Search

SrVO3 (SVO) is a prospective candidate to replace the conventional indium-tin-oxide (ITO) among the new transparent conducting oxide (TCO) generation. In this study, the structural, electrical, and optical properties of SVO thin films, both epitaxial and polycrystalline, are determined during and after heat treatments in the 150-250 {\deg}C range and under ambient environment in order to explore the chemical stability of this material. The use of these relatively low temperatures speeds up the natural ageing of the films, and allows to follow the evolution of their related properties. The combination of techniques rather sensitive to the film surface and of techniques sampling the film volume will emphasize the presence of a surface oxidation evolving in time at low annealing temperatures, whereas the perovskite phase is destroyed throughout the film for treatments above 200 {\deg}C. The present study is designed to understand the thermal degradation and long-term stability issues of vanadate-based TCOs, and to identify technologically viable solutions for the application of this group as new TCOs.

The synthesis of ultrasmall (2-5 nm) nanodiamonds purely from adamantane at pressure of 12 GPa is reported. Their structural features have been studied by Raman spectroscopy. The unusual vibration band containing a number of pronounced maxima at about 1147, 1245, 1344, and 1456 cm-1 was detected in Raman spectra. The band is confidently identified with the bending vibrational modes of CHx groups terminating the nanodiamonds surface. Excessively intense mode at 1344 cm-1 is explained by its coupling with the 1328 cm-1 diamond phonons. The Raman band found is proposed to be used for express recognition of ultrasmall nanodiamonds produced from adamantane and other hydrocarbons with a high hydrogen content. Moreover, polarized CH bonds on a diamond surface are sensitive to environmental conditions. This opens up opportunities for using the diamond produced from adamantane as ultrasmall nanosensors in biology, chemistry, and medicine, Comment: 12 pages, 6 figures

Two novel properties, unique for semiconductors: a negative electron affinity [1-2], and a high p-type surface electrical conductivity [3-4], were discovered in diamond at the end of the last century. Both properties appear when the diamond surface is hydrogenated. A natural question arises: is the influence of the surface hydrogen on diamond limited only to the electrical properties? Here, we report the first observation of a transparency peak at 1328 cm-1 in IR absorption of hydrogen-terminated pure (undoped) nanodiamonds. This new optical property is ascribed to Fano-type destructive interference between zone-center phonons and free carriers (holes) appearing in the near-surface layer of hydrogenated nanodiamond. Our work opens the way to exploring the physics of electron-phonon coupling in undoped diamonds and promises the application of the H-terminated nanodiamonds as a new optical material with an induced transparency in IR optical range., Comment: 15 pages, 7 figures

The Protvino accelerator facility located in the Moscow region, Russia, is in a good position to offer a rich experimental research program in the field of neutrino physics. Of particular interest is the possibility to direct a neutrino beam from Protvino towards the KM3NeT/ORCA detector, which is currently under construction in the Mediterranean Sea 40 km offshore Toulon, France. This proposal is known as P2O. Thanks to its baseline of 2595 km, this experiment would yield an unparalleled sensitivity to matter effects in the Earth, allowing for the determination of the neutrino mass ordering with a high level of certainty after only a few years of running at a modest beam intensity of $\approx$ 90 kW. With a prolonged exposure ($\approx$ 1500 kW*yr), a 2$\sigma$ sensitivity to the leptonic CP-violating Dirac phase can be achieved. A second stage of the experiment, comprising a further intensity upgrade of the accelerator complex and a densified version of the ORCA detector (Super-ORCA), would allow for up to a 6$\sigma$ sensitivity to CP violation and a 10$^\circ$-17$^\circ$ resolution on the CP phase after 10 years of running with a 450 kW beam, competitive with other planned experiments. The initial composition and energy spectrum of the neutrino beam would need to be monitored by a near detector, to be constructed several hundred meters downstream from the proton beam target. The same neutrino beam and near detector set-up would also allow for neutrino-nucleus cross section measurements to be performed. A short-baseline sterile neutrino search experiment would also be possible., Comment: 27 pages, 15 figures, 2 tables

