1,586 research outputs found
Periodic Structures with Rashba Interaction in Magnetic Field
We analyze the behaviour of a system of particles living on a periodic
crystal in the presence of a magnetic field B. This can be done by involving a
periodic potential U(x) and the Rashba interaction of coupling constant k_{so}.
By resorting the corresponding spectrum, we explicitly determine the band
structures and the Bloch spinors. These allow us to discuss the system
symmetries in terms of the polarizations where they are shown to be broken. The
dynamical spin will be studied by calculating different quantities. In the
limits: k_{so} and U(x)=0, we analyze again the system by deriving different
results. Considering the strong case, we obtain an interesting result that
is the conservation of the polarizations. Analyzing the critical point
\lambda_{k,\sigma}=\pm\sq{1\over 2}, we show that the Hilbert space associated
to the spectrum in z-direction has a zero mode energy similar to that of
massless Dirac fermions in graphene. Finally, we give the resulting energy
spectrum when B=0 and U(x) is arbitrary.Comment: 24 pages, references added, misprints corrected. Version to appear in
JP
Bloch's theory in periodic structures with Rashba's spin-orbit interaction
We consider a two-dimensional electron gas with Rashba's spin-orbit
interaction and two in-plane potentials superimposed along directions
perpendicular to each other. The first of these potentials is assumed to be a
general periodic potential while the second one is totally arbitrary. A general
form for Bloch's amplitude is found and an eigen-value problem for the band
structure of the system is derived. We apply the general result to the two
particular cases in which either the second potential represents a harmonic
in-plane confinement or it is zero. We find that for a harmonic confinement
regions of the Brillouin zone with high polarizations are associated with the
ones of large group velocity.Comment: 6 pages, 5 figure
Theory of weak continuous measurements in a strongly driven quantum bit
Continuous spectroscopic measurements of a strongly driven superconducting
qubit by means of a high-quality tank circuit (a linear detector) are under
study. Output functions of the detector, namely, a spectrum of voltage
fluctuations and an impedance, are expressed in terms of the qubit spectrum and
magnetic susceptibility. The nonequilibrium spectrum of the current
fluctuations in the qubit loop and the linear response function of the driven
qubit coupled to a heat bath are calculated with Bloch-Redfield and rotating
wave approximations. Backaction effects of the qubit on the tank and the tank
on the qubit are analyzed quantitatively. We show that the voltage spectrum of
the tank provides detailed information about a frequency and a decay rate of
Rabi oscillations in the qubit. It is found that both an efficiency of
spectroscopic measurement and measurement-induced decoherence of the qubit
demonstrate a resonant behaviour as the Rabi frequency approaches the resonant
frequency of the tank. We determine conditions when the spectroscopic
observation of the Rabi oscillations in the flux qubit with the tank circuit
can be considered as a weak continuous quantum measurement.Comment: 28 page
Radio-Frequency Method for Investigation of Quantum Properties of Superconducting Structures
We implement the impedance measurement technique (IMT) for characterization
of interferometer-type superconducting qubits. In the framework of this method,
the interferometer loop is inductively coupled to a high-quality tank circuit.
We show that the IMT is a powerful tool to study a response of externally
controlled two-level system to different types of excitations. Conclusive
information about qubits is obtained from the read-out of the tank properties.Comment: 10 pages, 10 figures;to be published in Fizika Nizkikh Temperatur
(Low Temperature Physics); v3: minor polishing; fina
Boundary form factors of the sinh-Gordon model with Dirichlet boundary conditions at the self-dual point
In this manuscript we present a detailed investigation of the form factors of
boundary fields of the sinh-Gordon model with a particular type of Dirichlet
boundary condition, corresponding to zero value of the sinh-Gordon field at the
boundary, at the self-dual point. We follow for this the boundary form factor
program recently proposed by Z. Bajnok, L. Palla and G. Takaks in
hep-th/0603171, extending the analysis of the boundary sinh-Gordon model
initiated there. The main result of the paper is a conjecture for the structure
of all n-particle form factors of two particular boundary operators in terms of
elementary symmetric polynomials in certain functions of the rapidity
variables. In addition, form factors of boundary "descendant" fields have been
constructedComment: 14 pages LaTex. Version to appear in J. Phys.
Spatial-temporal dynamics of the terahertz field generated by femtosecond filament
We present the study on spatial distribution of the maximum of terahertz field amplitude in time domain when generated by a femtosecond filament. It is shown that as a result of the propagation of the terahertz field forms a spherical wave front, on the edge of which the maximum of amplitude has a temporary delay in contrary to its central part
The Determinant Representation for a Correlation Function in Scaling Lee-Yang Model
We consider the scaling Lee-Yang model. It corresponds to the unique
perturbation of the minimal CFT model M(2,5). This is not a unitary model. We
used known expression for form factors in order to obtain a closed expression
for a correlation function of a trace of energy-momentum tensor. This
expression is a determinant of an integral operator. Similar determinant
representation were proven to be useful not only for quantum correlation
functions but also in matrix models.Comment: 14 pages, LaTeX, no figure
Order by quenched disorder in the model triangular antiferromagnet RbFe(MoO4)2
We observe a disappearance of the 1/3 magnetization plateau and a striking change of the magnetic configuration under a moderate doping of the model triangular antiferromagnet RbFe(MoO4)2. The reason is an effective lifting of degeneracy of mean-field ground states by a random potential of impurities, which compensates, in the low-temperature limit, the fluctuation contribution to free energy. These results provide a direct experimental confirmation of the fluctuation origin of the ground state in a real frustrated system. The change of the ground state to a least collinear configuration reveals an effective positive biquadratic exchange provided by the structural disorder. On heating, doped samples regain the structure of a pure compound, thus allowing for an investigation of the remarkable competition between thermal and structural disorder
Quasi two-dimensional antiferromagnet on a triangular lattice RbFe(MoO4)2
RbFe(MoO4)2 is a rare example of a nearly two-dimensional Heisenberg
antiferromagnet on a triangular lattice. Magnetic resonance spectra and
magnetization curves reveal that the system has a layered spin structure with
six magnetic sublattices. The sublattices within a layer are arranged in a
triangular manner with the magnetization vectors 120 degree apart. The H-T
phase diagram, containing at least five different magnetic phases is
constructed. In zero field, RbFe(MoO4)2 undergoes a phase transition at T_N=3.8
K into a non-collinear triangular spin structure with all the spins confined in
the basal plane. The application of an in-plane magnetic field induces a
collinear spin state between the fields H_c1=47 kOe and H_c2=71 kOe and
produces a magnetization plateau at one-third of the saturation moment. Both
the ESR and the magnetization measurements also clearly indicate an additional
first-order phase transition in a field of 35 kOe. The exact nature of this
phase transition is uncertain.Comment: 9 pages incl 11 figure
Synthesis and tribological properties of new fluoro-containing oligomers
Oligomers based on (polyfluoroalkyl)methyl oxiranes and thiiranes was first synthesized by the cationic polymerization in the presence of boron trifluoride etherate. Molecular weights of the products were defined by cryoscopic method. It was found that synthesized oligomers can be used as additives to industrial lubricants and sulfur oligomers are of the greatest positive tribological effect. © Pleiades Publishing, Ltd., 2013
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