477 research outputs found
Fictitious fluxes in doped antiferromagnets
In a tight binding model of charged spin-1/2 electrons on a square lattice, a
fully polarized ferromagnetic spin configuration generates an apparent U(1)
flux given by times the skyrmion charge density of the ferromagnetic
order parameter. We show here that for an antiferromagnet, there are two
``fictitious'' magnetic fields, one staggered and one unstaggered. The
staggered topological flux per unit cell can be varied between
with a negligible change in the value of the effective
nearest neighbor coupling constant whereas the magnitude of the unstaggered
flux is strongly coupled to the magnitude of the second neighbor effective
coupling.Comment: RevTeX, 5 pages including 4 figure
Phase diagram of solution of oppositely charged polyelectrolytes
We study a solution of long polyanions (PA) with shorter polycations (PC) and
focus on the role of Coulomb interaction. A good example is solutions of DNA
and PC which are widely studied for gene therapy. In the solution, each PA
attracts many PCs to form a complex. When the ratio of total charges of PA and
PC in the solution, , equals to 1, complexes are neutral and they condense
in a macroscopic drop. When is far away from 1, complexes are strongly
charged. The Coulomb repulsion is large and free complexes are stable. As
approaches to 1, PCs attached to PA disproportionate themselves in two
competing ways. One way is inter-complex disproportionation, in which PCs make
some complexes neutral and therefore condensed in a macroscopic drop while
other complexes become even stronger charged and stay free. The other way is
intra-complex disproportionation, in which PCs make one end of a complex
neutral and condensed in a small droplet while the rest of the complex forms a
strongly charged tail. Thus each complex becomes a "tadpole". These two ways
can also combine together to give even lower free energy. We get a phase
diagram of PA-PC solution in a plane of and inverse screening radius of the
monovalent salt, which includes phases or phase coexistence with both kinds of
disproportionation.Comment: 29 pages, 10 figures. Major change in results and tex
The pulling force of a single DNA molecule condensed by spermidine
In a recent experiment, a single DNA double helix is stretched and relaxed in
the presence of spermidine, a short positive polyelectrolyte, and the pulling
force is measured as a function of DNA extension. In a certain range of
spermidine concentration, a force plateau appears whose value shows maximum as
a function of spermidine concentration. We present a quantitative theory of
this plateau force based on the theory of reentrant condensation and derive
almost parabolic behavior of the plateau force as a function of the logarithm
of the spermidine concentration in the range of condensation. Our result is in
good agreement with experimental data.Comment: 4 pages, 4 figures. Small change in the text, no change in result
Invariant structure of the hierarchy theory of fractional quantum Hall states with spin
We describe the invariant structure common to abelian fractional quantum Hall
systems with spin. It appears in a generalization of the lattice description of
the polarized hierarchy that encompasses both partially polarized and
unpolarized ground state systems. We formulate, using the spin-charge
decomposition, conditions that should be satisfied so that the description is
SU(2) invariant. In the case of the spin- singlet hierarchy construction, we
find that there are as many SU(2) symmetries as there are levels in the
construction. We show the existence of a spin and charge lattice for the
systems with spin. The ``gluing'' of the charge and spin degrees of freedom in
their bulk is described by the gluing theory of lattices.Comment: 21 pages, LaTex, Submitted to Phys. Rev.
