Submitted for the MAR07 Meeting of The American Physical Society Effect of heavy electron mass m?... more Submitted for the MAR07 Meeting of The American Physical Society Effect of heavy electron mass m? on Andreev reflection (AR) in heavy-fermion/superconductor (HF/S) point-contacts H. STALZER, W.K. PARK, L.H. GREENE, Univ. of Illinois at Urbana-Champaign, J.L. SARRAO, J.D. THOMPSON, Los Alamos Nat. Lab., J. FREDERICK, P. CANFIELD, Ames Lab and Iowa State Univ., L.D. PHAM, Univ. of California, Davis, Z. FISK, Univ. of California, Irvine — We investigate the effect of m? on Andreev reflection in HF/S point-contacts (PC) by measuring the differential electrical conductance at temperatures between 1.5 and 10 K. An electrochemically etched Nb tip (Tc =9.2 K) is brought into contact with HF single crystals (CeCoIn5, CeRhIn5, YbAl3) of varying m?. Our conductance signals show a clear superconducting gap structure expected for PC in the Sharvin regime which can be fitted by the BlonderTinkham-Klapwijk model. Preliminary results on CeCoIn5 at temperatures above its Tc =2.3 K indicate an enhanc...
ABSTRACTThe structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xM... more ABSTRACTThe structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xMxO7-y (M = Ni,Zn,Fe and Co) are reported. Values of y, determined by titration, are found to be dependent on the nature and amount of the doping. The range of solubility is greater for the Fe and Co compounds (x = 1) than for those with Ni or Zn (x = 0.3). The undoped material is orthorhombic and remains orthorhombic after substitution for Cu by Ni or Zn, whereas a tetragonal phase is observed when Fe, Co are substituted for Cu. DC resistance and AC susceptibility measurements show that Tc is depressed from 90K (x = 0) to 45K (x = 0.2) for both the Ni and Zn doped compounds and Tc is destroyed in the Fe and Co doped compounds when x reaches 0.4. We suggest that a valence of 2 be assigned to the Ni and Zn and 3 to the Fe and Co ions.
Coherent multilayers of interheavy rare-earth metals have been synthesized by sputtering. The ant... more Coherent multilayers of interheavy rare-earth metals have been synthesized by sputtering. The antiferromagnetic-ferromagnetic transition temperature is suppressed with decreasing modulation wavelength in the TmnLum system.
We present a study of interdiffusion at interfaces of YBa2Cu3O7-x (YBCO) and metals, Au, Ag, and ... more We present a study of interdiffusion at interfaces of YBa2Cu3O7-x (YBCO) and metals, Au, Ag, and Pb by using X-ray reflectivity. YBCO thin films were epitaxially grown by off-axis sputter deposition and coevaporation, with the c-axis perpendicular to the SrTiO3 substrate surfaces. The capping layers were subsequently deposited on the YBCO film in situ and ex situ near room temperature.
The proximity effect in superconductor-semiconductor interfaces is observed using Raman scatterin... more The proximity effect in superconductor-semiconductor interfaces is observed using Raman scattering^1. Substrates of (100)-n^+ InAs (10^18-10^19cm-3) are coated with a high-quality ~100Åthick Nb film grown after a low-energy Ar-ion etch. The longitudinal optical phonon LO mode (237cm-1) and the plasmon-phonon coupled modes, L- (221cm-1) and L+ (position is carrier concentration dependent), are studied. An increase of the intensity ratio of
In the past, information obtained from planar tunneling into YBCO has been limited by superconduc... more In the past, information obtained from planar tunneling into YBCO has been limited by superconducting (SC) counter-electrode density of states effects and interface damage. Traditional fabrication methods such as SC Pb deposition [1] and more recent attempts using organic ligand barriers with non-SC Cu counter electrodes [2] lead to an altered YBCO surface. New molecular technology has produced the molecule
not available 4) BAUER Carsten Institute for Theoretical Physics, University of Cologne Quantum c... more not available 4) BAUER Carsten Institute for Theoretical Physics, University of Cologne Quantum criticality in metals In many systems of strongly correlated electrons, it is believed that quantum critical points play a crucial role in determining the physics over certain regions of phase space. While quantum critical phenomena in insulators are relatively well understood, their metallic counterparts pose a substantial theoretical challenge since order parameter fluctuations can interact with gapless fermionic excitations on the Fermi surface. This interplay, however, allows for a competition of orders in the vicinity of a metallic quantum critical point including the formation of unconventional superconductivity when driving the metallic system through a phase transition. Fortunately, for certain classes of metallic quantum critical points this rich physics can be studied by determinant quantum Monte Carlo simulations, without suffering from the notorious fermion ”sign problem”. I w...
Different synthesis techniques for the preparation of dense superconducting ceramics are discusse... more Different synthesis techniques for the preparation of dense superconducting ceramics are discussed, and a sol-gel process is shown to be very promising. The effect of oxygen content, and the effect of substitution of Ni and Zn for copper, on the structural, transport and superconducting properties of the La-Sr-Cu-O and Y-Ba-Cu-O systems are presented. It is found that substitution on the copper sites destroys Tc in the La-Sr-Cu-O system and decreases it in the Y-Ba-Cu-O system, and this effect is insensitive as to whether the third metal is magnetic (Ni) or diamagnetic (Zn). A detailed study of the YBa2Cu3O(7-y) system as a function of oxygen content (y) shows that superconductivity can be destroyed in these materials by the removal of oxygen and restored by reinjecting oxygen, either thermally at 500 C or at temperatures (80 C) compatible with device processing by means of a novel plasma oxidation process. Of scientific interest, the plasma process induces bulk superconductivity in the undoped La2CuO4.
