85 research outputs found
Superconductivity in the -carbide-type oxides Zr4Rh2Ox
We report on the synthesis and the superconductivity of ZrRhO
( = 0.4, 0.5, 0.6, 0.7, 1.0). These compounds crystallize in the
-carbide structure, which is a filled version of the complex
intermetallic TiNi structure. We find that in the system
ZrRhO, already a small amount ( 0.4) of oxygen addition
stabilizes the -carbide structure over the more common intermetallic
CuAl structure-type, in which ZrRh crystallizes. We show that
ZrRhO and ZrRhO are bulk superconductors with critical
temperatures of 2.8 K and 4.7 K in the resistivity, respectively.
Our analysis of the superconducting properties reveal both compounds to be
strongly type-II superconductors with critical fields up to (0)
8.8 mT and (0) 6.08 T. Our results support
that the -carbides are a versatile family of compounds for the
investigation of the interplay of interstitial doping on physical properties,
especially for superconductivity
Superconductivity in the η-carbide-type oxides Zr4Rh2Ox
We report on the synthesis and the superconductivity in (x = 0.4, 0.5, 0.6, 0.7, 1.0). These compounds crystallize in the η-carbide structure, which is a filled version of the complex intermetallic structure. We find that in the system , already a small amount (x 0.4) of oxygen addition stabilizes the η-carbide structure over the more common intermetallic structure-type, in which crystallizes. We show that and are bulk superconductors with critical temperatures of 2.8 K and 4.7 K in the resistivity, respectively. Our analysis of the superconducting properties reveal both compounds to be strongly type-II superconductors with critical fields up to (0) 8.8 mT and (0) 6.08 T. Our results support that the η-carbides are a versatile family of compounds for the investigation of the interplay of interstitial doping on physical properties, especially for superconductivity
Quantum Materials Discovery by Combining Chemical and Physical Design Principles
Abstract: Exploratory quantum materials discovery remains crucial to progress in material science. Due to the grand challenges that we are facing in predicting these materials and their properties from scratch, chemical design principles remain a key ingredient for the discovery of new materials. Chemical heuristics, structure, bonding, as well as global and local symmetries are at the very foundation of materials properties. In this regard, in this research, we aim to identify functional materials by composition-structure-property understanding. Materials discovery consists of a subset of methods and design principles that go hand in hand until a desired material or property is realized. However, materials synthesis is still far from a rational design approach. Rather, materials, and especially metastable materials, have to be accessed and synthesized in an exploratory, laboratory-intensive fashion. At the same time, quantum materials discovery is a vibrant highly active field of research that has seen various leaps of progress in recent years, and that holds the promise for many more in the coming years. Here, we lay out how we are discovering new materials and new materials physics in our and other chemical physics, or physical chemistry research groups, and how chemistry and chemical synthesis play a crucial role in this process.
Polytypism and superconductivity in the NbS2 system
We report on the phase formation and the superconducting properties in the NbS2 system. Specifically, we have performed a series of standardized solid-state syntheses in this system, which allow us to establish a comprehensive synthesis map for the formation of the two polytypes 2H-NbS2 and 3R-NbS2, respectively. We show that the identification of two polytypes by means of X-ray diffraction is not always unambiguous. Our physical property measurements on a phase-pure sample of 3R-NbS2, on a phase-pure sample of 2H-NbS2, and a mixed phase sample confirm earlier reports that 2H-NbS2 is a bulk superconductor and that 3R-NbS2 is not a superconductor above T = 1.75 K. Our results clearly show that specific heat measurements, as true bulk measurements, are crucial for the identification of superconducting materials in this and related systems. Our results indicate that for the investigation of van der Waals materials great care has to be taken on choosing the synthesis conditions for obtaining phase pure samples
Polytypism and Superconductivity in the NbS System
We report on the phase formation and the superconducting properties in the
NbS system. Specifically, we have performed a series of standardized
solid-state syntheses in this system, which allow us to establish a
comprehensive synthesis map for the formation of the two polytypes 2H-NbS
and 3R-NbS, respectively. We show that the identification of two polytypes
by means of X-ray diffraction is not always unambiguous. Our physical property
measurements on a phase-pure sample of 3R-NbS, on a phase-pure sample of
2H-NbS, and a mixed phase sample confirm earlier reports that 2H-NbS is
a bulk superconductor and that 3R-NbS is not a superconductor above
1.75 K. Our results clearly show that specific heat measurements, as true bulk
measurements, are crucial for the identification of superconducting materials
in this and related systems. Our results indicate that for the investigation of
van-der-Waals materials great care has to be taken on choosing the synthesis
conditions for obtaining phase pure samples.Comment: https://pubs.rsc.org/en/content/articlelanding/2021/dt/d0dt03636f#!divAbstrac
Short-range magnetic interactions and spin-glass behavior in the quasi-2D nickelate Pr4Ni3O8
The nickelate Pr4Ni3O8 features quasi-two-dimensional layers consisting of
three stacked square-planar NiO2 planes, in a similar way to the well-known
cuprate superconductors. The mixed-valent nature of Ni and its metallic
properties makes it a candidate for potentially unconventional
superconductivity. We have synthesized Pr4Ni3O8 by topotactic reduction of
Pr4Ni3O10 in 10 percent hydrogen gas, and report on measurements of
powder-neutron diffraction, magnetization and muon-spin rotation (uSR). We find
that Pr4Ni3O8 shows complicated spin-glass behavior with a distinct magnetic
memory effect in the temperature range from 2 to 300 K and a freezing
temperature T_s ~ 68 K. Moreover, the analysis of uSR spectra indicates two
magnetic processes characterized by remarkably different relaxation rates: a
slowly-relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions,
and a fast-relaxing signal, whose relaxation rate increases substantially below
~ 70 K which can be ascribed to the presence of short-range correlated regions.
