arXiv subjects

K. Ono

Publications and source records attributed to K. Ono.

At least 55 records · Page 3Linked to original sources

arXiv2013

Dependence of carrier doping on the impurity potential in transition-metal-substituted FeAs-based superconductors

In order to examine to what extent the rigid-band-like electron doping scenario is applicable to the transition metal-substituted Fe-based superconductors, we have performed angle-resolved photoemission spectroscopy studies of Ba(Fe$_{1-x}$Ni$_{x}$)$_2$As$_2$ (Ni-122) and Ba(Fe$_{1-x}$Cu$_{x}$)$_2$As$_2$ (Cu-122), and compared the results with Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ (Co-122). We find that Ni 3$\it{d}$-derived features are formed below the Fe 3$\it{d}$ band and that Cu 3$\it{d}$-derived ones further below it. The electron and hole Fermi surface (FS) volumes are found to increase and decrease with substitution, respectively, qualitatively consistent with the rigid-band model. However, the total extra electron number estimated from the FS volumes (the total electron FS volume minus the total hole FS volume) is found to decrease in going from Co-, Ni-, to Cu-122 for a fixed nominal extra electron number, that is, the number of electrons that participate in the formation of FS decreases with increasing impurity potential. We find that the N$\acute{\rm{e}}$el temperature $T_{\rm{N}}$ and the critical temperature $T_{\it{c}}$ maximum are determined by the FS volumes rather than the nominal extra electron concentration nor the substituted atom concentration.

cond-mat.supr-con↗

arXiv2012

Strongly spin-orbit coupled two-dimensional electron gas emerging near the surface of polar semiconductors

We investigate the two-dimensional (2D) highly spin-polarized electron accumulation layers commonly appearing near the surface of n-type polar semiconductors BiTeX (X = I, Br, and Cl) by angular-resolved photoemission spectroscopy. Due to the polarity and the strong spin-orbit interaction built in the bulk atomic configurations, the quantized conduction-band subbands show giant Rashba-type spin-splitting. The characteristic 2D confinement effect is clearly observed also in the valence-bands down to the binding energy of 4 eV. The X-dependent Rashba spin-orbit coupling is directly estimated from the observed spin-split subbands, which roughly scales with the inverse of the band-gap size in BiTeX.

cond-mat.mtrl-sci↗

arXiv2011

Angle-resolved photoemission spectroscopy study of PrFeAsO_{0.7}: Dependence of the electronic structure on the pnictogen height

We have performed an angle-resolved photoemission spectroscopy (ARPES) study of the iron-based superconductor PrFeAsO_{0.7} and examined the Fermi surfaces and band dispersions near the Fermi level. Heavily hole-doped electronic states have been observed due to the polar nature of the cleaved surfaces. Nevertheless, we have found that the ARPES spectra basically agree with band dispersions calculated in the local density approximation (LDA) if the bandwidth is reduced by a factor of ~2.5 and then the chemical potential is lowered by ~70 meV. Comparison with previous ARPES results on LaFePO reveals that the energy positions of the d_{3z^2-r^2}- and d_{yz,zx}-derived bands are considerably different between the two materials, which we attribute to the different pnictogen height as predicted by the LDA calculation.

cond-mat.supr-con↗

arXiv2010

Cotunneling effects in GaAs vertical double quantum dot

We observed lifting of Coulomb blockade in GaAs vertical double quantum dot with low potential barriers, induced by cotunneling mechanisms at dilution fridge temperature of 10 mK. Several distinct features were observed, compared to single dot case, and appropriate explanation for them was given

cond-mat.mes-hall↗

arXiv2010

Two- and Three-Dimensional Fermi Surfaces and their Nesting Properties in Superconducting BaFe2(As1-xPx)2

We have studied the three-dimensional shapes of the Fermi surfaces (FSs) of BaFe2(As1-xPx)2 (x=0.38), where superconductivity is induced by isovalent P substitution, by angle-resolved photoemission spectroscopy. Moderately strong electron mass enhancement has been identified for both the electron and hole FSs. Among two observed hole FSs, the nearly two-dimensional one shows good nesting with the outer two-dimensional electron FS, but its orbital character is different from the outer electron FS. The three-dimensional hole FS shows poor nesting with the electron FSs. The present results suggest that the three-dimensionality and the difference in the orbital character weaken FS nesting, leaving partial nesting among the outer electron FSs of dxy character and/or that within the three-dimensional hole FS, which may lead to the nodal superconductivity.

cond-mat.supr-con↗

arXiv2010

Mass renormalization in the band width-controlled Mott-Hubbard systems SrVO3 and CaVO3 studied by angle-resolved photoemission spectroscopy

