The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a searc... more The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a search for other structures that display high-temperature superconductivity. The discovery of superconductivity above 70 K in La 3-x Ba 3+ x Cu 6 O l4+y 3 raises some ...
Abstract Heat capacity, resistivity, and magnetic susceptability data have been obtained for the ... more Abstract Heat capacity, resistivity, and magnetic susceptability data have been obtained for the compounds REBa 2 Cu 3 O 7-x, where RE= Dy, Ho or Er. Neutron diffraction data on the Ho compound show a structure identical to that of YBa 2 Cu 3 O 7-x. Magnetic transitions ...
Heat capacity, resistivity and magnetic susceptibility data have been used to study electronic an... more Heat capacity, resistivity and magnetic susceptibility data have been used to study electronic and magnetic properties of REBa2Cu3O7−x compounds. Neutron diffraction on the Ho compound shows identical crystal structure to YBa2Cu3O6.8. All the compounds are superconducting at Tc=(93±2) K. Magnetic transitions are observed in the heat capacity data at Tm=2.2, 0.95, 0.17, and 0.59 K for RE=Gd, Dy, Ho, and Er, respectively, and the magnetically ordered state is found to coexist with superconductivity. Estimates have been obtained for the magnetic moment in the crystal field ground state and the energy splitting of the first excited state crystal field level.
The recent discovery of two types of metallic copper oxide compounds which are superconducting to... more The recent discovery of two types of metallic copper oxide compounds which are superconducting to above 90K has renewed interest in the search for new high temperature superconducting materials. It is significant that both classes of compounds, La2−xSrxCuO4−y and YBa2Cu3O7−δ are intimately related to the extensively studied perovskite family. Both compounds contain highly oxidized, covalently bonded Cu-O sublattices, however, they differ in geometry. In this paper we discuss the relationship of these features to the superconducting properties.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2010
Copper phthalocyanine (CuPc) thin film transistors were fabricated using a tapered edge bottom co... more Copper phthalocyanine (CuPc) thin film transistors were fabricated using a tapered edge bottom contact device geometry, and mobility saturation was observed for devices with CuPc thicknesses of 12 monolayers (MLs) and greater. The mobility saturation is attributed to a significantly decreased contact resistance resulting from a bilayer resist lift-off method, as compared with a single layer resist lift-off method. Threshold voltages are also found to saturate above 12 ML CuPc thicknesses.
Ultrathin cobalt phthalocyanine transistors of 4 ML have been fabricated for chemical sensing. Co... more Ultrathin cobalt phthalocyanine transistors of 4 ML have been fabricated for chemical sensing. Compared to 50 ML devices, the ultrathin transistors show faster response times, higher base line stabilities, and sensitivity enhancements of 1.5–20 for the five analytes tested. The enhanced response for the ultrathin transistors provides insight into the device physics. The absorption of analytes changes the surface doping level and trap energies. The changes in surface trap energies perturb the charge transport properties of the ultrathin devices, thereby, making these devices more sensitive.
Light illumination produces major, interesting changes of the electrical properties of oxygen def... more Light illumination produces major, interesting changes of the electrical properties of oxygen deficient La2/3Sr1/3MnO3-delta thin films. At small oxygen deficiency, the classical insulator-metal (I-M) transition at a temperature Tp decreases with increasing oxygen deficiency. The low-temperature metallic behavior in darkness shows a persistent increase of the conductivity with light. This photoconductivity increases with oxygen deficiency (from a few to 60%). At large oxygen deficiency, the films are semiconducting in darkness, from helium to room temperature and light induces a transient photoconductivity and a low-temperature I-M transition. The intriguing possibility of collective light induced magnetism is discussed.
The exchange bias of antiferromagnetic-ferromagnetic (AFM-FM) bilayers is found to be strongly de... more The exchange bias of antiferromagnetic-ferromagnetic (AFM-FM) bilayers is found to be strongly dependent on the ferromagnetic spin configuration. The widely accepted inverse proportionality of the exchange bias field with the ferromagnetic thickness is broken in FM layers thinner than the FM correlation length. Moreover, an anomalous thermal dependence of both exchange bias field and coercivity is also found. A model based on springlike domain walls parallel to the AFM-FM interface quantitatively accounts for the experimental results and, in particular, for the deviation from the inverse proportionality law. These results reveal the active role the ferromagnetic spin structure plays in AFM-FM hybrids which leads to a new paradigm of the exchange bias phenomenon.
We have developed a very sensitive, highly selective, non-destructive technique for screening inh... more We have developed a very sensitive, highly selective, non-destructive technique for screening inhomogeneous materials for the presence of superconductivity. This technique, based on phase sensitive detection of microwave absorption is capable of detecting 10(-12) cc of a superconductor embedded in a non-superconducting, non-magnetic matrix. For the first time, we apply this technique to the search for superconductivity in extraterrestrial samples. We tested approximately 65 micrometeorites collected from the water well at the Amundsen-Scott South pole station and compared their spectra with those of eight reference materials. None of these micrometeorites contained superconducting compounds, but we saw the Verwey transition of magnetite in our microwave system. This demonstrates that we are able to detect electro-magnetic phase transitions in extraterrestrial materials at cryogenic temperatures.
... M. B.Maple and Ivan K. Schuller Physics Department, University of California San D-iego, La J... more ... M. B.Maple and Ivan K. Schuller Physics Department, University of California San D-iego, La Jolla, California 92093-0319 (Received 12 August 1992) We show that illumination of oxygen-deficient metallic YBa2Cu30 films produces a change in the Hall coefficient, an increase ...
