85 research outputs found
Svojstva kuprata visokog Tc: neki noviji rezultati i otvorena pitanja
Thirteen years ago, late in 1986, several groups confirmed striking claims of the famous paper by Bednorz and Müller [Z Phys. B 64 (1986) 189] that announced the discovery of high-Tc superconductivity in cuprates. Some 60,000 papers later, we are still struggling to understand the high-Tc oxide superconductivity. Here we present some of the most relevant recent experiments and discuss some open questions across rather complex electronic phase diagram; we also note an important role of un-intentional and intentional disorder in these layered, high-Tc oxides.hydrogen bPrije trinaest godina, u kasnu jesen 1986 nekoliko je istraživačkih grupa potvrdilo rezultate članka Bednorza i M¨ullera koji je najavio epohalno otkriće visokotemperaturne supravodljivosti u kupratima. Skoro 60.000 članaka kasnije, mi se svi jos uvijek uvelike trudimo razumjeti visokotemperaturnu supravodljivost. U ovom
članku prikazujemo poneke od najvažnijih nedavnih eksperimenata i diskutiramo neke neriješene probleme u vrlo složenom elektronskom faznom dijagramu, te posebno naglašavamo važnu ulogu nenamjerne (intrinsične) i namjerno inducirane neuređenosti u tim ploškastim oksidnim supravodičima
Ferroelectric control of the spin texture in germanium telluride
The electrical manipulation of spins in semiconductors, without magnetic
fields or auxiliary ferromagnetic materials, represents the holy grail for
spintronics. The use of Rashba effect is very attractive because the
k-dependent spin-splitting is originated by an electric field. So far only tiny
effects in two-dimensional electron gases (2DEG) have been exploited. Recently,
GeTe has been predicted to have bulk bands with giant Rashba-like splitting,
originated by the inversion symmetry breaking due to ferroelectric
polarization. In this work, we show that GeTe(111) surfaces with inwards or
outwards ferroelectric polarizations display opposite sense of circulation of
spin in bulk Rashba bands, as seen by spin and angular resolved photoemission
experiments. Our results represent the first experimental demonstration of
ferroelectric control of the spin texture in a semiconductor, a fundamental
milestone towards the exploitation of the non-volatile electrically switchable
spin texture of GeTe in spintronic devices.Comment: 18 pages, 4 figure
Magnetic Proximity Effect as a Pathway to Spintronic Applications of Topological Insulators
Spin-based electronics in topological insulators (TIs) is favored by the long
spin coherence1,2 and consequently fault-tolerant information storage.
Magnetically doped TIs are ferromagnetic up to 13 K,3 well below any practical
operating condition. Here we demonstrate that the long range ferromagnetism at
ambient temperature can be induced in Bi2-xMnxTe3 by the magnetic proximity
effect through deposited Fe overlayer. This result opens a new path to
interface-controlled ferromagnetism in TI-based spintronic devices.Comment: accepted in Nano Letter
Zinc(II) tetraphenylporphyrin on Au(111) investigated by scanning tunnelling microscopy and photoemission spectroscopy measurements
Porphyrins are a versatile class of molecules, which have attracted attention over the years due to their electronic, optical and biological properties. Self-assembled monolayers of porphyrins were widely studied on metal surfaces in order to understand the supramolecular organization of these molecules, which is a crucial step towards the development of devices starting from thebottom-upapproach. This perspective could lead to tailor the interfacial properties of the surface, depending on the specific interaction between the molecular assembly and the metal surface. In this study, we revisit the investigation of the assembly of zinc-tetraphenylporphyrins on Au(111) in order to explore the adsorption of the molecular network on the noble metal substrate. The combined analysis of scanning tunneling microscopy (STM) imaging and core levels photoemission spectroscopy measurements support a peculiar arrangement of the ZnTPP molecular network, with Zn atoms occupying the bridge sites of the Au surface atoms. Furthermore, we prove that, at few-layers coverage, the interaction between the deposited layers allows a relevant molecular mobility of the adlayer, as observed by STM and supported by core levels photoemission analysis
Two Distinct Phases of Bilayer Graphene Films on Ru(0001)
By combining angle-resolved photoemission spectroscopy and scanning tunneling
microscopy we reveal the structural and electronic properties of multilayer
graphene on Ru(0001). We prove that large ethylene exposure allows to
synthesize two distinct phases of bilayer graphene with different properties.
The first phase has Bernal AB stacking with respect to the first graphene
layer, displays weak vertical interaction and electron doping. The long-range
ordered moir\'e pattern modulates the crystal potential and induces replicas of
the Dirac cone and minigaps. The second phase has AA stacking sequence with
respect to the first layer, displays weak structural and electronic modulation
and p-doping. The linearly dispersing Dirac state reveals the
nearly-freestanding character of this novel second layer phase
Narrowing of d bands of FeCo layers intercalated under graphene
We report on the electronic properties of an artificial system obtained by the intercalation of equiatomic FeCo layers under graphene grown on Ir(111). Upon intercalation, the FeCo film grows epitaxially on Ir(111), resulting in a lattice-mismatched system. By performing density functional theory calculations, we show that the intercalated FeCo layer leads to a pronounced corrugation of the graphene film. At the same time, the FeCo intercalated layers induce a clear transition from a nearly undisturbed to a strongly hybridized graphene π-band, as measured by angle-resolved photoemission spectroscopy. A comparison of experimental results with the computed band structure and the projected density of states unveils a spin-selective hybridization between the π band of graphene and FeCo-3d states. Our results demonstrate that the reduced dimensionality, as well as the hybridization within the FeCo layers, induces a narrowing and a clear splitting of Fe 3d-up and Fe 3d-down-spin bands of the confined FeCo layers with respect to bulk Fe and Co
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