982 research outputs found
Superconductivity in rubidium substituted Ba1-xRbxTi2Sb2O
We report on the synthesis and the physical properties of Ba1-xRbxTi2Sb2O (x
< 0.4) by x-ray diffraction, SQUID magnetometery, resistivity and specific heat
measurements. Upon hole doping by substituting Ba with Rb, we find
superconductivity with a maximum Tc = 5.4 K. Simultaneously, the
charge-density-wave (CDW) transition temperature is strongly reduced from T_CDW
55 K in the parent compound BaTi2Sb2O and seems to be suppressed for x > 0.2.
The bulk character of the superconducting state for the optimally doped sample
(x = 0.2) is confirmed by the occurrence of a well developed discontinuity in
the specific heat at Tc, with \DeltaC/Tc = 22 mJ/mol K2, as well as a large
Meissner-shielding fraction of approximately 40 %. The lower and the upper
critical fields of the optimally doped sample (x = 0.2) are estimated to
\mu0Hc1(0) = 3.8 mT and \mu0Hc2(0) = 2.3 T, respectively, indicating that these
compounds are strongly type-II superconductors
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
Tuning the critical magnetic field of the triplon Bose-Einstein condensation in BaSrCrO
The structure and magnetic interactions of the triplon Bose-Einstein
condensation candidates BaCrO and SrCrO have been
studied thoroughly in the literature, but little is known about a possible
triplon condensation in the corresponding solid solution
BaSrCrO. We have prepared various members of this solid
solution and systematically examined their magnetic properties in high magnetic
fields up to 60 T and at low temperatures down to 340 mK, by means of pulsed
field and cantilever magnetometry. From these experiments for
, we find that the critical fields of
BaSrCrO decrease monotonically as a function of the Sr
content . This change is in good agreement with the earlier reported
variation of the magnetic interactions in these compounds
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.
Adaptive sparse sampling for quasiparticle interference imaging
Quasiparticle interference imaging (QPI) offers insight into the band structure of quantum materials from the Fourier transform of local density of states (LDOS) maps. Their acquisition with a scanning tunneling microscope is traditionally tedious due to the large number of required measurements that may take several days to complete. The recent demonstration of sparse sampling for QPI imaging showed how the effective measurement time could be fundamentally reduced by only sampling a small and random subset of the total LDOS. However, the amount of required sub-sampling to faithfully recover the QPI image remained a recurring question. Here we introduce an adaptive sparse sampling (ASS) approach in which we gradually accumulate sparsely sampled LDOS measurements until a desired quality level is achieved via compressive sensing recovery. The iteratively measured random subset of the LDOS can be interleaved with regular topographic images that are used for image registry and drift correction. These reference topographies also allow to resume interrupted measurements to further improve the QPI quality. Our ASS approach is a convenient extension to quasiparticle interference imaging that should remove further hesitation in the implementation of sparse sampling mapping schemes
Adaptive Sparse Sampling for Quasiparticle Interference Imaging
Quasiparticle interference imaging (QPI) offers insight into the band
structure of quantum materials from the Fourier transform of local density of
states (LDOS) maps. Their acquisition with a scanning tunneling microscope is
traditionally tedious due to the large number of required measurements that may
take several days to complete. The recent demonstration of sparse sampling for
QPI imaging showed how the effective measurement time could be fundamentally
reduced by only sampling a small and random subset of the total LDOS. However,
the amount of required sub-sampling to faithfully recover the QPI image
remained a recurring question. Here we introduce an adaptive sparse sampling
(ASS) approach in which we gradually accumulate sparsely sampled LDOS
measurements until a desired quality level is achieved via compressive sensing
recovery. The iteratively measured random subset of the LDOS can be interleaved
with regular topographic images that are used for image registry and drift
correction. These reference topographies also allow to resume interrupted
measurements to further improve the QPI quality. Our ASS approach is a
convenient extension to quasiparticle interference imaging that should remove
further hesitation in the implementation of sparse sampling mapping schemes.Comment: 10 pages, 5 figure
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
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
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