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Description
Spin-orbit interactions are important in determining nuclear structure. They lead to a shift in the energy levels in the nuclear shell model, which could explain the sequence of magic numbers in nuclei. Also in nucleon-nucleon scattering, the large nucleon polarization observed perpendicular to the plane of scattering needs to be

Spin-orbit interactions are important in determining nuclear structure. They lead to a shift in the energy levels in the nuclear shell model, which could explain the sequence of magic numbers in nuclei. Also in nucleon-nucleon scattering, the large nucleon polarization observed perpendicular to the plane of scattering needs to be explained by adding the spin-orbit interactions in the potential. Their effects change the equation of state and other properties of nuclear matter. Therefore, the simulation of spin-orbit interactions is necessary in nuclear matter.

The auxiliary field diffusion Monte Carlo is an effective and accurate method for calculating the ground state and low-lying exited states in nuclei and nuclear matter. It has successfully employed the Argonne v6' two-body potential to calculate the equation of state in nuclear matter, and has been applied to light nuclei with reasonable agreement with experimental results. However, the spin-orbit interactions were not included in the previous simulations, because the isospin-dependent spin-orbit potential is difficult in the quantum Monte Carlo method. This work develops a new method using extra auxiliary fields to break up the interactions between nucleons, so that the spin-orbit interaction with isospin can be included in the Hamiltonian, and ground-state energy and other properties can be obtained.
ContributorsZhang, Jie (Author) / Schmidt, Kevin E (Thesis advisor) / Alarcon, Ricardo (Committee member) / Lebed, Richard (Committee member) / Shumway, John (Committee member) / Arizona State University (Publisher)
Created2014
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Description
A theoretical study of a three-dimensional (3D) N/S interface with arbitrary spin

polarization and interface geometry is presented. The 3D model gives the same intrinsic

spin polarization and superconducting gap dependence as the 1D model. This

demonstrates that the 1D model can be use to t 3D data.

Using this model, a Heusler alloy

A theoretical study of a three-dimensional (3D) N/S interface with arbitrary spin

polarization and interface geometry is presented. The 3D model gives the same intrinsic

spin polarization and superconducting gap dependence as the 1D model. This

demonstrates that the 1D model can be use to t 3D data.

Using this model, a Heusler alloy is investigated. Andreev reflection measurements

show that the spin polarization is 80% in samples sputtered on unheated MgO(100)

substrates and annealed at high temperatures. However, the spin polarization is

considerably smaller in samples deposited on heated substrates.

Ferromagnetic FexSi􀀀x alloys have been proposed as potential spin injectors into

silicon with a substantial spin polarization. Andreev Reflection Spectroscopy (ARS) is

utilized to determine the spin polarization of both amorphous and crystalline Fe65Si35

alloys. The amorphous phase has a significantly higher spin polarization than that of

the crystalline phase.

In this thesis, (1111) Fe SmO0:82F0:18FeAs and Pb superconductors are used to

measure the spin polarization of a highly spin-polarized material, La0:67Sr0:33MnO3.

Both materials yield the same intrinsic spin polarization, therefore, Fe-superconductors

can be used in ARS. Based on the behavior of the differential conductance for highly

spin polarized LSMO and small polarization of Au, it can be concluded that the Fe-Sc

is not a triplet superconductor.

Zero bias anomaly (ZBA), in point contact Andreev reflection (PCAR), has been

utilized as a characteristic feature to reveal many novel physics. Complexities at a

normal metal/superconducting interface often cause nonessential ZBA-like features,

which may be mistaken as ZBA. In this work, it is shown that an extrinsic ZBA,

which is due to the contact resistance, cannot be suppressed by a highly spin-polarized

current while a nonessential ZBA cannot be affected the contact resistance.

Finally, Cu/Cu multilayer GMR structures were fabricated and the GMR% measured

at 300 K and 4.5 K gave responses of 63% and 115% respectively. Not only

do the GMR structures have a large enhancement of resistance, but by applying an

external magnetic eld it is shown that, unlike most materials, the spin polarization

can be tuned to values of 0.386 to 0.415 from H = 0 kOe to H = 15 kOe.
ContributorsGifford, Jessica Anna (Author) / Chen, Tingyong (Thesis advisor) / Bennett, Peter (Committee member) / Nemanich, Robert (Committee member) / Tsen, Kong-Thon (Committee member) / Arizona State University (Publisher)
Created2015
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Description
In this dissertation two kinds of strongly interacting fermionic systems were studied: cold atomic gases and nucleon systems. In the first part I report T=0 diffusion Monte Carlo results for the ground-state and vortex excitation of unpolarized spin-1/2 fermions in a two-dimensional disk. I investigate how vortex core structure properties

