5 research outputs found
Superconductivity in Potassium-Doped Few-Layer Graphene
Here we report the successful synthesis of superconducting
potassium-doped
few-layer graphene (K-doped FLG) with a transition temperature of
4.5 K, which is 1 order of magnitude higher than that observed in
the bulk potassium graphite intercalation compound (GIC) KC<sub>8</sub> (<i>T</i><sub>c</sub> = 0.39 K). The realization of superconductivity
in K-doped FLG shows the potential for the development of new superconducting
electronic devices using two-dimensional (2D) graphene as a basis
material
Structural Channels and Atomic-Cluster Insertion in Cs<sub><i>x</i></sub>Bi<sub>4</sub>Te<sub>6</sub> (1 ≤ <i>x</i> ≤ 1.25) As Observed by Aberration-Corrected Scanning Transmission Electron Microscopy
Microstructural analyses based on
aberration-corrected scanning transmission electron microscopy (STEM)
observations demonstrate that low-dimensional Cs<sub><i>x</i></sub>Bi<sub>4</sub>Te<sub>6</sub> materials, known to be a novel
thermoelectric and superconducting system, contain notable structural
channels that go directly along the <i>b</i> axis, which
can be partially filled by atom clusters depending on the thermal
treatment process. We successfully prepared two series of Cs<sub><i>x</i></sub>Bi<sub>4</sub>Te<sub>6</sub> single-crystalline
samples using two different sintering processes. The Cs<sub><i>x</i></sub>Bi<sub>4</sub>Te<sub>6</sub> samples prepared using
an air-quenching method show superconductivity at approximately 4
K, while the Cs<sub><i>x</i></sub>Bi<sub>4</sub>Te<sub>6</sub> with the same nominal compositions prepared by slowly cooling are
nonsuperconductors. Moreover, atomic structural investigations of
typical samples reveal that the structural channels are often empty
in superconducting materials; thus, we can represent the superconducting
phase as Cs<sub>1–<i>y</i></sub>Bi<sub>4</sub>Te<sub>6</sub> with considering the point defects in the Cs layers. In addition,
the channels in the nonsuperconducting crystals are commonly partially
occupied by triplet Bi clusters. Moreover, the average structures
for these two phases are also different in their monoclinic angles
(β), which are estimated to be 102.3° for superconductors
and 100.5° for nonsuperconductors
Superconducting Continuous Graphene Fibers <i>via</i> Calcium Intercalation
Superconductors are important materials
in the field of low-temperature magnet applications and long-distance
electrical power transmission systems. Besides metal-based superconducting
materials, carbon-based superconductors have attracted considerable
attention in recent years. Up to now, five allotropes of carbon, including
diamond, graphite, C<sub>60</sub>, CNTs, and graphene, have been reported
to show superconducting behavior. However, most of the carbon-based
superconductors are limited to small size and discontinuous phases,
which inevitably hinders further application in macroscopic form.
Therefore, it raises a question of whether continuously carbon-based
superconducting wires could be accessed, which is of vital importance
from viewpoints of fundamental research and practical application.
Here, inspired by superconducting graphene, we successfully fabricated
flexible graphene-based superconducting fibers <i>via</i> a well-established calcium (Ca) intercalation strategy. The resultant
Ca-intercalated graphene fiber (Ca-GF) shows a superconducting transition
at ∼11 K, which is almost 2 orders of magnitude higher than
that of early reported alkali metal intercalated graphite and comparable
to that of commercial superconducting NbTi wire. The combination of
lightness and easy scalability makes Ca-GF highly promising as a lightweight
superconducting wire
Superconductivity in a Layered Cobalt Oxychalcogenide Na<sub>2</sub>CoSe<sub>2</sub>O with a Triangular Lattice
Unconventional superconductivity in bulk materials under
ambient
pressure is extremely rare among the 3d transition metal compounds
outside the layered cuprates and iron-based family. It is predominantly
linked to highly anisotropic electronic properties and quasi-two-dimensional
(2D) Fermi surfaces. To date, the only known example of a Co-based
exotic superconductor is the hydrated layered cobaltate, NaxCoO2·yH2O, and its superconductivity is realized in the vicinity of a spin-1/2
Mott state. However, the nature of the superconductivity in these
materials is still a subject of intense debate, and therefore, finding
a new class of superconductors will help unravel the mysteries of
their unconventional superconductivity. Here, we report the discovery
of superconductivity at ∼6.3 K in our newly synthesized layered
compound Na2CoSe2O, in which the edge-shared
CoSe6 octahedra form [CoSe2] layers with a perfect
triangular lattice of Co ions. It is the first 3d transition metal
oxychalcogenide superconductor with distinct structural and chemical
characteristics. Despite its relatively low TC, this material exhibits very high superconducting upper critical
fields, μ0HC2(0), which
far exceeds the Pauli paramagnetic limit by a factor of 3–4.
First-principles calculations show that Na2CoSe2O is a rare example of a negative charge transfer superconductor.
This cobalt oxychalcogenide with a geometrical frustration among Co
spins shows great potential as a highly appealing candidate for the
realization of unconventional and/or high-TC superconductivity beyond the well-established Cu- and Fe-based superconductor
families and opens a new field in the physics and chemistry of low-dimensional
superconductors
Atom-Thin SnS<sub>2–<i>x</i></sub>Se<sub><i>x</i></sub> with Adjustable Compositions by Direct Liquid Exfoliation from Single Crystals
Two-dimensional (2D) chalcogenide
materials are fundamentally and
technologically fascinating for their suitable band gap energy and
carrier type relevant to their adjustable composition, structure,
and dimensionality. Here, we demonstrate the exfoliation of single-crystal
SnS<sub>2–<i>x</i></sub>Se<sub><i>x</i></sub> (SSS) with S/Se vacancies into an atom-thin layer by simple
sonication in ethanol without additive. The introduction of vacancies
at the S/Se site, the conflicting atomic radius of sulfur in selenium
layers, and easy incorporation with an ethanol molecule lead to high
ion accessibility; therefore, atom-thin SSS flakes can be effectively
prepared by exfoliating the single crystal <i>via</i> sonication.
The <i>in situ</i> pyrolysis of such materials can further
adjust their compositions, representing tunable activation energy,
band gap, and also tunable response to analytes of such materials.
As the most basic and crucial step of the 2D material field, the successful
synthesis of an uncontaminated and atom-thin sample will further push
ahead the large-scale applications of 2D materials, including, but
not limited to, electronics, sensing, catalysis, and energy storage
fields