Ca1-xSrxVO3 is a Mott-Hubbard-type correlated electron system whose bandwidth can be varied by the V-O-V bond angle, but the actual effect of bandwidth control on the electronic structure has been controversial in previous photoemission experiments. In this work, band dispersions and Fermi surfaces of SrVO3 and CaVO3 are studied by angle-resolved photoemission spectroscopy. Near the Fermi level (EF), three bands forming cylindricalFermi surfaces derived from the three V 3d t2g orbitals have been observed. The observed band widths for both compounds are almost half of those predicted by local-density-approximation band-structure calculation, confirming mass renormalization caused by electron correlation. It has been clearly demonstrated that the width of the d band in CaVO3 is narrower than that in SrVO3, qualitatively consistent with the result of band-structure calculation. Roles of the orthorhombic lattice distortion and electron correlation in the observed band narrowing are discussed.

cond-mat.str-el↗

arXiv2010

Characteristic electronic structure and its doping evolution in lightly-doped to underdoped YBa2Cu3Oy

We have performed an angle resolved photoemission spectroscopy (ARPES) study of lightly-doped to underdoped YBa2Cu3Oy (YBCO) untwinned single crystals and a core-level x-ray photoemission spectroscopy (XPS) study of YBCO single and polycrystals. In the zone diagonal (nodal) direction, dispersive quasi-particle (QP) features crossing the Fermi level were observed down to the hole concentration of ~ 4%, which explains the metallic transport of the lightly-doped YBCO. The chemical potential shift estimated from XPS was more rapid than in the Bi2212 cuprates. Upon hole doping, very rapid spectral weight transfer from high binding energies to the QP feature, even faster than La2-xSrxCuO4, was observed.

cond-mat.supr-con↗

arXiv2009

Spin bottleneck in resonant tunneling through double quantum dots with different Zeeman splittings

We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g-factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.

cond-mat.mes-hall↗

arXiv2009

Lagrangian Floer theory on compact toric manifolds I

The present authors introduced the notion of \emph{weakly unobstructed} Lagrangian submanifolds and constructed their \emph{potential function} $\mathfrak{PO}$ purely in terms of $A$-model data in [FOOO2]. In this paper, we carry out explicit calculations involving $\mathfrak{PO}$ on toric manifolds and study the relationship between this class of Lagrangian submanifolds with the earlier work of Givental [Gi1] which advocates that quantum cohomology ring is isomorphic to the Jacobian ring of a certain function, called the Landau-Ginzburg superpotential. Combining this study with the results from [FOOO2], we also apply the study to various examples to illustrate its implications to symplectic topology of Lagrangian fibers of toric manifolds. In particular we relate it to Hamiltonian displacement property of Lagrangian fibers and to Entov-Polterovich's symplectic quasi-states.

math.SG↗

arXiv2009

Gate Adjustable Coherent Three and Four Level Mixing in a Vertical Quantum Dot Molecule

We study level mixing in the single particle energy spectrum of one of the constituent quantum dots in a vertical double quantum dot by performing magneto-resonant-tunneling spectroscopy. The device used in this study differs from previous vertical double quantum dot devices in that the single side gate is now split into four separate gates. Because of the presence of natural perturbations caused by anharmonicity and anistrophy, applying different combinations of voltages to these gates allows us to alter the effective potential landscape of the two dots and hence influence the level mixing. We present here preliminary results from one three level crossing and one four level crossings high up in the energy spectrum of one of the probed quantum dots, and demonstrate that we are able to change significantly the energy dispersions with magnetic field in the vicinity of the crossing regions.

cond-mat.mes-hall↗

arXiv2009

Enhanced superconducting gaps in the tri-layer high-$T_c$ cuprate Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$

We have investigated the optimally doped tri-layer cuprate Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ (Bi2223) by angle-resolved photoemission spectroscopy, and observed energy bands and Fermi surfaces originated from the outer and inner CuO$_2$ planes (OP and IP) separately. The OP band is overdoped (hole density $\sim$ 0.26/Cu) with a large d-wave gap of $Δ_0$ $\sim$ 43 meV while the IP is underdoped ($\sim$ 0.06/Cu) with an even large gap of $Δ_0$ $\sim$ 60 meV. We propose that the enhancement of the $Δ_0$ of IP is due to the minimal influence of out-of-plane disorder and that the OP gap is then enhanced through interlayer coupling, most likely a proximity effect from the IP.

cond-mat.supr-con↗

arXiv2009

Effects of out-of-plane disorder on the nodal quasiparticle and superconducting gap in single-layer Bi$_2$Sr$_{1.6}Ln_{0.4}$CuO$_{6+δ}$ ($Ln$ = La, Nd, Gd)

How out-of-plane disorder affects the electronic structure has been investigated for the single-layer cuprates Bi$_2$Sr$_{1.6}$$Ln$$_{0.4}$CuO$_{6+δ}$ ($Ln$ = La, Nd, Gd) by angle-resolved photoemission spectroscopy. We have observed that, with increasing disorder, while the Fermi surface shape and band dispersions are not affected, the quasi-particle width increases, the anti-nodal gap is enhanced and the superconducting gap in the nodal region is depressed. The results indicate that the superconductivity is significantly depressed by out-of-plane disorder through the enhancement of the anti-nodal gap and the depression of the superconducting gap in the nodal region.

cond-mat.supr-con↗

arXiv2009

Differences in the high-energy kink between hole- and electron-doped high-$T_{\rm c}$ superconductors

