1,254 research outputs found
The Matsubara-Fradkin Thermodynamical Quantization of Podolsky Electrodynamics
In this work we apply the Matsubara-Fradkin formalism and the Nakanishi's
auxiliary field method to the quantization of the Podolsky electrodynamics in
thermodynamic equilibrium. This approach allows us to write consistently the
path integral representation for the partition function of gauge theories in a
simple manner. Furthermore, we find the Dyson-Schwinger-Fradkin equations and
the Ward-Fradkin-Takahashi identities for the Podolsky theory. We also write
the most general form for the polarization tensor in thermodynamic equilibrium.Comment: Submitted to Physical Review
Heat transport through quantum Hall edge states: Tunneling versus capacitive coupling to reservoirs
We study the heat transport along an edge state of a two-dimensional electron
gas in the quantum Hall regime, in contact to two reservoirs at different
temperatures. We consider two exactly solvable models for the edge state
coupled to the reservoirs. The first one corresponds to filling and
tunneling coupling to the reservoirs. The second one corresponds to integer or
fractional filling of the sequence (with odd), and capacitive
coupling to the reservoirs. In both cases we solve the problem by means of
non-equilibrium Green function formalism. We show that heat propagates chirally
along the edge in the two setups. We identify two temperature regimes, defined
by , the mean level spacing of the edge. At low temperatures, , finite size effects play an important role in heat transport, for both
types of contacts. The nature of the contacts manifest themselves in different
power laws for the thermal conductance as a function of the temperature. For
capacitive couplings a highly non-universal behavior takes place, through a
prefactor that depends on the length of the edge as well as on the coupling
strengths and the filling fraction. For larger temperatures, ,
finite-size effects become irrelevant, but the heat transport strongly depends
on the strength of the edge-reservoir interactions, in both cases. The thermal
conductance for tunneling coupling grows linearly with , whereas for the
capacitive case it saturates to a value that depends on the coupling strengths
and the filling factors of the edge and the contacts.Comment: 15 pages, 5 figure
The imbalanced antiferromagnet in an optical lattice
We study the rich properties of the imbalanced antiferromagnet in an optical
lattice. We present its phase diagram, discuss spin waves and explore the
emergence of topological excitations in two dimensions, known as merons, which
are responsible for a Kosterlitz-Thouless transition that has never
unambiguously been observed.Comment: 4 pages, 5 figures, RevTe
Polaron action for multimode dispersive phonon systems
Path-integral approach to the tight-binding polaron is extended to multiple
optical phonon modes of arbitrary dispersion and polarization. The non-linear
lattice effects are neglected. Only one electron band is considered. The
electron-phonon interaction is of the density-displacement type, but can be of
arbitrary spatial range and shape. Feynman's analytical integration of ion
trajectories is performed by transforming the electron-ion forces to the basis
in which the phonon dynamical matrix is diagonal. The resulting polaron action
is derived for the periodic and shifted boundary conditions in imaginary time.
The former can be used for calculating polaron thermodynamics while the latter
for the polaron mass and spectrum. The developed formalism is the analytical
basis for numerical analysis of such models by path-integral Monte Carlo
methods.Comment: 9 page
Renormalization Group Study of Magnetic Catalysis in the 3d Gross-Neveu Model
Magnetic catalysis describes the enhancement of symmetry breaking quantum
fluctuations in chirally symmetric quantum field theories by the coupling of
fermionic degrees of freedom to a magnetic background configuration. We use the
functional renormalization group to investigate this phenomenon for interacting
Dirac fermions propagating in (2+1)-dimensional spacetime, described by the
Gross-Neveu model. We identify pointlike operators up to quartic fermionic
terms that can be generated in the renormalization group flow by the presence
of an external magnetic field. We employ the beta function for the fermionic
coupling to quantitatively analyze the field dependence of the induced spectral
gap. Within our pointlike truncation, the renormalization group flow provides a
simple picture for magnetic catalysis.Comment: 14 pages, 6 figures, typos correcte
Topological insulating phases in mono and bilayer graphene
We analyze the influence of different quadratic interactions giving rise to
time reversal invariant topological insulating phases in mono and bilayer
graphene. We make use of the effective action formalism to determine the
dependence of the Chern Simons coefficient on the different interactions
Incidence of the boundary shape in the effective theory of fractional quantum Hall edges
Starting from a microscopic description of a system of strongly interacting
electrons in a strong magnetic field in a finite geometry, we construct the
boundary low energy effective theory for a fractional quantum Hall droplet
taking into account the effects of a smooth edge. The effective theory obtained
is the standard chiral boson theory (chiral Luttinger theory) with an
additional self-interacting term which is induced by the boundary. As an
example of the consequences of this model, we show that such modification leads
to a non-universal reduction in the tunnelling exponent which is independent of
the filling fraction. This is in qualitative agreement with experiments, that
systematically found exponents smaller than those predicted by the ordinary
chiral Luttinger liquid theory.Comment: 12 pages, minor changes, replaced by published versio
Fractional Chern Insulators from the nth Root of Bandstructure
We provide a parton construction of wavefunctions and effective field
theories for fractional Chern insulators. We also analyze a strong coupling
expansion in lattice gauge theory that enables us to reliably map the parton
gauge theory onto the microsopic Hamiltonian. We show that this strong coupling
expansion is useful because of a special hierarchy of energy scales in
fractional quantum Hall physics. Our procedure is illustrated using the
Hofstadter model and then applied to bosons at 1/2 filling and fermions at 1/3
filling in a checkerboard lattice model recently studied numerically. Because
our construction provides a more or less unique mapping from microscopic model
to effective parton description, we obtain wavefunctions in the same phase as
the observed fractional Chern insulators without tuning any continuous
parameters.Comment: 9+3 pages, 6 figures; v2: added refs, amplified discussion of
deconfinement, improved discussion of translation invarianc
Tuning the effects of Landau-level mixing on anisotropic transport in quantum Hall systems
Electron-electron interactions in half-filled high Landau levels in
two-dimensional electron gases in a strong perpendicular magnetic field can
lead to states with anisotropic longitudinal resistance. This longitudinal
resitance is generally believed to arise from broken rotational invariance,
which is indicated by charge density wave (CDW) order in Hartree-Fock
calculations. We use the Hartree-Fock approximation to study the influence of
externally tuned Landau level mixing on the formation of interaction induced
states that break rotational invariance in two-dimensional electron and hole
systems. We focus on the situation when there are two non-interacting states in
the vicinity of the Fermi level and construct a Landau theory to study coupled
charge density wave order that can occur as interactions are tuned and the
filling or mixing are varied. We examine in detail a specific example where
mixing is tuned externally through Rashba spin-orbit coupling. We calculate the
phase diagram and find the possibility of ordering involving coupled striped or
triangular charge density waves in the two levels. Our results may be relevant
to recent transport experiments on quantum Hall nematics in which Landau-level
mixing plays an important role.Comment: 25 pages, 6 figure
- …