Institute For Festkorperphysik

Jena, Germany

Institute For Festkorperphysik

Jena, Germany
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Zocco D.A.,University of California at San Diego | Zocco D.A.,Institute For Festkorperphysik | Hamlin J.J.,University of California at San Diego | Hamlin J.J.,University of Florida | And 8 more authors.
Journal of Physics Condensed Matter | Year: 2014

Iridium-based 5d transition-metal oxides are attractive candidates for the study of correlated electronic states due to the interplay of enhanced crystal-field, Coulomb and spin-orbit interaction energies. At ambient pressure, these conditions promote a novel Jeff = 1/2 Mottinsulating state, characterized by a gap of the order of ∼0.1 eV. We present high-pressure electrical resistivity measurements of single crystals of Sr2IrO4 and Sr3Ir2O7. While no indications of a pressure-induced metallic state up to 55 GPa were found in Sr2IrO4, a strong decrease of the gap energy and of the resistance of Sr3Ir2O7 between ambient pressure and 104 GPa confirm that this compound is in the proximity of a metal-insulator transition. © 2014 IOP Publishing Ltd Printed in the UK.


Zheng Q.,Max Planck Institute for Chemical Physics of Solids | Gumeniuk R.,Max Planck Institute for Chemical Physics of Solids | Gumeniuk R.,TU Bergakademie Freiberg | Borrmann H.,Max Planck Institute for Chemical Physics of Solids | And 7 more authors.
Dalton Transactions | Year: 2016

Two new ternary borides TM7Fe3B8 (TM = Nb, Ta) were synthesized by high-temperature thermal treatment of samples obtained by arc-melting. This new type of structure with space group P6/mmm, comprises TM slabs containing isolated planar hexagonal [B6] rings and iron centered TM columns in a Kagome type of arrangement. Chemical bonding analysis in Nb7Fe3B8 by means of the electron localizability approach reveals two-center interactions forming the Kagome net of Fe and embedded B, while weaker multicenter bonding present between this net and Nb atoms. Magnetic susceptibility measurements reveal antiferromagnetic order below TN = 240 K for Nb7Fe3B8 and TN = 265 K for Ta7Fe3B8. Small remnant magnetization below 0.01μB per f.u. is observed in the antiferromagnetic state. The bulk nature of the magnetic transistions was confirmed by the hyperfine splitting of the Mössbauer spectra, the sizable anomalies in the specific heat capacity, and the kinks in the resistivity curves. The high-field paramagnetic susceptibilities fitted by the Curie-Weiss law show effective paramagnetic moments μeff ≈ 3.1μB/Fe in both compounds. The temperature dependence of the electrical resistivity also reveals metallic character of both compounds. Density functional calculations corroborate the metallic behaviour of both compounds and demonstrate the formation of a sizable local magnetic moment on the Fe-sites. They indicate the presence of both antiferro- and ferrromagnetic interactions. © 2016 The Royal Society of Chemistry.


Giovannini M.,University of Genoa | Giovannini M.,CNR Institute of Neuroscience | Hadwig M.,Institute For Festkorperphysik | Pasero R.,University of Genoa | And 5 more authors.
Journal of Physics Condensed Matter | Year: 2010

The phase relations of the CeCo9 + δSi 4 - δ system have been studied by means of scanning electron microscopy, electron microprobe analysis and x-ray diffraction. Essentially single phase samples CeCo9 + δSi4 - δ (structure-type LaFe9Si4 with space group I4/mcm) are formed in a narrow composition range - 0.3 ≤ δ < 0.1, where stoichiometric CeCo9Si4 exhibits full structural order in space group I4/mcm. The evolution of the ground state of correlated 3d and 4f electrons in the solid solution CeCo9 + δSi 4 - δ has been investigated by dc susceptibility, magnetization, specific heat and resistivity measurements. Stoichiometric CeCo9Si4 exhibits paramagnetic Kondo lattice behaviour with a largely reduced Co3d contribution to the magnetic susceptibility as compared to nearly ferromagnetic LaCo9Si4. Nonetheless, very similar to the solid solution LaCo9 + δSi 4 - δ, weak ferromagnetism is observed in CeCo 9 + δSi4 - δ for δ > 0 and is attributed to substitutional disorder at the Si-sublattice. © 2010 IOP Publishing Ltd.


