Satoshi Harashima

Stanford University, Palo Alto, California, United States

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Publications (9)41.09 Total impact

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    ABSTRACT: The conducting interface formed between LaAlO3 and SrTiO3 exhibits high electron mobility, tunable carrier densities, and is theoretically predicted to have long spin lifetimes. Thus, the LaAlO3/SrTiO3 heterostructure is a promising system for the transportation of spin information. We have investigated spin-dependent transport across Co/LaAlO3/SrTiO3 heterostructures using an all electrical three terminal geometry and observed Lorentzian magnetoresistance typically associated with Hanle spin dephasing. However, such a picture fails to explain all the experimentally observed behavior. Further, experiments with spin-unpolarized Au/LaAlO3/SrTiO3 heterojunctions support an alternative scenario involving current modulation by spin-dependent transport through defect states in the LaAlO3 barrier.
    Applied Physics Letters 01/2014; 105(3):032406-032406-4. · 3.52 Impact Factor
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    ABSTRACT: Mobility of electrons confined at the LaAlO3 /SrTiO3 interface is significantly enhanced by surface control using surface charges and adsorbates, reaching a low temperature value more than 20 000 cm(2) V(-1) s(-1) . A uniform trend that mobility increases with decreasing sheet carrier density is observed.
    Advanced Materials 07/2013; · 14.83 Impact Factor
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    ABSTRACT: We report the electron doping in the surface vicinity of KTaO_3 by inducing oxygen-vacancies via Ar^+ -irradiation. The doped electrons have high mobility (> 10^4 cm^2/Vs) at low temperatures, and exhibit Shubnikov-de Haas oscillations with both two- and three-dimensional components. A disparity of the extracted in-plane effective mass, compared to the bulk values, suggests mixing of the orbital characters. Our observations demonstrate that Ar^+ -irradiation serves as a flexible tool to study low dimensional quantum transport in 5d semiconducting oxides.
    Physical review. B, Condensed matter 05/2012; · 3.77 Impact Factor
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    ABSTRACT: We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, our measurements provide a direct upper bound for the potential Rashba spin splitting of only Δk(parallel)}~0.02 Å(-1) at the Fermi level. The polar nature of the KTaO3(100) surface appears to help mediate the formation of the 2DEG as compared to nonpolar SrTiO3(100).
    Physical Review Letters 03/2012; 108(11):117602. · 7.73 Impact Factor
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    ABSTRACT: KTaO3 (KTO), like SrTiO3 (STO), can be doped to create a high mobility perovskite oxide semiconductor. However, while the low dimensional electronic states of STO have attracted intense interest via spectroscopic [1,2] and transport [3] studies, analogous investigations in KTO have been limited. Of particular interest is the fact that the cubic crystal symmetry in KTO is preserved at low temperatures, in contrast to STO. Here we electron dope KTO via oxygen-vacancy formation by Ar^+-irradiation [4]. Below T = 10 K, the Hall mobility (> 10^4 cm^2/Vs) of the electrons is significantly higher than in previous studies of STO [4]. The angular dependence of the Shubnikov-de Haas oscillations indicates a Fermi surface without cubic symmetry, in contrast to that expected for bulk KTO. We discuss the possible origins of these data, including the formation of quantum well structures, the coexistence of surface and bulk electrons, and the suppression of cyclotron motion by finite size effects.[4pt] [1] A. F. Santander-Syro et al., Nature 469, 189 (2011).[0pt] [2] W. Meevasana et al., Nat. Mater. 10, 114 (2011).[0pt] [3] Y. Kozuka et al., Nature 462, 487 (2009).[0pt] [4] J. H. Ngai et al., Phys. Rev. B 81, 241307 (2010).
    02/2012;
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    ABSTRACT: The conduction at the LaAlO3/SrTiO3 interface [1] provides a playground for controlling metallicity and superconductivity in a thin electron gas. This can be achieved by varying the growth of the LaAlO3 layer, the thickness [2], and by field effect modulation [3]. A crucial question is whether the variation in conductivity is due to changes in the carrier density or mobility. Using magnetotransport studies of a gated structure, we find that the mobility variation is almost five times that of the sheet carrier density. Superconductivity can be suppressed at both positive and negative gate bias [4]. These results indicate that the relative disorder strength strongly increases across the superconductor-insulator transition. [4pt] [1] A. Ohtomo and H.Y. Hwang, Nature 427 423 (2004) [0pt] [2] C. Bell et al., Appl. Phys. Lett. 94, 222111 (2009) [0pt] [3] A. Caviglia et al., Nature 456 624 (2008) [0pt] [4] C. Bell et al., Phys. Rev. Lett. (in press)
    03/2010;
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    ABSTRACT: Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the superconducting LaAlO3/SrTiO3 interface can be gate modulated. A central issue is to determine the principal effect of the applied electric field. Using magnetotransport studies of a gated structure, we find that the mobility variation is almost 5 times that of the sheet carrier density. Furthermore, superconductivity can be suppressed at both positive and negative gate bias. These results indicate that the relative disorder strength strongly increases across the superconductor-insulator transition.
    Physical Review Letters 11/2009; 103(22):226802. · 7.73 Impact Factor
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    C. Bell, S. Harashima, Y. Hikita, H. Y. Hwang
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    ABSTRACT: The electronic transport properties of a series of LaAlO3/SrTiO3 interfaces were investigated, and a systematic thickness dependence of the sheet resistance and magnetoresistance was found for constant growth conditions. This trend occurs above the critical thickness of four unit cells, below which the LaAlO3/SrTiO3 interface is not conducting. A dramatic decrease in mobility of the electron gas of nearly two orders of magnitude was observed with increasing LaAlO3 thickness from 5 to 25 unit cells.
    Applied Physics Letters 06/2009; 94(22):222111-222111-3. · 3.52 Impact Factor
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    C. Bell, S Harashima, Y. Hikita, H. Y. Hwang
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    ABSTRACT: The electronic transport properties of a series of LaAlO_3 / SrTiO_3 interfaces were investigated, and a systematic thickness dependence of the sheet resistance and magnetoresistance was found for constant growth conditions. This trend occurs above the critical thickness of four unit cells, below which the LaAlO_3 / SrTiO_3 interface is not conducting. A dramatic decrease in mobility of the electron gas of nearly two orders of magnitude was observed with increasing LaAlO_3 thickness from five to 25 unit cells.
    03/2009;

Publication Stats

81 Citations
41.09 Total Impact Points

Institutions

  • 2013
    • Stanford University
      • Stanford Institute for Materials and Energy Sciences
      Palo Alto, California, United States
  • 2009–2012
    • The University of Tokyo
      • • Department of Applied Physics
      • • Department of Advanced Materials Science
      Tokyo, Tokyo-to, Japan