By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition $T_{CO}$=176 K in the mixed-valence quadruple perovskite (NaMn$_3$)Mn$_4$O$_{12}$. Below $T_{CO}$ we find satellite peaks indicating a commensurate structural modulation with the same propagation vector q =(1/2,0,-1/2) of the CE magnetic order that appears at low temperature, similarly to the case of simple perovskites like La$_{0.5}$Ca$_{0.5}$MnO$_3$. In the present case, the modulated structure together with the observation of a large entropy change at $T_{CO}$ gives evidence of a rare case of full Mn$^{3+}$/Mn$^{4+}$ charge and orbital order consistent with the Goodenough-Kanamori model., Comment: Accepted for publication in Phys. Rev. B Rapid Communications

Properties of complex oxide thin films can be tuned over a range of values as a function of mismatch, composition, orientation, and structure. Here, we report a strategy for growing structured epitaxial thermoelectric thin films leading to improved Seebeck coefficient. Instead of using single-crystal sapphire substrates to support epitaxial growth, Ca$_3$Co$_4$O$_9$ films are deposited, using the Pulsed Laser Deposition technique, onto Al$_2$O$_3$ polycrystalline substrates textured by Spark Plasma Sintering. The structural quality of the 2000 \AA thin film was investigated by Transmission Electron Microscopy, while the crystallographic orientation of the grains and the epitaxial relationships were determined by Electron Back Scatter Diffraction. The use of a polycrystalline ceramic template leads to structured films that are in good local epitaxial registry. The Seebeck coefficient is about 170 $\mu$V/K at 300 K, a typical value of misfit material with low carrier density. This high-throughput process, called combinatorial substrate epitaxy, appears to facilitate the rational tuning of functional oxide films, opening a route to the epitaxial synthesis of high quality complex oxides., Comment: Submitted to Applied Physics Letters (2013)

(CaCuO2)m/(La0.7Sr0.3MnO3)n superlattices, consisting of the infinite layers cuprate CaCuO2 and the optimally doped manganite La1-xSrxMnO3, were grown by pulsed laser deposition. The transport properties are dominated by the manganite block. X-Ray Absorption spectroscopy measurements show a clear evidence of an orbital reconstruction at the interface, ascribed to the hybridization between the Cu 3d3z2-r2 and the Mn 3d3z2-r2 orbitals via interface apical oxygen ions. Such a mechanism localizes holes at the interfaces, thus preventing charge transfer to the CaCuO2 block. Some charge (holes) transfer occurs toward the La0.7Sr0.3MnO3 block in strongly oxidized superlattices, contributing to the suppression of the magnetotransport properties., Comment: 20 pages, 6 figures

We report the occurrence of superconductivity, with maximum Tc = 40 K, in superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3. In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block, which is an antiferromagnetic insulator. Superconductivity, confined within few unit cells at the CaCuO2/SrTiO3 interface, shows up only when the SLs are grown in a highly oxidizing atmosphere, because of extra oxygen ions entering at the interfaces. Evidence is reported that the hole doping of the CuO2 planes is obtained by charge transfer from the interface layers, which act as charge reservoir., Comment: 18 pages, 8 figures

From electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and decay kinetics on photo-excitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. A large enhancement in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to a higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition.

We report a memory resistance (memristor) behavior with nonlinear current-voltage characteristics and bipolar hysteretic resistance switching in the nanocolumnar manganite (LSMO) films. The switching from a high (HRS) to a low (LRS) resistance occurs at a bias field ~1 MV/cm. Applied electric field drops mostly at the insulating interfacial LSMO layer and couples to correlated polarons at the LSMO(111)/LSMO(111) vertical interfaces. The observed memristance behaviour has an electronic (polaronic) origin and is caused by an electric-field-controlled Jahn-Teller (JT) effect, followed by the orbital reconstruction and formation of a metastable orbitally disordered interfacial phase (LRS). Compared to the earlier reported ionic memristor in Ti-O films, an electronic (polaronic) nano-sized LSMO memristor shows an additional (re-entrant) LRS-HRS switching at higher fields because of the second minimum in the elastic energy of a JT system., Comment: 10 pages, 4 figures

