2,096 research outputs found
Test Experiment for Time-Reversal Symmetry Breaking Superconductivity
A new experiment is proposed to probe the time-reversal symmetry of a
superconductor. It is shown that a time-reversal symmetry breaking
superconductor can be identified by the observation of a fractional flux in
connection with a Josephson junction in a special geometry.Comment: 4 pages, 2 figures available upon request, Revtex, MIT-CMT-OC
Metamagnetism of itinerant electrons in multi-layer ruthenates
The problem of quantum criticality in the context of itinerant ferro- or
metamagnetism has received considerable attention [S. A. Grigera et. al.,
Science 294, 329 (2001); C. Pfleiderer et. al., Nature, 414, 427 (2001)]. It
has been proposed that a new kind of quantum criticality is realised in
materials such as MnSi or Sr_3Ru_2O_7. We show based on a mean-field theory
that the low-temperature behaviour of the n-layer ruthenates
Sr_{n+1}Ru_nO_{3n+1} can be understood as a result of a Van Hove singularity
(VHS). We consider a single band whose Fermi energy, E_F, is close to the VHS
and deduce a complex phase diagram for the magnetism as a function of
temperature, magnetic field and E_F. The location of E_F with respect to the
VHS depends on the number of layers or can be tuned by pressure. We find that
the ferromagnetic quantum phase transition in this case is not of second but of
first order, with a metamagnetic quantum critical endpoint at high magnetic
field. Despite its simplicity this model describes well the properties of the
uniform magnetism in the single, double and triple layer ruthenates. We would
like to emphasise that the origin of this behaviour lies in the band structure.Comment: 7 pages, 3 figures, typos corrected and acknowledgement added, to
appear in the Europhysics Letter
Fractional vortices on grain boundaries --- the case for broken time reversal symmetry in high temperature superconductors
We discuss the problem of broken time reversal symmetry near grain boundaries
in a d-wave superconductor based on a Ginzburg-Landau theory. It is shown that
such a state can lead to fractional vortices on the grain boundary. Both
analytical and numerical results show the structure of this type of state.Comment: 9 pages, RevTeX, 5 postscript figures include
Dimensional crossover in SrRuO within slave-boson mean-field theory
Motivated by the anomalous temperature dependence of the c-axis resistivity
of SrRuO, the dimensional crossover from a network of perpendicular
one-dimensional chains to a two-dimensional system due to a weak hybridization
between the perpendicular chains is studied. The corresponding two-orbital
Hubbard model is treated within a slave-boson mean-field theory (SBMFT) to take
correlation effects into account such as the spin-charge separation on the
one-dimensional chains. Using an RPA-like formulation for the Green's function
of collective spinon-holon excitations the emergence of quasiparticles at
low-temperatures is examined. The results are used to discuss the evolution of
the spectral density and the c-axis transport within a tunneling approach. For
the latter a regime change between low- and high-temperature regime is found in
qualitative accordance with experimental data
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