Electrostatic theory of viral self-assembly: a toy model
Viruses self-assemble from identical capsid proteins and their genome
consisting, for example, of a long single stranded (ss) RNA. For a big class of
T = 3 viruses capsid proteins have long positive N-terminal tails. We explore
the role played by the Coulomb interaction between the brush of positive
N-terminal tails rooted at the inner surface of the capsid and the negative ss
RNA molecule. We show that viruses are most stable when the total contour
length of ss RNA is close to the total length of the tails. For such a
structure the absolute value of the total RNA charge is approximately twice
larger than the charge of the capsid. This conclusion agrees with structural
data.Comment: 4 pages, 2 figure
Non-monotonic swelling of a macroion due to correlation-induced charge inversion
It is known that a large, charged body immersed in a solution of multivalent
counterions may undergo charge inversion as the counterions adsorb to its
surface. We use the theory of charge inversion to examine the case of a
deformable, porous macroion which may adsorb multivalent ions into its bulk to
form a three-dimensional strongly-correlated liquid. This adsorption may lead
to non-monotonic changes in the size of the macroion as multivalent ions are
added to the solution. The macroion first shrinks as its bare charge is
screened and then reswells as the adsorbed ions invert the sign of the net
charge. We derive a value for the outward pressure experienced by such a
macroion as a function of the ion concentration in solution. We find that for
small deviations in the concentration of multivalent ions away from the neutral
point (where the net charge of the body is zero), the swollen size grows
parabolically with the logarithm of the ratio of multivalent ion concentration
to the concentration at the neutral point.Comment: 7 pages, 4 figures; typos fixed; final published versio
Hamiltonian theory of gaps, masses and polarization in quantum Hall states: full disclosure
I furnish details of the hamiltonian theory of the FQHE developed with Murthy
for the infrared, which I subsequently extended to all distances and apply it
to Jain fractions \nu = p/(2ps + 1). The explicit operator description in terms
of the CF allows one to answer quantitative and qualitative issues, some of
which cannot even be posed otherwise. I compute activation gaps for several
potentials, exhibit their particle hole symmetry, the profiles of charge
density in states with a quasiparticles or hole, (all in closed form) and
compare to results from trial wavefunctions and exact diagonalization. The
Hartree-Fock approximation is used since much of the nonperturbative physics is
built in at tree level. I compare the gaps to experiment and comment on the
rough equality of normalized masses near half and quarter filling. I compute
the critical fields at which the Hall system will jump from one quantized value
of polarization to another, and the polarization and relaxation rates for half
filling as a function of temperature and propose a Korringa like law. After
providing some plausibility arguments, I explore the possibility of describing
several magnetic phenomena in dirty systems with an effective potential, by
extracting a free parameter describing the potential from one data point and
then using it to predict all the others from that sample. This works to the
accuracy typical of this theory (10 -20 percent). I explain why the CF behaves
like free particle in some magnetic experiments when it is not, what exactly
the CF is made of, what one means by its dipole moment, and how the comparison
of theory to experiment must be modified to fit the peculiarities of the
quantized Hall problem
Transport in one dimensional Coulomb gases: From ion channels to nanopores
We consider a class of systems where, due to the large mismatch of dielectric
constants, the Coulomb interaction is approximately one-dimensional. Examples
include ion channels in lipid membranes and water filled nanopores in silicon
or cellulose acetate films. Charge transport across such systems possesses the
activation behavior associated with the large electrostatic self-energy of a
charge placed inside the channel. We show here that the activation barrier
exhibits non-trivial dependence on the salt concentration in the surrounding
water solution and on the length and radius of the channel.Comment: New references are have been added and discussed. 18 pages, 8 figure
Giant magnetic-field changes in radio-frequency absorption in LaSrMnO near the Curie temperature
The DC transport properties of and the radio-frequency (RF) wave absorption
(at 2.525 MHz) in a sample of LaSrMnO prepared by
floating-zone method are measured. The Curie temperature, , of the
sample is about 374 K. Giant temperature and magnetic-field variations in RF
absorption are found in the vicinity of . Relative change of the RF
absorption in magnetic field (magnetoabsorption) is about 67% in field 2.1 kOe
and about 55% in field 1 kOe. This giant magnetoabsorption effect can be used
to develop RF devices controlled by temperature and low magnetic field. A weak
temperature dependence of magnetoabsorption for the sample studied in the range
from room temperature to about 350 K makes it especially attractive for
practical use. The RF study supplemented with transport, magnetoresistive and
magnetic measurements enables us to discuss the optimal properties of manganite
samples for observation of giant magnetoabsorption in low field.Comment: Submitted to J. Magn. Magn. Mater., 14 pages including 7 figure
Spin symmetry breaking in bilayer quantum Hall systems
Based on the construction of generalized Halperin wave functions, we predict
the possible existence of a large class of broken spin symmetry states in
bilayer quantum Hall structures, generalizing the recently suggested canted
antiferromgnetic phase to many fractional fillings. We develop the appropriate
Chern-Simons theory, and establish explicitly that the low-lying neutral
excitation is a Goldstone mode and that the charged excitations are bimerons
with continuously tunable (through the canted antiferromagnetic order
parameter) electric charge on the individual merons.Comment: 4 page
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