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Search Results: 1 - 10 of 4747 matches for " Hiroshi Eisaki "
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Multi-Junction Switching in Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ Intrinsic Josephson Junctions
Hiromi Kashiwaya,Tetsuro Matsumoto,Hajime Shibata,Hiroshi Eisaki,Yoshiyuki Yoshida,Hiroshi Kambara,Shiro Kawabata,Satoshi Kashiwaya
Physics , 2010, DOI: 10.1143/APEX.3.043101
Abstract: We study the dynamics of multi-junction switching (MJS): several intrinsic Josephson junctions (IJJs) in an array switch to the finite voltage state simultaneously. The number of multi-switching junctions ($N$) was successfully tuned by changing the load resistance serially connected to an Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+\delta}$ IJJ array. The independence of the escape rates of $N$ in the macroscopic quantum tunneling regime indicates that MJS is a $successive$ switching process rather than a $collective$ process. The origin of MJS is explained by the gradient of a load curve and the relative magnitudes of the switching currents of quasiparticle branches in the current-voltage plane.
Optical control of non-equilibrium superconducting phase transition below Tc in a cuprate
Claudio Giannetti,Giacomo Coslovich,Federico Cilento,Gabriele Ferrini,Hiroshi Eisaki,Nobuhisa Kaneko,Martin Greven,Fulvio Parmigiani
Physics , 2008, DOI: 10.1103/PhysRevB.79.224502
Abstract: Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-arrangements, have been recently reported in complex transition-metal oxides. However, the optical control of a purely electronic phase transition, where the thermodynamic phase is determined by the distribution of excitations, has remained elusive. Here we report optical control of the electronic phase in an underdoped Bi2212 crystal through impulsive photoinjection of quasiparticles (QP) via ultrashort laser pulses, avoiding significant laser heating. An abrupt transition of the transient optical electronic response is observed at a critical fluence of Ipump=70 uJ/cm^2. We show that the measured dynamics is consistent with an inhomogenous first-order superconducting-to-normal state phase transition, triggered by a sudden shift of the chemical potential.
Superconductivity at 28.3 and 17.1 K in (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P)
Parasharam M. Shirage,Kunihiro Kihou,Chul-Ho Lee,Hijiri Kito,Hiroshi Eisaki,Akira Iyo
Physics , 2010, DOI: 10.1063/1.3508957
Abstract: We have successfully synthesized (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P) (Al-42622(Pn)) using high-pressure synthesis technique. Al-42622(Pn) exhibit superconductivity for both Pn = As and P with the transition temperatures of 28.3 K and 17.1 K, respectively. The a-lattice parameters of Al-42622(Pn) (a = 3.713 {\AA} and 3.692 {\AA} for Pn = As and P, respectively) are smallest among the iron-pnictide superconductors. Correspondingly, Al-42622(As) has the smallest As-Fe-As bond angle (102.1 {\deg}) and the largest As distance from the Fe planes (1.500 {\AA}).
Electronic States and Magnetic Propertis of Edge-sharing Cu-O Chains
Yoshiaki Mizuno,Takami Tohyama,Sadamichi Maekawa,Tatsuaki Osafune,Naoki Motoyama,Hiroshi Eisaki,Shinichi Uchida
Physics , 1997, DOI: 10.1103/PhysRevB.57.5326
Abstract: The electronic states and magnetic properties for the copper oxides containing edge-sharing Cu-O chains such as Li$_2$CuO$_2$, La$_6$Ca$_8$Cu$_{24}$O$_{41}$ and CuGeO$_3$ are systematically studied. The optical conductivity $\sigma(\omega)$ and the temperature dependence of the magnetic susceptibility $\chi(T)$ for single crystalline samples Li$_2$CuO$_2$ are measured as a reference system and analyzed by using the exact diagonalization method for small Cu-O clusters. It is shown that the spectral distribution of $\sigma(\omega)$ is different between edge-sharing and corner-sharing Cu-O-Cu bonds. The charge transfer gap in edge-sharing chains is larger than that of high-$T_{c}$ cuprates. The exchange interaction between nearest-neighbor copper ions in edge-sharing chains $J_1$ depends sensitively on the Cu-O-Cu bond angles. In addition to $J_1$, the exchange interaction between next-nearest-neighbor copper ions $J_2$ has sufficient contribution to the magnetic properties. We calculate $J_1$ and $J_2$ for all the copper oxides containing edge-sharing Cu-O chains and discuss the magnetic properties.
