Hikari Kimura - Academia.edu (original) (raw)

Papers by Hikari Kimura

Research paper thumbnail of Superconductivity and non-Fermi liquid behavior near antiferromagnetic quantum critical points inCeRh1−xCoxIn5

Physical Review B, Jul 29, 2005

Single crystals of CeRh 1−x Co x In 5 have been investigated by means of specific heat measuremen... more Single crystals of CeRh 1−x Co x In 5 have been investigated by means of specific heat measurements at zero pressure and electrical resistivity measurements under nearly hydrostatic pressure up to 28 kbar. Specific heat measurements for samples of CeRh 1−x Co x In 5 with cobalt concentrations of x = 0.65, 0.71, 0.77, 0.87, and 0.93 confirm the existence of antiferromagnetism for 0 ഛ x ഛ 0.7 and suggest the existence of a quantum critical point at x c ϳ 0.75. Entropy versus x isotherms below ϳ5 K and the normalized residual resistivity ͑0 K͒ / ͑290 K͒ versus x curve both display maxima near x c ϳ 0.75, suggesting further evidence for the existence and location of the quantum critical point. Electrical resistivity measurements under pressure for samples with x = 0.1, 0.2, 0.4, and 0.6 reveal antiferromagnetism, pressure-induced superconductivity, and the coexistence of antiferromagnetism and superconductivity. Normalized residual resistivity ͑0 K͒ / ͑290 K͒ versus pressure P curves and the evolution of the power-law exponent n favor the existence of quantum critical points at critical pressures P c ϳ 23 kbar, ϳ21 kbar, and ϳ7 kbar for samples with x = 0.1, 0.2, and 0.4, respectively.

Research paper thumbnail of Probing single molecules with the STM in the frequency and time domains

We have constructed a scanning tunneling microscope (STM) and combined it with a tunable femtosec... more We have constructed a scanning tunneling microscope (STM) and combined it with a tunable femtosecond laser (210 nm to 1040 nm) to probe single molecules with simultaneous spatial and temporal resolutions. Employing the RF lock-in amplifier to measure the laser-induced tunneling current that is directly synchronized with the high repetition rate of the laser (∼80 MHz), time resolved measurement of single molecules with atomic scale resolution can be achieved by varying the time delay between pairs of laser pulses in the two-pulse correlation or two-color pumpprobe configuration. A femtosecond laser system with widely tunable wavelength enables resonant excitation of single molecules that are partially decoupled electronically from the underlying metallic substrate by a thin oxide or additionally atomic or molecular layers. The experimental arrangement allows measurement of molecular lifetimes by two-photon photoemission spectroscopy and microscopy.

Research paper thumbnail of Probing the superconducting order parameter of high-Tc superconductor bismuth strontium calcium copper oxide by scanning Josephson tunneling microscopy

The technique of scanning tunneling microscopy (STM) with a normal metal tip has recently been us... more The technique of scanning tunneling microscopy (STM) with a normal metal tip has recently been used to study the high transition temperature ( TC) superconducting cuprates and has revealed many fascinating and complex features of quasiparticle excited states of these materials. For conventional superconductors, the Bardeen-Cooper-Schrieffer theory connects the pair amplitude and the superconducting gap as measured from the quasiparticle

Research paper thumbnail of Confinement-Induced Catalytic Dissociation of Hydrogen Molecules in a Scanning Tunneling Microscope

Journal of the American Chemical Society

Research paper thumbnail of Scanning Josephson tunneling microscopy of single-crystal Bi2Sr2CaCu2O8+δ with a conventional superconducting Tip

Physical Review Letters, 2008

We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed be... more We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi 2 Sr 2 CaCu 2 O 8+δ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson IcRn product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local IcRn product and the local energy gap. \end{abstract} (Body) Remarkable scanning tunneling microscopy (STM) studies on the high-T C superconducting cuprate (HTSC), Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) reveal spectral and energy gap inhomogeneities (1, 2), periodic electronic structure in the superconducting (SC) state (3) and structure inside vortex cores (4) as well as in the "pseudogap" state at temperatures above Tc (5). In these experiments the energy gap Δ is taken to be half the energy separation between the quasiparticle (QP) coherence peaks as observed in dI/dV spectra. The appearance of Δ has also been observed at a

Research paper thumbnail of Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi 2 Sr 2 ... more Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a novel scanning tunneling microscope (STM) equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wavefunction of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe 2. The relevant

Research paper thumbnail of Scanninng Josephson Tunneling Microscopy of Single Crystal Bi2Sr2CaCu2O8+delta from a Conventional Superconducting Tip

Using a scanning tunneling microscope with superconducting Pb-coated tips (S-STM), we have observ... more Using a scanning tunneling microscope with superconducting Pb-coated tips (S-STM), we have observed the thermally fluctuated Josephson Effect between the tip and conventional superconductors. Such STM-based Josephson junctions are a powerful tool that can directly probe the phase of the superconducting condensate via the Josephson Effect as well as characterize the quasiparticle spectrum, both on a nanometer length scale. In this talk we present data from Josephson junctions formed between the S-STM tips and Bi2Sr2CaCu2O8+delta single crystals. These results clearly show c-axis Josephson tunneling between a conventional superconductor and both overdoped and optimally doped Bi2Sr2CaCu2O8+delta. Josephson measurements at various surface locations indicate an inhomogeneous structure of the ICRN product in overdoped Bi2Sr2CaCu2O8+delta. These local ICRN data of the Bi2Sr2CaCu2O8+delta are related to the local superconducting gap. This work is supported by DOE Grant No. DE-FG02-05ER46194.

