F. La Mattina

Publications (10)14.74 Total impact

• Article: Experimental evidence for two gaps in the high-temperature La1.83Sr0.17CuO4 superconductor.

  R Khasanov, A Shengelaya, A Maisuradze, F La Mattina, A Bussmann-Holder, H Keller, K A Müller
  [show abstract] [hide abstract]
  ABSTRACT: The in-plane magnetic field penetration depth (lambda(ab)) in single-crystal La1.83Sr0.17CuO4 was investigated by muon-spin rotation (muSR). The temperature dependence of lambda(ab)(-2) has an inflection point around 10-15 K, suggesting the presence of two superconducting gaps: a large gap (Delta(1)(d)) with d-wave and a small gap (Delta(2)(s)) with s-wave symmetry. The zero-temperature values of the gaps at mu(0)H=0.02 T were found to be Delta(1)(d)(0)=8.2(1) meV and Delta(2)(s)(0)=1.57(8) meV.
  Physical Review Letters 03/2007; 98(5):057007. · 7.37 Impact Factor
• Article: Electroluminescence in SrTiO 3 :Cr single-crystal nonvolatile memory cells

  S. F. Alvarado, F. La Mattina, J. G. Bednorz
  [show abstract] [hide abstract]
  ABSTRACT: Metal–insulator–metal (M–I–M) structures involving transition-metal oxides and, more recently, also perovskite oxides with resistive switching effects have attracted substantial interest in research aimed at nonvolatile memories of nanometer dimensions. Although some models are presently under discussion, it is still not clear whether the fundamental switching mechanism is an interface or a bulk property, or a combination of both. Extended defects, such as dislocation lines and changes in the oxygen vacancy concentration, are considered responsible for the conducting state, and local reduction/oxidation processes have been proposed to be responsible for the resistive switching. In addition, the role of dopants has not been discussed in depth. Here we report on an electric-field-controlled electron trapping/detrapping process involved in the resistive switching in Cr-doped SrTiO3. Electroluminescence (EL) measurements reveal that during resistive switching, light emission is observed only in the switching transition from high to low conductivity. The EL spectrum is typical for Cr3+ in an octahedral ligand field, indicating that the switching process involves trapping/detrapping of electrons at the Cr site. With increasing conductivity of SrTiO3, we observe a change from the predominant (R-line) to the vibronically red-shifted transition, which points to a modification of the Cr-occupied lattice sites.
  Applied Physics A-materials Science & Processing - APPL PHYS A-MAT SCI PROCESS. 01/2007; 89(1):85-89.
• Source

  Available from: A. Bussmann-Holder

  Article: Mixed order parameter symmetries in cuprate superconductors

  A. Bussmann-Holder, R. Khasanov, A. Shengelaya, A. Maisuradze, F. La Mattina, H. Keller, K. A. Mueller
  [show abstract] [hide abstract]
  ABSTRACT: The recent observation of an inflection point in the temperature dependence of the in-plane magnetic field dependence (lambda_ab) is investigated within a two-band model with coupled order parameters of different symmetries. While the dominant order parameter has d-wave symmetry, the smaller one is of s-wave symmetry. Superconductivity is robust in the d-wave channel and induced via interband interactions in the s-wave subsystem.
  11/2006;
• Article: Muon-spin-rotation measurements of the penetration depth in Li_ {2} Pd_ {3} B

  R. Khasanov, I. L. Landau, C. Baines, F. La Mattina, A. Maisuradze, K. Togano, H. Keller
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the magnetic field penetration depth λ in the ternary boride superconductor Li2Pd3B (Tc≃7.3 K) have been carried out by means of muon-spin rotation (μSR). The absolute values of λ, the Ginzburg-Landau parameter κ, and the first Hc1 and second Hc2 critical fields at T=0 obtained from μSR were found to be λ(0)=252(2) nm, κ(0)=27(1), μ0Hc1(0)=9.5(1) mT, and μ0Hc2(0)=3.66(8) T, respectively. The zero-temperature value of the superconducting gap Δ0=1.31(3) meV was found, corresponding to the ratio 2Δ0∕kBTc=4.0(1). At low temperatures λ(T) saturates and becomes constant below T≃0.2Tc, in agreement with what is expected for s-wave BCS superconductors. Our results suggest that Li2Pd3B is a s-wave BCS superconductor with only one isotropic energy gap.
  Phys. Rev. B. 06/2006; 73(21).
• Source

