43 research outputs found
Normal metal to ferromagnetic superconductor tunneling
We study the point-contact tunneling between normal metal and ferromagnetic
superconductor. In the case of magnon-induced pairing the tunneling conductance
is continuous and smooth function of the applied voltage. For small values of
the applied voltage the Ohm law holds. We show that one can obtain the
magnetization and the superconducting order parameter from the tunneling
conduc- tance. In the case of paramagnon-induced superconductivity the
tunneling does not depend on the magnetization. We argue that tunneling
experiment can unambiguously determine the correct pairing mechanism in the
ferromagnetic superconductors.Comment: 6 pages, 4 figur
Spin-Wave Theory of the Spiral Phase of the t-J Model
A graded H.P,realization of the SU(2|1) algebra is proposed.A spin-wave
theory with a condition that the sublattice magnetization is zero is
discussed.The long-range spiral phase is investigated.The spin-spin correlator
is calculated.Comment: 17 page
Magnon-Paramagnon Effective Theory of Itinerant Ferromagnets
The present work is devoted to the derivation of an effective
magnon-paramagnon theory starting from a microscopic lattice model of
ferromagnetic metals. For some values of the microscopic parameters it
reproduces the Heisenberg theory of localized spins. For small magnetization
the effective model describes the physics of weak ferromagnets in accordance
with the experimental results. It is written in a way which keeps O(3) symmetry
manifest,and describes both the order and disordered phases of the system.
Analytical expression for the Curie temperature,which takes the magnon
fluctuations into account exactly, is obtained. For weak ferromagnets is
well below the Stoner's critical temperature and the critical temperature
obtained within Moriya's theory.Comment: 14 pages, changed content,new result
A Model for Superconductivity in Ferromagnetic ZrZn2
This article proposes that superconductivity in the ferromagnetic state of
ZrZn is stabilized by an exchange-type interaction between the magnetic
moments of triplet-state Cooper pairs and the ferromagnetic magnetization
density. This explains why superconductivity occurs in the ferromagnetic state
only, and why it persists deep into the ferromagnetic state. The model of this
article also yields a particular order parameter symmetry, which is a
prediction that can be checked experimentally.Comment: 4 pages, revised version accepted in PR
Phase diagrams of in Double Exchange Model with added antiferromagnetic and Jahn-Teller interaction
The phase diagram of the multivalent manganites , in
space of temperature and doping , is a challenge for the theoretical
physics. It is an important test for the model used to study these compounds
and the method of calculation. To obtain theoretically this diagram for
, we consider the two-band Double Exchange Model for manganites with
added Jahn-Teller coupling and antiferromagnetic Heisenberg term. In order to
calculate Curie and N\'{e}el temperatures we derive an effective Heisenberg
model for a vector which describes the local orientation of the total
magnetization of the system. The exchange constants of this model are different
for different space directions and depend on the density of electrons,
antiferromagnetic constants and the Jahn-Teller energy. To reproduce the well
known phase transitions from A-type antiferromagnetism to ferromagnetism at low
and C-type antiferromagnetism to G-type antiferromagnetism at large , we
argue that the antiferromagnetic exchange constants should depend on the
lattice direction. We show that ferromagnetic to A-type antiferromagnetic
transition results from the Jahn-Teller distortion. Accounting adequately for
the magnon-magnon interaction, Curie and N\'{e}el temperatures are calculated.
The results are in very good agreement with the experiment and provide values
for the model parameters, which best describe the behavior of the critical
temperature for .Comment: 13 pages, 5 figure
Theory of Ferromagnetic Superconductivity
It is argued that the pairing symmetry realized in a ferromagnetic
superconductor UGe must be a non-unitary triplet pairing. This particular
state is free from the Pauli limitation and can survive under a huge internal
molecular filed. To check our identification we examine its basic properties
and several experiments are proposed. In particular, the external field is used
to raise by controlling the internal spontaneous dipole field.Comment: 4 pages, no figure
Chiral effective action with heavy quark symmetry
We derive an effective action combining chiral and heavy quark symmetry,
using approximate bosonization techniques of QCD. We explicitly show that the
heavy-quark limit is compatible with the large (number of color) limit in
the meson sector, and derive specific couplings between the light and heavy
mesons (, , ...) and their chiral partners. The relevance of this
effective action to solitons with heavy quarks describing heavy baryons is
discussed.Comment: 14 pages, SUNY-NTG-92/2
The -boson-fermion realizations of quantum suprealgebra
We show that our construction of realizations for Lie algebras and quantum
algebras can be generalized to quantum superalgebras, too. We study an example
of quantum superalgebra and give the boson-fermion realization
with respect to one pair od q-deformed boson operator and 2 pairs of fermions.Comment: 8 page