Presentazione sul tema: "Dr. Gabriella Maria De Luca"— Transcript della presentazione:
1 Dr. Gabriella Maria De Luca Researcher SPIN-Institute.Crescita e caratterizzazione strutturale di film epitassiali di sistemi a forti correlazioni elettroniche di interesse per l’elettronica avanzataCNR-SPINDr. M. Salluzzo ResearcherProf. R. Vaglio Director
2 OSSIDI METALLI DI TRANSIZIONE Gli ossidi metalli di transizione rappresentano una classe di materiali di enorme interesse nell'ambito della moderna fisica dello stato solido. Essi sono caratterizati da particolarissime proprietà fisiche, spesso legata alla presenza di forti correlazioni elettroniche.Forte interazione elettrone-elettroneElettroni molto localizzatiCampo elettricocaricheorbitalespinPressioneCampo magneticoThese materials are examples of strongly correlated electronic systems, where the electron-electron Coulomb repulsion interaction is strong and electrons are almost localized or barely mobile. Here a naive single-particle approximation (considering a moving electron as an independent particle in the effective medium) does not hold  Moreover, in this class of materials not only charge and spin interactions are of relevance, but even the lattice and orbital ones (Figure 1). These interactions lead to the coexistence of several competing states, as exemplified by the complex phase diagrams these materials present (see sect. 1.3) .
4 Effetto Jahn-Teller Interazione magnetica degli spin In base all'effetto Jahn-Teller (o distorsione Jahn-Teller) ogni molecola non lineare con uno stato elettronico fondamentale degenere subisce una distorsione geometrica che rimuove la degenerazioneThe presence in the unit cell of the octhaedron bo6 structure is the main characteristic of the TMO perovskite.It is believed that many of the electronic properties of these compound are strongly correlated to the bo6 structureIf we look the elctronic structure of the 3d level is completely degenerate, but the presence of 6 oxygen ions introduce a crystal fiels splitting of the 3d orbital in eg and t2g twofold and threefold degenerate respectvely in particular one of the main characteristic in this stucture is the variability overlap of the atomic orbital among the 3d transition metal oxide ions in different structural configurationsDeu to a pariodic among of ions in a crystal lattice two effec are….Interazione magnetica degli spinFormazione di bande e conduzione metallica degli elettroni
5 Ossidi innovativi per L’elettronica 40mm25mmFiltri a microondeMemorie FeRamSensori magneticiCircuitiSchermiLCDMemsattuatoriMagnetoresistenza colossale LSMOSuperconduttoriYBCOIsteresiPZT, BLTOssidi conduttivi trasparentiAlta costantedielettrica- BSTPiezoelettricitàFilm sottili –Ossidi di MetalloMemorie dinamiche (Gigabit)
6 Interfaccia Ossidi Metalli di Transizioni NOVEL FUNCTIONALITIESPr0.7Ca0.3MnO3/La0.7Sr0.3MnO3 SL, PLD-MODAInterfacciaLayer by layer growthRHEED, LEED and in situ SPMSrMnO3/LaMnO3Antiferromagnete/AntiferromagneteFerromagneteThe combination of strongly correlated materials with given characteristics providesBaCuO2/CaCuO2Isolante/IsolanteSuperconduttore ad Alta TcLaAlO3/SrTiO3Isolante/IsolanteConduttore , SuperconduttoreNdBCO/SrTiO3Superconduttore /IsolanteTransizione Superconduttore/Isolante
7 Joule effect Evaporator Magnetron sputtering gun Sistema di SputteringHEATERJoule effect EvaporatorMagnetron sputtering gunDiode sputtering gunField Effect Device (FET)Multi Chamber Sputtering system:Three sputtering source+evaporatorwe present experimental results on the field effect doping of NdBCO thin films characterized by a carrier density near the superconducting-insulating transition.Drain Source channel length L=25µmDrain Source channel width W=50 µm
