Coherent transport in extremely underdoped Nd1.2Ba1.8Cu3Oz nanostructures

Proximity-effect and resistance magneto-fluctuations measurements in submicron Nd1.2Ba1.8Cu3Oz (NBCO) nano-loops are reported to investigate coherent charge transport in the non-superconducting state. We find an unexpected inhibition of cooper pair transport, and a destruction of the induced superconductivity, by lowering the temperature from 6K to 250mK. This effect is accompanied by a significant change in the conductance-voltage characteristics and in the zero bias conductance response to the magnetic field pointing to the activation of a strong pair breaking mechanism at lower temperature. The data are discussed in the framework of mesoscopic effects specific to superconducting nanostructures, proximity effect and high temperature superconductivity.Comment: to appear on new journal of Physic

Increased expression of autophagy-related genes in Alzheimer's Disease-Type 2 Diabetes Mellitus comorbidity models in cells

The association between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) has been extensively demonstrated, but despite this, the pathophysiological mechanisms underlying it are still unknown. In previous work, we discovered a central role for the autophagy pathway in the common alterations observed between AD and T2DM. In this study, we further investigate the role of genes belonging to this pathway, measuring their mRNA expression and protein levels in 3xTg-AD transgenic mice, an animal model of AD. Moreover, primary mouse cortical neurons derived from this model and the human H4Swe cell line were used as cellular models of insulin resistance in AD brains. Hippocampal mRNA expression showed significantly different levels for Atg16L1, Atg16L2, GabarapL1, GabarapL2, and Sqstm1 genes at different ages of 3xTg-AD mice. Significantly elevated expression of Atg16L1, Atg16L2, and GabarapL1 was also observed in H4Swe cell cultures, in the presence of insulin resistance. Gene expression analysis confirmed that Atg16L1 was significantly increased in cultures from transgenic mice when insulin resistance was induced. Taken together, these results emphasise the association of the autophagy pathway in AD-T2DM co-morbidity, providing new evidence about the pathophysiology of both diseases and their mutual interaction

Spin-Hall Current and Nonlocal Transport in Ferromagnet-Free Multi-band models for Sr Ti O_3-Based Nanodevices in the presence of impurities

We compute the spin-Hall conductance in a multiband model describing the two-dimensional electron gas formed at a LaAlO_3/SrTiO_3 interface in the presence of a finite concentration of impurities. Combining linear response theory with a systematic calculation of the impurity contributions to the self-energy, as well as to the vertex corrections of the relevant diagrams, we recover the full spin-Hall vs. sheet conductance dependence of LaAlO_3/SrTiO_3 as reported in [Nano Lett. 20, 395 (2020)], finding a very good agreement with the experimental data below and above the Lifshitz transition. In particular, we demonstrate that the multiband electronic structure leads to only a partial, instead of a complete, screening of the spin-Hall conductance, which decreases with increasing the carrier density. Our method can be generalized to other two-dimensional systems characterized by a broken inversion symmetry and multiband physics.Comment: 21 pages, 11 .eps figure

Experimental Determination of Momentum-Resolved Electron-Phonon Coupling

We provide a novel experimental method to quantitatively estimate the electron-phonon coupling and its momentum dependence from resonant inelastic x-ray scattering (RIXS) spectra based on the detuning of the incident photon energy away from an absorption resonance. We apply it to the cuprate parent compound NdBa$_2$Cu$_3$O$_6$ and find that the electronic coupling to the oxygen half-breathing phonon mode is strongest at the Brillouin zone boundary, where it amounts to $\sim 0.17$ eV, in agreement with previous studies. In principle, this method is applicable to any absorption resonance suitable for RIXS measurements and will help to define the contribution of lattice vibrations to the peculiar properties of quantum materials.Comment: 6 pages, 3 figure

Structural, Electronic and Magnetic Properties of a Few Nanometer-Thick Superconducting NdBa₂Cu₃O₇ Films

Abstract: Epitaxial films of high critical temperature (Tc) cuprate superconductors preserve their transport properties even when their thickness is reduced to a few nanometers. However, when approaching the single crystalline unit cell (u.c.) of thickness, Tc decreases and eventually, superconductivity is lost. Strain originating from the mismatch with the substrate, electronic reconstruction at the interface and alteration of the chemical composition and of doping can be the cause of such changes. Here, we use resonant inelastic x-ray scattering at the Cu L3 edge to study the crystal field and spin excitations of NdBa2Cu3O7x ultrathin films grown on SrTiO3, comparing 1, 2 and 80 u.c.-thick samples. We find that even at extremely low thicknesses, the strength of the in-plane superexchange interaction is mostly preserved, with just a slight decrease in the 1 u.c. with respect to the 80 u.c.-thick sample. We also observe spectroscopic signatures for a decrease of the hole-doping at low thickness, consistent with the expansion of the c-axis lattice parameter and oxygen deficiency in the chains of the first unit cell, determined by high-resolution transmission microscopy and x-ray diffraction

