[Theory-seminars] Reminder: Physics Colloquium today Monday, February 11

[Mary Fox]

________________________________
From: Wilkinson, Ellie V <evwilk at wm.edu>
Sent: Monday, February 11, 2019 9:13 AM
To: physics2017 at physics.wm.edu
Cc: undergrads2017 at physics.wm.edu
Subject: Reminder: Physics Colloquium today Monday, February 11


Monday, February 11, 2019

4:00 PM

Small Hall, Room 111



Xiaoqian Chen [Host E. Rossi]

Material Sciences Division, Lawrence Berkeley National Laboratory

Title of Talk:  “Charge Density Wave Memory in a Cuprate Superconductor La2-xBaxCuO4”

Abstract:
Charge density wave (CDW) order is known to coexist with superconductivity in essentially all underdoped cuprates. Yet, its precise nature and the relationship with superconductivity is still unclear. Specifically, whether the CDW is static or fluctuating is a long-standing question whose answer will provide deep insight into whether the CDW order competes or cooperates with superconductivity.

In the first part of my talk, I will show how performing diffraction with coherent x-rays can be a test for dynamics. Coherent x-ray scattering from electronic and magnetic orders result in complex interference (speckle) patterns. These speckle patterns are dependent on the detailed order parameter configuration and therefore provide insight into their structure, motion, and dynamics. By correlating speckle positions over time, we showed that the CDW domains in underdoped cuprate La2-xBaxCuO4 (LBCO) are surprisingly static, with no evidence of significant fluctuation well into the superconducting state.



Is the static nature of CDW order in LBCO universal for all underdoped cuprates? Motivated by this question, I will discuss in the second part of my talk, the CDW pinning mechanism in LBCO. By tracking the history of CDW speckle patterns upon thermal cycling, we have found an unexpected pinning mechanism where memory is only lost on cycling across the structural transition at 240(3) K that restores the 4-fold symmetry of the copper-oxide planes instead of the CDW ordering temperature at 54K.



Finally, I would like to end my talk by diving into the exciting world of coherent x-ray physics and discuss its capability for current and future research

________________________________

Friday, February 15, 2019

4:00 PM

Small Hall, Room 111



Chia Cheng Chang [Host J. Dudek]

Lawrence Berkeley National Laboratory

Title of Talk:  “Predicting the neutron lifetime from the Standard Model”

Abstract:
>From quarks and gluons, the emergence of nucleons and their properties can be predicted from the modern theory of the strong interaction, quantum chromodynamics. Precise predictions from the Standard Model in tandem with observations from experiments provides a window for revealing new physics beyond. One such example is the neutron lifetime, where tension at 4 standard deviations is measured between independent experiments. With the maturation of lattice quantum chromodynamics over the past decades, I will present our published result of $g_A$, which governs the neutron lifetime, to one percent precision commensurate with measurements from experiment. With the arrival of near-exascale computing made available by the largest supercomputers in the world, I will show improvements to $g_A$ which are approaching enough precision to start revealing possible hints of physics beyond the Standard Model. I will conclude by discussing future calculations with promising potential towards predicting the radius of the proton, and other observables that may help us understand the origin of matter.

Cookies & Coffee will be served in Small 122 at 3:30pm

Cheers,



Ellie Wilkinson

The College of William & Mary

Physics Admin/REU Coordinator

evwilk at wm.edu<mailto:evwilk at wm.edu>

757-221-3503








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