Physics and Astronomy Calendar

Week of Monday, September 17th 2018

Monday, September 17th 2018
12:15 pm:
Speaker: Matt Fritts, University of Minnesota
Subject: Detector R&D for SuperCDMS

SuperCDMS is a direct-detection dark matter search employing cryogenic semiconductor detectors. One focus for SuperCDMS is low-mass WIMPs that would deposit very low energies in a detector; thus the detectors are designed for low energy thresholds and high energy resolution. Recent R&D efforts have taken resolution to the limit of single electron-hole pairs produced by ionizing events. WIMP searches with low-threshold detectors depend on the ionization yield for nuclear-recoil events, which is not well known at such low energies. One attempt to measure this is based on neutron capture. If WIMPs turn out to have high masses, then high exposures become important, and larger detectors will be needed. Recently 150mm-diameter CDMS-style detectors have been made and tested. I will report on our R&D efforts in each of these areas.

Faculty Host: Vuk Mandic

Tuesday, September 18th 2018
11:15 am:
Nuclear Physics Seminar in Tate 301-20
There will be no seminar this week.
1:25 pm:
Space Physics Seminar in Tate 301-20
Speaker: Benjamin Frigo Vaz , Bionanotechnology Lab, UMn
Subject: Orbital Mirrors for Terraforming Mars
4:00 pm:

Wednesday, September 19th 2018
1:25 pm:
Speaker: Ali Yazdani, Princeton University
Subject: Visualizing quantum Hall liquids and their boundary modes

In a series of experiment on 2D electron gas at the surface of Bi, we have been able to probe a number of novel features of quantum Hall liquids for the first time. First, we have been able to use the scanning tunneling microscope (STM) to directly visualize Landau orbits in real space. This new technique has been used to show that the electronic states associated with the valley state on the surface of Bi form nematic quantum Hall liquids. [1] By tuning the magnetic field, we have been able to stabilize different type nematic fluids, and have been able uncover a ferroelectric quantum Hall liquid that forms when only one of the valley get occupied.[2] We are able to demonstrate that the formation of these quantum Hall phases are driven by electron-electron interaction. Finally, in the most recent experiment, we have been able to uncover domain walls between different nematic quantum Hall states and to direct image the 1D Luttinger liquids that form at such interfaces. This new type of Luttinger liquids can become metallic or insulating depending on the number of valley-textured edge modes.[3]

[1] B. Feldman et al. Science 354 6310 (2016).
[2] Randeria et al. Nature Physics, 14 1709 (2018)
[3] Randeria et al. in preparation. (2018)

Faculty Host: Andrey Chubukov
Organizational Meeting
4:40 pm:
CM Journal Club in PAN 110
Subject: No journal club this week

We will meet on September 26th. Then the plan would be a regular meeting every other week.

Thursday, September 20th 2018
10:10 am:
Biophysics Seminar in 110 PAN
Speaker:  Prakash Kara, Professor in the Department of Neuroscience, University of Minnesota
Subject: Determining the precision of networks in the living brain with multi-photon microscopy
Speaker: Trevor Knuth & Liliya Williams
Subject: To be announced
3:35 pm:
Speaker: Ali Yazdani, Princeton University
Subject: Spotting the elusive Majorana under the microscope
Refreshments in atrium after the Colloquium.

Ettore Majorana famously considered that there may be fermions in nature that are their own antiparticle — and then he mysteriously disappeared just after proposing the idea in 1938. In recent years, we have learned how to engineer materials that harbor quasiparticles that behave similar to fermions Majorana had envisioned. In particular, there has been a focus on one-dimensional topological superconductor that harbor Majorana zero modes (MZM) that can potentially be used to make fault-tolerant topological quantum computation possible. Recently, we have proposed and implemented a platform for realization of topological superconductivity and MZM in chains of magnetic atoms on the surface of a superconductor [1,2]. In this talk, I will describe this platform and the series of experiments we have performed to establish the presence of these exotic quasi-particle using spectroscopic mapping with the STM. [2-4] These include a recent study of the unique spin signature of MZM.[4] Finally, if there is time I will describe some ongoing experiment on realization of MZM in a platform based on chiral quantum spin Hall edge states.

[1] S. Nadj-Perge et al. PRB 88, 020407 (2013).
[2] S. Nadj-Perge et al. Science 346, 6209 (2014).
[3] B. E. Feldman et al. Nature Physics 13, 286 (2016).
[4] S. Jeon et al. Science 358, 772 (2017).

Friday, September 21st 2018
12:20 pm:
Speaker: Scott Dossa
Subject: Simulating Crystal Growth in an Optical Floating Zone Furnace
No seminar this week.

Vainshteinfest: Insights info Quantum Field Theory

1:00 - 1:45 pm
"Monopoles versus the instanton-dyons"
Edward Shuryak
State University of New York, Stony Brook

1:45 - 2:30 pm
"Generalized state sums and quantum distillations"
Mithat Ünsal
North Carolina State University

2:30 - 3:00 pm
Coffee break

3:00 - 3:45 pm
"Comments on the Theta term in Yang-Mills theory"
Zohar Komargodski
Weizmann Institute of Science

3:45 - 4:30 pm
"The Arkady mechanism"
Cédric Deffayet
Institut d'astrophysique de Paris

"Monopoles versus the instanton-dyons"
Edward Shuryak
State University of New York, Stony Brook

Abstract: Magnetic monopoles explained confinement and flux tubes, unusual kinetics of quark-gluon plasma, and, recently, even observed properties of jet quenching. But in QCD-like theories there is no classical solutions of this kind. Instantons and their constituents, the instant-dyons, lead to systematic semiclassical theory, which recently explained deconfinement and Chiral phase transitions in a variety of settings. The talk will briefly review that, and focus on the nature of the so called Poisson duality, confirming that these two languages are dual to each other, and lead to the same partition function. At the end we show what does it tell us about QCD monopoles.

"Generalized state sums and quantum distillations"
Mithat Ünsal
North Carolina State University

Abstract: I describe a generalization of the notion of partition function in general quantum field theories. The thermal partition function is a state sum over the Hilbert space, which typically has non-analyticities, and can be used to study phase transitions, and thermodynamics. I will describe graded states sums which may be controllably tuned to be analytic. As such, they can be used to interpolate between weak and strong coupling regime of QFTs. I will show that this notion is useful to understand general non-perturbative aspects of quantum field theory, providing examples from 2d QFTs, and 4d QCD.

"Comments on the Theta term in Yang-Mills theory"
Zohar Komargodski
Weizmann Institute of Science

"The Arkady mechanism"
Cédric Deffayet
Institut d'astrophysique de Paris

Abstract: I will review the "Vainshtein mechanism", first formulated in
the context of massive gravity by Arkady in 1972 and now routinely used in
various theories beyond General Relativity.

Party for Terry Thibeault, no colloquium.
Speaker: Sarah Robins , Department of Philosophy - University of Kansas
Subject: The Neurophilosophy of Memory: Reconciling Stable Engrams and Neural Dynamics
Refreshments served at 3:15 p.m.
4:40 pm:
Speaker: Martin Greven, Condensed Matter
Subject: New developments and opportunities in quantum materials research
8:00 pm:
Observing Night in 510-02 Tate
Rooftop observing through our historic telescope in the dome of the John T. Tate Hall. Presentation followed by outdoor observing (weather-permitting).

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