201 research outputs found
High pressure growth and electron transport properties of superconducting SmFeAsO1-xHx single crystals
We report the single crystal growth and characterization of the highest Tc
iron-based superconductor SmFeAsO1-xHx. Some sub-millimeter-sized crystals were
grown using the mixture flux of Na3As + 3NaH + As at 3.0 GPa and 1473 K. The
chemical composition analyses confirmed 10% substitution of hydrogen for the
oxygen site (x = 0.10), however, the structural analyses suggested that the
obtained crystal forms a multi-domain structure. By using the FIB technique we
fabricated the single domain SmFeAsO0.9H0.10 crystal with the Tc of 42 K, and
revealed the metallic conduction in in-plane (rhoab), while semiconducting in
the out-of-plane (rhoc). From the in-plane Hall coefficient measurements, we
confirmed that the dominant carrier of SmFeAsO0.9H0.10 crystal is an electron,
and the hydride ion occupied at the site of the oxygen ion effectively supplies
a carrier electron per iron following the equation: O2- = H- + e-.Comment: 4 figures, 2 table
Electrides as a New Platform of Topological Materials
Recent discoveries of topological phases realized in electronic states in
solids have revealed an important role of topology, which ubiquitously appears
in various materials in nature. Many well-known materials have turned out to be
topological materials, and this new viewpoint of topology has opened a new
horizon in material science. In this paper we find that electrides are suitable
for achieving various topological phases, including topological insulating and
topological semimetal phases. In the electrides, in which electrons serve as
anions, the bands occupied by the anionic electrons lie near the Fermi level,
because the anionic electrons are weakly bound by the lattice. This property of
the electrides is favorable for achieving band inversions needed for
topological phases, and thus the electrides are prone to topological phases.
From such a point of view, we find many topological electrides, YC
(nodal-line semimetal (NLS)), ScC (insulator with Zak phase),
SrBi (NLS), HfBr (quantum spin Hall system), and LaBr (quantum anomalous
Hall insulator), by using ab initio calculation. The close relationship between
the electrides and the topological materials is useful in material science in
both fields.Comment: 12 pages, 9 figure
Quantum Phase transition under pressure in a heavily hydrogen-doped iron-based superconductor LaFeAsO
Hydrogen (H)-doped LaFeAsO is a prototypical iron-based superconductor.
However, its phase diagram extends beyond the standard framework, where a
superconducting (SC) phase follows an antiferromagnetic (AF) phase upon carrier
doping; instead, the SC phase is sandwiched between two AF phases appearing in
lightly and heavily H-doped regimes. We performed nuclear magnetic resonance
(NMR) measurements under pressure, focusing on the second AF phase in the
heavily H-doped regime. The second AF phase is strongly suppressed when a
pressure of 3.0 GPa is applied, and apparently shifts to a highly H-doped
regime, thereby a "bare" quantum critical point (QCP) emerges. A quantum
critical regime emerges in a paramagnetic state near the QCP, however, the
influence of the AF critical fluctuations to the SC phase is limited in the
narrow doping regime near the QCP. The optimal SC condition ( 48 K)
is unaffected by AF fluctuations
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