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Thursday,
05 June 2025 |
Video-Recording for any system with MP4-support - Video.mp4 (ca. 632 Mb) |
15:15 – 16:50 |
"Hidden
Order in Amorphous Materials: from gravitational wave detectors
to topological materials"
Speaker: Prof. Frances Hellman
(Physics Dept at UC Berkeley)
Abstract:
Amorphous (glassy) materials lack
structural order, making them difficult to
describe
or to calculate their properties compared to crystalline materials which
consist
of spatially repeated atoms. This
difficulty, however, does not preclude
their
applicability or scientific impact.
Various properties, including topological
electronic
states, seem to rely on the periodicity of the lattice for their derivation,
yet are found in amorphous
materials; recent advances have enabled explanation.
Intriguingly, there exists the notion of
an "ideal glass", which while remaining
thoroughly
disordered, lacks imperfections in that disorder and thus approaches
the uniqueness of a crystal,
including low entropy. LIGO (laser interferometric
gravitational
observatory) relies on amorphous coatings for their mirrors;
mechanical
losses in these coatings are the limiting noise factor and are associated
with universal yet poorly
understand atomic motions associated with defects
in the amorphous
structure. Amorphous silicon (a-Si) is
the single material where
these
losses can be tuned over several decades, from below detectable limits to high
in the range commonly seen in
glassy systems, in a way seemingly connected with
creating
a near-ideal glass. I will discuss the underlying phenomena of these results,
which
lie in a hidden order.
About the Speaker:
Frances Hellman received her BA in Physics
from Dartmouth College in 1978, and
her PhD in Applied Physics from
Stanford University in 1985. After a 2 year postdoc
in thin film magnetism at
AT&T Bell Labs, she went to UCSD as an assistant
professor
in 1987, where she received tenure in 1994 and became a full professor
in 2000. She joined the
Physics Dept at UC Berkeley in Jan 2005, and served as
Chair of the Department from 2007 to 2013.
She als has an appointment
in the UCB
Materials Science and Engineering Dept. as
well as at LBNL in the Materials
Sciences Division.
She has been on a large number of national and local science boards,
including
the NSF Advisory Board on Math and Physical Sciences, the NRC Board
on Physics and Astronomy, the
NRC Solid State Sciences Committee, the DOE Division
of Materials Science and
Engineering Council, ICAM (Institute for Complex Adaptive
Matter), the APS Committee on the Status
of Women in Physics, the APS Panel on
Public Policy, the editorial board for the
Review of Scientific Instruments, the
Elementary Institute of Science (in San
Diego), COSMOS, a statewide math and science
summer
program for high school students, and the SF Exploratorium. She won the
APS Keithley
Award in 2006, "In recognition of using emerging micromachining
techniques
to significantly extend the range of calorimetry into
the realm of nanoscale
science
by construction of Si based microcalorimeters capable
of operating in extreme
environments
with unprecedented sensitivity and accuracy", is a Fellow of the APS,
and has been Chair of both the
APS Division of Materials Physics and the APS Topical
Group on Magnetism and its Applications.