University of Southern California
Song, Kok Wee.
Electronic correlation effects in multi-band systems.
Degree: PhD, Physics, 2014, University of Southern California
The recent dominant trends in condensed matter physics
research can be roughly summarized into three newly discovered
materials: topological insulators, graphene, and iron‐based
superconductors. All these materials exhibit many intriguing
properties which are fundamentally related to their electronic band
structure. Therefore, this lead to many intense investigations on
multi‐band electronic system to explore new physics. ❧ The physics
of multi‐band electronic structure is fascinating in several
aspects. Without many‐body effects, because of the gauge freedom of
Bloch states, topological insulators can give rise a robust
metallic behavior at its boundaries. In graphene, the touching
between conduction and valence band at Fermi level yields a new
criticality class which exhibit many unconventional electronic
properties, especially its quasi‐relativistic behavior. Turning to
the many‐body effects, for instance, the iron‐based superconductors
can sustain an superconducting ground state despite of no
attractive interactions in the system. Therefore, a deeper
understanding for the conventional notions in condensed matter
physics has put forward by many of these experimental observations.
❧ In this thesis, the many‐body effects in multi‐band systems are
the main focus, especially the study of graphene and iron‐based
superconductors which can be compared to experiments. These
theoretical studies intend to understand how the underlying
electronic bands degree of freedom can give rise to Fermi‐liquid
instabilities, and how these effects can be related to intriguing
physical properties. ❧ We first study the electrons correlation
effects in bilayer graphene by a renormalization group technique.
In this study, we build a microscopic model of bilayer graphene
from a tight‐binding approach. In our finding, the peculiar Fermi
surface configuration leads to critical behavior which is beyond
the Fermi‐liquid paradigm. Furthermore, due to the
electron‐electron interactions between different bands, excitonic
instabilities are found in many different scattering channels. This
analysis suggest a collection of competing orders in the system
ground states. This result is consistent with the experimental
observation that bilayer graphene is an insulator. ❧ Next, we study
nematic order in the metallic phase of iron pnictides. In contrast
to graphene, the density of states is finite at the Fermi surface.
By careful investigating the scattering processes near these Fermi
surface, and then identifying the most relevant collective modes
from these processes, we find that a Pomeranchuk instability can be
driven by magnetic fluctuations. This instability eventually leads
to the break down of the isotropic metallic phase which electronic
system exhibit broken crystalline rotational symmetry but preserve
translation symmetry. As the experiment suggests, this can be a
candidate for nematic order in the metallic phase.
Advisors/Committee Members: Haas, Stephan W. (Committee Chair), Bickers, Gene (Committee Member), Dappen, Werner (Committee Member), Däppen, Werner (Committee Member), Daeppen, Werner (Committee Member), Haselwandter, Christoph (Committee Member), Jonckheere, Edmond A. (Committee Member).
Subjects/Keywords: excitonic instabilties; Fermi liquid; graphene; iron pnictides; nematic order; superconductivity
to Zotero / EndNote / Reference
APA (6th Edition):
Song, K. W. (2014). Electronic correlation effects in multi-band systems. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275
Chicago Manual of Style (16th Edition):
Song, Kok Wee. “Electronic correlation effects in multi-band systems.” 2014. Doctoral Dissertation, University of Southern California. Accessed April 19, 2019.
MLA Handbook (7th Edition):
Song, Kok Wee. “Electronic correlation effects in multi-band systems.” 2014. Web. 19 Apr 2019.
Song KW. Electronic correlation effects in multi-band systems. [Internet] [Doctoral dissertation]. University of Southern California; 2014. [cited 2019 Apr 19].
Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275.
Council of Science Editors:
Song KW. Electronic correlation effects in multi-band systems. [Doctoral Dissertation]. University of Southern California; 2014. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2275