Failure of the empirical OCT law in the Bi2Sr2CuO6+d compound

We have studied the evolution of the thermoelectric power S(T) with oxygen doping of single-layered Bi2Sr2CuO6+d thin films and ceramics in the overall superconducting (Tc, S290K) phase diagram. While the universal relation between the room-temperature thermopower S290K and the critical temperature is found to hold in the strongly overdoped region (d>0.14), a strong violation is observed in the underdoped part of the phase diagram. The observed behaviour is compared with other cuprates and the different scenarios are discussed.Comment: 7 pages, 5 figure

Strain Induced Self-Assembly in Complex Oxide Thin Films

Trabajo presentado a la Conferencia "BNC-b Research Meeting" celebrada en Barcelona el 14 de julio de 2011.We acknowledge financial support from Spanish MICINN (MAT2009-08024), CONSOLIDER (CSD2007-00041) and FEDER program. ZK thanks the Spanish MICINN for the financial support through the RyC program.Peer reviewe

Infrared and Raman spectra of LiV2O5 single crystals

The phonon dynamics of LiV2O5 single crystals is studied using infrared and Raman spectroscopy techniques. The infrared-active phonon frequencies and dielectric constants are obtained by oscillator fitting procedure of the reflectivity data measured at room temperature. The Raman scattering spectra are measured at room temperature and at T=10 K in all nonequivalent polarized configurations. The assignment of the phonons is done by comparing the infrared and Raman spectra of LiV2O5 and NaV2O5. The factor-group-analysis of the LiV2O5 crystal symmetry and of its constituent layers is performed to explain the symmetry properties of the observed modes. We concluded that layer symmetry dominates in the vibrational properties of this compound.Comment: 10 pages, 5 figure

Interfacial effects in La2/3Sr1/3MnO3 thin films with different complex oxide capping layers

Interfacialeffects in sputtered La2/3Sr1/3MnO3thin films with different capping layers (MgO, LaAlO3, SrTiO3, NdGaO3, and Au) have been locally investigated by means of x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Mn L3,2-edge. Data were acquired by using the total electron yield detection mode thus guaranteeing maximum sensitivity to the interface. The data show that LaAlO3 capping almost does not modify the bulklike Mn valence at the interface. In case of SrTiO3 and Au, the presence of divalent Mn is detected, whereas MgO and NdGaO3 capping lead to an increase of the Mn valence oxidation state. The modification of the nominal Mn valence state leads to depressed surfacemagnetization.We acknowledge financial support from the Spanish MEC (MAT2009-08024 and MAT2008-04931/NAN), CONSOLIDER (CSD2007-00041) and FEDER program. The research leading to these results has received funding from the European Community’s Seventh Framework Program (FP7/2007-2013) under Grant No. 226716. Z.K. thanks the Spanish MEC for the financial support through the RyC program.Peer reviewe

Thermopower in the strongly overdoped region of single-layer Bi2Sr2CuO6+d superconductor

The evolution of the thermoelectric power S(T) with doping, p, of single-layer Bi2Sr2CuO6+d ceramics in the strongly overdoped region is studied in detail. Analysis in term of drag and diffusion contributions indicates a departure of the diffusion from the T-linear metallic behavior. This effect is increased in the strongly overdoped range (p~0.2-0.28) and should reflect the proximity of some topological change.Comment: 4 pages, 4 figure

Growth kinetics engineered magnetoresistance response in La2/3Sr1/3MnO3 thin films

