Superfluids of Fermions in spin-orbit coupled systems and photons inside a cavity.
Degree: PhD, Physics and Astronomy, 2015, Mississippi State University
This dissertation introduces some new properties of both superfluid phases of fermions
with spin-orbit coupling (SOC) and superradiant phases of photons in an optical cavity. The
effects of SOC on the phase transition between normal and superfluid phase are revealed;
an unconventional crossover driven by SOC from the Bardeen-Cooper-Schrieffer (BCS)
state to the Bose-Einstein condensate (BEC) state is verified in three different systems; and
two kinds of excitations, a Goldstone mode and a Higgs mode, are demonstrated to occur
in a quantum optical system.
We investigate the BCS superfluid state of two-component atomic Fermi gases in the
presence of three kinds of SOCs. We find that SOC drives a class of BCS to BEC crossover
that is different from the conventional one without SOC. Here, we extend the concepts of
the coherence length and Cooper-pair size in the absence of SOC to Fermi systems with
SOC. We study the dependence of chemical potential, coherence length, and Cooper-pair
size on the SOC strength and the scattering length in three dimensions (3D) (or the twobody
binding energy in two dimensions (2D)) for three attractively interacting Fermi gases
with 3D Rashba, 3D Weyl, and 2D Rashba SOC respectively.
By adding a population imbalance to a Fermi gas with Rashba-type SOC, we also map
out the finite-temperature phase diagram. Due to a competition between SOC and population
imbalance, the finite-temperature phase diagram reveals a large variety of new features,
including the expanding of the superfluid state regime and the shrinking of both the phase
separation and the normal regimes. We find that the tricritical point moves toward a regime
of low temperature, high magnetic field, and high polarization as the SOC strength increases.
Besides Fermi fluids, this dissertation also gives a new angle of view on the superradiant
phase in the Dicke model. Here, we demonstrate that Goldstone and Higgs modes can be
observed in an optical system with only a few atoms inside a cavity. The model we study
is the <i>U</i>(1)/<i>Z</i>2
Dicke model with N qubits (two-level atoms) coupled to a single photon
Advisors/Committee Members: Dr. Yaroslav Koshka (committee member), Dr. R. Torsten Clay (committee member), Dr. Steven R. Gwaltney (committee member), Dr. Seong-Gon Kim (committee member), Dr. Jinwu Ye (chair).
Subjects/Keywords: Cooper-pair size; superradiant phase; Dicke model; Goldstone mode; Higgs mode; phase diagram; Bose-Einstein condensate; Fermi gas; spin-orbit coupling
to Zotero / EndNote / Reference
APA (6th Edition):
Yu, Y. (2015). Superfluids of Fermions in spin-orbit coupled systems and photons inside a cavity. (Doctoral Dissertation). Mississippi State University. Retrieved from http://sun.library.msstate.edu/ETD-db/theses/available/etd-05142015-120012/ ;
Chicago Manual of Style (16th Edition):
Yu, Yi-Xiang. “Superfluids of Fermions in spin-orbit coupled systems and photons inside a cavity.” 2015. Doctoral Dissertation, Mississippi State University. Accessed January 22, 2020.
MLA Handbook (7th Edition):
Yu, Yi-Xiang. “Superfluids of Fermions in spin-orbit coupled systems and photons inside a cavity.” 2015. Web. 22 Jan 2020.
Yu Y. Superfluids of Fermions in spin-orbit coupled systems and photons inside a cavity. [Internet] [Doctoral dissertation]. Mississippi State University; 2015. [cited 2020 Jan 22].
Available from: http://sun.library.msstate.edu/ETD-db/theses/available/etd-05142015-120012/ ;.
Council of Science Editors:
Yu Y. Superfluids of Fermions in spin-orbit coupled systems and photons inside a cavity. [Doctoral Dissertation]. Mississippi State University; 2015. Available from: http://sun.library.msstate.edu/ETD-db/theses/available/etd-05142015-120012/ ;