  Available from: A. Bussmann-Holder

  Article: Evidence for complex order parameter in La_{1.83}Sr_{0.17}CuO_4

  R. Khasanov, A. Shengelaya, A. Maisuradze, F. La Mattina, A. Bussmann-Holder, H. Keller, K A Müller
  [show abstract] [hide abstract]
  ABSTRACT: The in-plane magnetic field penetration depth (\lambda_{ab}) in single-crystal La_{1.83}Sr_{0.17}CuO_4 was investigated by means of the muon-spin rotation (\muSR) technique. The temperature dependence of \lambda^{-2}_{ab} has an inflection point around 10-15K, suggesting the presence of two superconducting gaps: a large gap (\Delta_1^d) with d-wave and a small gap (\Delta_2^s) with s-wave symmetry. The zero-temperature values of the gaps at \mu_0H=0.02T were found to be \Delta_1^d(0)=8.2(2)meV and \Delta_2^s(0)=1.57(8)meV. Comment: 5 pages, 3 figures
  06/2006;
• Source

  Available from: arxiv.org

  Article: Muon-spin-rotation measurements of the penetration depth in Li_2Pd_3B

  R. Khasanov, I. L. Landau, C. Baines, F. La Mattina, A. Maisuradze, K. Togano, H. Keller
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the magnetic field penetration depth $\lambda$ in the ternary boride superconductor Li$_2$Pd$_3$B ($T_c\simeq7.3$ K) have been carried out by means of muon-spin rotation ($\mu$SR). The absolute values of $\lambda$, the Ginzburg-Landau parameter $\kappa$, and the first $H_{c1}$ and the second $H_{c2}$ critical fields at T=0 obtained from $\mu$SR were found to be $\lambda(0)=252(2)$ nm, $\kappa(0)=27(1)$, $\mu_0H_{c1}(0)=9.5(1)$ mT, and $\mu_0H_{c2}(0)=3.66(8)$ T, respectively. The zero-temperature value of the superconducting gap $\Delta_0=$1.31(3) meV was found, corresponding to the ratio $2\Delta_0/k_BT_c=4.0(1)$. At low temperatures $\lambda(T)$ saturates and becomes constant below $T\simeq 0.2T_c$, in agreement with what is expected for s-wave BCS superconductors. Our results suggest that Li$_2$Pd$_3$B is a s-wave BCS superconductor with the only one isotropic energy gap. Comment: 6 pages, 7 figures
  01/2006;
• Article: Magnetic penetration depth in RbOs2 O6 studied by muon spin rotation

  R. Khasanov, D. G. Eshchenko, D. di Castro, A. Shengelaya, F. La Mattina, A. Maisuradze, C. Baines, H. Luetkens, J. Karpinski, S. M. Kazakov, H. Keller
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the magnetic field penetration depth lambda in the pyrochlore superconductor RbOs2O6 (Tc~=6.3K) were carried out by means of the muon-spin-rotation (muSR) technique. At low temperatures lambda-2(T) saturates and becomes constant below T~=0.2Tc , in agreement with what is expected for weak-coupled s -wave BCS superconductors. The value of lambda at T=0 was found to be in the range of 250-300 nm. muSR and equilibrium magnetization measurements both reveal that at low temperatures lambda is almost (at the level of 10%) independent of the applied magnetic field. This result suggests that the superconducting energy gap in RbOs2O6 is isotropic.
  Physical Review B - PHYS REV B. 01/2005; 72(10).
• Source

