1,160 research outputs found
Magnetism and Superconductivity in (RE)Ni2B2C: The Case of TmNi2B2C
The recently reported coexistence of an oscillatory magnetic order with the
wave vector Q=0.241 \AA^{-1} and superconductivity in TmNi2B2C is analyzed
theoretically. It is shown that the oscillatory magnetic order and
superconductivity interact predominantly via the exchange interaction between
localized moments (LM's) and conduction electrons, while the electromagnetic
interaction between them is negligible. In the coexistence phase of the clean
TmNi2B2C the quasiparticle spectrum should have a line of zeros at the Fermi
surface, giving rise to the power law behavior of thermodynamic and transport
properties. Two scenarios of the origin of the oscillatory magnetic order in
TmNi2B2C are analyzed: a) due to superconductivity and b) independently on
superconductivity. Experiments in magnetic field are proposed in order to
choose between them.Comment: 12 pages with 2 PS figures, RevTe
Superconducting Plasma Excitation at Microwave Frequencies in Parallel Magnetic Fields in
Josephson plasma resonance has been studied in a wide microwave frequency
range between 10 and 52 GHz in a magnetic field parallel to the -plane in
under-doped \BI. Above about 30 GHz two resonance modes were observed: one
(LT mode) appears at low temperatures and another (HT mode) at higher
temperatures, leaving a temperature gap between two regions. These two
resonance modes exhibit a sharp contrast each other both on temperture and
magnetic field dependences and show distinct characters different entirely from
the c-axis Josephson plasma resonance. From temperature and field scan
experiments at various frequencies it is suggested that the LT mode can be
attributed to the coupled Josephson plasma mode with Josephson vortices, while
the HT mode is a new plasma mode associated possibly with the periodic array of
Josephson vortices.Comment: submitted to Physica C (Prceedings of Plasma2000, Sendai
Strongly disordered Hubbard model in one dimension: spin and orbital infinite randomness and Griffiths phases
We study by the strong disorder renormalization group (RG) method the
low-energy properties of the one-dimensional Hubbard model with random-hopping
matrix-elements , and with random on-site Coulomb repulsion
terms . There are two critical phases, corresponding
to an infinite randomness spin random singlet for strong interactions () and to an orbital infinite randomness fixed point for vanishing
interactions (). To each critical infinite randomness
fixed point is connected a Griffiths phase, the correlation length and
dynamical exponent of which have well defined asymptotic dependences on the
corresponding quantum control parameter. The theoretical predictions for the
scaling in the vicinity of the critical points compare well to numerical RG
simulations.Comment: 9 pages, 7 figure
Conventional Magnetic Superconductors: Coexistence of Singlet Superconductivity and Magnetic Order
The basic physics of bulk magnetic superconductors (MS) related to the
problem of the coexistence of singlet superconductivity (SC) and magnetic order
is reviewed. The interplay between exchange (EX) and electromagnetic (EM)
interaction is discussed and argued that the singlet SC and uniform
ferromagnetic (F) order practically never coexist. In case of their mutual
coexistence the F order is modified into a domain-like or spiral structure
depending on magnetic anisotropy. It turns out that this situation is realized
in several superconductors such as , ,
with electronic and in with nuclear magnetic order.
The later problem is also discussed here.
The coexistence of SC and antiferromagnetism is more favorable than with the
modified F order. Very interesting physics is realized in systems with SC and
weak-ferromagnetism which results in an very reach phase diagram.
The properties of magnetic superconductors in magnetic field are very
peculiar, especially near the (ferro)magnetic transition temperature where the
upper critical field becomes smaller than the thermodynamical critical field.
The extremely interesting physics of Josephson junctions based on MS with
spiral magnetic order is also discussed. The existence of the triplet pairing
amplitude () in MS with
rotating magnetization (the effect recently rediscovered in SFS junctions)
gives rise to the so called -contact. Furthermore, the interplay of the
superconducting and magnetic phase in such a contact renders possibilities for
a new type of coupled Josephson-qubits.Comment: 28 pages, 3 figures; submitted for the Special Issue Comptes de
l'Academie des Sciences: Problems of the Coexistence of Magnetism and
Superconductivity, edited by A. Buzdi
Nondemolition measurements of a single quantum spin using Josephson oscillations
We consider a Josephson junction containing a single localized spin 1/2
between conventional singlet superconducting electrodes. We study the spin
dynamics and measurements when a dc-magnetic field acts on
the spin and the junction is embedded into a dissipative circuit. We show that
when tunneling or a voltage are turned on at time the Josephson current
starts to oscillate with an amplitude depending on the initial () value of
the spin -component, . At low temperatures, when effects of
quasiparticles may be neglected, this procedure realizes a
quantum-non-demolition (QND) measurement of .Comment: 4 pages, 1 figure; average value of spin z operator changed to
eigenvalue S_
Radiation Due to Josephson Oscillations in Layered Superconductors
We derive the power of direct radiation into free space induced by Josephson
oscillations in intrinsic Josephson junctions of highly anisotropic layered
superconductors. We consider the super-radiation regime for a crystal cut in
the form of a thin slice parallel to the c-axis. We find that the radiation
correction to the current-voltage characteristic in this regime depends only on
crystal shape. We show that at large enough number of junctions oscillations
are synchronized providing high radiation power and efficiency in the THz
frequency range. We discuss crystal parameters and bias current optimal for
radiation power and crystal cooling.Comment: 4 pages, 1 figure, to be published in Phys. Rev. Let
Ballistic Four-Terminal Josephson Junction: Bistable States and Magnetic Flux Transfer
The macroscopic quantum interference effects in ballistic Josephson
microstructures are investigated. The studied system consists of four bulk
superconductors (terminals) which are weakly coupled through the mesoscopic
rectangular normal metal (two dimensional electron gas). We show that nonlocal
electrodynamics of ballistic systems leads to specific current-phase relations
for the mesoscopic multiterminal Josephson junction. The nonlocal coupling of
supercurrents produces the "dragging" effect for phases of the superconducting
order parameter in different terminals. The composite Josephson junction, based
on this effect, exhibits the two -level system behaviour controlled by the
external magnetic flux. The effect of magnetic flux transfer in a system of
nonlocally coupled superconducting rings is studied.Comment: 12pages LaTex, 6 figures; e-mail: [email protected]
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