Submitted for the MAR07 Meeting of The American Physical Society Effect of heavy electron mass m?... more Submitted for the MAR07 Meeting of The American Physical Society Effect of heavy electron mass m? on Andreev reflection (AR) in heavy-fermion/superconductor (HF/S) point-contacts H. STALZER, W.K. PARK, L.H. GREENE, Univ. of Illinois at Urbana-Champaign, J.L. SARRAO, J.D. THOMPSON, Los Alamos Nat. Lab., J. FREDERICK, P. CANFIELD, Ames Lab and Iowa State Univ., L.D. PHAM, Univ. of California, Davis, Z. FISK, Univ. of California, Irvine — We investigate the effect of m? on Andreev reflection in HF/S point-contacts (PC) by measuring the differential electrical conductance at temperatures between 1.5 and 10 K. An electrochemically etched Nb tip (Tc =9.2 K) is brought into contact with HF single crystals (CeCoIn5, CeRhIn5, YbAl3) of varying m?. Our conductance signals show a clear superconducting gap structure expected for PC in the Sharvin regime which can be fitted by the BlonderTinkham-Klapwijk model. Preliminary results on CeCoIn5 at temperatures above its Tc =2.3 K indicate an enhanc...
ABSTRACTThe structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xM... more ABSTRACTThe structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xMxO7-y (M = Ni,Zn,Fe and Co) are reported. Values of y, determined by titration, are found to be dependent on the nature and amount of the doping. The range of solubility is greater for the Fe and Co compounds (x = 1) than for those with Ni or Zn (x = 0.3). The undoped material is orthorhombic and remains orthorhombic after substitution for Cu by Ni or Zn, whereas a tetragonal phase is observed when Fe, Co are substituted for Cu. DC resistance and AC susceptibility measurements show that Tc is depressed from 90K (x = 0) to 45K (x = 0.2) for both the Ni and Zn doped compounds and Tc is destroyed in the Fe and Co doped compounds when x reaches 0.4. We suggest that a valence of 2 be assigned to the Ni and Zn and 3 to the Fe and Co ions.
Coherent multilayers of interheavy rare-earth metals have been synthesized by sputtering. The ant... more Coherent multilayers of interheavy rare-earth metals have been synthesized by sputtering. The antiferromagnetic-ferromagnetic transition temperature is suppressed with decreasing modulation wavelength in the TmnLum system.
We present a study of interdiffusion at interfaces of YBa2Cu3O7-x (YBCO) and metals, Au, Ag, and ... more We present a study of interdiffusion at interfaces of YBa2Cu3O7-x (YBCO) and metals, Au, Ag, and Pb by using X-ray reflectivity. YBCO thin films were epitaxially grown by off-axis sputter deposition and coevaporation, with the c-axis perpendicular to the SrTiO3 substrate surfaces. The capping layers were subsequently deposited on the YBCO film in situ and ex situ near room temperature.
The proximity effect in superconductor-semiconductor interfaces is observed using Raman scatterin... more The proximity effect in superconductor-semiconductor interfaces is observed using Raman scattering^1. Substrates of (100)-n^+ InAs (10^18-10^19cm-3) are coated with a high-quality ~100Åthick Nb film grown after a low-energy Ar-ion etch. The longitudinal optical phonon LO mode (237cm-1) and the plasmon-phonon coupled modes, L- (221cm-1) and L+ (position is carrier concentration dependent), are studied. An increase of the intensity ratio of
In the past, information obtained from planar tunneling into YBCO has been limited by superconduc... more In the past, information obtained from planar tunneling into YBCO has been limited by superconducting (SC) counter-electrode density of states effects and interface damage. Traditional fabrication methods such as SC Pb deposition [1] and more recent attempts using organic ligand barriers with non-SC Cu counter electrodes [2] lead to an altered YBCO surface. New molecular technology has produced the molecule
not available 4) BAUER Carsten Institute for Theoretical Physics, University of Cologne Quantum c... more not available 4) BAUER Carsten Institute for Theoretical Physics, University of Cologne Quantum criticality in metals In many systems of strongly correlated electrons, it is believed that quantum critical points play a crucial role in determining the physics over certain regions of phase space. While quantum critical phenomena in insulators are relatively well understood, their metallic counterparts pose a substantial theoretical challenge since order parameter fluctuations can interact with gapless fermionic excitations on the Fermi surface. This interplay, however, allows for a competition of orders in the vicinity of a metallic quantum critical point including the formation of unconventional superconductivity when driving the metallic system through a phase transition. Fortunately, for certain classes of metallic quantum critical points this rich physics can be studied by determinant quantum Monte Carlo simulations, without suffering from the notorious fermion ”sign problem”. I w...
Different synthesis techniques for the preparation of dense superconducting ceramics are discusse... more Different synthesis techniques for the preparation of dense superconducting ceramics are discussed, and a sol-gel process is shown to be very promising. The effect of oxygen content, and the effect of substitution of Ni and Zn for copper, on the structural, transport and superconducting properties of the La-Sr-Cu-O and Y-Ba-Cu-O systems are presented. It is found that substitution on the copper sites destroys Tc in the La-Sr-Cu-O system and decreases it in the Y-Ba-Cu-O system, and this effect is insensitive as to whether the third metal is magnetic (Ni) or diamagnetic (Zn). A detailed study of the YBa2Cu3O(7-y) system as a function of oxygen content (y) shows that superconductivity can be destroyed in these materials by the removal of oxygen and restored by reinjecting oxygen, either thermally at 500 C or at temperatures (80 C) compatible with device processing by means of a novel plasma oxidation process. Of scientific interest, the plasma process induces bulk superconductivity in the undoped La2CuO4.
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