Research
Experience for Undergraduates Program
UC Davis Physics and Astronomy Department
June 16 to August 23, 2024
Research Project Areas:
Project Descriptions
Condensed Matter Experiment
Dr. Chiang's laboratory uses highresolution microscopy to study
the surfaces of metals deposited on both semiconductor and metal
substrates. This work improves our understanding of twodimensional
materials growth and transformation, which are of technological
importance in semiconductor devices, magnetic disks, and heterogeneous
catalysis. Understanding how the surface orders during the processes of
surface reconstruction, adsorption of atoms and molecules, and phase
transformations allows better control of the surface structure and
properties. Dr. Chiang's group has recently measured the unusually
high rate of mass transport of Pb atoms during island formation
at 220283K on Ge(111). An REU
student will work with a graduate student in growing thin films of metals
on semiconductors and imaging their surface changes at the nanometer to
micron scale. The student will learn to operate sophisticated ultrahigh
vacuum surface equipment: either a low energy electron microscope for
realtime measurements at 10 nm lateral resolution of surface dynamical
processes as a function of both temperature and adsorbate coverage, or
a variable temperature scanning tunneling microscope for atomicscale
imaging of nucleation and growth at steps and defects. The student will
also use image processing software to analyze the measurements.
Dr. Curro's group studies the behavior of strongly correlated electron
materials at low temperature using Nuclear Magnetic Resonance (NMR).
There are numerous cases in the natural world where the collective
behavior of a group differs dramatically from that of the individual
particles. A prime example is the flocking of birds, which cannot
be understood by investigating a single bird. These beautiful and
unexpected phenomena are known as emergent behavior, and play a role in
all realms of science, from the behavior of animals and people, to the
quantum mechanical realm of the electron. In some cases electrons in
condensed matter exhibit behavior typical of individual particles, but
they can also do unexpected and surprising things. Superconductivity,
for example, arises because of interactions between electrons that
enables them to enter into a new quantum phase of matter. The group
uses NMR to investigate these new types of quantum behavior of electrons,
in materials such as heavy fermions, iron pnictides, and transition
metal oxides. An REU student can participate in handson or computational
aspects of the work.
The Vishik group uses angleresolved photoemission spectroscopy (ARPES)
and other photoemission techniques, as well as ultrafast optics to learn
about electronic structure and dynamics in quantum materials. Quantum
materials are characterized by emergence, whereby the properties of a
manyelectron system cannot be derived in a reductionist manner from the
properties of one electron. As a result, these materials often yield
experimental surprises, which can be discovered with precision tools
sensitive to electrons such as the ones in this lab. The emergent
phenomena studied include unconventional superconductivity, strong
electronic correlations, topologically protected electronic states, and
exciton condensation. An REU student would study one of the materials
systems currently under investigation (including but not limited to: copper
oxide superconductors, transition metal dichalcogenides, 3D topological
insulators, magnetic Weyl semimetals), and simultaneously learn about
optical systems, ultrahigh vacuum systems, instrumentation programming,
data analysis, cryogenic systems, and data analysis.
Dr. Yu investigates charge transport in lowdimensional
materials using spatially resolved optoelectronic techniques. Irradiating
a spot on the sample with a laser creates charge carriers. They
move depending on sample characteristics and applied fields, and
are detected as currents reaching fixed electrodes on the sample.
By successively focusing the laser on different spots, his group
can determine the lifetime and distance traveled by the excited carriers,
and much more. One possible project for an REU student is to study
hybrid halide perovskites for solar energy harvesting and light emitting
devices. The other one is on topological insulators for spintronics and
quantum computing. The student will have the opportunity of synthesizing
materials, fabricating nanodevices, as well as optoelectronic
measurements.
Below 2 Kelvin, liquid helium becomes superfluid, with unusual
properties from zero viscosity to high thermal conductivity to quantized
vortices. While helium is the only superfluid on Earth, neutrons deep
inside neutron stars also form a superfluid. The behavior of vortices
in the neutron superfluid may explain the observed glitches in neutron
stars' rotation, where the angular momentum abruptly increases. Dr.