The Spin Dynamics of the Spin Ladder, Dimer Chain Material Sr14Cu24O41
Roger S Eccleston,Masatomo Uehara,Jun Akimitsu,Hiroshi Eisaki,Naoki Motoyama,Shin-ichi Uchida,.
Physics , 1997, DOI: 10.1103/PhysRevLett.81.1702
Abstract: We have performed inelastic neutron scattering on a single crystal sample of Sr14Cu24O41 to study the spin dynamics of the Cu2O3 spin ladder layers, and CuO2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV and 500 meV are best fitted with a dispersion with a spin gap of 32.5+/-0.1 meV and a maximum of 193.52.4 meV, consistent with a coupling along the ladders, J|| = 130 meV and a rung coupling J^=72 meV. We find that excitations with an energy transfer of approximately 11.5 meV can be described solely in terms of a dimer chain with an antiferromagnetic intra-dimer coupling, J1 = 11.2 meV, between next-nearest-neighbour Cu ions and a ferromagnetic inter-dimer coupling, J2 = -1.1 meV. The dimers are separated by two Cu ions providing a periodicity for the dimer chain of five units.
Energy-dependent scaling of incoherent spectral weight and the origin of the waterfalls in high-Tc cuprates
Qiang Wang,Zhe Sun,Eli Rotenberg,Helmuth Berger,Hiroshi Eisaki,Yoshihiro Aiura,D. S. Dessau
Physics , 2009,
Abstract: The exotic physics in condensed matter systems, such as high-Tc superconductivity in cuprates, is due to the properties of the elementary excitations and their interactions. The dispersion of the electronic states revealed by angle-resolved photoemission spectroscopy (ARPES) provides a chance to understand these excitations. Recently, a "high energy anomaly" or "waterfall-like" feature in cuprates' dispersion has been reported and studied theoretically. Most of the current views argue that it is the result of some many-body effect at a specific high energy scale (e.g. ~ 0.3eV), though there are other arguments that this is an artificial effect. Here, we report a systematic ARPES study on the "high energy anomaly" in Bi2212 samples over multiple Brillouin zones and with a large variety of ARPES matrix elements. We find that the incoherent weight of the electron spectral function at high binding energy is intimately linked to the energy of the dispersive coherent weight through an unexpected but simple relationship with no special energy scales. This behavior in concert with strong k-dependent matrix element effects gives rise to the heavily studied "waterfall" behavior.
Photoinduced changes of the chemical potential in superconducting Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$
Tristan L. Miller,Christopher L. Smallwood,Wentao Zhang,Hiroshi Eisaki,Joseph Orenstein,Alessandra Lanzara
Physics , 2015, DOI: 10.1103/PhysRevB.92.144506
Abstract: The chemical potential of a superconductor is of critical importance since, at equilibrium, it is the energy where electrons pair and form the superconducting condensate. However, in non-equilibrium measurements, there may be a difference between the chemical potential of the quasiparticles and that of the pairs. Here we report a systematic time- and angle-resolved photoemission study of the pump-induced change in the chemical potential of an optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) sample in both its normal and superconducting states. The change in chemical potential can be understood by separately considering the change in the valence band energy relative to the vacuum, and the change in chemical potential relative to the valence band energy. We attribute the former effect to a changing potential barrier at the sample surface, and the latter effect to the conservation of charge in an asymmetrical density of states. The results indicate that the pair and quasiparticle chemical potentials follow each other even on picosecond timescales.