  Available from: Dmitry Eshchenko

  Article: Study of the magnetic penetration depth in RbOs_2O_6

  R. Khasanov, D G Eshchenko, D. Di Castro, A. Shengelaya, F. La Mattina, A. Maisuradze, C. Baines, H. Luetkens, J. Karpinski, S. M. Kazakov, H. Keller
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the magnetic field penetration depth \lambda in the pyrochlore superconductor RbOs_2O_6 (T_c\simeq6.3 K) were carried out by means of the muon-spin-rotation (\muSR) technique. At low temperatures \lambda^{-2}(T) saturates and becomes constant below T\simeq 0.2T_c, in agreement with what is expected for weak-coupled s-wave BCS superconductors. The value of \lambda at T=0 was found to be in the range of 250 nm to 300 nm. \muSR and equilibrium magnetization measurements both reveal that at low temperatures $\lambda$ is almost (at the level of 10%) independent of the applied magnetic field. This result suggests that the superconducting energy gap in RbOs_2O_6 is isotropic. Comment: 8 pages, 9 figures
  11/2004;
• Article: Pressure effects on the transition temperature and the magnetic field penetration depth in the pyrochlore superconductor RbOs2O6.

  R Khasanov, D G Eshchenko, J Karpinski, S M Kazakov, N D Zhigadlo, R Brütsch, D Gavillet, D Di Castro, A Shengelaya, F La Mattina, A Maisuradze, C Baines, H Keller
  [show abstract] [hide abstract]
  ABSTRACT: Magnetization measurements under hydrostatic pressure up to 8 kbar in the pyrochlore superconductor RbOs2O6 (T(c) approximately or equal 6.3 K at p=0) were carried out. A positive pressure effect on T(c) with dT(c)/dp=0.090(3) K/kbar was observed, whereas no pressure effect on the magnetic penetration depth lambda was detected. The pressure independent ratio 2 Delta(0)/k(B)T(c)=3.72(2) (Delta(0) is the superconducting gap at zero temperature) was found to be close to the BCS value 3.52. Magnetization and muon-spin rotation measurements of lambda(T) indicate that RbOs2O6 is an adiabatic s-wave BCS-type superconductor. The value of lambda extrapolated to zero temperature and ambient pressure was estimated to be 230(30) nm.
  Physical Review Letters 11/2004; 93(15):157004. · 7.37 Impact Factor
• Article: Controlled oxygen vacancies and space correlation with Cr^{3+} in SrTiO_ {3}

  F. La Mattina, J. G. Bednorz, S. F. Alvarado, A. Shengelaya, K. A. Müller, H. Keller
  [show abstract] [hide abstract]
  ABSTRACT: By means of electron paramagnetic resonance (EPR) measurements on thermally reduced Cr-doped SrTiO3, we find a strong correlation between the Cr3+ ions and oxygen vacancies (Vos). A charge compensation associated with the creation of Vos induced by thermal reduction causes the valence of the Cr ions to change from 4+ to 3+. This induces a symmetry change in the crystal field experienced by the Cr atom from cubic to axial. On the other hand, in Cr/Nb-codoped samples, where Vos are absent, the Cr3+ EPR signal is isotropic, indicating that these Cr ions occupy an octahedral site of cubic symmetry. From the angular dependence of the EPR spectra we determine an axial crystal field parameter (D≃8 MHz), which is consistent with a perturbation induced by a Vo localized at the third coordination sphere of Cr3+. This is in contrast to other transition-metal dopants, where the Vo is located at the first coordination sphere. Thus we identify a linear complex of the form Cr3+-O-Ti3+-Vo-Ti3+, which is unique in its structure, and which, furthermore, might account for the stabilization of the insulating state in reduced Cr-doped SrTiO3 crystals.
  Phys. Rev. B. 80(7).
• Article: Magnetic penetration depth in RbOs_ {2} O_ {6} studied by muon spin rotation

  R. Khasanov, D. G. Eshchenko, D. Di Castro, A. Shengelaya, F. La Mattina, A. Maisuradze, C. Baines, H. Luetkens, J. Karpinski, S. M. Kazakov, H. Keller
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the magnetic field penetration depth λ in the pyrochlore superconductor RbOs2O6(Tc≃6.3 K) were carried out by means of the muon-spin-rotation (μSR) technique. At low temperatures λ−2(T) saturates and becomes constant below T≃0.2Tc, in agreement with what is expected for weak-coupled s-wave BCS superconductors. The value of λ at T=0 was found to be in the range of 250–300 nm. μSR and equilibrium magnetization measurements both reveal that at low temperatures λ is almost (at the level of 10%) independent of the applied magnetic field. This result suggests that the superconducting energy gap in RbOs2O6 is isotropic.
  Phys. Rev. B. 72(10).