Abstract
Weyl semimetals (WSMs) hosting Weyl points (WPs) with different chiralities attract great interest as an object to study chirality-related physical properties, topological phase transitions, ...and topological superconductivity. Quantum oscillation measurements and theoretical calculations imply that the type-II WPs in NbIrTe
4
are robust against the shift of chemical potential making it a good material for pressure studies on topological properties. Here we report the results of electrical transport property measurements and Raman spectroscopy studies under pressures up to 65.5 GPa accompanied by theoretical electronic structure calculations. Hall resistivity data reveal an electronic transition indicated by a change of the charge carrier from multiband character to hole-type at ~12 GPa, in agreement with the calculated Fermi surface. An onset of superconducting transition is observed at pressures above 39 GPa, with critical temperature increasing as pressure increases. Moreover, theoretical calculations indicate that WPs persist up to highly reduced unit cell volume (−17%), manifesting that NbIrTe
4
is a candidate of topological superconductor.
Abstract
Chiral intermetallic phases may show unusual chemical and physical properties with nontrivial structure-property relationship. It is therefore of particular interest to study the structural ...conversion between domains of different handedness. Here, the atomic decoration of the enantiomorph exchange area within single crystal of the Weyl semimetal CoSi is determined by a combination of atomic-resolution scanning transmission electron microscopy imaging, single crystal X-ray diffraction and quantum chemical analysis of atomic interactions. Two-atomic CoSi units are shown to be the bonding base for the FeSi-type structure and may be considered as ‘pseudo-molecules’, thinking of molecular organic crystals. Tiny reorganisation of atomic interactions within these units results in the appearance of sequence ‘faults’ in the structure pattern i.e. in a different structural motif in the enantiomorph exchange area, which – contrary to the A and B enantiomorphs of CoSi – contains an inversion centre and allows a local enantiomorph ‘conversion’. Due to the special features of atomic interactions, the reorganisation of multi-atomic bonds leads to slightly higher total energy. This appears within one and the same grain which is prepared by the short distance chemical vapor transport.
We report on the inelastic response of AV
2
Al
20
(with A = Sc, La and Ce) probed by high-resolution inelastic neutron scattering experiments. Intense signals associated with the dynamics of Sc, La ...and Ce are identified in the low-energy range at 6-14 meV in ScV
2
Al
20
and at 8-16 meV in LaV
2
Al
20
and CeV
2
Al
20
. Their response to temperature changes between 2 and 300 K reveals a very weak softening of the modes upon heating in LaV
2
Al
20
and CeV
2
Al
20
and a distinguished blue shift by about 2 meV in ScV
2
Al
20
. By means of density functional theory (DFT) and lattice dynamics calculations (LDC) we show that the unusual anharmonicity of the Sc-dominated modes is due to the local potential of Sc featured by a strong quartic term. The vibrational dynamics of ScV
2
Al
20
as well as of LaV
2
Al
20
and CeV
2
Al
20
is reproduced by a set of eigenmodes. To screen the validity of the DFT and LDC results they are confronted with data from X-ray diffraction measurements. The effect of the strong phonon renormalization in ScV
2
Al
20
on thermodynamic observables is computed on grounds of the LDC derived inelastic response. To set the data in a general context of AV
2
Al
20
compounds and their physical properties we report in addition computer and experimental results of the binary V
2
Al
20
compound.
Neutron spectroscopy and
ab initio
calculations indicate the apparent glass-like lattice thermal conductivity
κ
l
of the nano-cage compound ScV
2
Al
20
as an effect of phonon renormalization predetermined by the crystal's ground state properties.
Weyl semimetal is a unique topological phase with topologically protected band crossings in the bulk and robust surface states called Fermi arcs. Weyl nodes always appear in pairs with opposite ...chiralities, and they need to have either time‐reversal or inversion symmetry broken. When the time‐reversal symmetry is broken the minimum number of Weyl points (WPs) is two. If these WPs are located at the Fermi level, they form an ideal Weyl semimetal (WSM). In this study, intrinsic ferromagnetic (FM) EuCd2As2 are grown, predicted to be an ideal WSM and studied its electronic structure by angle‐resolved photoemission spectroscopy, and scanning tunneling microscopy which agrees closely with the first principles calculations. Moreover, anomalous Hall conductivity and Nernst effect are observed, resulting from the non‐zero Berry curvature, and the topological Hall effect arising from changes in the band structure caused by spin canting produced by magnetic fields. These findings can help realize several exotic quantum phenomena in inorganic topological materials that are otherwise difficult to assess because of the presence of multiple pairs of Weyl nodes.
