Publications by Davor Pavuna | EPFL Graph Search

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Properties of ultra-thin films are different from their single crystal counterparts due to the presence of (substrate induced) strain, different degree and type of (growth induced) disorder and different average doping (distribution of oxygen vacancies, for example). Here we briefly summarize main results on ultra-thin (99 --> 1 unit cell (UC)) superconducting oxide films grown by laser ablation. Systematic studies show that BSCCO-2212, 2201, 2223, and LSCO-214 exhibit conductor-like Fermi edge, whereas mat

Superconductivity in high-Tc cuprates is particularly sensitive to disorder due to the unconventional d-wave pairing symmetry. We investigated effects of disorder on the spectral properties of Bi2Sr2CaCu2O8+x high-Tc superconductor. We found that already small defect densities suppress the characteristic spectral signature of the superconducting state. The spectral line shape clearly reflects new excitations within the gap, as expected for de

We briefly summarize well established and the latest experimental results concerning the doping dependence of the so-called pseudogap (T*) and emphasize that surface related techniques, like ARPES or tunneling, give somewhat higher value of T* as compared to the bulk techniques, like specific heat. In the underdoped regime most theoretical models differ in extrapolating the T*-line to zero doping. As underdoped cuprates are rather inhomogeneous and the disorder plays an important role, the complete microsco

One of the important problems for electrical applications of high-temperature superconductors is the contact resistance between the superconductor and a normal metallic wire. In this paper, the authors report a simple method of contact preparation for high-T//c copper-oxide materials (Y-Ba-Cu-O). Based on high-temperature metallization, it reduces the contact resistance from typically 1 OMEGA mm** minus 2 down to APP 1STH 10 mu OMEGA mm minus **2 (77 K), and makes it possible to measure the critical cur

Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (

We report the in-plane (rho (ab)) and out-of-plane (rho (c)) resistivities in the 4-800 K range on single crystals of Tl2Ba2CaCu2O8 high-T-c cuprate with T-c = 111 K (rho (c)/rho (ab) approximate to 1000). rho (ab)(T) exhibits "usual" linear behavior and rho (c)(T) follows generally metallic-like, positive slope in the 150-400 K temperature range. There is a clear crossover to semiconductor-like behavior close to T-c. However, for the first time in a chainless high-T-c cuprate we observe a crossover above 5

Experimental studies of quasi-crystalline Al100-xMnx(Si) alloys have shown that the magnitude of electrical resistivity as well as the excess specific heat term Δγ are proportional to the percentage of manganese in the samples as is the case in dilute Al-Mn alloys. The authors argue that the excess specific heat term and the high resistivity (about 150-200 μΩ cm for the quasi-crystalline phase) can be accounted for within the extended Friedel-Anderson s-d model in which the dominant scattering is due to the

We studied structural changes in a 5 unit cell thick La1.96Sr0.04CuO4 film, epitaxially grown on a LaSrAlO4 substrate with a single unit cell buffer layer, when ultra-high electric fields were induced in the film by applying a gate voltage between the film ...

We report on in-plane paraconductivity measurements in thin YBa2Cu3O6.9 films. Our analysis of the data shows that the temperature dependence of paraconductivity is affected by lattice disorder and deviates at all temperatures from the universal power laws predicted by both scaling and mean-field theories. This gives evidence for the absence of critical fluctuations and for the failure of the Aslamazov-Larkin universal relation between critical exponent and dimensionality of the spectrum of Gaussian fluctua

We used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4, LSCO) and a cuprate insulator (La2CuO4, LCO), in which interface superconductivity occurs in a layer that is just one-half unit cell thi ...

We have optimized laser ablation thin film deposition and transfer procedures within synchrotron vault, specifically to perform angle-integrated and angle-resolved photoemission spectroscopy (ARPES) on high-T-c and related films without cleaving the samples. However, the chain-containing phases like YBCO-123 easily loose surface oxygen and do not exhibit stable Fermi edge, hence are not suitable for ARPES studies. Direct in situ ARPES studies on strained LSCO-214 films show striking strain effects on the el

We summarize some of the main results on photoemission spectroscopy in the field of high T-c superconductivity, beginning with a discussion of several open questions. We then briefly analyze our experiments that illustrate the role of doping and of intentionally introduced disorder (by electron bombardment) in Bi2Sr2CaCu2O8+x single crystals.

