311 research outputs found
Evolution of magnetic fluctuations through the Fe-induced paramagnetic to ferromagnetic transition in CrB
In itinerant ferromagnets, the quenched disorder is predicted to dramatically
affect the ferromagnetic to paramagnetic quantum phase transition driven by
external control parameters at zero temperature. Here we report a study on
Fe-doped CrB, which, starting from the paramagnetic parent, orders
ferromagnetically for Fe-doping concentrations larger than \%. In parent CrB, B nuclear magnetic resonance data reveal
the presence of both ferromagnetic and antiferromagnetic fluctuations. The
latter are suppressed with Fe-doping, before the ferromagnetic ones finally
prevail for . Indications for non-Fermi liquid behavior, usually
associated with the proximity of a quantum critical point, were found for all
samples, including undoped CrB. The sharpness of the ferromagnetic-like
transition changes on moving away from , indicating significant
changes in the nature of the magnetic transitions in the vicinity of the
quantum critical point. Our data provide constraints for understanding quantum
phase transitions in itinerant ferromagnets in the limit of weak quenched
disorder.Comment: 8 pages, 7 figure
Superconducting NdCeCuO Bicrystal Grain Boundary Josephson Junctions
We have studied the electric transport properties of symmetrical [001] tilt
NdCeCuO bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO
bicrystal substrates with misorientation angles of 24 and 36.8 degree. The
superconducting properties of the NdCeCuO-GBJs are similar to those of GBJs
fabricated from the hole doped high temperature superconductors (HTS). The
critical current density Jc decreases strongly with increasing misorientation
angle. The products of the critical current Ic and the normal resistance Rn
(about 0.1 mV at 4.2 K) are small compared to the gap voltage and fit well to
the universal scaling law (IcRn is proportional to the square root of Jc) found
for GBJs fabricated from the hole doped HTS. This suggests that the symmetry of
the order parameter, which most likely is different for the electron and the
hole doped HTS has little influence on the characteristic properties of
symmetrical [001] tilt GBJs.Comment: 3 pages, 4 figures, to be published in Applied Physics Letter
Andreev Bound States in High Temperature Superconductors
Andreev bound states (ABS) at the surface of superconductors are expected for
any pair potential showing a sign change in different k-directions with their
spectral weight depending on the relative orientation of the surface and the
pair potential. We report on the observation of ABS in HTS employing tunneling
spectroscopy on bicrystal grain boundary Josephson junctions (GBJs). The
tunneling spectra were studied as a function of temperature and applied
magnetic field. The tunneling spectra of GBJ formed by YBCO, BSCCO, and LSCO
show a pronounced zero bias conductance peak that can be interpreted in terms
of Andreev bound states at zero energy that are expected at the surface of HTS
having a d-wave symmetry of the order parameter. In contrast, for the most
likely s-wave HTS NCCO no zero bias conductance peak was observed. Applying a
magnetic field results in a shift of spectral weight from zero to finite
energy. This shift is found to depend nonlinearly on the applied magnetic
field. Further consequences of the Andreev bound states are discussed and
experimental evidence for anomalous Meissner currents is presented.Comment: 17 pages, 10 figures, to appear in Eur. Phys. J.
Termination dependent topological surface states of the natural superlattice phase BiSe
We describe the topological surface states of BiSe, a compound in the
infinitely adaptive Bi-BiSe natural superlattice phase series,
determined by a combination of experimental and theoretical methods. Two
observable cleavage surfaces, terminating at Bi or Se, are characterized by
angle resolved photoelectron spectroscopy and scanning tunneling microscopy,
and modeled by ab-initio density functional theory calculations. Topological
surface states are observed on both surfaces, but with markedly different
dispersions and Kramers point energies. BiSe therefore represents the
only known compound with different topological states on differently terminated
surfaces.Comment: 5 figures references added Published in PRB:
http://link.aps.org/doi/10.1103/PhysRevB.88.08110
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