Under the terms of the Creative Commons Attribution (CC BY) license to their work.A route to engineer the intrinsic colossal magnetoresistance (CMR) response in manganite thin films through an accurate control of the growth kinetics is presented. It is shown that under specific growth conditions, a particular strained state, substantially different from that of bulk-like materials and standard films, can be quenched up to film thicknesses around 60 nm. This strained state exhibits the same structural fingerprints of the interfacial dead layer in standard films and promotes surface morphology instabilities, which end up with the formation of self-organized nanopits array. At the same time, it has profound effects on the intrinsic magnetoelectronic properties of the films that exhibit an enhanced intrinsic CMR response.We acknowledge financial support from the Spanish MEC (MAT2011-29081 and MAT2012-33207), CONSOLIDER (CSD2007-00041), and FEDER program. Z.K. thanks the Spanish MINECO for the financial support through the RyC program. We thank Helmholtz-Zentrum Berlin for the allocation of neutron/synchrotron radiation beamtime. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 312284.Peer Reviewe

Self-arranged misfit dislocation network formation upon strain release in La0.7Sr0.3MnO3/LaAlO3(100) epitaxial films under compressive strain

Santiso, José et al.Lattice-mismatched epitaxial films of LaSrMnO (LSMO) on LaAlO (001) substrates develop a crossed pattern of misfit dislocations above a critical thickness of 2.5 nm. Upon film thickness increases, the dislocation density progressively increases, and the dislocation spacing distribution becomes narrower. At a film thickness of 7.0 nm, the misfit dislocation density is close to the saturation for full relaxation. The misfit dislocation arrangement produces a 2D lateral periodic structure modulation (Λ≈ 16 nm) alternating two differentiated phases: one phase fully coherent with the substrate and a fully relaxed phase. This modulation is confined to the interface region between film and substrate. This phase separation is clearly identified by X-ray diffraction and further proven in the macroscopic resistivity measurements as a combination of two transition temperatures (with low and high T). Films thicker than 7.0 nm show progressive relaxation, and their macroscopic resistivity becomes similar than that of the bulk material. Therefore, this study identifies the growth conditions and thickness ranges that facilitate the formation of laterally modulated nanocomposites with functional properties notably different from those of fully coherent or fully relaxed material.This research was funded by the Spanish MINECO (projects: MAT2011-29081-C02, MAT2012-33207 and MAT2013-47869-C4-1-P, Consolider-Ingenio CSD2008-00023) and the European Union Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 645658. We also acknowledge financial aid from the Generalitat de Catalunya (2014 SGR 501 and 2014 SGR 1216). J. S. thanks the support of Ministry of Education and Science through program “Salvador de Madariaga” for a grant (ref: PRX14/00297) to perform a stay at MIT. Z.K. is grateful for the support from the Ministry of Education, Science, and Technological Development of the Republic of Serbia through Project III45018. Q.L. and B.Y. thank the National Science Foundation for support through the MIT Center of Materials Science and Engineering MRSEC under grant no. DMR-1419807. This work made use of the Shared Experimental Facilities supported in part by the MRSEC Program of the National Science Foundation under award number DMR – 1419807. We thank Dr. Belén Ballesteros (ICN2, Barcelona) and Prof. Marie-Jo Casanova (CEMES, Toulouse) for their assistance with transmission electron microscopy experiments. We are grateful to J. Rubio-Zuazo and the ESRF for providing assistance in using beamline BM25. We also thank HZB for the allocation of synchrotron radiation beamtime at Bessy.Peer Reviewe

Competing misfit relaxation mechanisms in epitaxial correlated oxides

Strain engineering of functional properties in epitaxial thin films of strongly correlated oxides exhibiting octahedral-framework structures is hindered by the lack of adequate misfit relaxation models. Here we present unreported experimental evidence of a four-stage hierarchical development of octahedral-framework perturbations resulting from a progressive imbalance between electronic, elastic, and octahedral tilting energies in La 0.7Sr0.3MnO3 epitaxial thin films grown on SrTiO3 substrates. Electronic softening of the Mn-O bonds near the substrate leads to the formation of an interfacial layer clamped to the substrate with strongly degraded magnetotransport properties, i.e., the so-called dead layer, while rigid octahedral tilts become relevant at advanced growth stages without significant effects on charge transport and magnetic orderin