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Dr. Gabriella Maria De Luca

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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 avanzata CNR-SPIN Dr. M. Salluzzo Researcher Prof. R. Vaglio Director

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-elettrone Elettroni molto localizzati Campo elettrico cariche orbitale spin Pressione Campo magnetico These 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 [1] 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) [2].

3 Cu content x Temperature [K]

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 degenerazione The 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 structure If 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 configurations Deu to a pariodic among of ions in a crystal lattice two effec are…. Interazione magnetica degli spin Formazione di bande e conduzione metallica degli elettroni

5 Ossidi innovativi per L’elettronica
40mm 25mm Filtri a microonde Memorie FeRam Sensori magnetici Circuiti Schermi LCD Mems attuatori Magnetoresistenza colossale LSMO Superconduttori YBCO Isteresi PZT, BLT Ossidi conduttivi trasparenti Alta costante dielettrica- BST Piezoelettricità Film sottili – Ossidi di Metallo Memorie dinamiche (Gigabit)

6 Interfaccia Ossidi Metalli di Transizioni
NOVEL FUNCTIONALITIES Pr0.7Ca0.3MnO3/La0.7Sr0.3MnO3 SL, PLD-MODA Interfaccia Layer by layer growth RHEED, LEED and in situ SPM SrMnO3/LaMnO3 Antiferromagnete/Antiferromagnete Ferromagnete The combination of strongly correlated materials with given characteristics provides BaCuO2/CaCuO2 Isolante/Isolante Superconduttore ad Alta Tc LaAlO3/SrTiO3 Isolante/Isolante Conduttore , Superconduttore NdBCO/SrTiO3 Superconduttore /Isolante Transizione Superconduttore/Isolante

7 Joule effect Evaporator Magnetron sputtering gun
Sistema di Sputtering HEATER Joule effect Evaporator Magnetron sputtering gun Diode sputtering gun Field Effect Device (FET) Multi Chamber Sputtering system: Three sputtering source+evaporator we 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=25µm Drain 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, equipped also 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.
Ferroelettricità Ferromagnetismo ABO3 Orbitali d parzialmente occupati. Ferroelettricità convenzionale favorita da “d0- ness”. Tesi: Daniele Preziosi

14 Configurazione elettronica Bi3+=[Xe]4f145d106s2 6p0
BiMnO3 a = A b = A c = A b = ° 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

15 Effetto della distanza target-substrato

16 Target-Substrate distance Effect
D=45mm D=40mm D=30mm BiMnO3+Mn3O4+ Bi2Ox(g) BiMnO3 2dsinθ = nλ

17 Strain In condizioni di crescita epitassiale nel piano ab si puo’ avere: Compressive Strain Tensile Strain E’ 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 layer It can be defined as the ration between the lattice parameters of the substrate and bulk film The 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 PFM Il metodo è basato sulla rivelazione delle vibrazioni elettromeccaniche locali del campione causate da una tensione alternata.

19 Luce di Sincrotrone Weak 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 superconductors M. 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
SrTiO3 LaAlO3 photons

21 X-ray Absorption spectroscopy at Cu L2,3 edge
3d10L LHB UHB CT EF 3d10 4s 2p states ZR M. 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[1] (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.[2] 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° a b c x-ray m+ m- Both orbital and spin magnetic components along the field can be obtained (with chemical and orbital sensitivity) from the circular dichroic XAS. B TEY and FY configuration onthis 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 edge Sum rules these 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
Laboratorio Caratterizzazione strutturale e di trasporto di film epitassiali BiMnO3 e SrMnO3 Studio interfacce superconduttive Implementazione della tecnica PFM per l’analisi di materiali multiferroici

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