The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a searc... more The observation of superconductivity above 90 K in the YBaCuO system 1, 2 has prompted a search for other structures that display high-temperature superconductivity. The discovery of superconductivity above 70 K in La 3-x Ba 3+ x Cu 6 O l4+y 3 raises some ...
Abstract Heat capacity, resistivity, and magnetic susceptability data have been obtained for the ... more Abstract Heat capacity, resistivity, and magnetic susceptability data have been obtained for the compounds REBa 2 Cu 3 O 7-x, where RE= Dy, Ho or Er. Neutron diffraction data on the Ho compound show a structure identical to that of YBa 2 Cu 3 O 7-x. Magnetic transitions ...
Heat capacity, resistivity and magnetic susceptibility data have been used to study electronic an... more Heat capacity, resistivity and magnetic susceptibility data have been used to study electronic and magnetic properties of REBa2Cu3O7−x compounds. Neutron diffraction on the Ho compound shows identical crystal structure to YBa2Cu3O6.8. All the compounds are superconducting at Tc=(93±2) K. Magnetic transitions are observed in the heat capacity data at Tm=2.2, 0.95, 0.17, and 0.59 K for RE=Gd, Dy, Ho, and Er, respectively, and the magnetically ordered state is found to coexist with superconductivity. Estimates have been obtained for the magnetic moment in the crystal field ground state and the energy splitting of the first excited state crystal field level.
The recent discovery of two types of metallic copper oxide compounds which are superconducting to... more The recent discovery of two types of metallic copper oxide compounds which are superconducting to above 90K has renewed interest in the search for new high temperature superconducting materials. It is significant that both classes of compounds, La2−xSrxCuO4−y and YBa2Cu3O7−δ are intimately related to the extensively studied perovskite family. Both compounds contain highly oxidized, covalently bonded Cu-O sublattices, however, they differ in geometry. In this paper we discuss the relationship of these features to the superconducting properties.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2010
Copper phthalocyanine (CuPc) thin film transistors were fabricated using a tapered edge bottom co... more Copper phthalocyanine (CuPc) thin film transistors were fabricated using a tapered edge bottom contact device geometry, and mobility saturation was observed for devices with CuPc thicknesses of 12 monolayers (MLs) and greater. The mobility saturation is attributed to a significantly decreased contact resistance resulting from a bilayer resist lift-off method, as compared with a single layer resist lift-off method. Threshold voltages are also found to saturate above 12 ML CuPc thicknesses.
Ultrathin cobalt phthalocyanine transistors of 4 ML have been fabricated for chemical sensing. Co... more Ultrathin cobalt phthalocyanine transistors of 4 ML have been fabricated for chemical sensing. Compared to 50 ML devices, the ultrathin transistors show faster response times, higher base line stabilities, and sensitivity enhancements of 1.5–20 for the five analytes tested. The enhanced response for the ultrathin transistors provides insight into the device physics. The absorption of analytes changes the surface doping level and trap energies. The changes in surface trap energies perturb the charge transport properties of the ultrathin devices, thereby, making these devices more sensitive.
Light illumination produces major, interesting changes of the electrical properties of oxygen def... more Light illumination produces major, interesting changes of the electrical properties of oxygen deficient La2/3Sr1/3MnO3-delta thin films. At small oxygen deficiency, the classical insulator-metal (I-M) transition at a temperature Tp decreases with increasing oxygen deficiency. The low-temperature metallic behavior in darkness shows a persistent increase of the conductivity with light. This photoconductivity increases with oxygen deficiency (from a few to 60%). At large oxygen deficiency, the films are semiconducting in darkness, from helium to room temperature and light induces a transient photoconductivity and a low-temperature I-M transition. The intriguing possibility of collective light induced magnetism is discussed.
The exchange bias of antiferromagnetic-ferromagnetic (AFM-FM) bilayers is found to be strongly de... more The exchange bias of antiferromagnetic-ferromagnetic (AFM-FM) bilayers is found to be strongly dependent on the ferromagnetic spin configuration. The widely accepted inverse proportionality of the exchange bias field with the ferromagnetic thickness is broken in FM layers thinner than the FM correlation length. Moreover, an anomalous thermal dependence of both exchange bias field and coercivity is also found. A model based on springlike domain walls parallel to the AFM-FM interface quantitatively accounts for the experimental results and, in particular, for the deviation from the inverse proportionality law. These results reveal the active role the ferromagnetic spin structure plays in AFM-FM hybrids which leads to a new paradigm of the exchange bias phenomenon.
We have developed a very sensitive, highly selective, non-destructive technique for screening inh... more We have developed a very sensitive, highly selective, non-destructive technique for screening inhomogeneous materials for the presence of superconductivity. This technique, based on phase sensitive detection of microwave absorption is capable of detecting 10(-12) cc of a superconductor embedded in a non-superconducting, non-magnetic matrix. For the first time, we apply this technique to the search for superconductivity in extraterrestrial samples. We tested approximately 65 micrometeorites collected from the water well at the Amundsen-Scott South pole station and compared their spectra with those of eight reference materials. None of these micrometeorites contained superconducting compounds, but we saw the Verwey transition of magnetite in our microwave system. This demonstrates that we are able to detect electro-magnetic phase transitions in extraterrestrial materials at cryogenic temperatures.
... M. B.Maple and Ivan K. Schuller Physics Department, University of California San D-iego, La J... more ... M. B.Maple and Ivan K. Schuller Physics Department, University of California San D-iego, La Jolla, California 92093-0319 (Received 12 August 1992) We show that illumination of oxygen-deficient metallic YBa2Cu30 films produces a change in the Hall coefficient, an increase ...
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