75 research outputs found

### Chern-Simons Theory and Dynamics of Composite Fermions

We propose a (4+1) dimensional Chern-Simons field theoretical description of
the fractional quantum Hall effect. It suggests that composite fermions reside
on a momentum manifold with a nonzero Chern number. Based on derivations from
microscopic wave functions, we further show that the momentum manifold has a
uniformly distributed Berry curvature. As a result, composite fermions do not
follow the ordinary Newtonian dynamics as commonly believed, but the more
general symplectic one. For a Landau level with the particle-hole symmetry, the
theory correctly predicts its Hall conductance at half-filling as well as the
symmetry between an electron filling fraction and its hole counterpart.Comment: 5 pages, no figur

### Attractive electron-electron interaction induced by geometric phase in a Bloch band

We investigate electron pairing in the presence of the Berry curvature field
that ubiquitously exists in ferromagnetic metals with spin-orbit coupling. We
show that a sufficiently strong Berry curvature field on the Fermi surface can
transform a repulsive interaction between electrons into an attractive one in
the p-wave channel. We also reveal a topological possibility for turning an
attractive s-wave interaction into one in the p-wave channel, even if the Berry
curvature field only exists inside the Fermi surface (circle). We speculate
that these novel mechanism might be relevant to the recently discovered
ferromagnetic superconductors such as UGe$_{2}$ and URhGe.Comment: 4 pages, 3 figure

### Asymmetry of the Geometrical Resonances of Composite Fermions

We propose an experiment to test the uniform-Berry-curvature picture of
composite fermions. We show that the asymmetry of geometrical resonances
observed in a periodically modulated composite fermion system can be explained
with the uniform-Berry-curvature picture. Moreover, we show that an alternative
way of modulating the system, i.e., modulating the external magnetic field,
will induce an asymmetry opposite to that of the usual periodic grating
modulation which effectively modulates the Chern-Simons field. The experiment
can serve as a critical test of the uniform-Berry-curvature picture, and probe
the dipole structure of composite fermions proposed by Read.Comment: 6 pages, 2 figure

### Critical velocities for a superfluid in a periodic potential

In contrast to the homogeneous superfluid which has only one critical
velocity, there exist two critical velocities for a superfluid in a periodic
potential. The first one, which we call inside critical velocity, is for a
macroscopic impurity to move frictionlessly in the periodic superfluid system;
the second, which is called trawler critical velocity, is the largest velocity
of the lattice relative to the lab frame for the superfluidity to maintain. The
results are relevant to the superfluidity observed in the Bose-Einstein
condensate in an optical lattice and supersolid helium.Comment: extensive revision, 4 pages and 4 figure

### Mapping a fractional quantum Hall state to a fractional Chern insulator

We establish a variational principle for properly mapping a fractional
quantum Hall (FQH) state to a fractional Chern insulator (FCI). We find that
the mapping has a gauge freedom which could generate a class of FCI ground
state wave functions appropriate for different forms of interactions.
Therefore, the gauge should be fixed by a variational principle that minimizes
the interaction energy of the FCI model. For a soft and isotropic
electron-electron interaction, the principle leads to a gauge coinciding with
that for maximally localized \emph{two-dimensional} projected Wannier functions
of a Landau level.Comment: 8 pages, 5 figure

### Quantum Anomalous Hall Insulator of Composite Fermions

We show that a weak hexagonal periodic potential could transform a
two-dimensional electron gas with an even-denominator magnetic filling factor
to a quantum anomalous Hall insulator of composite fermions, giving rise to
fractionally quantized Hall effect. The system provides a realization of the
Haldane honeycomb-net model, albeit in a composite fermion system. We further
propose a trial wave function for the state, and numerically evaluate its
relative stability against the competing Hofstadter state. Possible sets of
experimental parameters are proposed.Comment: 5 pages, 4 figures, 2 tables, detailed supplementary file adde

### Self-consistent Single-band Approximation for Interacting Boson Systems

Traditionally, the single-band approximation for interacting many-body
systems is done with pre-determined single-particle Wannier functions, ignoring
the dependence of the Wannier function on interaction. We show that the
single-band approximation has to be done self-consistently to properly account
the interaction effect on the Wannier functions. This self-consistent
single-band approximation leads to a nonlinear equation for Wannier functions,
which can be recast into a set of nonlinear equations for Bloch functions.
These equations are simplified for two special cases, the superfluid regime and
deep in the Mott insulator regime. A simple example with double-well potential
is used to illustrate our results.Comment: 4 pages, 2 figure

### Heat Superconductivity

Electrons/atoms can flow without dissipation at low temperature in
superconductors/superfluids. The phenomenon known as
superconductivity/superfluidity is one of the most important discoveries of
modern physics, and is not only fundamentally important, but also essential for
many real applications. An interesting question is: can we have a
superconductor for heat current, in which energy can flow without dissipation?
Here we show that heat superconductivity is indeed possible. We will show how
the possibility of the heat superconductivity emerges in theory, and how the
heat superconductor can be constructed using recently proposed time crystals.
The underlying simple physics is also illustrated. If the possibility could be
realized, it would not be difficult to speculate various potential
applications, from energy tele-transportation to cooling of information
devices.Comment: 12 pages, 2 figures. Correct an issue pointed out by Jing-ning Zhang.
Figures and text update

### Reply to Comment on: "Radiation-Induced 'Zero-Resistance State' and the Photon Assisted Transport"

We show that the comment by A.F. Volkov ignores a delicate issue in the
conductance measurement for a hall bar system. In such system, $\rho
_{xx}\approx \rho_{xy}^{2}\sigma_{xx}$ while $\sigma_{xy}\gg \sigma_{xx}$, as
correctly pointed out in Ref.3. We clarify that the so called "zero resistance
state" is actually a "zero conductance state". A discussion concerning the
phase transition induced by the negative conductance is presented.Comment: 1 pag

### Effective Interacting Hamiltonian and Pairing Symmetry of LaOFeAs

We establish the general form of effective interacting Hamiltonian for
LaOFeAs system based on the symmetry consideration. The peculiar symmetry
property of the electron states yields unusual form of electron-electron
interaction. Based on the general effective Hamiltonian, we determine all the
ten possible pairing states. More physical considerations would further reduce
the list of the candidates for the pairing state.Comment: 4 pages, 2 figures, update figures, table and discussio

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