57 research outputs found
Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers
A promising route to tailoring the electronic properties of quantum materials
and devices rests on the idea of orbital engineering in multilayered oxide
heterostructures. Here we show that the interplay of interlayer charge
imbalance and ligand distortions provides a knob for tuning the sequence of
electronic levels even in intrinsically stacked oxides. We resolve in this
regard the -level structure of layered SrIrO by electron spin
resonance. While canonical ligand-field theory predicts -factors
for positive tetragonal distortions as present in SrIrO, the
experiment indicates . This implies that the iridium
levels are inverted with respect to their normal ordering. State-of-the-art
electronic-structure calculations confirm the level switching in SrIrO,
whereas we find them in BaIrO to be instead normally ordered. Given the
nonpolar character of the metal-oxygen layers, our findings highlight the
tetravalent transition-metal 214 oxides as ideal platforms to explore
-orbital reconstruction in the context of oxide electronics
Rolled-up self-assembly of compact magnetic inductors, transformers and resonators
Three-dimensional self-assembly of lithographically patterned ultrathin films
opens a path to manufacture microelectronic architectures with functionalities
and integration schemes not accessible by conventional two-dimensional
technologies. Among other microelectronic components, inductances,
transformers, antennas and resonators often rely on three-dimensional
configurations and interactions with electromagnetic fields requiring
exponential fabrication efforts when downscaled to the micrometer range. Here,
the controlled self-assembly of functional structures is demonstrated. By
rolling-up ultrathin films into cylindrically shaped microelectronic devices we
realized electromagnetic resonators, inductive and mutually coupled coils.
Electrical performance of these devices is improved purely by transformation of
a planar into a cylindrical geometry. This is accompanied by an overall
downscaling of the device footprint area by more than 50 times. Application of
compact self-assembled microstructures has significant impact on electronics,
reducing size, fabrication efforts, and offering a wealth of new features in
devices by 3D shaping.Comment: 19 pages, 3 figures, 6 supplementary figure
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RolledâUp SelfâAssembly of Compact Magnetic Inductors, Transformers, and Resonators
3D self-assembly of lithographically patterned ultrathin films opens a path to manufacture microelectronic architectures with functionalities and integration schemes not accessible by conventional 2D technologies. Among other microelectronic components, inductances, transformers, antennas, and resonators often rely on 3D configurations and interactions with electromagnetic fields requiring exponential fabrication efforts when downscaled to the micrometer range. Here, the controlled self-assembly of functional structures is demonstrated. By rolling up ultrathin films into cylindrically shaped microelectronic devices, electromagnetic resonators, inductive and mutually coupled coils are realized. Electrical performance of these devices is improved purely by transformation of a planar into a cylindrical geometry. This is accompanied by an overall downscaling of the device footprint area by more than 50 times. Application of compact self-assembled microstructures has significant impact on electronics, reducing size, fabrication efforts, and offering a wealth of new features in devices by 3D shaping
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Phononic-magnetic dichotomy of the thermal Hall effect in the Kitaev material Na2 Co2 TeO6
The quest for a half-quantized thermal Hall effect of a Kitaev system represents an important tool to probe topological edge currents of emergent Majorana fermions. Pertinent experimental findings for α-RuCl3 are, however, strongly debated, and it has been argued that the thermal Hall signal stems from phonons or magnons rather than from Majorana fermions. Here, we investigate the thermal Hall effect of the Kitaev candidate material Na2Co2TeO6, and we show that the measured signal emerges from at least two components, phonons and magnetic excitations. This dichotomy results from our discovery that the longitudinal and transversal heat conductivities share clear phononic signatures, while the transversal signal changes sign upon entering the low-temperature, magnetically ordered phase. Our results demonstrate that uncovering a genuinely quantized magnetic thermal Hall effect in Kitaev topological quantum spin liquids such as α-RuCl3 and Na2Co2TeO6 requires disentangling phonon vs magnetic contributions, including potentially fractionalized excitations such as the expected Majorana fermions
Magnetic resonance study of rare-earth titanates
We present a nuclear magnetic resonance (NMR) and electron spin resonance
(ESR) study of rare-earth titanates derived from the spin-1/2 Mott insulator
YTiO. Measurements of single-crystalline samples of (Y,Ca,La)TiO in a
wide range of isovalent substitution (La) and hole doping (Ca) reveal several
unusual features in the paramagnetic state of these materials. Y NMR
demonstrates a clear discrepancy between the static and dynamic local magnetic
susceptibilities, with deviations from Curie-Weiss behavior far above the Curie
temperature . No significant changes are observed close to , but a
suppression of fluctuations is detected in the NMR spin-lattice relaxation time
at temperatures of about . Additionally, the nuclear spin-spin
relaxation rate shows an unusual peak in dependence on temperature for all
samples. ESR of the unpaired Ti electron shows broad resonance lines at all
temperatures and substitution/doping levels, which we find to be caused by
short electronic spin-lattice relaxation times. We model the relaxation as an
Orbach process that involves a low-lying electronic excited state, which
enables the determination of the excited-state gap from the temperature
dependence of the ESR linewidths. We ascribe the small gap to Jahn-Teller
splitting of the two lower Ti orbitals. The value of the gap closely
follows and is consistent with the temperatures at which deviations from
Curie-Weiss fluctuations are observed in NMR. These results provide insight
into the interplay between orbital and spin degrees of freedom in rare-earth
titanates and indicate that full orbital degeneracy lifting is associated with
ferromagnetic order
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Probing the magnetic superexchange couplings between terminal CuII ions in heterotrinuclear bis(oxamidato) type complexes
The reaction of one equivalent of [n-Bu4N]2[Ni(opboR2)] with two equivalents of [Cu(pmdta)(X)2] afforded the heterotrinuclear CuIINiIICuII containing bis(oxamidato) type complexes [Cu2Ni(opboR2)(pmdta)2]X2 (R = Me, X = NO3â (1); R = Et, X = ClO4â (2); R = n-Pr, X = NO3â (3); opboR2 = o-phenylenebis(NR-substituted oxamidato); pmdta = N,N,Nâ,Nâ,Nâ-pentamethyldiethylenetriamine). The identities of the heterotrinuclear complexes 1â3 were established by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction studies, which revealed the cationic complex fragments [Cu2Ni(opboR2)(pmdta)2]2+ as not involved in any further intermolecular interactions. As a consequence thereof, the complexes 1â3 possess terminal paramagnetic [Cu(pmdta)]2+ fragments separated by [NiII(opboR2)]2â bridging units representing diamagnetic SNi = 0 states. The magnetic field dependence of the magnetization M(H) of 1â3 at T = 1.8 K has been determined and is shown to be highly reproducible with the Brillouin function for an ideal paramagnetic spin = 1/2 system, verifying experimentally that no magnetic superexchange couplings exists between the terminal paramagnetic [Cu(pmdta)]2+ fragments. Susceptibility measurements versus temperature of 1â3 between 1.8â300 K were performed to reinforce the statement of the absence of magnetic superexchange couplings in these three heterotrinuclear complexes
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