Speaker: John Sous, (University of British Columbia)
Date: Thursday, November 9th
Time: 12:00-1:00 pm
Includes Pizza.
Title: Phonon-mediated repulsion, sharp transitions and (quasi)self-trapping in the extended Peierls-Hubbard model
Abstract: Particle-phonon coupling is generically expected to lead to a screening of the bare particle-particle interactions. If low-energy overscreening occurs, the resulting attractive interactions are responsible for conventional superconductivity as described by the Bardeen-Cooper-Schrieffer theory. I will demonstrate that Peierls-type particle-phonon coupling not only leads to an enhanced repulsion between identical fermions/hard-core bosons, but also generates an additional effective interaction not of density-density type and thus not involved in screening. This interaction moves pairs of neighbor particles as a whole; this has unusual consequences such as a (quasi)self-trapping transition for a bound pair even when the individual particles are very mobile. These results open new directions in the study and understanding of the effects of particle-boson coupling, relevant for understanding behavior in Physics, e.g. in quantum materials; Chemistry, e.g. in optoelectronic processes; and Biology, e.g. in photosynthesis and DNA.
Location: B-106 @ Center for Astrophysics (60 Garden Street)
Directions: After entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, B-106 will be at the end of the hallway on the left side.
Dear students and postdocs,
tomorrow, Wednesday, November 15th, we will take this week’s ITAMP/HQOC speaker Tongcang Li out for lunch at Russel House Tavern. If you would like to join, please sign up via the following link (limited to 8 people):
https://docs.google.com/spreadsheets/d/1aY3B6-XNLVZFr6iX502cG36IuJ7IFTKp6Pf…
We meet at LISE cafe at 11:40.
Best,
Hannes
Dear group,
As mentioned in the group meeting today, during the odyssey maintenance
period on Monday, December 4, they will be updating the firmware for our
/n/aagfs01 filesystem. If you have files on here, please do not touch them
during this time period (7 AM-11 AM).
Let me know if you have any questions. I will probably send a follow-up
email that morning.
Best,
Danny
Dear all,
here's the info for my defense tomorrow. would love to see you there if you
can make it.
cheers!
Adrian
---------- Forwarded message ----------
From: Pomerantz, Elizabeth J. <Elizabeth_Pomerantz(a)hms.harvard.edu>
Date: Thu, Nov 30, 2017 at 1:40 PM
Subject: Dissertation Defense Seminar- TOMORROW, 12/1/2017- Adrián Jinich
To: SYSBIOPHD_STUDENT(a)listserv.med.harvard.edu
*Systems Biology PhD Program*
*Harvard University*
*[image: Harvard_shield-GSAS small]*
*DISSERTATION SEMINAR*
*“The Thermodynamics of carbon redox biochemistry:*
*A quantum chemical approach”*
*Adrián Jinich*
*Friday, December 1st*
*3:00pm *
Northwest Building 453
Cambridge, MA
Advisor: Alan Aspuru-Guzik
--
Adrian Jinich
Aspuru-Guzik Lab
Harvard University
12 Oxford Street
Cambridge, MA 02138
ajinich(a)fas.harvard.edu
http://aspuru.chem.harvard.edu/adrian-jinich/
Reminder: Thomas Barthel is talking today at 2pm, in room 6C-442.
----------------------------------------------------
Speaker: Thomas Barthel (Duke University)
Date/time: Thursday Nov 30th, 2 PM
Location: 6C-442
*Title: *Typical 1d quantum systems at finite temperatures can be
simulated efficiently
on classical computers
*Abstract:*
It is by now well-known that ground states of gapped one-dimensional (1d)
quantum-many body systems with short-range interactions can be studied
efficiently using classical computers and matrix product state techniques.
A corresponding result for finite temperatures was missing.
For 1d systems that can be described by an appropriate 1+1d field theory, I
show that the cost for the classical simulation at finite temperatures
grows in fact only polynomially with the inverse temperature and is
system-size independent -- even for quantum critical systems. In
particular, the thermofield double state (TDS), a purification of the
equilibrium density operator, can be obtained efficiently in matrix-product
form. The argument is based on the scaling behavior of Rényi entanglement
entropies in the TDS. At finite temperatures, they obey the area law. For
quantum critical, conformally invariant systems, the Rényi entropies are
found to grow only logarithmically with inverse temperature. For gapped
systems, they converge to a constant. The field-theoretical results are
confirmed by quasi-exact numerical simulations for integrable and
non-integrable spin systems, and interacting bosons.
Ref: T. Barthel, arXiv:1708.09349 (2017)
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ITAMP/HQOC Joint Quantum Sciences Seminar
Wednesday, November 29, 2017
4:00 PM, Jefferson 250
Prof. Pierre Pillet, Purdue University
“Interplay between two, few- and manybody effects in a dense, cold and disordered gases in strong dipole-dipole coupling”
Dipole-dipole long-range interactions between two atoms in dense and cold atomic media play a crucial role in many configurations by considering ground state atoms as well as highly-excited Rydberg atoms. They may alter the coherent scattering of light by a dense and cold atomic sample. They open also many opportunities for studying few-body and many-body physics, and hopefully for simulating many different quantum systems. A cold, disordered and dense cesium Rydberg gas in Förster resonant configurations is an interesting example of out-of-equilibrium quantum system. The atoms are prepared in a state, np, exchanging internal energy by a resonant way
ITAMP/HQOC Joint Quantum Sciences Seminar
Wednesday, November 29, 2017
4:00 PM, Jefferson 250
Prof. Pierre Pillet, Purdue University
“Interplay between two, few- and manybody effects in a dense, cold and disordered gases in strong dipole-dipole coupling”
Dipole-dipole long-range interactions between two atoms in dense and cold atomic media play a crucial role in many configurations by considering ground state atoms as well as highly-excited Rydberg atoms. They may alter the coherent scattering of light by a dense and cold atomic sample. They open also many opportunities for studying few-body and many-body physics, and hopefully for simulating many different quantum systems. A cold, disordered and dense cesium Rydberg gas in Förster resonant configurations is an interesting example of out-of-equilibrium quantum system. The atoms are prepared in a state, np, exchanging internal energy by a resonant way
ITAMP Lunch Seminar
Speaker: Adrian Feiguin, (Northeastern University)
Date: Thursday, November 30th
Time: 12:00-1:00 pm
Includes Pizza.