An interface modification of LCMO-BTO superlattices was found to massively influence magnetic and magnetotransport properties. Moreover it determines the crystal structure of the manganite layers, changing it from orthorhombic (Pnma) for the conventional superlattice (cSL), to rhombohedral (R-3c) for the modified one (mSL). While the cSL shows extremely nonlinear ac transport, the mSL is an electrically homogeneous material. The observations go beyond an oversimplified picture of dead interface layers and evidence the importance of electronic correlations at perovskite interfaces.

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the Standard Model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments., Comment: Report of Working Group 3 of the CERN Workshop ``Flavour in the era of the LHC'', Geneva, Switzerland, November 2005 -- March 2007

PROZA-M experiment results as well the proposal of a new spin program with the use of a polarized proton beam are presented. Significant asymmetries were observed in inclusive $\pi^0$ production. The new program proposes to study a wealth of single- and double-spin observables in various reactions using longitudinally and transversely polarized proton beams at U70. The main goal is to define gluon contribution to nucleon spin by measuring double-spin asymmetry in charmonium production., Comment: 18 pages, 20 figures, Talk given at Advanced Study Institute Symmetries and Spin (July 19 - 26, Prague, Czech Republic)

Epitaxial La3/4Ca1/4MnO3/MgO(100) (LCMO) thin films show unusual rhombohedral (R-3c) structure with a new perovskite superstructure due to unique ordering of La and Ca at the A-site positions. Very sharp insulator-metal and para-ferromagnetic phase transitions at temperatures up to TMI ~ TC=295 K were observed. The ordered films were electronically homogeneous down to 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate broadened phase transitions as well as mesoscopic phase separation for T<

Motivated by recent progress in experimental techniques of electric dipole moment (EDM) measurements, we study correlations between the neutron and electron EDMs in common supersymmetric models. These include minimal supergravity (mSUGRA) with small CP phases, mSUGRA with a heavy SUSY spectrum, the decoupling scenario and split SUSY. In most cases, the electron and neutron EDMs are found to be observable in the next round of EDM experiments. They exhibit certain correlation patterns. For example, if d_n ~ 10^{-27} e cm is found, d_e is predicted to lie in the range 10^{-28}-10^{-29} e cm., Comment: 16 pages,12 figures. To appear in JHEP. A note on stability of the correlations added in Conclusions; refs. and footnotes added

We study flavour issues in nonsupersymmetric intersecting brane models. Specifically, the purpose of the present paper is twofold: (i) to determine whether realistic flavour structures can be obtained in these models, and (ii) to establish whether the non-supersymmetric models address the gauge hierarchy problem. To this end, we find that realistic flavour structures, although absent at tree level, can arise even in the simplest models after effects of 4 fermion instanton--induced operators and radiative corrections have been taken into account. On the other hand, our analysis of flavour changing neutral currents (FCNC), electric dipole moments (EDM), supernova SN1987A and other constraints shows that the string scale has to be rather high, 10^4 TeV. This implies that non-supersymmetric intersecting brane models face a severe finetuning problem. Finally, we comment on how non--trivial flavour structures can arise in supersymmetric models., Comment: 33 pages, 11 figures, matches the NPB version

The far-infrared dielectric response of superlattices (SL) composed of superconducting YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) and ferromagnetic La$_{0.67}$% Ca$_{0.33}$MnO$_{3}$ (LCMO) has been investigated by ellipsometry. A drastic decrease of the free carrier response is observed which involves an unusually large length scale of d$^{crit}\approx $20 nm in YBCO and d$^{crit}\approx $10 nm in LCMO. A corresponding suppression of metallicity is not observed in SLs where LCMO is replaced by the paramagnetic metal LaNiO$_{3}$. Our data suggest that either a long range charge transfer from the YBCO to the LCMO layers or alternatively a strong coupling of the charge carriers to the different and competitive kind of magnetic correlations in the LCMO and YBCO layers are at the heart of the observed metal/insulator transition. The low free carrier response observed in the far-infrared dielectric response of the magnetic superconductor RuSr$_{2}$GdCu$_{2}$O$_{8}$ is possibly related to this effect.