Ferromagnetic EuCd2As2 exhibits anomalous Hall conductivity and Nernst effect, resulting from the non‐zero Berry curvature close to the Fermi level. Scanning tunneling microscopy and angle‐resolved photoemission spectroscopy are used to investigate its electronic structure which is in agreement with first principles calculations.
While electrons moving perpendicular to a magnetic field are confined to cyclotron orbits, they can move freely parallel to the field. This simple fact leads to complex current flow in clean, low ...carrier density semi-metals, such as long-ranged current jets forming along the magnetic field when currents pass through point-like constrictions. Occurring accidentally at imperfect current injection contacts, the phenomenon of "current jetting" plagues the research of longitudinal magneto-resistance, which is particularly important in topological conductors. Here we demonstrate the controlled generation of tightly focused electron beams in a new class of micro-devices machined from crystals of the Dirac semi-metal Cd3As2. The current beams can be guided by tilting a magnetic field and their range tuned by the field strength. Finite element simulations quantitatively capture the voltage induced at faraway contacts when the beams are steered towards them, supporting the picture of controlled electron jets. These experiments demonstrate direct control over the highly non-local signal propagation unique to 3D semi-metals in the current jetting regime, and may lead to applications akin to electron optics in free space.
We present the synthesis and characterization of novel cyclometalated ruthenium N-heterocyclic carbene (NHC) complexes of the general formula Ru(C^C*)(bpy)2PF6 (bpy = 2,2′-bipyridine), with the ...C^C* ligand being based on different 1-phenylimidazoles. They were synthesized in a one-pot procedure starting from the corresponding p-cymene NHC complexes Ru(C^C*)(p-cymene)Cl. Their structural, spectroscopic, and electrochemical properties were investigated by NMR, X-ray, UV/vis, and CV, as well as density functional theory methods. Because of the stronger electron-donating carbene ligands, these complexes represent a new class of bisheteroleptic dyes with improved photophysical and electrochemical properties.
The MnPc(py)
2 complex was obtained in the reaction of MnPc with purified and dry pyridine under non-oxidation conditions. It crystallises in the centrosymmetric space group
P2
1/
c of the monoclinic ...system with two molecules per unit cell. The Mn
2+ cation is coordinated by four
N-isoindole atoms of phthalocyaninato(2−) macrocycle and axially by two nitrogen atoms of pyridine molecules into a tetragonal bipyramid. The MnPc(py)
2 crystals are moderately stable under air, but in pyridine solution the MnPc(py)
2 complex undergoes oxidation by O
2 yieldings the binuclear manganese(III) μ-oxo complex (MnPcpy)
2O as evidenced by the UV–Vis spectroscopy. The magnetic susceptibility measurement performed on solid sample of MnPc(py)
2 shows the Curie–Weiss behaviour in the temperature region of 300–15 K. The calculated magnetic moment
μ
eff indicates three unpaired electrons (
S=3/2), thus the ground state configuration of Mn ion is (a
1g)
2(e
g)
2(b
2g)
1, and the MnPc(py)
2 complex is the intermediate spin complex. Below 5.5 K (
T
N) the magnetic susceptibility sharply decreases due to the cooperative intermolecular antiferromagnetic interactions.
The MnPc(py)
2 complex was obtained in crystalline form in the reaction of MnPc with purified and dry pyridine. The MnPc(py)
2 is unstable in oxidation conditions and transforms into MnPc(py)
2O. The calculated magnetic moment
μ
eff indicates three unpaired electrons (
S=3/2). Below 5.5 K (
T
N) the magnetic susceptibility sharply decreases due to the co-operative intermolecular antiferromagnetic interactions.
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