Condensed Matter Sack Lunch Seminar

semester, 2008

Tuesday, January 22nd 2008
12:20 pm:
Speaker: There will be no seminar this week.

Tuesday, January 29th 2008
12:20 pm:
Speaker: Mathew Loth, U of MN
Subject: Multiple Protons Biund by a Single Electron in a Strong Magnetic Field

Tuesday, February 5th 2008
12:20 pm:
Speaker: DR. M. Warusawithana, Pennsylvania State University
Subject: New Electronic Functionality and Quantum Devices through Nanostructured Interfaces

Interfaces between materials have led to revolutionary discoveries. When precisely crafted at the atomic scale, proximity effects, reduced dimensionality and symmetry breaking compete at interfaces to bring out quantum phenomena and unforeseen functionality. In this talk I will discuss examples from my work where heteroepitaxial interfaces play a pivotal role in the aggregate response of a system. These include: 1. Dielectric superlattices consisting of precisely integer molecular layers of titanate phases - CaTiO3, BaTiO3 and SrTiO3, where the symmetry of the superlattice and hence its electronic response was controlled by the sequence of interfaces built into the structure. 2. Mixed-valent manganites, where ordered pseudo alloys constructed through digital superlattices to have the same average doping as their random alloy counterparts albeit with removed structural disorder, resulted in modified electronic and magnetic properties. 3. Extreme heteroepitaxy between SrTiO3 and (001) Si avoiding the formation of an amorphous interfacial SiO2 layer where a commensurately strained SrTiO3 film and thus a strain induced ferroelectric directly on silicon was obtained. Through these examples, I will show how such nanoscale sample design, when carefully combined with other techniques, can be used to probe basic and applied physics.

Tuesday, February 12th 2008
12:20 pm:
Speaker: Dr. Abhay Pasupathy, Princeton University
Subject: Visualizing Superconducting Pair Formation at the Atomic Scale

Tuesday, February 19th 2008
12:20 pm:
Speaker: Dr. T. Baturina, Institute for Solid State Physics, Russia
Subject: Two faces of Cooper pairing: Superconductor and Superinsulator
This seminar is part of the condensed matter experiment faculty search

The microscopic mechanism behind the superconductivity is the formation of bound pairs of electrons (Cooper pairing). So far the complete disappearance of the electrical resistance was the major known consequence of Cooper pairing. I will present novel findings, demonstrating that Cooper pairing is responsible not only for the zero-resistive superconducting state but, paradoxically, also for the zero-conducting superinsulating state. The latter is dual to the superconducting state: It appears at a finite temperature and has all the attributes complementary to the superconducting state, namely, the magnetic field dependent critical temperature and the threshold voltage, which plays the same role as critical current, breaking down the zero-resistance state of superconducting films.

Tuesday, February 26th 2008
12:20 pm:
Speaker: Dr. J. Bao, Harvard University
Subject: Nanophotonics, Nanofabrication and Nanomaterials

This talk will present my recent work at the intersection of photonics, nanofabrication, and materials design. I will start with an overview of the light emission properties of semiconductor nanowires, including single-nanowire light-emitting diodes, and optically pumped ultraviolet nanowire lasers. Then, I will introduce nanoskiving as a technique for engineering the optical response of metallic nanostructures. Finally, I will discuss two novel approaches for the design of new nanomaterials: point-defect engineered silicon for silicon photonics and rotationally twinned nanowires as a new type of superlattice.

Tuesday, March 4th 2008
12:20 pm:
Student practice talks

Tuesday, March 11th 2008
12:20 pm:
There will be no seminar this week.

Tuesday, March 18th 2008
12:20 pm:
There will be no seminar this week.

Tuesday, March 25th 2008
12:20 pm:
Speaker: Xiang Leng, University of Minnesota
Subject: Interfacial Effect in Oxides

Tuesday, April 1st 2008
12:20 pm:
Speaker: Feng Guo, University of Minnesota
Subject: Low Frequency Noise in Magnetic Tunnel Junctions

Tuesday, April 8th 2008
12:20 pm:
Speaker: Eric Garlid, University of Minnesota
Subject: Bias Dependence of Electrical Spin Injection and Detection in Lateral Fe/GaAs Devices

Tuesday, April 15th 2008
12:20 pm:
Speaker: Yen Hsiang Lin, University of Minnesota
Subject: Tuning the Superconductor-insulator Transition by Magnetic Fields

Thursday, April 24th 2008
1:25 pm:
Speaker: LiDong Pan, University of Minnesota
Subject: Surface induced ordering effect in a smectic liquid crystal compound
Note: Change of date, time and room. This week only.