Pezoldt J.,TU Ilmenau | Schroter B.,Institute For Festkorperphysik
Materials Science Forum | Year: 2011

XPD and XRD measurements revealed a difference in the crystallographic polarity of 3C-SiC(111) grown on Si(111) carbonized by ethene diluted in hydrogen at atmospheric pressure in a rapid thermal chemical vapour deposition reactor and the crystallographic polarity of 3C-SiC(111) formed in an ethene hydrogen gas mixture at low pressures. In the first case C-face polar material was formed, whereas in the second case the grown expitaxial layer exhibits Si-face surface polarity. © (2011) Trans Tech Publications.


Shukrinov Yu.M.,Max Planck Institute for the Physics of Complex Systems | Shukrinov Yu.M.,International University of Nature, Society and Man «Dubna» | Seidel P.,Institute For Festkorperphysik | Il'ichev E.,Institute of Photonic Technology | And 5 more authors.
Journal of Physics: Conference Series | Year: 2012

We study the phase dynamics and the resonance features of coupled Josephson junctions in layered superconductors and their manifestations in the current- voltage characteristics and temporal dependence of the electric charge in the superconducting layers. Results on the effect of the external radiation and shunting of the stack of Josephson junctions by LC-elements are presented. We discuss the ideas concerning the experimental observation of these resonances.


Grosse V.,Institute For Festkorperphysik | Grosse V.,THEVA Dunnschichttechnik GmbH | Schmidl F.,Institute For Festkorperphysik | Seidel P.,Institute For Festkorperphysik
Applied Physics Letters | Year: 2012

We report on the study of the low temperature electronic transport in strontium titanate thin films having a thickness of 25-30 nm. I-V characteristics measured below 4.2 K show unique structures which are evidence for the occurrence of a Coulomb blockade. Simulations of the measured characteristics suggest that this behavior is closely related to the formation of nanoscopic metallic islands within an insulating matrix which arrange in a network connected via tunneling currents. © 2012 American Institute of Physics.


Bali R.,Helmholtz Center Dresden | Bali R.,University of Western Australia | Wintz S.,Helmholtz Center Dresden | Wintz S.,Institute For Festkorperphysik | And 14 more authors.
Nano Letters | Year: 2014

Ferromagnetism in certain alloys consisting of magnetic and nonmagnetic species can be activated by the presence of chemical disorder. This phenomenon is linked to an increase in the number of nearest-neighbor magnetic atoms and local variations in the electronic band structure due to the existence of disorder sites. An approach to induce disorder is through exposure of the chemically ordered alloy to energetic ions; collision cascades formed by the ions knock atoms from their ordered sites and the concomitant vacancies are filled randomly via thermal diffusion of atoms at room temperature. The ordered structure thereby undergoes a transition into a metastable solid solution. Here we demonstrate the patterning of highly resolved magnetic structures by taking advantage of the large increase in the saturation magnetization of Fe 60Al40 alloy triggered by subtle atomic displacements. The sigmoidal characteristic and sensitive dependence of the induced magnetization on the atomic displacements manifests a sub-50 nm patterning resolution. Patterning of magnetic regions in the form of stripes separated by ∼40 nm wide spacers was performed, wherein the magnet/spacer/magnet structure exhibits reprogrammable parallel (↑/spacer/↑) and antiparallel (↑/spacer/↓) magnetization configurations in zero field. Materials in which the magnetic behavior can be tuned via ion-induced phase transitions may allow the fabrication of novel spin-transport and memory devices using existing lateral patterning tools. © 2013 American Chemical Society.


Koslowski B.,Institute For Festkorperphysik | Tschetschetkin A.,Institute For Festkorperphysik | Maurer N.,Institute For Festkorperphysik | Mena-Osteritz E.,Institute For Organische Chemie Ii Und Neue Materialien | And 2 more authors.
Beilstein Journal of Nanotechnology | Year: 2011