Research paper thumbnail of Superconductivity and non-Fermi liquid behavior near antiferromagnetic quantum critical points inCeRh1−xCoxIn5

Physical Review B, Jul 29, 2005

Single crystals of CeRh 1−x Co x In 5 have been investigated by means of specific heat measuremen... more Single crystals of CeRh 1−x Co x In 5 have been investigated by means of specific heat measurements at zero pressure and electrical resistivity measurements under nearly hydrostatic pressure up to 28 kbar. Specific heat measurements for samples of CeRh 1−x Co x In 5 with cobalt concentrations of x = 0.65, 0.71, 0.77, 0.87, and 0.93 confirm the existence of antiferromagnetism for 0 ഛ x ഛ 0.7 and suggest the existence of a quantum critical point at x c ϳ 0.75. Entropy versus x isotherms below ϳ5 K and the normalized residual resistivity ͑0 K͒ / ͑290 K͒ versus x curve both display maxima near x c ϳ 0.75, suggesting further evidence for the existence and location of the quantum critical point. Electrical resistivity measurements under pressure for samples with x = 0.1, 0.2, 0.4, and 0.6 reveal antiferromagnetism, pressure-induced superconductivity, and the coexistence of antiferromagnetism and superconductivity. Normalized residual resistivity ͑0 K͒ / ͑290 K͒ versus pressure P curves and the evolution of the power-law exponent n favor the existence of quantum critical points at critical pressures P c ϳ 23 kbar, ϳ21 kbar, and ϳ7 kbar for samples with x = 0.1, 0.2, and 0.4, respectively.

Research paper thumbnail of Probing single molecules with the STM in the frequency and time domains

We have constructed a scanning tunneling microscope (STM) and combined it with a tunable femtosec... more We have constructed a scanning tunneling microscope (STM) and combined it with a tunable femtosecond laser (210 nm to 1040 nm) to probe single molecules with simultaneous spatial and temporal resolutions. Employing the RF lock-in amplifier to measure the laser-induced tunneling current that is directly synchronized with the high repetition rate of the laser (∼80 MHz), time resolved measurement of single molecules with atomic scale resolution can be achieved by varying the time delay between pairs of laser pulses in the two-pulse correlation or two-color pumpprobe configuration. A femtosecond laser system with widely tunable wavelength enables resonant excitation of single molecules that are partially decoupled electronically from the underlying metallic substrate by a thin oxide or additionally atomic or molecular layers. The experimental arrangement allows measurement of molecular lifetimes by two-photon photoemission spectroscopy and microscopy.

Research paper thumbnail of Probing the superconducting order parameter of high-Tc superconductor bismuth strontium calcium copper oxide by scanning Josephson tunneling microscopy

The technique of scanning tunneling microscopy (STM) with a normal metal tip has recently been us... more The technique of scanning tunneling microscopy (STM) with a normal metal tip has recently been used to study the high transition temperature ( TC) superconducting cuprates and has revealed many fascinating and complex features of quasiparticle excited states of these materials. For conventional superconductors, the Bardeen-Cooper-Schrieffer theory connects the pair amplitude and the superconducting gap as measured from the quasiparticle

Research paper thumbnail of Confinement-Induced Catalytic Dissociation of Hydrogen Molecules in a Scanning Tunneling Microscope

Journal of the American Chemical Society

Research paper thumbnail of Scanning Josephson tunneling microscopy of single-crystal Bi2Sr2CaCu2O8+δ with a conventional superconducting Tip

Physical Review Letters, 2008

We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed be... more We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi 2 Sr 2 CaCu 2 O 8+δ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson IcRn product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local IcRn product and the local energy gap. \end{abstract} (Body) Remarkable scanning tunneling microscopy (STM) studies on the high-T C superconducting cuprate (HTSC), Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) reveal spectral and energy gap inhomogeneities (1, 2), periodic electronic structure in the superconducting (SC) state (3) and structure inside vortex cores (4) as well as in the "pseudogap" state at temperatures above Tc (5). In these experiments the energy gap Δ is taken to be half the energy separation between the quasiparticle (QP) coherence peaks as observed in dI/dV spectra. The appearance of Δ has also been observed at a

Research paper thumbnail of Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi 2 Sr 2 ... more Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a novel scanning tunneling microscope (STM) equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wavefunction of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe 2. The relevant

Research paper thumbnail of Scanninng Josephson Tunneling Microscopy of Single Crystal Bi2Sr2CaCu2O8+delta from a Conventional Superconducting Tip

Using a scanning tunneling microscope with superconducting Pb-coated tips (S-STM), we have observ... more Using a scanning tunneling microscope with superconducting Pb-coated tips (S-STM), we have observed the thermally fluctuated Josephson Effect between the tip and conventional superconductors. Such STM-based Josephson junctions are a powerful tool that can directly probe the phase of the superconducting condensate via the Josephson Effect as well as characterize the quasiparticle spectrum, both on a nanometer length scale. In this talk we present data from Josephson junctions formed between the S-STM tips and Bi2Sr2CaCu2O8+delta single crystals. These results clearly show c-axis Josephson tunneling between a conventional superconductor and both overdoped and optimally doped Bi2Sr2CaCu2O8+delta. Josephson measurements at various surface locations indicate an inhomogeneous structure of the ICRN product in overdoped Bi2Sr2CaCu2O8+delta. These local ICRN data of the Bi2Sr2CaCu2O8+delta are related to the local superconducting gap. This work is supported by DOE Grant No. DE-FG02-05ER46194.