ABSTRACT Bilayer graphene shows opening of electric-field-induced band gap, the size of which is ... more ABSTRACT Bilayer graphene shows opening of electric-field-induced band gap, the size of which is proportional to the intensity of the electric field. We report electronic transport measurements on superconducting proximity effect in planar dual-gated bilayer-graphene Josephson junction with Pb0.93In0.07 (PbIn) electrodes (δPbIn ˜ 1.1meV, Tc = 7.0 K). The junction resistance along the charge-neutral point (CNP) increases as we modulate top- and back-gate voltages away from the zero-gap CNP. The resistive state near the CNP shows a variable-range-hopping-type insulating behavior in R-T curve with lowering temperature crossing the superconducting transition of PbIn electrodes. However, a highly doped regime shows metallic R-T behavior and junction becomes superconducting below Tc. Moreover, magnetic-field-induced Fraunhofer supercurrent modulation, microwave-induced Shapiro steps, and multiple Andreev reflection (MAR) are observed, which indicate the formation of genuine Josephson coupling across the planar junctions below Tc with sufficiently transparent superconductor-bilayer graphene interface. The separatrix of the superconductor-insulator transition corresponds to the square junction conductance of Gsq˜ 6-8e^2/h.
ABSTRACT We have measured both the c-axis and the ab-plane resistivities on carefully fabricated ... more ABSTRACT We have measured both the c-axis and the ab-plane resistivities on carefully fabricated Bi2Sr2CaCu2O8−x single crystals in a magnetic fieldH‖c. Low temperature data in the mixed state for both directions show a thermally activated behavior with the same field dependence of the activation energy,U∝H −1/3. The results were analyzed in terms of a theoretical model that was recently proposed.
We have measured the ab-plane, c-axis, and the secondary voltage of Bi2Sr2CaCu2Os-~ single crysta... more We have measured the ab-plane, c-axis, and the secondary voltage of Bi2Sr2CaCu2Os-~ single crystals sinmltaneously in low magnetic fields for both H I1 e and H ]1 lb. The peak in V~ reduces sharply in a field ~ low as 40 G for H I] c, whereas it survives up to 1000 G for H H lb. We compared the results with the calculation ba.sed on a simple resistor equivalent-circuit model.
We made electrical transport measurements along the c-axis of SmFeAsO 0.85 single crystals, in bo... more We made electrical transport measurements along the c-axis of SmFeAsO 0.85 single crystals, in both three-and four-terminal configurations, focusing on examining the possible formation of Josephson coupling between FeAs superconducting layers.
In a conventional Josephson junction of graphene, the supercurrent is not turned off even at the ... more In a conventional Josephson junction of graphene, the supercurrent is not turned off even at the charge neutrality point, impeding further development of superconducting quantum information devices based on graphene. Here we fabricate bipolar Josephson junctions of graphene, in which a p-n potential barrier is formed in graphene with two closely spaced superconducting contacts, and realize supercurrent ON/OFF states using electrostatic gating only. The bipolar Josephson junctions of graphene also show fully gate-driven macroscopic quantum tunnelling behaviour of Josephson phase particles in a potential well, where the confinement energy is gate tuneable. We suggest that the supercurrent OFF state is mainly caused by a supercurrent dephasing mechanism due to a random pseudomagnetic field generated by ripples in graphene, in sharp contrast to other nanohybrid Josephson junctions. Our study may pave the way for the development of new gate-tuneable superconducting quantum information devices.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2000
We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes... more We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes as a new kind of mask material. By irradiating ions of 300 eV energy on a nanotube-coated Au/Ti thin layer on a substrate, Au/Ti nanowires were successfully formed just underneath ...
ABSTRACT Bilayer graphene shows opening of electric-field-induced band gap, the size of which is ... more ABSTRACT Bilayer graphene shows opening of electric-field-induced band gap, the size of which is proportional to the intensity of the electric field. We report electronic transport measurements on superconducting proximity effect in planar dual-gated bilayer-graphene Josephson junction with Pb0.93In0.07 (PbIn) electrodes (δPbIn ˜ 1.1meV, Tc = 7.0 K). The junction resistance along the charge-neutral point (CNP) increases as we modulate top- and back-gate voltages away from the zero-gap CNP. The resistive state near the CNP shows a variable-range-hopping-type insulating behavior in R-T curve with lowering temperature crossing the superconducting transition of PbIn electrodes. However, a highly doped regime shows metallic R-T behavior and junction becomes superconducting below Tc. Moreover, magnetic-field-induced Fraunhofer supercurrent modulation, microwave-induced Shapiro steps, and multiple Andreev reflection (MAR) are observed, which indicate the formation of genuine Josephson coupling across the planar junctions below Tc with sufficiently transparent superconductor-bilayer graphene interface. The separatrix of the superconductor-insulator transition corresponds to the square junction conductance of Gsq˜ 6-8e^2/h.
ABSTRACT We have measured both the c-axis and the ab-plane resistivities on carefully fabricated ... more ABSTRACT We have measured both the c-axis and the ab-plane resistivities on carefully fabricated Bi2Sr2CaCu2O8−x single crystals in a magnetic fieldH‖c. Low temperature data in the mixed state for both directions show a thermally activated behavior with the same field dependence of the activation energy,U∝H −1/3. The results were analyzed in terms of a theoretical model that was recently proposed.
We have measured the ab-plane, c-axis, and the secondary voltage of Bi2Sr2CaCu2Os-~ single crysta... more We have measured the ab-plane, c-axis, and the secondary voltage of Bi2Sr2CaCu2Os-~ single crystals sinmltaneously in low magnetic fields for both H I1 e and H ]1 lb. The peak in V~ reduces sharply in a field ~ low as 40 G for H I] c, whereas it survives up to 1000 G for H H lb. We compared the results with the calculation ba.sed on a simple resistor equivalent-circuit model.
We made electrical transport measurements along the c-axis of SmFeAsO 0.85 single crystals, in bo... more We made electrical transport measurements along the c-axis of SmFeAsO 0.85 single crystals, in both three-and four-terminal configurations, focusing on examining the possible formation of Josephson coupling between FeAs superconducting layers.
In a conventional Josephson junction of graphene, the supercurrent is not turned off even at the ... more In a conventional Josephson junction of graphene, the supercurrent is not turned off even at the charge neutrality point, impeding further development of superconducting quantum information devices based on graphene. Here we fabricate bipolar Josephson junctions of graphene, in which a p-n potential barrier is formed in graphene with two closely spaced superconducting contacts, and realize supercurrent ON/OFF states using electrostatic gating only. The bipolar Josephson junctions of graphene also show fully gate-driven macroscopic quantum tunnelling behaviour of Josephson phase particles in a potential well, where the confinement energy is gate tuneable. We suggest that the supercurrent OFF state is mainly caused by a supercurrent dephasing mechanism due to a random pseudomagnetic field generated by ripples in graphene, in sharp contrast to other nanohybrid Josephson junctions. Our study may pave the way for the development of new gate-tuneable superconducting quantum information devices.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2000
We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes... more We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes as a new kind of mask material. By irradiating ions of 300 eV energy on a nanotube-coated Au/Ti thin layer on a substrate, Au/Ti nanowires were successfully formed just underneath ...
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Papers by H. Lee