The temperature dependence of the DC resistivity and AC magnetic susceptibility was investigated in bulk ceramics of the BiPbSrCaCuO system with 2212-free (2223) phase. The temperature domain needed to synthesize this phase was small and, according to the actual temperature used, the superconducting properties of the samples were strongly modified. The corresponding X-ray diffraction lines of the 110 K phase can be indexed in the pseudo-orthorhombic unit cell with parameters 5.40×5.41×37 Å3. SEM microprobe

We present measurements for the resistivity of

c' axis oriented YBa2Cu3O7-δ (YBCO) films grown on (100) SrTiO3 substrates by both laser ablation and ion beam sputtering. The effect of the magnetic field on the resistivity is investigated with the field parallel to the

c' axis. The zero field transition widths vary from 1 K to 4 K in different films. However the data exhibits 3d X-Y critical scaling having introduced an `effective' magnetic field characteristic of the length scale of the disorder in the f

The authors report experimental evidence for an enhanced density of states at the Fermi level in Al86Mn14 and Al75Mn20Si5 quasicrystals (QC) as indicated by the low-temperature specific heat and resistivity. The excess specific-heat term Δγ is proportional to the Mn concentration in these QC samples as is the case for dilute AlMn alloys. Spin-glass-like behavior is observed in both QC samples. In Al-Mn-Si, the relative frequency dependence of the AC susceptibility cusp is comparable to canonical spin glasse

Superconducting YBa2Cu3O7-δ (YBCO) thin films have been grown in situ on Si with conducting indium-tin-oxide (ITO) buffer layers. ITO allows YBCO to be electrically connected to the underlying Si substrate. Both the YBCO film and ITO buffer layer, grown by ion beam sputtering, are textured and polycrystalline with a combined room-temperature resistivity of about 2 mΩ cm. Superconducting onsets are 92 K with zero resistance at 68 K

The authors analysis of in-plane paraconductivity measurements on YBa2Cu3O7-δ (YBCO) films indicates that short-wavelength cutoff effects are significant even very close to the critical point because of the short coherence length ξ. Consequently, the Aslamazov-Larkin (AL) and Lawrence-Doniach expressions are inapplicable to YBCO in the whole Ginzburg-Landau mean-field region, while a generalized AL expression in three-dimensions, that replaces the conventional AL expression in the case of short ξ, accounts

Angle-resolved photoemission spectroscopy reveals very surprising strain-induced effects on the electronic band dispersion of epitaxial La2-xSrxCuO4-delta thin films. In strained films we measure a band that crosses the Fermi level (E-F) well before the Brillouin zone boundary. This is in contrast to the flat band reported in unstrained single crystals and in our unstrained films, as well as in contrast to the band flattening predicted by band structure calculations for in-plane compressive strain. In spite

We report on improved structural, crystallographic and electrical properties of epitaxial NdBa2Cu3O7-delta (NBCO) films grown on SrTiO3 by 'off-axis' pulsed laser deposition (PLD). Transport and XRD studies show that the c-axis-oriented epitaxial films, with critical temperatures of 90-92 K, are mono phase and single-crystalline. Furthermore, very smooth, almost outgrowth-free surfaces and crystal coherences of up to 0.8 mum (to our knowledge the best value ever reported for high-T-c films) were obtained.

Measurements of critical temperature T-c in superconducting YBa2Cu3O6.9 films with reduced long-range structural order show the validity of the empirical scaling relation Delta T-c proportional to r(c)(-2) between disorder-induced reduction of T-c and structural coherence length r(c) in the ab-plane. This result is quantitatively explained by the disorder-induced confinement of the charge carriers within each ordered domain of size r(c). Our analysis of the data based on this picture enables us to precisely

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Systematic studies of (magneto)transport, structural and electronic properties of ultra-thin films of high-T-c cuprates and related layered oxides

Defect-induced changes in the spectral properties of high-Tc cuprates

On the doping variation of the pseudogap in high-T-c cuprates

IMPROVED LOW CONTACT RESISTANCE IN HIGH-T//c Y-Ba-Cu-O CERAMIC SUPERCONDUCTORS

Direct angle resolved photoemission spectroscopy and superconductivity of strained high- T c films

Crossovers in the out-of-plane resistivity of superconducting Tl2Ba2CaCu2O8 single crystals

Electronic properties and resonant states in Al-Mn(-Si) alloys

Oxygen Displacement in Cuprates under Ionic Liquid Field-Effect Gating

Evidence for nonuniversal behavior of paraconductivity caused by predominant short-wavelength Gaussian fluctuations in YBa2Cu3O6.9

Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4/La2CuO4 films and the organic superconductors kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

Direct photoemission spectroscopy and electronic properties of in situ grown, strained high-T-c and related oxide films

Photoemission experiments on high-T-c superconductors: Recent progress and some open questions

Microstructure and electrical properties of pure 110 K phase in the BiPbSrCaCuO system

3d X-Y scaling of the resistivity and the effect of disorder in YBa2Cu3O7-δ thin films

Experimental evidence for the existence of enhanced density of states and canonical spin-glass behavior in Al-Mn (-Si) quasicrystals

In situ growth of superconducting YBa2Cu3O7-δ thin films on Si with conducting indium-tin-oxide buffer layers

Non-universal behaviour of paraconductivity in YBa2Cu3O7-δ films

Strain and high temperature superconductivity: Unexpected results from direct electronic structure measurements in thin films

Improved structural properties and crystal coherence of superconducting NdBa2Cu3O7-delta films grown by pulsed laser ablation

Scaling between superconducting critical temperature and structural coherence length in TBa2Cu3O6.9 films