Zieve's group has set up an experiment to monitor a vessel of
rotating superfluid helium for similar glitch behavior. If observed,
the conditions for glitches to occur can be tested far more easily in the
lab than by observing distant stars. An REU student will help carry out
lowtemperature measurements, analyze data, and make improvements to
the setup.
Condensed Matter Theory
Dr. Scalettar's group uses classical and quantum Monte Carlo simulations
to study magnetic, metalinsulator, superfluid and superconducting
transitions in condensed matter and in atomic condensates. We have
recently also used these approaches to examine optimizing quantum state
transfer (QST) in arrays of qubits. Projects generally involve studying
a simple model to see if it can capture the qualitative physics of a
particular experimental system. Typically an REU student begins by
learning some of the fundamentals of the Monte Carlo method and
statistical mechanics, or in the case of QST the matrix formulation of
quantum mechanics, before learning about an open question in the field
and writing a research code to address it. (An introductory college
programming class provides sufficient background.) Dr. Scalettar's group
includes postdoctoral researchers, graduate and undergraduate students
with whom the REU student can work.
Work of past REU students can be found here:
 Tyler Cary: Phys. Rev. B85, 134506 (2012).
 Nicole Hartman: Phys. Rev. B93, 235143 (2016).
 Thomas Blommel: Phys. Rev. Lett. 120, 187003 (2018).
 Amelia Broman and Jack Mucciaccio, Phys. Rev. B105, 195429 (2022).
 Claire Kvande, Phys. Rev. B108, 075119 (2023).
Dr. Singh's project involves series expansion methods, such as
hightemperature series expansions or expansions in coupling
constants, which provide controlled ways to
study thermodynamic properties of macroscopic manybody systems. They are
straightforward to calculate and analyze, and useful for understanding
a variety of systems and experimental probes, including magnetic
susceptibility and specific heat of spin models, spinwave spectra
of magnetically ordered phases, critical phenomena near quantum phase
transitions, and quantum entanglement in manybody systems. A summer
project will focus on one of these problems. The student will learn
and apply certain expansion methods. To complete the project within the
REU timeframe, the student should have some prior knowledge of quantum
mechanics and computer programming.
Complex Systems and Computational Physics
Dr. Crutchfield investigates the structures and patterns that emerge in
complex systems. Topics include nonlinear dynamics, thermodynamics of
nanoscale information processing, quantum computation and dynamics,
interacting multiagent systems, distributed robotics, and evolution
(both as optimization, as pursued in computer science, and as a model
of emergent biological organization). A main thrust is programming that
automatically discovers emergent structures and builds filters to identify
similar patterns. An REU student will develop a particular numerical
simulation, track its output as additional complexity is introduced,
and analyze resulting patterns. The student will become familiar with
mathematical concepts from statistical mechanics, dynamical systems,
information theory, and the theory of computation. Only minimal
prior programming background is needed for a successful experience,
but enjoyment of mathematical and computational work is key.
Nuclear Physics Experiment
With the nuclear group's experiments running at Brookhaven's Relativistic
Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) at CERN,
an REU student will mainly do calculations and data analysis. As one
example, the production of hadrons in heavy ion collisions at RHIC
has been parameterized as a function of the number of participating
nucleons and the number of binary collisions. These numbers are useful
when comparing measured quantities as a function of the centrality of the
collision to calculations done for the same centralities. Unfortunately,
neither of the numbers can be measured directly in the experiment.
Instead their values are obtained by comparing the measured distribution
of charge multiplicity to the corresponding distributions obtained
from phenomenological Glauber calculations. Applied to nucleusnucleus
collisions, Glauber theory calculates crosssections from quantitative
considerations of the geometrical configuration of the nuclei. An REU
student will write, compile and validate code for a Glauber calculation.
Ultimately, from a probability distribution for nucleons within the
nucleus (based on the measurements of nuclear matter density) and a
fundamental crosssection for nucleonnucleon collisions, the code will
calculate the numbers of participating nucleons and binary collisions as
a function of impact parameter. Time permitting, the student can apply
phenomenological models to obtain the charge multiplicity and compare
the results to measured distributions.