Tuesday, April 29th 2008
12:20 pm:
Speaker: Tanner Schulz, University of Minnesota
Subject: Examining Hysteresis Loop Criticality Using Co/CoO Thin Films

Tuesday, May 6th 2008
12:20 pm:
Speaker: Prof. M. Greven, Stanford University
Subject: Crystal Growth, Neutron Scattering and Spin Correlations: A Tale of two Complex Oxides

The study of quantum phase transitions in the presence of disorder is at the forefront of research in the field of correlated electron systems, yet there have been relatively few experimental model materials. We have succeeded in the growth of large single crystals of the randomly-diluted spin-1/2 square-lattice Heisenberg antiferromagnet La2(Cu,Zn,Mg)O4 up to high dilution concentrations. Our neutron scattering measurements of the instantaneous antiferromagnetic (AF) spin correlations, complemented by numerical experiments, demonstrate that this compound is an excellent system for the study of site percolation in the quantum spin-1/2 limit [1]. High transition-temperature (Tc) superconductivity develops near AF phases, and it is possible that magnetic excitations contribute to the superconducting (SC) pairing mechanism. In order to assess the role of antiferromagnetism, it is essential to understand the doping and temperature dependence of the two-dimensional AF spin correlations. The phase diagram is asymmetric with respect to electron and hole doping, and for the comparatively less-studied electron-doped materials, the AF phase extends much further with doping and it appears to overlap with the SC phase: the archetypical compound Nd(2-x)CexCuO{4\pm\delta} shows bulk superconductivity above x \approx 0.13 , while evidence for AF order has been found up to x\approx 0.17 . However, our new inelastic magnetic neutron scattering measurements point to the distinct possibility that genuine long-range antiferromagnetism and superconductivity do not co-exist. Our measurements furthermore demonstrate that the pseudogap phenomenon in the electron-doped materials arises from a build-up of spin correlations [2].

[1] O.P. Vajk et al., Science 296, 1691 (2002).
[2] E.M. Motoyama et al., Nature 455, 186 (2007).

Tuesday, May 13th 2008
12:20 pm:
Speaker: Boris Spivak, University of Washington, Seattle
Subject: Theory of disordered d-wave superconductors

We predict that d-wave (or other exotic)superconductors demonstrate (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.

Tuesday, May 20th 2008
12:20 pm:
The seminar has ended for the semester. It will return in September 2008

Tuesday, September 2nd 2008
12:20 pm:
There will be no seminar this week.

Tuesday, September 9th 2008
12:20 pm:
Speaker: Yves Adjallah, University of Minnesota
Subject: Electronic Transport in Co-Deposited Amorphous/Nanocrystalline Films

Tuesday, September 16th 2008
12:20 pm:
Speaker: Te-Yu Chen, University of Minnesota
Subject: Dynamics of exchange biased vortices

Tuesday, September 23rd 2008
12:20 pm:
Speaker: Anthony Hatke, University of Minnesota
Subject: Non-linear transport in microwave-irradiated quantum Hall systems

Tuesday, September 30th 2008
12:20 pm:
Speaker: Feng Guo, University of Minnesota
Subject: Low Frequency Noise in Magnetic Tunnel Junctions Part II

Tuesday, October 7th 2008
12:20 pm:
Speaker: Matthew Parker, University of Minnesota
Subject: Extinction Time in a Predator-Prey Relationship

Tuesday, October 14th 2008
12:20 pm:
Speaker: Xi Chen, University of Minnesota
Subject: Spin-wave mediated interaction between spin torque nano-oscillators

Tuesday, October 21st 2008
12:20 pm:
Speaker: Sun Wang , University of Minnesota
Subject: Recovery of a reversed phase sequence in one liquid crystal ternary mixture system

Tuesday, October 28th 2008
12:20 pm:
Speaker: Yen-Hsiang Lin, University of Minnesota
Subject: Tuning the Superconductor-Insulator Transitions by Perpendicular Magnetic Fields

Tuesday, November 4th 2008
12:20 pm:
Speaker: Alex Levchenko, University of Minnesota
Subject: Coulomb drag in quantum circuits

Tuesday, November 11th 2008
12:20 pm:
Speaker: Mun K. Chan, University of Minnesota
Subject: Nuclear field effects in ferromagnet-semiconductor heterostructures

Tuesday, November 18th 2008
12:20 pm:
Speaker: Li Dong Pan, University of Minnesota
Subject: Phase behavior of Free Standing AFLC Films

Tuesday, November 25th 2008
12:20 pm:
Speaker: Robert O'Connell, University of Minnesota
Subject: Image Enhancement of Superparamagnetic Iron Oxides Using a Novel MRI Technique

Tuesday, December 2nd 2008
12:20 pm:
Speaker: Bryce Beverlin II , University of Minnesota
Subject: Coherent oscillations from real and modeled neurons

Tuesday, December 9th 2008
12:20 pm:
Speaker: Stephen Snyder, University of Minnesota
Subject: Anomalous magnetic field response in Zn nanowires

Tuesday, December 16th 2008
12:20 pm:
There will be no seminar this week.

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