Terthiophene (3T) molecules adsorbed on herringbone (HB) reconstructed Au(111) surfaces in the low coverage regime were investigated by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) under ultra-high vacuum conditions. The 3T molecules adsorb preferentially in fcc regions of the HB reconstruction with their longer axis oriented perpendicular to the soliton walls of the HB and at maximum mutual separation. The latter observation points to a repulsive interaction between molecules probably due to parallel electrical dipoles formed during adsorption. Constant-separation (I-V) and constantcurrent (z-V) STS clearly reveal the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, which are found at -1.2 eV and +2.3 eV, respectively. The HOMO-LUMO gap corresponds to that of a free molecule, indicating a rather weak interaction between 3T and Au(111). According to conductivity maps, the HOMO and LUMO are inhomogeneously distributed over the adsorbed 3T, with the HOMO being located at the ends of the linear molecule, and the LUMO symmetrically with respect to the longer axis of the molecule at the center of its flanks. Analysis of spectroscopic data reveals details of the contrast mechanism of 3T/Au(111) in STM. For that, the Shockley-like surface state of Au(111) plays an essential role and appears shifted outwards from the surface in the presence of the molecule. As a consequence, the molecule can be imaged even at a tunneling bias within its HOMO-LUMO gap. A more quantitative analysis of this detail resolves a previous discrepancy between the fairly small apparent STM height of 3T molecules (1.4-2.0 nm, depending on tunneling bias) and a corresponding larger value of 3.5 nm based on X-ray standing wave analysis. An additionally observed linear decrease of the differential tunneling barrier at positive bias when determined on top of a 3T molecule is compared to the bias independent barrier obtained on bare Au(111) surfaces. This striking difference of the barrier behavior with and without adsorbed molecules is interpreted as indicating an adsorption-induced dimensionality transition of the involved tunneling processes. © 2011 Koslowski et al.


Tyborski C.,Institute For Festkorperphysik | Herziger F.,Institute For Festkorperphysik | Maultzsch J.,Institute For Festkorperphysik
Physica Status Solidi (B) Basic Research | Year: 2015

We performed resonance Raman spectroscopy on HiPCO-produced single-walled carbon nanotubes in the spectral region of 846 and 1692cm-1, using laser excitation energies between 1.58 and 2.73eV. We observe a characteristic peak around 846cm-1 and its overtones around 1692cm-1. Especially the latter was controversially discussed in the past and has been assigned to a double-resonant Raman process involving two oTO phonons. We demonstrate that both peaks slightly depend on the excitation laser energy by means of their shape, intensity, and peak position. Following the model proposed by Dobardžić et al., we relate both peaks to oTO Γ-point phonons. As we analyze both, the first-order band and its overtone simultaneously, we are able to provide a unified explanation of these low-intensity Raman bands in carbon nanotubes. Raman spectrum of an HiPCO-produced buckypaper carbon nanotube sample at 2.33eV laser energy. Both insets show a magnification of the oTO-related first- and second-order Raman bands, which we discuss in this article. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


PubMed | Institute For Festkorperphysik
Type: | Journal: Beilstein journal of nanotechnology | Year: 2011

Terthiophene (3T) molecules adsorbed on herringbone (HB) reconstructed Au(111) surfaces in the low coverage regime were investigated by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) under ultra-high vacuum conditions. The 3T molecules adsorb preferentially in fcc regions of the HB reconstruction with their longer axis oriented perpendicular to the soliton walls of the HB and at maximum mutual separation. The latter observation points to a repulsive interaction between molecules probably due to parallel electrical dipoles formed during adsorption. Constant-separation (I-V) and constant-current (z-V) STS clearly reveal the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, which are found at -1.2 eV and +2.3 eV, respectively. The HOMO-LUMO gap corresponds to that of a free molecule, indicating a rather weak interaction between 3T and Au(111). According to conductivity maps, the HOMO and LUMO are inhomogeneously distributed over the adsorbed 3T, with the HOMO being located at the ends of the linear molecule, and the LUMO symmetrically with respect to the longer axis of the molecule at the center of its flanks. Analysis of spectroscopic data reveals details of the contrast mechanism of 3T/Au(111) in STM. For that, the Shockley-like surface state of Au(111) plays an essential role and appears shifted outwards from the surface in the presence of the molecule. As a consequence, the molecule can be imaged even at a tunneling bias within its HOMO-LUMO gap. A more quantitative analysis of this detail resolves a previous discrepancy between the fairly small apparent STM height of 3T molecules (1.4-2.0 nm, depending on tunneling bias) and a corresponding larger value of 3.5 nm based on X-ray standing wave analysis. An additionally observed linear decrease of the differential tunneling barrier at positive bias when determined on top of a 3T molecule is compared to the bias independent barrier obtained on bare Au(111) surfaces. This striking difference of the barrier behavior with and without adsorbed molecules is interpreted as indicating an adsorption-induced dimensionality transition of the involved tunneling processes.

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