Experimental Particle Physics
The Crocker Nuclear Laboratory, supervised by Dr. Prebys, is adjacent
to the Physics Building. It houses a cyclotron with proton beams tunable
from 4 MeV to 67.5 MeV. This is a rare energy range for today's machines,
and the machine has several specialized uses, from simulating radiation
effects of outer space to medical treatment via proton therapy. This
leads to numerous unique opportunities for handson experience
for undergraduates, who can participate in all aspects of planning,
simulation, data taking, and analysis. One possible project for a student
working with Dr. Prebys is to measure the energydependent production
cross section for protons on various nuclear targets, which surprisingly
is unknown for many materials. The student will insert thin foils of
the target material in a stack of aluminum plates, which lower the beam
energy to the desired value. After irradiation the student will remove
the foils, assay them with a sensitive photon detector, and identify
the characteristic spectra of the daughter particles of interest.
Theoretical Particle Physics
Hamiltonian truncation is a variational approximation method in
quantum mechanics that involves truncating the space of states to
a finitedimensional vector space. In this approximation, the Hamiltonian
is a finitedimensional matrix that can be diagonalized numerically.
In recent years, this approximation has been applied to study quantum
field theories to perform calculations in stronglycoupled theories
where no perturbative expansion is possible. In this project, the
student will apply these methods to simple quantum field theories in
1+1 spacetime dimensions. Students should have a strong background in
quantum mechanics at the advanced undergraduate level, some exposure
to quantum field theory, and some experience in scientific computation,
preferably using C++.
Precision Measurement
Dr. Aggarwal's research group uses precision quantum measurements to
unravel our mysterious universe via her hunt for gravitational waves
(GW), dark matter, GWs produced by dark matter, and dark matter signatures
in GWdetectors.
One direct search for dark matter is the ARIADNE experiment, where
Dr. Aggarwal and her collaborators look for spindependent forces mediated
by the axion. The axion is a hypothetical particle which if discovered
will not only solve the strong CP problem, but might also be a portion of
dark matter. The experiment searches for a new beyondthestandard model
force mediated by the axion in the form of a fictitious magnetic field, of
the order of 10^21 T, many orders of magnitude smaller than the Earth's
field. This requires an extremely precise magnetometer  nuclear magnetic
resonance on highly polarized He3. Unfortunately the He3 can easily be
depolarized, which destroys the pristine axion signal. Since a main source
of depolarization is magnetic field gradients, we need to characterize
the magnetic fields emanating from the many components of the experiment.
An REU student will characterize the magnetism of the rotation stage
being built for the ARIADNE experiment. This will require building the
testing assembly, taking lownoise magnetometry measurements, analyzing
the data and presenting it in a format useful to the collaboration. This
result would be a part of a future publication and possibly a conference
poster.
Astrophysics
Dr. Jones studies how galaxies form in the early universe and evolve over
time, using the world's most sensitive telescopes. His group studies
gravitationally lensed galaxies which appear larger and brighter on the
sky thanks to strong magnification, allowing resolution of their spatial
structure even at great distances. From spectroscopic observations
they address several topics including the formation of the first galaxy
disks, the cycle of gas into and out of galaxies, and the distribution
of heavy elements. An REU student will work on one of these aspects
using data collected from Keck Observatory or the James Webb Space
Telescope. Familiarity with computer
programming and some knowledge of statistics, including curve fitting,
is desirable.
Dr. Wetzel's group uses the nation's most powerful supercomputers to
simulate the formation of galaxies, including the physics of dark matter,
gas hydrodynamics, star formation, and stellar evolution. They use these
simulations to model the formation of our own Milky Way galaxy. An REU
student will work on a project to model the formation and dynamical
evolution of stars in simulations of Milky Waylike galaxies and compare
with observations of the Milky Way and similar galaxies today. The
student ideally should have some familiarity with Python, including data
visualization with Matplotlib and array manipulation with NumPy and SciPy.