We conclude that the complex spin-freezing process in Pr4Ni3O8 is governed by
these multiple magnetic interactions. It is possible that the complex magnetism
in Pr4Ni3O8 is detrimental to the occurrence of superconductivity
Sb2Se3(100): A strongly anisotropic surface
Interest in antimony selenide (Sb2Se3) has been constantly growing in the recent past, especially for its promising properties for applications in the field of solar energy technologies. Surprisingly, the surface properties of this material, which is built from van der Waals stacked one-dimensional (1D) ribbons, have not been studied in detail yet. Here we demonstrate that Sb2Se3 crystals cleave along the (100) planes. The resulting surface shows a pronounced 1D structure, reflecting the stacking of ribbons in the bulk crystal. The cleaving process leads to the formation of slightly tilted surface domains, with the tilt angles oriented invariably along the ribbon directions, suggesting a strong anisotropy of the internal friction forces. Our angle-resolved photoemission data reveal that the 1D character of the crystalline structure of this material is also reflected in its electronic band structure
Preparation and Characterization of High-Entropy Alloy (TaNb)(ZrHfTi) Superconducting Films
We report on the preparation and the physical properties of superconducting
(TaNb)_1-x(ZrHfTi)_x high-entropy alloy films. The films were prepared by means
of magnetron sputtering at room temperature, with x ranging from 0 to 1 with an
average thickness of 600 - 950 nm. All films crystallize in a pseudo
body-centered cubic (BCC) structure. For samples with x < 0.65, the
normal-state properties are metallic, while for x > 0.65 the films are weakly
insulating. The transition from metallic to weakly insulating occurs right at
the near-equimolar stoichiometry. We find all films, except for x = 0 or 1, to
become superconducting at low temperatures, and we interpret their
superconducting properties within the Bardeen-Cooper-Schrieffer (BCS)
framework. The highest transition temperature T_c = 6.9 K of the solid solution
is observed for x = 0.43. The highest upper-critical field B_c2(0) = 11.05 T is
found for the near-equimolar ratio x = 0.65, where the mixing entropy is the
largest. The superconducting parameters derived for all the films from
transport measurements are found to be close to those that are reported for
amorphous superconductors. Our results indicate that these films of
high-entropy alloys are promising candidates for superconducting device
fabrication
Discovery of superconductivity in Nb<sub>4</sub>SiSb<sub>2</sub> with a V<sub>4</sub>SiSb<sub>2</sub>-type structure and implications of interstitial doping on its physical properties
We report on the discovery of NbSiSb. This compound is a new superconductor with a T of 1.6 K. The channel void positions of this phase can be partly filled with Cu, Pd, or Pt, which leads to a lowering of the transition temperature
Superconducting order parameter of the nodal-line semimetal NaAlSi
Nodal-line semimetals are topologically non-trivial states of matter
featuring band crossings along a closed curve, i.e. nodal-line, in momentum
space. Through a detailed analysis of the electronic structure, we show for the
first time that the normal state of the superconductor NaAlSi, with a critical
temperature of 7 K, is a nodal-line semimetal, where the
complex nodal-line structure is protected by non-symmorphic mirror crystal
symmetries. We further report on muon spin rotation experiments revealing that
the superconductivity in NaAlSi is truly of bulk nature, featuring a fully
gapped Fermi-surface. The temperature-dependent magnetic penetration depth can
be well described by a two-gap model consisting of two -wave symmetric gaps
with 0.6(2) meV and 1.39(1) meV. The zero-field muon
experiment indicates that time-reversal symmetry is preserved in the
superconducting state. Our observations suggest that notwithstanding its
topologically non-trivial band structure, NaAlSi may be suitably interpreted as
a conventional London superconductor, while more exotic superconducting gap
symmetries cannot be excluded. The intertwining of topological electronic
states and superconductivity renders NaAlSi a prototypical platform to search
for unprecedented topological quantum phases
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