99 research outputs found
Determination of the phase diagram of the electron doped superconductor Ba(FeCo)As
Systematic measurements of the resistivity, heat capacity, susceptibility and
Hall coefficient are presented for single crystal samples of the electron-doped
superconductor Ba(FeCo)As. These data delineate an
phase diagram in which the single magnetic/structural phase transition that is
observed for undoped BaFeAs at 134 K apparently splits into two
distinct phase transitions, both of which are rapidly suppressed with
increasing Co concentration. Superconductivity emerges for Co concentrations
above , and appears to coexist with the broken symmetry state for
an appreciable range of doping, up to . The optimal
superconducting transition temperature appears to coincide with the Co
concentration at which the magnetic/structural phase transitions are totally
suppressed, at least within the resolution provided by the finite step size
between crystals prepared with different doping levels. Superconductivity is
observed for a further range of Co concentrations, before being completely
suppressed for and above. The form of this phase diagram
is suggestive of an association between superconductivity and a quantum
critical point arising from suppression of the magnetic and/or structural phase
transitions
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
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
Bulk Fermi surface coexistence with Dirac surface state in BiSe: a comparison of photoemission and Shubnikov-de Haas measurements
Shubnikov de Haas (SdH) oscillations and Angle Resolved PhotoEmission
Spectroscopy (ARPES) are used to probe the Fermi surface of single crystals of
Bi2Se3. We find that SdH and ARPES probes quantitatively agree on measurements
of the effective mass and bulk band dispersion. In high carrier density
samples, the two probes also agree in the exact position of the Fermi level EF,
but for lower carrier density samples discrepancies emerge in the position of
EF. In particular, SdH reveals a bulk three-dimensional Fermi surface for
samples with carrier densities as low as 10^17cm-3. We suggest a simple
mechanism to explain these differences and discuss consequences for existing
and future transport studies of topological insulators.Comment: 5 mages, 5 figure
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