Harvard University Department of Physics

R.I.P. Professor Nicolaas Bloembergen

Nicolaas (Nico) Bloembergen, Gerhard Gade University Professor, Emeritus, and 1981 Nobel Laureate, passed away at his home in Tucson, Arizona, on September 5, 2017.

Mimicking Birdsongs

Mahadevan Lab has developed a simple device to recreate complex birdsongs with the help of soft materials and mathematical modeling. The study finds that the inherent complexity in birdsongs might actually be the result of a simple controllable instability in the structure of the specialized organ used to create song, known as a syrinx...

Mach-Zehnder Interferometry Using Spin- and Valley-Polarized Quantum Hall Edge States in Graphene

Confined to a two-dimensional plane, electrons in a strong magnetic field travel along the edge in one-dimensional quantum Hall channels that are protected against backscattering. These channels can be used as solid-state analogs of monochromatic beams of light...

UPCOMING EVENTS

Tomorrow

CMP Seminar: Carlos Bolech (Univ. Cincinnati), hosted by Eugene Demler
Start: 12:00pm - End: 01:00pm
- 12:00pm
- Title: "Bosonization and the description of sharply localized states in the continuum"
  
  Abstract: In this talk, we will critically reexamine the bosonization-debosonization procedure for systems including localized features or boundaries. First, by focusing on the case of a tunneling junction out of equilibrium, we will show that the conventional bosonization approach can give results that are not consistent with a direct solution of the problem even at the qualitative level, thus highlighting possible inconsistencies that can adversely affect the results of all types of calculations. We will subsequently report on a "consistent bosonization-debosonization" procedure that we have developed to resolve the aforementioned non-equilibrium transport puzzle and argue that it should be widely applicable [1]. This new framework takes the form of additional considerations, related to the regularization of fermionic bilinears, that supplement the conventional bosonization procedure and it can be carried over to the study of other systems. We will then discuss its application to the two-lead Kondo junction [2], that besides being a key theoretical prototype of a non-equilibrium strongly correlated system is also of continuing experimental relevance. The discussion will be focused on the Toulouse limit of that problem.
  
  [1] N. Shah and C. J. Bolech, Phys. Rev. B 93, 085440 (2016)
  [2] C. J. Bolech and N. Shah, Phys. Rev. B 93, 085441 (2016)
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Friday, September 22nd

CMP Special Seminar: Philipp Stegmann (University of Duisburg-Essen), hosted by Eugene Demler
Start: 11:00am - End: 12:00pm
- 11:00am
- Title: Generalized factorial cumulants of electron tunneling in Coulomb-blockade systems
  
  Abstract: Tunneling of electrons through Coulomb-blockade systems such as quantum dots or metallic islands is a stochastic process. The number of the transferred electrons per time interval is determined by a probability distribution also referred to as the full counting statistics. Recently developed electrometers allow for the observation of each electron transported through a Coulomb-blockade system in real time. Therefore, the probability distribution can be directly measured. In this talk, we will introduce generalized factorial cumulants as a new tool to analyze the information contained in the probability distribution. These cumulants can detect correlations between the tunneling electrons [1,2] or a violation of detailed balance [3]. Moreover, we use the cumulants to count coherent spin precessions in a quantum-dot spin valve. In a recent experiment, we identified coherent excitations of manganese complexes coupled to a carbon nanotube. We also introduce a mathematical procedure called inverse counting statistics [4]. The procedure yields, solely from a few experimentally measured cumulants, a lower bound for the system dimension and the full spectrum of relaxation rates.
  
  [1] P. Stegmann, B. Sothmann, A. Hucht, and J. König, Phys. Rev. B 92, 155413 (2015).
  
  [2] P. Stegmann and J. König, Phys. Rev. B 94, 125433 (2016).
  
  [3] P. Stegmann and J. König, Phys. Status Solidi B 254, 1600507 (2017).
  
  [4] P. Stegmann and J. König, New J. Phys. 19, 023018 (2017).
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Monday, September 25th

Monday Colloquium: Achim Rosch (University of Cologne), title TBA
Start: 04:15pm - End: 05:30pm
- 04:15pm
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Tuesday, September 26th

CMP Special Seminar: Achim Rosch (U. of Cologne)
Start: 01:15pm - End: 02:15pm
- 01:15pm
- Title: Whirls in magnets: from skyrmions to magnetic monopoles
  
  Abstract: Weak perturbations can drive an interacting many-particle system far from its initial equilibrium state if one is able to pump into degrees of freedom approximately protected by conservation laws. This concept has for example been used to realize Bose–Einstein condensates of photons, magnons and excitons. Integrable quantum systems, like the one-dimensional Heisenberg model, are characterized by an infinite set of conservation laws. Here, we develop a theory of weakly driven integrable systems and show that pumping can induce large spin or heat currents even in the presence of integrability breaking perturbations, since it activates local and quasi-local approximate conserved quantities. The resulting steady state is qualitatively captured by a truncated generalized Gibbs ensemble with Lagrange parameters that depend on the structure but not on the overall amplitude of perturbations nor the initial state. We suggest to use spin-chain materials driven by terahertz radiation to realize integrability-based spin and heat pumps.
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Wednesday, September 27th

Xingbo Yang; Needleman group - Harvard University
Start: 05:30pm - End: 07:00pm
- 05:30pm
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