Physics and Astronomy Calendar

Week of Monday, September 18th 2017

Monday, September 18th 2017
12:15 pm:
12:30 pm:
National Postdoc Association Townhall in Mayo Memorial Auditorium, Room 3-100

We will be reviewing what we have done over the past year, including: explaining changes to the FLSA and its status under the new administration, advocating for postdoctoral rights with the White House, travelling to DC, changing our position in the University Senate, changing mentoring at the U, trying to create a career office, advocating with the National Postdoc Association, and more.

Food to be provided

More information about this event can be found on the PDA Website.

Tuesday, September 19th 2017
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.
2:00 pm:
National Postdoc Association Seminar in Weaver-Densford Hall W2-110
Speaker: Noro Andriamanalina
Subject: My IDP

A seminar reviewing an efficient process at creating the professional agreement that guarantees a successful postdoctoral appointment and improving the relationship between you and your mentor.

More information about this event can be found on the PDA Website.

4:30 pm:
There will be no seminar this week.

Wednesday, September 20th 2017
1:25 pm:
Speaker: Natalia Drichko, Johns Hopkins University
Subject: From spin liquid candidate to dipole liquid in quasi-two dimensional organic Mott insulators: a Raman scattering study.

One of the simplest models representing lattice frustration in magnetic materials is the triangular lattice Heisenberg antiferromagnet. It was shown theoretically that it orders into 120 degree order. However, a large number of spin liquid candidates on triangular lattice are found among quasi-two-dimensional molecular- based Mott insulators. One explanation is that new charge degrees of freedom that can emerge in molecular-based Mott insulators resulting in a quantum dipole liquid state. Studies of the materials has been hampered by a lack of spectroscopic information, since neutron scattering has generally not been possible.

We use Raman scattering to detect spectrum of magnetic excitations in these magnetic compounds. At first I will demonstrate a Raman scattering study of the helical antiferromagnet α -SrCr2O4 (T_N=42K). Further, we identify magnetic excitations in an antiferromagnetic compound k-(BEDT-TTF)2Cu[N(CN)2]Cl and a spin liquid candidate k-(BEDT-TTF)2Cu2(CN)3. We show that their spectrum of excitations is very different from that of another triangular lattice Mott insulator k-(BEDT-TTF)2Hg(SCN)2Br. Our data demonstrate the emergence of an on-site dipole degree of freedom in the latter material. Raman scattering allows us to detect dipole fluctuations both with vibrational molecular spectroscopy and through observation of a collective mode at about 8 meV. Heat capacity of k-(BEDT-TTF)2Hg(SCN)2Br demonstrates a linear term at low temperatures, supporting a scenario where composite spin and electric dipole degrees of freedom remain fluctuating down to the lowest temperatures.

Faculty Host: Natalia Perkins
3:00 pm:

An ice cream social for postdocs on campus! Show up, have some free ice cream, play games, talk to your fellow coworkers, and have a chance to relax on campus!

More information about this event can be found on the PDA Website.

Speaker: D. Cronin-Hennessy, University of Minnesota
Subject: Paper reading: "Mechanical Detection and Measurement of the Angular Momentum of Light" by Richard A. Beth
4:30 pm:
CM Journal Club in PAN 120
Speaker: No CM Journal Club

Thursday, September 21st 2017
10:10 am:
Speaker: Prof. Bo Huang UCSF, Pharmaceutical Chemistry
Subject: Watching in the inner life of a cell: beyond super-resolution microscopy
Note room change, this week only.
Speaker: Evan Tyler and Pat Kelly
3:35 pm:
Speaker: Yan Song, University of Minnesota
Subject: Formation of Alfvenic Electromagnetic Plasma Structures and Auroral Particle Acceleration: -- Exploring Theory of High Energy Plasma Physics

The acceleration of charged particles to high energy and the associated emission of electromagnetic (EM) radiation produced by the accelerated electrons and ions, occur throughout space and cosmic plasmas. During these processes, a large part of stored free magnetic energy can rapidly and efficiently convert into the kinetic energy of charged particles producing non-thermal high energy particles and EM radiation. To find the mechanism of such high energy particle acceleration is one of the most important unsolved problems in space and cosmic plasmas.

In general, applying parallel electrostatic electric fields associated with charge separation is the simplest and powerful method to directly accelerate particles to high energy. However, once the electric fields are produced, they will quickly short themselves out by the motion of free charges. Thus, a central question in auroral physics is to find the mechanism by which long-lasting parallel electrostatic electric fields can be generated.

I will present the theory of the generation of parallel electrostatic electric fields (Song and Lysak, 2001, 2006), and point out that the generation of parallel electric fields is favored by a low plasma density and high magnetic shear. In the auroral current system, nonlinear Alfvenic interactions between Alfven wave packets can produce EM plasma structures, such as Alfvenic Double Layers. The Alfvenic Double Layer consists of localized long-lasting electrostatic electric fields, which are embedded in low density cavities and surrounded by enhanced magnetic stresses. These structures are dynamical in nature, where the Poynting flux carried by Alfven waves continuously supplies energy to the Alfvenic Double Layers to maintain strong electrostatic electric fields for a fairly long time. These structures become a new fundamental dynamical state in cosmic plasmas, which constitute powerful high energy particle accelerators.