We have performed an angle-resolved photoemission spectroscopy (ARPES) study of Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$ (NCCO) in order to elucidate the origin of the high-energy kink (HEK) observed in the high-$T_{\rm c}$ superconductors (HTSCs). The energy scale of the HEK in NCCO is large compared with that in hole-doped HTSCs, consistent with previous ARPES studies. From measurement in a wide momentum region, we have demonstrated that between the hole- and electron-doped HTSCs the energy position of the HEK is shifted approximately by the amount of the chemical potential difference. Also, we have found that around $(π, 0)$ the HEK nearly coincides with the band bottom while around the node the band reaches the incoherent region and the HEK appears at the boundary between the coherent and incoherent regions.

cond-mat.supr-con↗

arXiv2008

Canonical models of filtered $A_\infty$-algebras and Morse complexes

The purpose of this paper is two-fold. First we explain the construction of the canonical model of filtered $A_\infty$-algebras given in the authors' book [FOOO]. The canonical model plays a crucial role in the study of Lagrangian Floer theory on toric manifolds in our recent papers, arXiv:0802.1703 and arXiv:0810.5654. Then using a variation of the arguments used in that construction, we define a natural filtered $A_\infty$-structure on the Morse complex of a Morse function and its $A_\infty$ homotopy to the $A_\infty$-algebras on a Lagrangian submanifold constructed in [FOOO]. The corresponding graphical moduli spaces `summing over trees' involve holomorphic discs connected by the gradient flow lines.

math.SG↗

arXiv2008

Universal versus Material-Dependent Two-Gap Behaviors in the High-Tc Cuprates: Angle-Resolved Photoemission Study of La2-xSrxCuO4

We have investigated the doping and temperature dependences of the pseudogap/superconducting gap in the single-layer cuprate La$_{2-x}$Sr$_x$CuO$_4$ by angle-resolved photoemission spectroscopy. The results clearly exhibit two distinct energy and temperature scales, namely, the gap around ($π$,0) of magnitude $Δ^*$ and the gap around the node characterized by the d-wave order parameter $Δ_0$, like the double-layer cuprate Bi2212. In comparison with Bi2212 having higher $T_c$'s, $Δ_0$ is smaller, while $Δ^*$ and $T^*$ are similar. This result suggests that $Δ^*$ and $T^*$ are approximately material-independent properties of a single CuO$_2$ plane, in contrast the material-dependent $Δ_0$, representing the pairing strength.

cond-mat.str-el↗

arXiv2008

Effects of chemical pressure on the Fermi surface and band dispersion in the electron-doped high-Tc superconductors

We have performed angle-resolved photoemission spectroscopy (ARPES) measurements and first-principles electronic structure calculations on the electron-doped high-Tc superconductors Ln1.85Ce0.15CuO4 (Ln = Nd, Sm, and Eu). The observed Fermi surface and band dispersion show such changes that with decreasing ionic size of Ln3+, the curvature of the Fermi surface or -t'/t decreases, where t and t' are transfer integrals between the nearest-neighbor and next-nearestneighbor Cu sites, respectively. The increase of t with chemical pressure is found to be significant, which may explain the apparently inconsistent behavior seen in the hole-doped La2-xSrxCuO4 under epitaxial strain [M. Abrecht et al., Phys. Rev. Lett. 91, 057002 (2003)]. A gap due to the antiferromagnetism opens even in the nodal region for the Sm and Eu compounds, and the gap size increases in going from Ln = Sm to Eu.

cond-mat.supr-con↗

arXiv2008

Doping evolution of the electronic structure in the single-layer cuprates Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$: Comparison with other single-layer cuprates

We have performed angle-resolved photoemission and core-level x-ray photoemission studies of the single-layer cuprate Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$ (Bi2201) and revealed the doping evolution of the electronic structure from the lightly-doped to optimally-doped regions. We have observed the formation of the dispersive quasi-particle band, evolution of the Fermi ``arc'' into the Fermi surface and the shift of the chemical potential with hole doping as in other cuprates. The doping evolution in Bi2201 is similar to that in Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_2$ (Na-CCOC), where a rapid chemical potential shift toward the lower Hubbard band of the parent insulator has been observed, but is quite different from that in La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO), where the chemical potential does not shift, yet the dispersive band and the Fermi arc/surface are formed around the Fermi level already in the lightly-doped region. The (underlying) Fermi surface shape and band dispersions are quantitatively analyzed using tight-binding fit, and the deduced next-nearest-neighbor hopping integral $t'$ also confirm the similarity to Na-CCOC and the difference from LSCO.

cond-mat.supr-con↗

arXiv2007

Large nuclear Overhauser fields detected in vertically-coupled double quantum dots

We report the electrical induction and detection of dynamic nuclear polarization in the spin-blockade regime of double GaAs vertical quantum dots. The largest Overhauser field observed was about 4 Tesla, corresponding to a nuclear polarization of about 40% in the present device. A phenomenological model is presented to provide a qualitative understanding of our results.

cond-mat.mes-hall↗