9 Caratterizzazione Elettrica FET The devices are characterized by transport and charge measurements, using the experimental setup sketched in fig.3a. A source-drain current is injected in the NdBCO channel through a Keithley 6220 current source, while the source drain resistance is measured through a Keithely 2182A nanovoltmeter. For each measurement the current direction is switched from positive to negative and the resulting voltages are averaged to get the value of the resistance. In case of more then 5% differences between the two values of Vds polarity, the data are considered affected by unknown systematic errors and discarded. Even very insulating samples, show ohmic Ids vs. Vds characteristics in the normal state. All the devices were studied in the linear regime where the condition Vgate>> Vds holds. The charge across the gate dielectric is measured through a Keithley 6517A electrometer, equippedalso with an high voltage dc source. The leakage current in the device at cryogenic temperatures is always below 1-2 nA (not limited by the dielectric characteristic but by the cabling assembly), allowing static charge to be measured with very high accuracy. In this way we could acquire simultaneously the channel resistance and the induced polarization, i.e. the charge induced at the interface. The latter can be directly transformed in holes per cm2 or holes per CuO2 planes, assuming that charges are transformed in carriers.Misura della carica insieme a misure di trasporto
11 Cosa vuol dire Multiferroico Multi-ferroic magnetoelectrics,H. Schmid, Ferroelectrics 162, 317 (1994)
12 Effetto MagnetoElettrico (ME) L'effetto ME è caratterizzato dalla comparsa di una P grazie ad un campo magnetico B e viceversa, di una M grazie ad un campo elettrico E.
13 La chimica che promuove una funzionalità spesso ne proibisce un'altra. FerroelettricitàFerromagnetismoABO3Orbitali d parzialmente occupati.Ferroelettricità convenzionale favorita da “d0- ness”.Tesi: Daniele Preziosi
14 Configurazione elettronica Bi3+=[Xe]4f145d106s2 6p0 BiMnO3a = Ab = Ac = Ab = °L'ossido perovskite sino ad allora conosciuto, con Bi3+ come componente, era il BiFeO3. AFM sotto 370 K e FE sotto 840 K.Configurazione elettronica Bi3+=[Xe]4f145d106s2 6p0
17 StrainIn condizioni di crescita epitassiale nel piano ab si puo’ avere:Compressive StrainTensile StrainE’ stato dimostrato che lo strain puo’ modificare la temperatura critica di fim molto sottili.Is due to different lattice parameters between substrate and film appearing immediately in the first deposited layerIt can be defined as the ration between the lattice parameters of the substrate and bulk filmThe elastic deformation of the unit cell can mimic the effect of an external uniaxial pressure on the sample in this wqy the strain effect was demostrated to be effective in modifying the critical temperature of very thin fims
18 Misure PFMIl metodo è basato sulla rivelazione delle vibrazioni elettromeccaniche locali del campione causate da una tensione alternata.
19 Luce di SincrotroneWeak magnetism in insulating and superconducting cuprates G. M. De Luca, G. Ghiringhelli, M. Moretti Sala, S. Di Matteo, M. W. Haverkort, H. Berger, V. Bisogni, J. C. Cezar, N. B. Brookes, and M. Salluzzo Phys. Rev. B 82, (2010) (Editor’s suggestion)Intense paramagnon excitations in a large family of high-termperature superconductorsM. Le Tacon, G. Ghiringhelli, J. Chaloupka, M. Moretti Sala, V. Hinkov, M.W. Haverkort, M. Minola, M. Bakr, K. J. Zhou, S. Blanco-Canosa, C. Monney, Y. T. Song, G. L. Sun, C. T. Lin, G. M. De Luca, M. Salluzzo, G. Khaliullin, T. Schmitt, L. Braicovich and B. Keimer Nature Phys 7, 725–730 (2011).
