Condensed Matter Seminars

Is there a future for ferromagnetic semiconductors?

Speaker: 
Margaret Dobrowolska-Furdyna
Event Date and Time: 
Thu, 2012-04-12 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Mona Berciu
Intended Audience: 
Graduate
GaMnAs is a ferromagnetic semiconductor which is considered to be an ideal candidate for spintronic applications. However, the bottleneck is that its highest critical temperature so far achieved is about 200 K.

Dissipative and quasi-thermal effects at long times after a quantum quench

Speaker: 
Aditi Mitra (NYU)
Event Date and Time: 
Fri, 2012-03-16 13:00 - 14:00
Location: 
Hennings 318
Local Contact: 
Jean-Sébastien Bernier, Fei Zhou
Intended Audience: 
Graduate

How an interacting many-particle system prepared in an initial state which is far from equilibrium evolves in time, and how it thermalizes if at all, is an important and open question which is also of experimental relevance. In this talk I will consider a system of interacting bosons that are initially out of equilibrium due to an interaction quench.

A view of electron-phonon coupling in the high-Tc cuprates and its interplay with the Coulomb interactions

Speaker: 
Steven Johnston (Leibniz Institute, Dresden)
Event Date and Time: 
Mon, 2012-03-12 12:00
Location: 
Hennings 318
Local Contact: 
Mona Berciu
Intended Audience: 
Graduate

A large number of viewpoints exist regarding the nature of the electron-phonon (e-ph) interaction in the high-Tc cuprates, covering the spectrum from primary pairing mediator in polaronic scenarios all the way to playing a negligible role. Recently this issue has been prominent in the context of a set of low-energy renormalizations observed in the electronic structure of the cuprates by various spectroscopies - such as angle-resolved photoemission spectroscopy - where the e-ph interaction has been proposed as a possible interpretation.

A Typology for Quantum Hall Liquids

Speaker: 
Boris Spivak (University of Washington)
Event Date and Time: 
Fri, 2012-02-17 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Joshua Folk
Intended Audience: 
Graduate

The Pfaffian phase of electrons in the proximity of a half-filled Landau level is understood to be a p+ip superconductor of composite fermions. We consider the properties of this paired quantum Hall phase when the pairing scale is small, i.e. in the weak-coupling, BCS, limit, where the coherence length is much larger than the charge screening length. We find that, as in a Type I superconductor, the vortices attract so that, upon varying the magnetic field from its magic value at nu = 5/2, the system exhibits a Coulomb frustrated phase separation.

Effect of Strain and Dimensionality on the Properties of Manganites

Speaker: 
Carolina Adamo (Dep't of Materials Science and Eng., Cornell Universityi)
Event Date and Time: 
Thu, 2012-02-09 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Andrea Damascelli
Intended Audience: 
Graduate

Strain and dimensional confinement can be used to tune magnetic and ferroelectric properties or enhance device performance. In epitaxial films, the different lattice spacing of an underlying substrate can be used to impose a biaxial strain. We have studied the effect of the substrate-induced biaxial strain on the electrical conductivity and magnetic properties of manganite compounds. Epitaxial (001) La0.7Sr0.3MnO3 thin films have been grown by reactive molecular-beam epitaxy (MBE) on single crystalline substrates, varying the substrate-induced biaxial strain from −2.3% to +3.2%.

The amplitude mode at the superfluid-Mott insulator transition

Speaker: 
David Pekker (Caltech)
Event Date and Time: 
Fri, 2012-02-10 13:00
Location: 
Henning 318
Local Contact: 
Fei Zhou
Intended Audience: 
Graduate
We study a two dimensional gas of repulsively interacting bosons in the presence of both an optical lattice and a trap using optical lattice modulation spectroscopy. The strongly interacting superfluid supports two types of low energy modes associated with the symmetry breaking at the phase transition: gapless phase (Goldstone) modes and gapped amplitude (Anderson-Higgs) modes.

Condensed matter without matter: towards many-body states with light

Speaker: 
Andrew Houck (Princeton University)
Event Date and Time: 
Thu, 2012-01-26 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Joshua Folk
Intended Audience: 
Graduate
Photons do not interact strongly in nature, and have thus been relegated to a role as a tool rather than an object of study in condensed matter physics. However, in cavity quantum electrodynamics, the strong interaction of light with a single atom can lead to strong atom-mediated photon-photon interactions, even when the light and atomic transitions are not resonant. Recent theoretical proposals have predicted phase transitions in arrays of these cavities, demonstrating that complex matter-like phenomena can emerge from a sea of interacting photons.

Electron-phonon coupling in underdoped cuprates

Speaker: 
Andrey Mischenko (Cross-Correlated Materials Research Group, Riken, Japan)
Event Date and Time: 
Mon, 2011-12-05 12:00
Location: 
Hennins 318

The angle resolved photoemission spectra (ARPES) and optical conductivity (OC) of the underdoped high temperature superconductors is studied in the framework of the low density limit of the t-J-Holstein.

Understanding the complex dynamics of superconducting cuprates by broadband ultrafast spectroscopy

Speaker: 
Claudio Giannetti (Universita Cattolica del Sacro Cuore)
Event Date and Time: 
Thu, 2011-11-24 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Andrea Damascelli
Intended Audience: 
Graduate
In strongly-correlated systems the electronic properties at the Fermi energy are intertwined with those at high energy scales and are strongly affected by different degrees of freedom, such as lattice vibration, bosonic excitations of electronic origin, quasi-particle excitations. Broadband ultrafast spectroscopy is emerging as the premier technique to disentangle the subtle interplay of the different degrees of freedom, on the basis of the different characteristic timescales and spectral responses.
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