January 24, 2008

  Professor Gene Stanley reviewed “Random Processes in Physics and Finance” (M. Lax, W. Cai, M. Xu) in Physics Today:

  “The term ‘econophysics’ was introduced just 14 years ago, but the tradition of physicists being fascinated by random processes in finance has a history much older than that. In fact, both Nicolaus Copernicus and Isaac Newton invested considerable intellectual energy in attempting to understand the economic problems of their day.”

  To read the full review, click here.

• Alex Marin Memorial Site

  January 24, 2006

  Please visit our online memorial to Alexander Marin. If you have any materials you would like to share, please send them to Richard Laskey.

Student Spotlight:

Ian Cohen. Full-time physicist. Part-time troubadour.