Structural Analysis on Iron-Based Superconductor Pr1111 System with Oxygen Deficiency and Flourine Substitution
Katsuaki Kodama,Motoyuki Ishikado,Fumitaka Esaka,Akira Iyo,Hiroshi Eisaki,Shin-ichi Shamoto
Physics , 2011, DOI: 10.1143/JPSJ.80.034601
Abstract: We have performed structural analyses on iron-based superconductors, PrFeAsO$_{1-y}$ and PrFeAsO$_{1-x}$F$_x$, systematically, by means of Rietveld method on neutron powder diffraction data. The shifts of iron ion valence from +2, $\delta$, are accurately determined from the occupancies of O and O$_{1-x}$F$_x$ sites obtained by the Rietveld analysis and F-concentration obtained by secondary ion-microprobe mass spectrometry. $T_\textrm{c}$-$\delta$ curve of PrFeAsO$_{1-y}$ is different from the curve of PrFeAsO$_{1-x}$F$_x$, indicating that $\delta$ is not a principal parameter for $T_\textrm{c}$ in so-called 1111 system. Structural parameters of the FeAs layers, for example, As-Fe-As bond angle and As-height from Fe layer, are different between both systems with similar $\delta$-values. Their parent compounds are also found to have different structural parameters, possibly due to the different synthetic conditions. These results suggest that the difference of structural parameters of FeAs layer is the origin of the discrepancy of $T_\textrm{c}$-$\delta$ curves of both systems and the $T_\textrm{c}$-value in the 1111 system is sensitive to the structural parameters. It may be attribute to an energy balance of the conducting bands contributing to the superconductivity.
Multiplet resonance lifetimes in resonant inelastic X-ray scattering involving shallow core levels
L. Andrew Wray,Wanli Yang,Hiroshi Eisaki,Zahid Hussain,Yi-De Chuang
Physics , 2012, DOI: 10.1103/PhysRevB.86.195130
Abstract: Resonant inelastic X-ray scattering (RIXS) spectra of model copper- and nickel-based transition metal oxides are measured over a wide range of energies near the M-edge (h$\nu$=60-80eV) to better understand the properties of resonant scattering involving shallow core levels. Standard multiplet RIXS calculations are found to deviate significantly from the observed spectra. However, by incorporating the self consistently calculated decay lifetime for each intermediate resonance state within a given resonance edge, we obtain dramatically improved agreement between data and theory. Our results suggest that these textured lifetime corrections can enable a quantitative correspondence between first principles predictions and RIXS data on model multiplet systems. This accurate model is also used to analyze resonant elastic scattering, which displays the elastic Fano effect and provides a rough upper bound for the core hole shake-up response time.
Understanding the re-entrant superconducting phase diagram of an iron-pnictide Ca$_4$Al$_2$O$_6$Fe$_2$(As$_{1-x}$P$_x$)$_2$
Hidetomo Usui,Katsuhiro Suzuki,Kazuhiko Kuroki,Nao Takeshita,Parasharam Maruti Shirage,Hiroshi Eisaki,Akira Iyo
Physics , 2013, DOI: 10.1103/PhysRevB.87.174528
Abstract: Recently, a very rich phase diagram has been obtained for an iron-based superconductor Ca4Al2O6Fe2(As1-xPx)2. It has been revealed that nodeless (x=0) and nodal (x = 1) superconductivity are separated by an antiferromagnetic phase. Here we study the origin of this peculiar phase diagram using a five orbital model constructed from first principles band calculation, and applying the fluctuation exchange approximation assuming spin fluctuation mediated pairing. Based on the calculation results, we propose a scenario where the frustration in momentum space degrades superconductivity in the intermediate x regime, while antiferromangetism takes place due to a very good nesting. In order to see whether the present theoretical scenario is consistent with the actual nature of the competition between superconductivity and antiferromagnetism, we also perform hydrostatic pressure experiment for Ca4Al2O6Fe2(As1-xPx)2. In the intermediate x regime where antiferromagnetism occurs at ambient pressure, applying hydrostatic pressure smears out the antiferromagnetic transition, but superconductivity does not take place. This supports our scenario that superconductivity is suppressed by the momentum space frustration in the intermediate x regime, apart from the presence of the antiferromangnetism.
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