We show that string models with low energy supersymmetry which accommodate the fermion mass hierarchy generally give non-universal soft trilinear couplings (A-terms). In conjunction with the apparently large Cabibbo-Kobayashi-Maskawa (CKM) phase, this results in large fermion EDMs even in the absence of CP violating phases in the supersymmetry breaking terms and the mu-term. Nonobservation of the EDMs therefore implies that strings select special flavor and/or supersymmetry breaking patterns., Comment: Revtex, 4 pages, FCNC discussion added, to appear in Phys Rev Lett (title changed in journal)

We study the possibility of spontaneous CP violation in string models with the dilaton field stabilized at a phenomenologically acceptable value. We consider three mechanisms to stabilize the dilaton: multiple gaugino condensates, a nonperturbative Kahler potential, and a superpotential based on S-duality, and analyze consequent CP phases in the soft SUSY breaking terms. Due to non-universality forced upon the theory by requiring a non-trivial CKM phase, the EDM problem becomes more severe. Even if there are no complex phases in the VEVs of the SUSY breaking fields, the electric dipole moments are overproduced by orders of magnitude. We also address the question of modular invariance of the physical CP phases., Comment: matches the PRD version

We analyze the chargino contributions to the K-\bar K mixing and epsilon-prime in the mass insertion approximation and derive the corresponding bounds on the mass insertion parameters. We find that the chargino contributions can significantly enlarge the regions of the parameter space where CP violation can be fully supersymmetric. In principle, the observed values of epsilon and epsilon-prime may be entirely due to the chargino -- up-squark loops., Comment: 9 pages, 2 figures, to appear in PLB

We systematically analyze constraints on supersymmetric theories imposed by the experimental bounds on the electron, neutron, and mercury electric dipole moments. We critically reappraise the known mechanisms to suppress the EDMs and conclude that only the scenarios with approximate CP-symmetry or flavour-off-diagonal CP violation remain attractive after the addition of the mercury EDM constraint., Comment: 34 pages, 18 figures, to appear in Nucl. Phys. B

We analyze the possibility of simultaneous electron, neutron, and mercury electric dipole moment (EDM) cancellations in the mSUGRA and D--brane models. We find that the mercury EDM constraint practically rules out the cancellation scenario in D-brane models whereas in the context of mSUGRA it is still allowed with some fine-tuning., Comment: 10 pages, to appear in Phys. Rev. Lett

We revisit the supersymmetric CP problem and find that it can be naturally resolved if the origin of CP violation is closely related to the origin of flavour structures. In this case, the supersymmetry breaking dynamics do not bring in any new CP-violating phases. This mechanism requires hermitian Yukawa matrices which naturally arise in models with a U(3) flavour symmetry. The neutron electric dipole moment (NEDM) is predicted to be within one-two orders of magnitude below the current experimental limit. The model also predicts a strong correlation between A_{CP}(b --> s gamma)and the NEDM. The strong CP problem is mitigated although not completely solved., Comment: revtex, 4 pages

We discuss the possibility of the existence of a long-lived top squark ($\tau\ll 10^{10} years$) and its motivation. If the stop is indeed metastable, it forms hadrons. We study properties of the low-energy stop-containing hadrons and their signatures in collider experiments., Comment: 14 pages, 2 figures

Recently it has been demonstrated that large phases in softly broken supersymmetric theories are consistent with electric dipole moment constraints, and are motivated in some (Type I) string models. Here we consider whether large flavor-independent soft phases may be the dominant (or only) source of all CP violation. In this framework $\epsilon$ and $\epsilon'/\epsilon$ can be accommodated, and the SUSY contribution to the B system mixing can be large and dominant. An unconventional flavor structure of the squark mass matrices (with enhanced super-CKM mixing) is required for consistency with B and K system observables., Comment: 9 pages, 1 figure; revised version to appear in Phys.Rev.Lett