Two-dimensional electron gas at the (001) surface of ferromagnetic EuTiO3

Studies on oxide quasi-two-dimensional electron gas (q2DEG) have been a playground for the discovery of novel and sometimes unexpected phenomena, like the reported magnetism at the surface of SrTiO3 (001) and at the interface between nonmagnetic LaAlO3 and SrTiO3 band insulators. However, magnetism in this system is weak and there is evidence of a nonintrinsic origin. Here, by using in situ high-resolution angle-resolved photoemission, we demonstrate that ferromagnetic EuTiO3, the magnetic counterpart of SrTiO3 in the bulk, hosts a q2DEG at its (001) surface. This is confirmed by density functional theory calculations with Hubbard U terms in the presence of oxygen divacancies in various configurations, all of them leading to a spin-polarized q2DEG related to the ferromagnetic order of Eu-4f magnetic moments. The results suggest EuTiO3(001) as a new material platform for oxide q2DEGs, characterized by broken inversion and time-reversal symmetries

Determining the Electron-Phonon Coupling in Superconducting Cuprates by Resonant Inelastic X-ray Scattering: Methods and Results on Nd1+x_{1+x}Ba2−x_{2-x}Cu3_3O7−δ_{7-\delta}

The coupling between lattice vibration quanta and valence electrons can induce charge density modulations and decisively influence the transport properties of materials, e.g. leading to conventional superconductivity. In high critical temperature superconductors, where electronic correlation is the main actor, the actual role of electron-phonon coupling (EPC) is being intensely debated theoretically and investigated experimentally. We present an in-depth study of how the EPC strength can be obtained directly from resonant inelastic x-ray scattering (RIXS) data through the theoretical approach derived by Ament et al. [EPL 95, 27008 (2011)]. The role of the model parameters (e.g. phonon energy $\omega_0$, intermediate state lifetime $1/\Gamma$, EPC matrix element $M$, and detuning energy $\Omega$) is thoroughly analyzed, providing general relations among them that can be used to make quantitative estimates of the dimensionless EPC $g = (M/\omega_0)^2$ without detailed microscopic modeling. We then apply these methods to very high resolution Cu $L_3$ edge RIXS spectra of three Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-\delta}$ films. For the insulating antiferromagnetic parent compound the value of $M$ as a function of the in-plane momentum transfer is obtained for Cu-O bond-stretching (breathing) and bond-bending (buckling) phonon branches. For the underdoped and the nearly optimally doped samples, the effects of Coulomb screening and of charge-density-wave correlations on $M$ are assessed. In light of the anticipated further improvements of the RIXS experimental resolution, this work provides a solid framework for an exhaustive investigation of the EPC in cuprates and other quantum materials.Comment: 21 pages, 16 figure

Determining the electron-phonon coupling in superconducting cuprates by resonant inelastic x-ray scattering: Methods and results on Nd1+xBa2-xCu3O7-δ

The coupling between lattice vibration quanta and valence electrons can induce charge-density modulations and decisively influence the transport properties of materials, e.g., leading to conventional superconductivity. In high-critical-temperature superconductors, where electronic correlation is the main actor, the actual role of electron-phonon coupling (EPC) is being intensely debated theoretically and investigated experimentally. We present an in-depth study of how the EPC strength can be obtained directly from resonant inelastic x-ray scattering (RIXS) data through the theoretical approach derived by Ament et\ua0al. [Europhys. Lett. 95, 27008 (2011)]. The role of the model parameters (e.g., phonon energy ω0, intermediate state lifetime 1/Γ, EPC matrix element M, and detuning energy Ω) is thoroughly analyzed, providing general relations among them that can be used to make quantitative estimates of the dimensionless EPC g=(M/ω0)2 without detailed microscopic modeling. We then apply these methods to very high-resolution Cu L3-edge RIXS spectra of three Nd1+xBa2−xCu3O7−δ films. For the insulating antiferromagnetic parent compound, the value of M as a function of the in-plane momentum transfer is obtained for Cu-O bond-stretching (breathing) and bond-bending (buckling) phonon branches. For the underdoped and the nearly optimally doped samples, the effects of Coulomb screening and of charge-density-wave correlations on M are assessed. In light of the anticipated further improvements of the RIXS experimental resolution, this work provides a solid framework for an exhaustive investigation of the EPC in cuprates and other quantum materials