In this paper, we illustrate an approach to discriminate between\ud epitaxial strain and other factors responsible for the decrease of the\ud metal-insulator transition temperature (T-P) in thin La0.7Sr0.3MnO3\ud films grown by pulsed laser deposition. Using this approach, we have\ud estimated the effect of the biaxial strain on T-P. Ultrathin films,\ud independent of epitaxial strain, do not show any metal-insulator\ud transition over the full temperature range. This finding confirms the\ud existence of an interface dead layer. The strain-independent decrease in\ud T-P, relative to its bulk value, observed for a much wider thickness\ud range (up to about 1000 A) can most likely be attributed to oxygen\ud deficiency. (C) 2004 American Institute of Physics

The effects of neutron irradiation on normal state and superconducting properties of epitaxial magnesium diboride thin films are studied up to fluences of 10 20 cm −2 . All the properties of the films change systematically upon irradiation. Critical temperature is suppressed and, at the highest fluence, no superconducting transition is observed down to 1.8 K. Residual resistivity progressively increases from 1 to 190 ⍀ cm; c axis expands and then saturates at the highest damage level. We discuss the mechanism of damage through the comparison with other damage procedures. The normal state magnetoresistivity of selected samples measured up to high fields ͑28 and 45 T͒ allows to determine unambiguously the scattering rates in each band; the crossover between the clean and dirty limit in each sample can be monitored. This set of samples, with controlled amount of disorder, is suitable to study the puzzling problem of critical field in magnesium diboride thin films. The measured critical field values are extremely high ͑of the order of 50 T in the parallel direction at low fluences͒ and turns out to be rather independent of the experimental resistivity, at least at low fluences. A simple model to explain this phenomenology is presented.

The nature of the metal-insulator transition in thin films and superlattices of LaNiO3 only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate–film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO3 films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO3 substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO2 termination). Electronic structure measurements using X-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal-insulator transition.

We report on the growth and characterization of ultrathin YBa2Cu3O 7−δ (YBCO) films on MgO (110) substrates, which exhibit superconducting properties at thicknesses down to 3 nm. YBCO nanowires, with thicknesses down to 10 nm and widths down to 65 nm, have been also successfully fabricated. The nanowires protected by a Au capping layer show superconducting properties close to the as-grown films, and critical current densities, which are only limited by vortex dynamics. The 10 nm thick YBCO nanowires without the Au capping present hysteretic current voltage characteristics, characterized by a voltage switch which drives the nanowires directly from the superconducting to the normal state. Such bistability is associated in NbN nanowires to the presence of localized normal domains within the superconductor. The presence of the voltage switch, in ultrathin nanostructures characterized by high sheet resistance values, though preserving high quality superconducting properties, make our nanowires very attractive devices to engineer single photon detectors.arXiv:1708.04721v1 [cond-mat.supr-con]

The magnetic and electronic modifications induced at the interfaces in (SrMnO3)n/(LaMnO3)2n superlattices have been investigated by linear and circular magnetic dichroism in the Mn L2,3 x-ray absorption spectra. Together with theoretical calculations, our data demonstrate that the charge redistribution across interfaces favors in-plane ferromagnetic (FM) order and eg(x 2 − y 2 ) orbital occupation, in agreement with the average strain. Far from interfaces, inside LaMnO3, electron localization and local strain favor antiferromagnetism (AFM) and eg(3z 2 − r 2 ) orbital occupation. For n = 1 the high density of interfacial planes ultimately leads to dominant FM order forcing the residual AFM phase to be in-plane too, while for n ≥ 5 the FM layers are separated by AFM regions having out-of-plane spin orientation.PACS numbers: 75.47. Lx, 78.70.Dm, 72.10.Di, 73.21.Cd, Interfaces between different transition metal oxides (TMO) have been widely demonstrated to be sources of interesting and unexpected electronic and magnetic properties.Metallic conductivity arises, for example, at the interface between two insulators, such as LaAlO 3 /SrTiO 3 [1] and LaTiO 3 /SrTiO 3 [2], while ferromagnetism (FM) occurs at the interface between the antiferromagnet (AFM) CaMnO 3 and the paramagnet CaRuO 3 [3]. In this context, strain driven spin-orbital coupled states arising in manganites make the interfaces between these compounds very interesting for engineering unique collective states. As a matter of fact, a certain amount of theoretical and experimental studies on superlattices (SLs) composed by the two AFM insulators, SrMnO 3 (SMO) and LaMnO 3 (LMO), appeared in literature during the last years [4,5,6,7,8,9,10,11,12]. The ordered sequence of the atomic layers in the digital SMO/LMO SLs [4,5], together with the electronic reconstruction arising from the interfacial Mn 3+ /Mn 4+ mixed valence, give rise to peculiar transport, magnetic and orbital properties, when different layering and strain conditions occur. In the particular case of (SMO) n /(LMO) 2n the La:Sr ratio is 2:1, in analogy with the optimal composition of La 2/3 Sr 1/3 MnO 3 (LSMO). In such a case, the metal-insulator transition (MIT) and the magnetic properties depend on the thickness of the constituent blocks [4,5,6,7], although in a non trivial way. Indeed, saturation magnetization does not linearly decrease with n [4] and both fast and viscous spin populations are present, the latter associated to FM/AFM pinning [8]. Therefore, the development of the FM metallic phase at the interfaces is well established and the coexistance of the FM and AFM phases was inferred. However, the knowledge of the mutual dependence of the AFM and FM phases with n is still uncertain, but it could open further perspectives in the control of the low dimensional magnetic properties, thus in the engineering of the TMO magnetic heterostructures. In addition, as the role of interfacial Mn e g electrons is known to be important, the influence of strain and reduced dimensionality on the transpor...