Low-temperature ferromagnetism in La4Ba2Cu2O10

Mizuno, Fumio; Masuda, H.; Hirabayashi, I.; Tanaka, Shōji; Hasegawa, M.; Mizutani, Uichiro

doi:10.1038/345788a0

Cited by 69 publications

(30 citation statements)

References 8 publications

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“…Finally, we show the possibility of the atomic-scale 0-π transition in a three-dimensional junction using realistic materials. Here we focus on La 2 BaCuO 5 (LBCO) [11] which is an important representative FI in spintronics. According to a first-principle band calculation [12], the bottom of the minority spin band is at the Γ point whose wave number is (k a , k b , k c ) = (0, 0, 0), where k j for j = a, b, and c is the wave number along j axis (see Fig.…”

Section: (B)mentioning

confidence: 99%

JosephsonπState in a Ferromagnetic Insulator

et al. 2010

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We predict anomalous atomic-scale 0-π transitions in a Josephson junction with a ferromagneticinsulator (FI) barrier. The ground state of such junction alternates between 0-and π-states when thickness of FI is increasing by a single atomic layer. We find that the mechanism of the 0-π transition can be attributed to thickness-dependent phase-shifts between the wave numbers of electrons and holes in FI. Based on these results, we show that stable π-state can be realized in junctions based on high-Tc superconductors with La2BaCuO5 barrier.PACS numbers: 74.50.+r, 03.67.Lx The developing field of superconducting spintronics comprises a plenty of fascinating phenomena that may complement nonsuperconducting spintronics devices [1]. Mesoscopic hybrid structures consisting of superconducting and magnetic materials have attracted considerable attention as devices with novel functionalities [2]. One of most interesting effects is the formation of π-states in superconductor/ferromagnetic-metal/superconductor (S/FM/S) Josephson junctions [3]. Under appropriate conditions a ferromagnet can become a π-phase shifter, providing the phase difference φ = π between two superconductors in the ground state in contrast to φ = 0 in ordinary Josephson junctions. Recently a quiet qubit based on S/FM/S π-junction [4] has been suggested as a promising device to realize quantum computation because the spontaneously generated two-level system in this structure is robust against decoherence due to external fluctuations. However, low energy quasiparticle excitations in a FM provide strong dissipation [5]. Therefore Josephson π junctions with a nonmetallic interlayers are highly desired for qubit applications [6]. Moreover, from the fundamental view point, the Josephson transport through a f erromagnetic insulator (FI) has been studied based on phenomenological models [7] and not yet been explored explicitly.In this Letter, we study theoretically the Josephson effect in superconductor/ferromagneticinsulator/superconductor (S/FI/S) junctions using the tight-binding model. We show that the ground state in such structures alternates between the 0-and π-states when the thickness of a FI (L F ) is increasing by a single atomic layer. This remarkable effect originates from the characteristic band structure of a FI. Quasiparticles in the electron and hole branches acquire different phase shifts while propagating across a FI. We will show that the phase difference is exactly πL F due to the band structure of a FI, thus providing the atomic-scale 0-π transition. This mechanism is in striking contrast to the proximity induced 0-π transition in conventional S/FM/S junctions. On the basis of the obtained results, we predict a stable π-state in a Josephson junction based on high-T c superconductors with a La 2 BaCuO 5 barrier, where electric current flows along the c axis of cuprates.Let us first consider an S/FI/S junction in the twodimensional tight-binding model as shown in Fig. 1(a). The vector r = jx + my points to a lattice site, where

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Section: (B)mentioning

confidence: 99%

JosephsonπState in a Ferromagnetic Insulator

et al. 2010

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“…The exchange splitting V ex of La422 is numerically estimated to be 0.34 eV. Since the exchange splitting is large and the bands are originally half-filled, La422 becomes FI with a Curie temperature of 5 K [28]. Another possible candidates for the FI barrier are spinels [34,35], e.g., NiFe 2 O 4 , rare-earth monopnictides [36][37][38][39], e.g., GdN, and Yttrium iron garnet (Y 3 Fe 5 O 12 ) [40,41].…”

Section: Modelmentioning

confidence: 99%

“…2. Experimental studies as well as a first principle calculations indicate that the band structure of an oxide ferromagnet La 4 Ba 2 Cu 2 O 10 (La422) [28][29][30] and K 2 CuF 4 [31][32][33] can be described by Fig. 2(b) in which the up-and down-spin bands are located below and above the Fermi energy respectively.…”

Section: Modelmentioning

confidence: 99%

Spectrum of Andreev bound states in Josephson junctions with a ferromagnetic insulator

Kawabata

Tanaka

Golubov

et al. 2012

Journal of Magnetism and Magnetic Materials

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Ferromagnetic-insulator (FI) based Josephson junctions are promising candidates for a coherent superconducting quantum bit as well as a classical superconducting logic circuit. Recently the appearance of an intriguing atomic-scale 0-π transition has been theoretically predicted. In order to uncover the mechanism of this phenomena, we numerically calculate the spectrum of Andreev bound states in a FI barrier by diagonalizing the Bogoliubov-de Gennes equation. We show that Andreev spectrum drastically depends on the parity of the FI-layer number L and accordingly the π (0) state is always more stable than the 0 (π) state if L is odd (even).

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“…The crystal structure of LBCO has tetragonal symmetry with space group 4 / P mbm . In 1990, Mizuno et al, found that LBCO undergoes a ferromagnetic transition at 5.2 K [24]. The exchange splitting ex V is estimated to be 0.34 eV by a first-principle band calculation using the spin-polarized local density approximation [27].…”

Section: Magnetic and Electronic Properties Of Ferromagnetic Insulatorsmentioning

confidence: 99%

“…1. One of the representative material of FI is half-filled La 2 BaCuO 5 (LBCO) [24][25][26]. The crystal structure of LBCO has tetragonal symmetry with space group 4 / P mbm .…”

Section: Magnetic and Electronic Properties Of Ferromagnetic Insulatorsmentioning

confidence: 99%

Theory of quantum transport in Josephson junctions with a ferromagnetic insulator

Kawabata

Asano

2010

Low Temperature Physics

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We investigate the Josephson transport through ferromagnetic insulators (FIs) by taking into account the band structure of FIs explicitly. Using the recursive Green's function method, we found the formation of a π-junction in such systems. Moreover the atomic-scale 0-π oscillation is induced by increasing the thickness of FI and its oscillation period is universal, i.e., just single atomic layer. Based on these results, we show that stable π-state can be realized in junctions based on high-T c superconductors with La 2 BaCuO 5 barrier. Such FI-based Josephson junctions may become an element in the architecture of future quantum computers.

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Low-temperature ferromagnetism in La4Ba2Cu2O10

Cited by 69 publications

References 8 publications

JosephsonπState in a Ferromagnetic Insulator

JosephsonπState in a Ferromagnetic Insulator

Spectrum of Andreev bound states in Josephson junctions with a ferromagnetic insulator

Theory of quantum transport in Josephson junctions with a ferromagnetic insulator

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