In this dissertation two kinds of strongly interacting fermionic systems were studied: cold atomic gases and nucleon systems. In the first part I report T=0 diffusion Monte Carlo results for the ground-state and vortex excitation of unpolarized spin-1/2 fermions in a two-dimensional disk. I investigate how vortex core structure properties behave over the BEC-BCS crossover. The vortex excitation energy, density profiles, and vortex core properties related to the current are calculated. A density suppression at the vortex core on the BCS side of the crossover and a depleted core on the BEC limit is found. Size-effect dependencies in the disk geometry were carefully studied. In the second part of this dissertation I turn my attention to a very interesting problem in nuclear physics. In most simulations of nonrelativistic nuclear systems, the wave functions are found by solving the many-body Schrödinger equations, and they describe the quantum-mechanical amplitudes of the nucleonic degrees of freedom. In those simulations the pionic contributions are encoded in nuclear potentials and electroweak currents, and they determine the low-momentum behavior. By contrast, in this work I present a novel quantum Monte Carlo formalism in which both relativistic pions and nonrelativistic nucleons are explicitly included in the quantum-mechanical states of the system. I report the renormalization of the nucleon mass as a function of the momentum cutoff, an Euclidean time density correlation function that deals with the short-time nucleon diffusion, and the pion cloud density and momentum distributions. In the two nucleon sector the interaction of two static nucleons at large distances reduces to the one-pion exchange potential, and I fit the low-energy constants of the contact interactions to reproduce the binding energy of the deuteron and two neutrons in finite volumes. I conclude by showing that the method can be readily applied to light-nuclei.
ContributorsMadeira, Lucas (Author) / Schmidt, Kevin E (Thesis advisor) / Alarcon, Ricardo (Committee member) / Beckstein, Oliver (Committee member) / Erten, Onur (Committee member) / Arizona State University (Publisher)
Created2018
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Description
This work presents analysis and results for the NPDGamma experiment, measuring

the spin-correlated photon directional asymmetry in the $\vec{n}p\rightarrow

d\gamma$ radiative capture of polarized, cold neutrons on a parahydrogen

target. The parity-violating (PV) component of this asymmetry

$A_{\gamma,PV}$ is unambiguously related to the $\Delta I = 1$ component of

the hadronic weak interaction

This work presents analysis and results for the NPDGamma experiment, measuring

the spin-correlated photon directional asymmetry in the $\vec{n}p\rightarrow

d\gamma$ radiative capture of polarized, cold neutrons on a parahydrogen

target. The parity-violating (PV) component of this asymmetry

$A_{\gamma,PV}$ is unambiguously related to the $\Delta I = 1$ component of

the hadronic weak interaction due to pion exchange. Measurements in the second

phase of NPDGamma were taken at the Oak Ridge National Laboratory (ORNL)

Spallation Neutron Source (SNS) from late 2012 to early 2014, and then again in

the first half of 2016 for an unprecedented level of statistics in order to

obtain a measurement that is precise with respect to theoretical predictions of

$A_{\gamma,PV}=O(10^{-8})$. Theoretical and experimental background,

description of the experimental apparatus, analysis methods, and results for

the high-statistics measurements are given.
ContributorsBlyth, David (Author) / Alarcon, Ricardo O (Thesis advisor) / Ritchie, Barry G. (Committee member) / Comfort, Joseph R. (Committee member) / Schmidt, Kevin E (Committee member) / Arizona State University (Publisher)
Created2017
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Description
I describe the first continuous space nuclear path integral quantum Monte Carlo method, and calculate the ground state properties of light nuclei including Deuteron, Triton, Helium-3 and Helium-4, using both local chiral interaction up to next-to-next-to-leading-order and the Argonne $v_6'$ interaction. Compared with diffusion based quantum Monte Carlo methods such

I describe the first continuous space nuclear path integral quantum Monte Carlo method, and calculate the ground state properties of light nuclei including Deuteron, Triton, Helium-3 and Helium-4, using both local chiral interaction up to next-to-next-to-leading-order and the Argonne $v_6'$ interaction. Compared with diffusion based quantum Monte Carlo methods such as Green's function Monte Carlo and auxiliary field diffusion Monte Carlo, path integral quantum Monte Carlo has the advantage that it can directly calculate the expectation value of operators without tradeoff, whether they commute with the Hamiltonian or not. For operators that commute with the Hamiltonian, e.g., the Hamiltonian itself, the path integral quantum Monte Carlo light-nuclei results agree with Green's function Monte Carlo and auxiliary field diffusion Monte Carlo results. For other operator expectations which are important to understand nuclear measurements but do not commute with the Hamiltonian and therefore cannot be accurately calculated by diffusion based quantum Monte Carlo methods without tradeoff, the path integral quantum Monte Carlo method gives reliable results. I show root-mean-square radii, one-particle number density distributions, and Euclidean response functions for single-nucleon couplings. I also systematically describe all the sampling algorithms used in this work, the strategies to make the computation efficient, the error estimations, and the details of the implementation of the code to perform calculations. This work can serve as a benchmark test for future calculations of larger nuclei or finite temperature nuclear matter using path integral quantum Monte Carlo.
ContributorsChen, Rong (Author) / Schmidt, Kevin E (Thesis advisor) / Alarcon, Ricardo O (Committee member) / Beckstein, Oliver (Committee member) / Comfort, Joseph R. (Committee member) / Shovkovy, Igor A. (Committee member) / Arizona State University (Publisher)
Created2020