It has been broadly considered that the magnetic reconnection is a fundamental physical process which is responsible for almost all high energy plasma processes in space and cosmic plasmas. Magnetic reconnection is described as a process occurring when oppositely directed magnetic field lines in a plasma are cut and rejoined. I will show that the crucial components of magnetic reconnection lack support from fundamental physical theory, and suggest that we should use the fundamental physical laws and principles to study “reconnection” related processes.

Friday, September 22nd 2017
10:10 am:
Nuclear Physics Seminar in Tate 301-20
There will be no seminar this week.

The postdoc research symposium is a poster session where postdocs will have the chance to interact with judges and representatives from local industry. There will be awards both from the PDA and local companies and the awards ceremony will feature various speakers

You can register posters for the poster session here, there is no fee, there is a limit to the number of poster spots available.

If you have questions, please direct them to We hope you'll take advantage of this opportunity to build a stronger postdoc community at the U.

Limited poster printing is available. Contact with questions.

More information about this event can be found on the PDA Website.

12:20 pm:
Speaker: Daniel Shaffer, University of Minnesota
Subject: Properties of the Superconducting Gap in NbSe_2 Monolayers in Presence of in-Plane Magnetic Field.

NbSe_2 monolayers have been observed to superconduct in presence of relatively large (~35T) in-plane magnetic fields (as compared to the naïve Pauli limit estimate), an effect attributed to large out-of-plane spin orbit coupling (referred to in the literature as Ising SOC) in the niobium atom that pins electron spins perpendicular to the NbSe_2 plane. This lead some theorists to speculate about the effect of such magnetic fields on the nature of the superconducting gap function, which due to the SOC may be topologically non-trivial. In particular, it has been suggested that for fields above the Pauli limit, NbSe_2 becomes a nodal topological superconductor. In order to investigate this claim, I perform an RG analysis (without SOC) and solve the linearized gap equation using a simplified single band model that incorporates SOC. It turns out that while there exists a self-consistent solution to the gap equation in which an in-plane magnetic field induces a phase transition from a fully gapped phase to a nodal one, such a solution is neither favored by RG nor likely to occur in a real system due to in-plane (Rashba) SOC caused by ripples in the monolayer, which leads instead to a topologically trivial gap.

Speaker: Marilena Loverde (Stonybrook U.)
Subject: Neutrinos, Quintessence, and Structure Formation in the Universe

The large-scale structure of our universe (the distribution of galaxies on very large-scales for instance) contains a wealth of information about the origin, evolution, and matter content of the universe. Extracting this information relies crucially on understanding how galaxies and other biased objects trace the large-scale matter distribution. In a universe such as our own, with both cold dark matter and massive neutrinos, or in alternative cosmologies with clustered quintessence, this problem is much more complicated. I will discuss new tools that my group has developed to study gravitational evolution in cosmologies with multiple fluids, the novel signatures we have identified including a new probe of neutrino mass, and the broader implications for models of large-scale structure.

There will be no colloquium this week.
Speaker: Alison Gopnik, Department of Psychology, University of California - Berkeley
Subject: When Children are Better Learners than Adults: Theory Formation, Causal Models, and the Evolution of Learning
Refreshments served at 3:15 p.m.

In the past 15 years, we have discovered that even young children are adept at inferring causal relationships and that they do so in much the same way as scientists, using causal models and inductive inference to construct intuitive theories of the world. But are there differences in the ways that younger children, older children and adults learn? And do socioeconomic status and culture make a difference? I will present several studies showing a surprising pattern. Not only can preschoolers learn abstract higher-order principles from data, but younger learners are actually better at inferring unusual or unlikely principles than older learners and adults. This pattern also holds for children in Peru and in Headstart programs in Oakland, California. I relate this pattern to computational ideas about search and sampling, to evolutionary ideas about human life history, and to neuroscience findings about the negative effects of frontal control on wide exploration. My hypothesis is that our distinctively long, protected human childhood allows an early period of broad hypothesis search, exploration and creativity, before the demands of goal-directed action set in.

4:40 pm:
Speaker: Martin Greven, University of Minnesota
Subject: Doped Mott insulators and unconventional superconductors: exciting experimental research opportunities

Saturday, September 23rd 2017
08:30 am:
An International Conference Honoring Mitchell Luskin on the Occasion of his 65th Birthday

Summary: Multiscale modeling, theory, and computation have made fundamental contributions to many areas of physical, chemical, and biological sciences. Recent theoretical and experimental advances present new challenges for multiscale theory and computation. This conference will seek to stimulate new approaches and collaborations by bringing together both senior and junior researchers with expertise spanning molecular to continuum scales and stochastic to deterministic methods.

Some examples of talks of possible interest to Physics on the schedule:
Epitaxially Strained Elastic Films: Quantum Dots and Dislocations
The Problem of Small Temperatures in a Quantum Gas
Multiscale Dynamical Systems
Wandering in Flatland: the Wonders of 2D Materials
"Metastability: a Journey from Stochastic Processes to Semiclassical Analysis
Spin-Diffusions and Diffusive Molecular Dynamics

Register here

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