20 Physical phenomena at metal transition oxides heterostructures SrTiO3LaAlO3photons
21 X-ray Absorption spectroscopy at Cu L2,3 edge 3d10LLHBUHBCTEF3d104s2p statesZRM. Salluzzo,G. Ghiringhelli, N. B. Brookes, G. M. De Luca, F. Fracassi, and R. Vaglio Phys. Rev. B 75, (2007)M. Salluzzo, G. Ghiringhelli, J. C. Cezar, N. B. Brookes, G. M. DeLuca, F. Fracassi, and R. Vaglio Phys Rev Lett. 100, (2008)is a widely-used technique for determining the local geometric and/or electronic structure of matter Metal L-edge XAS is an experimental technique that involves the excitation of a metal 2p electron to unfilled metal d orbitals (eg. 3d for first-row transition metals). According to the selection rules, the transition is formally electric-dipole allowed, which not only makes it more intense than an electric-dipole forbidden metal K pre-edge (1s → 3d transition), but also makes it more feature-rich as the lower required energy (~ eV scandium to copper) results in a higher-resolution experiment. In the simplest case, that of a cupric (CuII) complex, the 2p → 3d transition produces a 2p53d10 final state. The 2p5 core hole created in the transition has an orbital angular momentum L=1 which then couples to the spin angular momentum S=1/2 to produce J = 3/2 and J=1/2 final states. These states are directly observable in the L-edge spectrum as the two main peaks (Figure 1). The peak at lower energy (~930 eV) has the greatest intensity and is called the L3-edge while the peak at higher energy (~950 eV) has less intensity and is called the L2-edge.In cuprates Cu-O hybridization creates ZR single where Cu is in the virtual Cu3+ state. A ligand hole produces another feature due to 2p63d9→ c2p53d10L
22 X-ray Magnetic Circular Dichroism q=90°abcx-raym+m-Both orbital and spin magnetic components along the field can be obtained (with chemical and orbital sensitivity) from the circular dichroic XAS.BTEY and FY configurationonthis research line The XMCD spectrum is defined as the difference spectrum of two absorption spectrum acquired with either opposite polarization or magnetization. The XMCD effect is opposite in sign at the L3 and L2 edge because of the opposite sign of the spin-orbit coupling in the 2p states: l+s for 2p3/2, and l-s for 2p1/2. The different coupling gives rise to a unique feature of XMCD, its ability to separate spin and orbital moment. The spin momentum is proportional to the difference of the integrated XMCD intensity at the L3 and the L2 edge, the orbital momentum is proportional to the sum. Sum rules have been developed, which are used to quantitatively determine the spin and orbital magnetic moment per atom.SUM RULES
23 XMCD on cuprate thin films XMCD at the Cu L2,3 edgeSum rulesthese experiments showed that in undoped, underdoped and even in superconducting and optimally doped cuprates, the Dzyaloshinskii-Moriya (DM) interactionwithin the CuO2 planes survives and gives rise to an out of plane spin canting, which creates a spin component perpendicular to the CuO2 planes aligned by an external magnetic field [Fig.6b].The effective out-of-plane spin moment at 4 T, determined using the sum rules, is shown as functionof the temperature in Fig.7.In LCO the component of the spin moment along the c-axis shows, from 9 K to 280 K, the trend expected in the case of field-induce weak-ferromagnetism in an antiferromagnetic system (see Ref. 7).The magnetic moment goes to zero above 250 K, i.e. close to the Nèel temperature. On the contrary, as shown in Fig.7c, in the superconducting samples the c-axis spin moment increases as the inverse of the temperature, like in a paramagnet and independently of the doping it goes to zero, within the experimental error, above 130 K. Moreover, the same spin moment measured at 9 K, is linear as a function of the magnetic field, with no remnant magnetic moment at zero field, as shown for YBCO and NdBCO in Fig.2b. In LCO, on the contrary, the magnetic moment is zero up to 2-3 Tesla and jump to a value comparable to those measured in the other cuprates at 4 Tesla. In the latter case a remnant ferromagnetic component intercepts the zero field axis at a value different from zero, typical of a weak ferromagnetic behavior.
24 Studio interfacce superconduttive LaboratorioCaratterizzazione strutturale e di trasporto di film epitassiali BiMnO3 e SrMnO3Studio interfacce superconduttiveImplementazione della tecnica PFM per l’analisi di materiali multiferroici
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