Interband and intraband optical transitions in InAs nanocrystal quantum dots: A pseudopotential approach

An atomistic pseudopotential method is used to investigate the electronic and optical properties of spherical InAs nanocrystals. Our calculated interband (valence-to-conduction) absorption spectra reproduce the features observed experimentally both qualitatively and quantitatively. The results relative to intraband (valence-to-valence and conduction-to-conduction) absorption successfully reproduce the recently measured photoinduced absorption spectra, which had so far been addressed only qualitatively. They exclude the hypothesis of a thermal activation process between dot-interior-delocalized hole states to explain the temperature dependence observed experimentally. Furthermore, based on the agreement of our data with the experimental valence intersublevel transitions and the almost complete overlap of the latter with scanning tunneling microscopic (STM) measurements, we question the simplistic attribution of the observed STM peaks obtained for negative bias

Evidence for anisotropic triplet superconductor order parameter in half-metallic ferromagnetic La0.7Ca0.3Mn3O proximity coupled to superconducting Pr1.85Ce0.15CuO4

Scanning tunneling spectroscopy measurements performed on La_0.7Ca_0.3MnO_3 (LCMO) films epitaxially grown on Pr_1.85Ce_0.15CuO_4 (PCCO) reveal localized penetration of superconductivity into the LCMO up to distances much larger than is possible for Cooper pairs in a singlet spin state to exist. This long-range proximity effect is manifested in the tunneling spectra as gaps and, less abundantly, as zero-bias conductance peaks (ZBCPs). Since ZBCPs were not found on the bare PCCO films, their appearance is attributed to an anisotropic (p-wave or d-wave) triplet-pairing superconductor order parameter induced in the LCMO.This is the final version of the manuscript, originally published by APS here: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.85.104504. Copyright 2014 American Physical Society

Correlation between Ferromagnetic Layer Easy Axis and the Tilt Angle of Self Assembled Chiral Molecules

The spin-spin interactions between chiral molecules and ferromagnetic metals were found to be strongly affected by the chiral induced spin selectivity effect. Previous works unraveled two complementary phenomena: magnetization reorientation of ferromagnetic thin film upon adsorption of chiral molecules and different interaction rate of opposite enantiomers with a magnetic substrate. These phenomena were all observed when the easy axis of the ferromagnet was out of plane. In this work, the effects of the ferromagnetic easy axis direction, on both the chiral molecular monolayer tilt angle and the magnetization reorientation of the magnetic substrate, are studied using magnetic force microscopy. We have also studied the effect of an applied external magnetic field during the adsorption process. Our results show a clear correlation between the ferromagnetic layer easy axis direction and the tilt angle of the bonded molecules. This tilt angle was found to be larger for an in plane easy axis as compared to an out of plane easy axis. Adsorption under external magnetic field shows that magnetization reorientation occurs also after the adsorption event. These findings show that the interaction between chiral molecules and ferromagnetic layers stabilizes the magnetic reorientation, even after the adsorption, and strongly depends on the anisotropy of the magnetic substrate. This unique behavior is important for developing enantiomer separation techniques using magnetic substrates

Correlation of tunneling spectra with surface nano-morphology and doping in thin YBa2Cu3O7-delta films

Tunneling spectra measured on thin epitaxial YBa2Cu3O7-delta films are found to exhibit strong spatial variations, showing U and V-shaped gaps as well as zero bias conductance peaks typical of a d-wave superconductor. A full correspondence is found between the tunneling spectra and the surface morphology down to a level of a unit-cell step. Splitting of the zero bias conductance peak is seen in optimally-doped and overdoped films, but not in the underdoped ones, suggesting that there is no transition to a state of broken time reversal symmetry in the underdoped regimeComment: accepted to ep

Magnetic field dependence of the proximity-induced triplet superconductivity at ferromagnet/superconductor interfaces

Long-ranged superconductor proximity effects recently found in superconductor-ferromagnetic (S-F) systems are generally attributed to the formation of triplet-pairing correlations due to various forms of magnetic inhomogeneities at the S-F interface. In order to investigate this conjecture within a single F layer coupled to a superconductor, we performed scanning tunneling spectroscopy on bilayers of La2/3Ca1/3MnO3 (LCMO) ferromagnetic thin-films grown on high temperature superconducting films of YBa2Cu3O7- (YBCO) or Pr1.85Ca0.15CuO4 (PCCO) under various magnetic fields. We find a strong correlation between the magnitude of superconductor-related spectral features measured on the LCMO layer and the degree of magnetic inhomogeneity controlled by the external magnetic field. This corroborates theoretical predictions regarding the role played by magnetic inhomogeneities in inducing triplet-pairing at S-F interfaces.This research was supported in parts by the joint German-Israeli DIP Project (G.K. and O.M.), the United States-Israel Binational Science Foundation (O.M.), the Harry de Jur Chair in Applied Science (O.M.), the Karl Stoll Chair in advanced materials at the Technion (G.K.), the Leverhulme Trust through an International Network Grant (J.W.A.R., M.G.B. and O.M.) and the Royal Society (J.W.A.R.).This is the accepted manuscript version. The final published version is available from the publishers at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.180506. © 2014 AP