208 research outputs found
STM imaging of impurity resonances on BiSe
In this paper we present detailed study of the density of states near defects
in BiSe. In particular, we present data on the commonly found
triangular defects in this system. While we do not find any measurable
quasiparticle scattering interference effects, we do find localized resonances,
which can be well fitted by theory once the potential is taken to be extended
to properly account for the observed defects. The data together with the fits
confirm that while the local density of states around the Dirac point of the
electronic spectrum at the surface is significantly disrupted near the impurity
by the creation of low-energy resonance state, the Dirac point is not locally
destroyed. We discuss our results in terms of the expected protected surface
state of topological insulators.Comment: 5 pages, 6 figure
STM imaging of a bound state along a step on the surface of the topological insulator BiTe
Detailed study of the LDOS associated with the surface-state-band near a
step-edge of the strong topological-insulator Bi2Te3, reveal a one-dimensional
bound state that runs parallel to the stepedge and is bound to it at some
characteristic distance. This bound state is clearly observed in the bulk gap
region, while it becomes entangled with the oscillations of the warped surface
band at high energy, and with the valence band states near the Dirac point.
Using the full effective Hamiltonian proposed by Zhang et al., we obtain a
closed formula for this bound state that fits the data and provide further
insight into the general topological properties of the electronic structure of
the surface band near strong structural defects.Comment: 5 pages, 4 figure
Charge dynamics of the spin-density-wave state in BaFeAs
We report on a thorough optical investigation of BaFeAs over a broad
spectral range and as a function of temperature, focusing our attention on its
spin-density-wave (SDW) phase transition at K. While
BaFeAs remains metallic at all temperatures, we observe a depletion in
the far infrared energy interval of the optical conductivity below ,
ascribed to the formation of a pseudogap-like feature in the excitation
spectrum. This is accompanied by the narrowing of the Drude term consistent
with the transport results and suggestive of suppression of scattering
channels in the SDW state. About 20% of the spectral weight in the far infrared
energy interval is affected by the SDW phase transition
The influence of magnetic order on the magnetoresistance anisotropy of FeCuTe
We performed resistance measurements on FeCuTe with
in the presence of in-plane applied magnetic fields,
revealing a resistance anisotropy that can be induced at a temperature far
below the structural and magnetic zero-field transition temperatures. The
observed resistance anisotropy strongly depends on the field orientation with
respect to the crystallographic axes, as well as on the field-cooling history.
Our results imply a correlation between the observed features and the
low-temperature magnetic order. Hysteresis in the angle-dependence indicates a
strong pinning of the magnetic order within a temperature range that varies
with the Cu content. The resistance anisotropy vanishes at different
temperatures depending on whether an external magnetic field or a remnant field
is present: the closing temperature is higher in the presence of an external
field. For the resistance anisotropy closes above the
structural transition, at the same temperature at which the zero-field
short-range magnetic order disappears and the sample becomes paramagnetic. Thus
we suggest that under an external magnetic field the resistance anisotropy
mirrors the magnetic order parameter. We discuss similarities to nematic order
observed in other iron pnictide materials.Comment: 11 pages, 9 figure
Electrical switching in a magnetically intercalated transition metal dichalcogenide.
Advances in controlling the correlated behaviour of transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics-a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations and reduced cross-talk1-3. Here, we present measurements on the intercalated transition metal dichalcogenide Fe1/3NbS2 that exhibits antiferromagnetic ordering below 42 K (refs. 4,5). We find that remarkably low current densities of the order of 104 A cm-2 can reorient the magnetic order, which can be detected through changes in the sample resistance, demonstrating its use as an electronically accessible antiferromagnetic switch. Fe1/3NbS2 is part of a larger family of magnetically intercalated transition metal dichalcogenides, some of which may exhibit switching at room temperature, forming a platform from which to build tuneable antiferromagnetic spintronic devices6,7
Charge dynamics of the Co-doped BaFeAs
We report on a thorough optical investigation over a broad spectral range and
as a function of temperature of the charge dynamics in
Ba(CoFe)As compounds for Co-doping ranging between 0 and
18%. For the parent compound as well as for =0.025 we observe the opening of
a pseudogap, due to the spin-density-wave phase transition and inducing a
reshuffling of spectral weight from low to high frequencies. For compounds with
0.051 0.11 we detect the superconducting gap, while at =0.18 the
material stays metallic at all temperatures. We describe the effective metallic
contribution to the optical conductivity with two Drude terms, representing the
combination of a coherent and incoherent component, and extract the respective
scattering rates. We establish that the transport properties in the normal
phase are dominated by the coherent Drude term for 00.051 and by the
incoherent one for 0.0610.18, respectively. Finally through spectral
weight arguments, we give clear-cut evidence for moderate electronic
correlations for 00.061, which then crossover to values appropriate
for a regime of weak interacting and nearly-free electron metals for
0.11
Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate -LiIrO
Honeycomb iridates such as -LiIrO are argued to realize
Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly
other couplings. While systems with pure Kitaev interactions are candidates to
realize a quantum spin liquid ground state, in -LiIrO it has
been shown that the balance of magnetic interactions leads to the
incommensurate spiral spin order at ambient pressure below 38 K. We study the
fragility of this state in single crystals of -LiIrO using
resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to
3.0 GPa. RXS is a direct probe of the underlying electronic order, and we
observe the abrupt disappearance of the =(0.57, 0, 0) spiral order at a
critical pressure GPa with no accompanying change in the symmetry
of the lattice. This dramatic disappearance is in stark contrast with recent
studies of -LiIrO that show continuous suppression of the spiral
order in magnetic field; under pressure, a new and possibly nonmagnetic ground
state emerges
Band and momentum dependent electron dynamics in superconducting as seen via electronic Raman scattering
We present details of carrier properties in high quality single crystals obtained from electronic Raman
scattering. The experiments indicate a strong band and momentum anisotropy of
the electron dynamics above and below the superconducting transition
highlighting the importance of complex band-dependent interactions. The
presence of low energy spectral weight deep in the superconducting state
suggests a gap with accidental nodes which may be lifted by doping and/or
impurity scattering. When combined with other measurements, our observation of
band and momentum dependent carrier dynamics indicate that the iron arsenides
may have several competing superconducting ground states.Comment: 5 pages, 4 figure
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