25 research outputs found
Preparation of magnetic tips for spin-polarized STM on Fe_{1+y}Te
The interplay of electronic nematic modulations, magnetic order,
superconductivity and structural distortions in strongly correlated electron
materials calls for methods which allow characterizing them simultaneously - to
allow establishing directly the relationship between these different phenomena.
Spin-polarized STM enables studying both, electronic excitations as well as
magnetic structure in the same measurement at the atomic scale. Here we
demonstrate preparation of magnetic tips, both ferromagnetic and
antiferromagnetic, on single crystals of FeTe. This opens up preparation of
spin-polarized tips without the need for sophisticated ultra-high vacuum
preparation
Time-reversal symmetry breaking versus superstructure
One of the mysteries of modern condenced-matter physics is the nature of the
pseudogap state of the superconducting cuprates. Kaminski et al.1 claimed to
have observed signatures of time-reversal symmetry breaking in the pseudogap
regime in underdoped Bi2Sr2CaCu2O8+d (Bi2212). Here we argue that the observed
dichroism is due to the 5x1 superstructure replica of the electronic bands and
therefore cannot be considered as evidence for the spontaneous time-reversal
symmetry breaking in cuprates.Comment: 5 pages, pd
Influence of the Fermi Surface Morphology on the Magnetic Field-Driven Vortex Lattice Structure Transitions in YBaCuO0, 0.15
We report small-angle neutron scattering measurements of the vortex lattice
(VL) structure in single crystals of the lightly underdoped cuprate
superconductor YBa2Cu3O6.85. At 2 K, and for fields of up to 16 T applied
parallel to the crystal c-axis, we observe a sequence of field-driven and
first-order transitions between different VL structures. By rotating the field
away from the c-axis, we observe each structure transition to shift to either
higher or lower field dependent on whether the field is rotated towards the
[100] or [010] direction. We use this latter observation to argue that the
Fermi surface morphology must play a key role in the mechanisms that drive the
VL structure transitions. Furthermore, we show this interpretation is
compatible with analogous results obtained previously on lightly overdoped
YBa2Cu3O7. In that material, it has long-been suggested that the high field VL
structure transition is driven by the nodal gap anisotropy. In contrast, the
results and discussion presented here bring into question the role, if any, of
a nodal gap anisotropy on the VL structure transitions in both YBa2Cu3O6.85 and
YBa2Cu3O7
Doping dependence of the chemical potential and surface electronic structure in YBa2Cu3O6+x and La2-xSrxCuO4 using hard x-ray photoemission spectroscopy
The electronic structure of YBa2Cu3O6+x and La2-xSrxCuO4 for various values
of x has been investigated using hard x-ray photoemission spectroscopy. The
experimental results establish that the cleaving of YBa2Cu3O6+x compounds
occurs predominantly in the BaCuO3 complex leading to charged surfaces at
higher x and to uncharged surfaces at lower x values. The bulk component of the
core level spectra exhibits a shift in binding energy as a function of x, from
which a shift of the chemical potential as a function of hole concentration in
the CuO2 layers could be derived. The doping dependence of the chemical
potential across the transition from a Mott-Hubbard insulator to a
Fermi-liquid-like metal is very different in these two series of compounds. In
agreement with previous studies in the literature the chemical potential shift
in La2-xSrxCuO4 is close to zero for small hole concentrations. In YBa2Cu3O6+x,
similar to all other doped cuprates studied so far, a strong shift of the
chemical potential at low hole doping is detected. However, the results for the
inverse charge susceptibility at small x shows a large variation between
different doped cuprates. The results are discussed in view of various
theoretical models. None of these models turns out to be satisfactory.Comment: 18 pages, 15 figure
Particle-hole asymmetric superconducting coherence peaks in overdoped cuprates
To elucidate the superconductor to metal transition at the end of
superconducting dome, the overdoped regime has stepped onto the center stage of
cuprate research recently. Here, we use scanning tunneling microscopy to
investigate the atomic-scale electronic structure of overdoped trilayer Bi-2223
and bilayer Bi-2212 cuprates. At low energies the spectroscopic maps are well
described by dispersive quasiparticle interference patterns. However, as the
bias increases to the superconducting coherence peak energy, a virtually
non-dispersive pattern with sqrt(2)*sqrt(2) periodicity emerges. Remarkably,
the position of the coherence peaks exhibits evident particle-hole asymmetry
which also modulates with the same period. We propose that this is an extreme
quasiparticle interference phenomenon, caused by pairing-breaking scattering
between flat anti-nodal Bogoliubov bands, which is ultimately responsible for
the superconductor to metal transition.Comment: 15 pages, 4 figure