Research
Experience for Undergraduates Program
UC Davis Physics and Astronomy Department
June 12 to August 20, 2022
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.
Dr. Taufour's group designs, grows, and studies new materials with bizarre
ground states. These are often strongly correlated electron materials in
which the interactions of many electrons give rise to unusual phenomena,
sometimes with the potential for practical applications. These physical
properties can be explored and controlled with low temperatures, high
magnetic fields, and high pressures. An REU student will take part in the
Taufour group's ongoing research efforts and learn how to grow single
crystals of novel intermetallic compounds. The student will collaborate
with other research groups at UC Davis to further characterize and
understand the physical properties of the new crystals.
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 is setting 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 work on one
or more of the mechanical assembly, electronics, and programming required.
Condensed Matter Theory
Dr. Scalettar's group uses Quantum Monte Carlo simulations to study
magnetic, metalinsulator, superfluid and superconducting transitions in
condensed matter and in atomic condensates. 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 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:
 Helen Craig: Phys. Rev. B76, 125103 (2007).
 Miriam Huntley: Phys. Rev. Lett. 100, 116405 (2008).
 Brianna Dillon: Phys. Rev. B82, 184412 (2010).
 Tyler Cary: Phys. Rev. B85, 134506 (2012).
 Nicole Hartman: Phys. Rev. B93, 235143 (2016).
 Thomas Blommel: Phys. Rev. Lett. 120, 187003 (2018).
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.
Experimental Particle Physics
Hamiltonian truncation is an approximation in quantum mechanics that
involves truncating the space of states to a finitedimensional vector
space and numerically diagonalizing the Hamiltonian, which becomes a
finitedimensional matrix. This approximation scheme goes back to the
early days of quantum mechanics, where it is known as the RayleighRitz
variational method. In recent years, this approximation has been applied
to study quantum field theories where weak coupling expansions fail. In
this project, the student will begin by using Hamiltonian truncation
to numerically analyze simple quantum mechanical models defined using
constraints. These are relevant for the application of Hamiltonian
truncation to gauge theories. Depending on the background knowledge of
the student and progress made, the project can move on to analyzing simple
quantum field theories in 2 spacetime dimensions. Students should have a
solid background in quantum mechanics and some experience in scientific
computation, preferably using Python. Some exposure to quantum field
theory is useful, but is not an absolute requirement.
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. Familiarity with computer
programming and some knowledge of statistics, including curve fitting,
is strongly preferred.
Understanding the constraints on cosmological models from cosmological
data, such as temperature and polarization power spectra of the cosmic
microwave background, often requires computations that require tens
to hundreds of cpus working for hours to tens of hours. The bulk of
this time is spent solving the coupled EinsteinBoltzmann equations to
produce model spectra at tens of thousands of locations in the parameter
space. A student will use convolutional neural nets to train an emulator
to produce such spectra and then apply it to estimating constraints on
cosmological model parameters from data from sky surveys made with the
South Pole Telescope equipped with its thirdgeneration camera (SPT3G),
as well as other publicly available data. The expected great reduction
in computer resources required will allow for rapid testing of impacts
of various sources of systematic error on our constraints on cosmological
parameters and model spaces.
Dr. Richter uses highresolution, infrared spectroscopy to study
molecules, particularly in star and planet forming regions. The molecules
can be diagnostics of temperature, gas motions, and chemical processes.
His work involves analyzing observations from current instruments at
observatories such as SOFIA and the GeminiNorth 8m, and developing future
instruments for the 30m telescope and a possible space mission using an
immersion grating. Generally, an REU student might reduce existing data,
develop analysis tools, or investigate potential future observations, such
as simulating observations of an extrasolar planet atmosphere. A student
interested in building instruments could work on preliminary designs.
Familiarity with computers and programming languages is a must.
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 and
its lowmass satellite galaxies. An REU student will work on a project
to model the orbital and starformation histories of these satellite
galaxies, to explore how they can help us understand the early Universe
during the epoch of reionization. Familiarity with Python, including
data visualization with Matplotlib and array manipulation with NumPy
and SciPy, is strongly preferred.