Title: Spin incoherent behavior in strongly correlated low dimensional systems
Abstract: When electrons (or other quantum particles with an internal ``spin" degree of freedom) are confined in one spatial dimension, they loose their identity as individual particles. The excitations become collective modes carrying spin, and charge, with each degree of freedom being characterized by a different energy scale. While the basic theoretical understanding of spin-charge separation in one-dimension, known as ``Luttinger liquid theory'', has existed for some time, recently a previously unidentified regime of strongly interacting one-dimensional systems at finite temperature came to light: The ``spin-incoherent Luttinger liquid". This occurs when the temperature is larger than the characteristic spin energy scale. The key to establishing both Luttinger liquid behavior and spin-incoherent Luttinger liquid behavior in experiment is detailed knowledge of the spectral properties.
I will present a numerical study of the finite-temperature spectral properties of a one-dimensional fermionic gas in the spin-incoherent regime using the time-dependent density matrix renormalization group method. This approach enables us to quantitatively handle the experimentally relevant and theoretically challenging ``crossover" regime between the Luttinger liquid and spin-incoherent Luttinger liquid limits. Finally, I will show that spin-incoherent behavior can be realized in the *ground-state* of model Hamiltonians, such as Hubbard ladders, and the Kondo lattice.
Location: B-106 @ Center for Astrophysics (60 Garden Street)
Directions: After entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, B-106 will be at the end of the hallway on the left side.
Please forward to your groups.
Center for Excitonics Seminar Series presents:
Exciting Metal-organic Frameworks: Electrons, Phonons, and Photons
November 28, 2017 at 4:30pm/rm: 34-401A
Aron Walsh
Department of Materials, Imperial College London
[http://www.rle.mit.edu/excitonics/wp-content/uploads/2017/10/1Walsh-Aron-27…]
Metal-organic frameworks (MOFs) are porous ordered arrays of inorganic clusters supported by organic linking units. They have attracted attention for gas storage, separation and catalysis, which rely on weak chemical bonding with an absorbate. The recent focus has shifted to physical responses, with examples of magnetic, optical, ferroelectric, and photovoltaic compounds. I will discuss progress in the understanding of how hybrid frameworks interact with charge, heat, and light.
The optical response of MOFs can be tuned by chemical modification of the organic and inorganic building blocks[1]. The control of electrical conductivity and redox activity in MOF thin-films is opening a new dimension of applications[2,3]. The combination of chemical diversity, mechanical flexibility, and electronic control in a single family of compounds could enable metal-organic frameworks to become the semiconductors of the future.
Beyond porous frameworks, I will also discuss progress in the understanding of organic-inorganic halide perovskites, such as methylammonium lead iodide, which have attracted significant attention for solar energy conversion. These compounds have been termed ‘plastic crystals’ owing to the rotational-vibrational activity of the molecular components, as well as the large anharmonic thermal displacements of the inorganic framework. We have been developing models to describe the temporal behaviour of hybrid perovskites that have been validated through a combination of quasi-elastic neutron scattering, time-resolved vibrational spectroscopy, and inelastic X-ray scattering. There remains significant challenges relating to the fundamental chemistry and physics of this growing family of hybrid compounds.
This research has been supported by the Royal Society and the European Research Council, with a wide collaboration network including simulations by Drs. Katrine Svane, Jarvist Frost, and Jonathan Skelton.
1. “Chemical principles for electroactive metal–organic frameworks” MRS Bulletin 41, 870 (2016)
2. “Metallic conductivity in a two-dimensional cobalt dithiolene metal−organic framework” J. Am. Chem. Soc. 139, 10863 (2017)
3. “Is iron unique in promoting electrical conductivity in MOFs?” Chemical Science 8, 4450 (2017)
4. “Atomistic origins of high-performance in hybrid halide perovskite solar cells†Nano Lett., 14, 2584 (2014)
5. “Direct observation of dynamic symmetry breaking above room temperature in methylammonium lead iodide perovskite” ACS Energy Lett. 1, 880 (2016)
Aron Walsh is a Royal Society University Research Fellow and Full Professor in the Department of Materials. Aron joined Imperial College London in October 2016. He was awarded his PhD in Chemistry from Trinity College Dublin. He then worked for the US Department of Energy at the National Renewable Energy Laboratory (NREL), followed by a Marie Curie Fellowship hosted at University College London, and a European Research Council Fellowship held at the University of Bath. His research involves cutting-edge materials theory and similation applied to problems across solid state chemistry and physics, including materials for solar cells and solar fuels, information storage, batteries, thermoelectrics and solid-state lighting. He has a particular expertise in the theory of semiconductors and dielectrics, and is developing innovative solutions for materials data, informatics and design.
The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S. Department Of Energy,
Office Of Science And Office Of Basic Energy Sciences
LIGHT REFRESHMENTS WILL BE SERVED!