铁磁/超导多层结构中的自旋三重配对
|
摘要
通过自洽求解Bogoliubov-de Gennes方程研究了具有非共线界面磁矩的铁磁-超导-铁磁多层结构中的自旋三重配对,发现非共线磁矩可以在界面区域引起一个自旋倒易散射。该散射能够将超导体中的自旋单重对转化为铁磁体中自旋相同的三重对。当超导两侧铁磁体的磁矩结构对称时,自旋相同的三重对可以分别在超导和铁磁区域的局域态密度中引起一个尖锐的零能电导峰。当铁磁体的磁矩反对称时,两侧铁磁体之间将会发生交错Andreev反射并形成自旋单重对,从而在局域态密度的零能电导峰中心产生一个明显的凹陷。局域态密度的这些特征可以通过实验测量微分电导谱加以验证。
The study investigates spin triplet pairing correlations in ferromagnet-superconductor-ferromagnet multilayer structure with noncollinear interfacial magnetizations,via self-consistent solution of the Bogoliubov-de Gennes equations. The result shows that noncollinear magnetic configuration leads to spin-flip scattering at the interfacial regions,which can convert spin singlet pairs in the superconductor into the equal spin triplet pairs in the ferromagnets. If the magnetizations of the ferromagnetic layers on both sides of superconductor are constructed symmetrically,the equal spin triplet pairs could induce a very sharp zero energy conductance peak( ZECP) in the local density of the states( LDOS) in the superconducting region and ferromagnetic region. However,when the magnetic moments of ferromagnets have antsymmetric structures,the crossed Andreev reflection will occur between two spatially separated ferromagnetic layers so as to form the spin singlet pairs in the system. This effect could induce an obvious concavity in center of ZECP. The feature of LDOS can be demonstrated by measuring the local differential conductance spectra in experiment.
The study investigates spin triplet pairing correlations in ferromagnet-superconductor-ferromagnet multilayer structure with noncollinear interfacial magnetizations,via self-consistent solution of the Bogoliubov-de Gennes equations. The result shows that noncollinear magnetic configuration leads to spin-flip scattering at the interfacial regions,which can convert spin singlet pairs in the superconductor into the equal spin triplet pairs in the ferromagnets. If the magnetizations of the ferromagnetic layers on both sides of superconductor are constructed symmetrically,the equal spin triplet pairs could induce a very sharp zero energy conductance peak( ZECP) in the local density of the states( LDOS) in the superconducting region and ferromagnetic region. However,when the magnetic moments of ferromagnets have antsymmetric structures,the crossed Andreev reflection will occur between two spatially separated ferromagnetic layers so as to form the spin singlet pairs in the system. This effect could induce an obvious concavity in center of ZECP. The feature of LDOS can be demonstrated by measuring the local differential conductance spectra in experiment.
引文
[1]BUZDIN A I.Proximity effects in superconductor-ferromagnet heterostructures[J].Rev Mod Phys,2005,77(3):935-976.
[2]BERGERET F S,VOLKOV A F,EFETOV K B.Odd triplet superconductivity and related phenomena in superconductorferromagnet structures[J].Rev Mod Phys,2005,77(4):1321-1373.
[3]GOLUBOV A A,KUPRIYANOV M Y,LL’ICHEV E.The current-phase relation in Josephson junctions[J].Rev Mod Phys,2004,76(2):411-469.
[4]ESCHRIG M.Spin-polarized supercurrents for spintronics[J].Phys Today,2011,64(1):43-49.
[5]BERGERET F S,VOLKOV A F,EFETOV K B.Long-Range Proximity Effects in Superconductor-Ferromagnet Structures[J].Phys Rev Lett,2001,86(18):4096-4099.
[6]KADIGROBOV A,SHEKHTER R I,JONSON M.Quantum spin fluctuations as a source of long-range proximity effects in diffusive ferromagnet-superconductor structures[J].Europhys Lett,2001,54(3):394-400.
[7]RICHARD C,HOUZET M,MEYER J S.Superharmonic Long-Range Triplet Current in a Diffusive Josephson Junction[J].Phys Rev Lett,2013,110(21):217004[5pages].
[8]BERGERET F S,VOLKOV A F,EFETOV K B.Manifestation of triplet superconductivity in superconductor-ferromagnet structures[J].Phys Rev B,2003,68(6):064513[11 pages].
[9]GREIN R,LFWANDER T,METALIDIS G,et al.Theory of superconductor-ferromagnet point-contact spectra:The case of strong spin polarization[J].Phys Rev B,2010,81(9):094508[17 pages].
[10]GENNES P G.Superconductivity of Metals and Alloys[M].New York:Benjamin,1999:137-170.
[11]HALTERMAN K,VALLS O T,BARSIC P H.Induced triplet pairing in clean s-wave superconductor/ferromagnet layered structures[J].Phys Rev B,2008,77(17):174511[14 pages].
[12]ESCHRIG M,KOPU J,CUEVAS J C,et al.Theory of Half-Metal/Superconductor Heterostructures[J].Phys Rev Lett,2003,90(13):137003[4 pages].
[13]ASANO Y,TANAKA Y,GOLUBOV A A.Josephson Effect due to Odd-Frequency Pairs in Diffusive Half Metals[J].Phys Rev Lett,2007,98(10):107002[4 pages].
[14]ASANO Y,SAWA Y,TANAKA Y,et al.Odd-frequency pairs and Josephson current through a strong ferromagnet[J].Phys Rev B,2007,76(22):224525[11 pages].
[15]BRAUDE V,NAZAROV Y V.Fully Developed Triplet Proximity Effect[J].Phys Rev Lett,2007,98(7):077003[4 pages].
[16]ESCHRIG M,LFWANDER T.Triplet supercurrents in clean and disordered half-metallic ferromagnets[J].Nature Physics,2008,4(2):138-143.
[2]BERGERET F S,VOLKOV A F,EFETOV K B.Odd triplet superconductivity and related phenomena in superconductorferromagnet structures[J].Rev Mod Phys,2005,77(4):1321-1373.
[3]GOLUBOV A A,KUPRIYANOV M Y,LL’ICHEV E.The current-phase relation in Josephson junctions[J].Rev Mod Phys,2004,76(2):411-469.
[4]ESCHRIG M.Spin-polarized supercurrents for spintronics[J].Phys Today,2011,64(1):43-49.
[5]BERGERET F S,VOLKOV A F,EFETOV K B.Long-Range Proximity Effects in Superconductor-Ferromagnet Structures[J].Phys Rev Lett,2001,86(18):4096-4099.
[6]KADIGROBOV A,SHEKHTER R I,JONSON M.Quantum spin fluctuations as a source of long-range proximity effects in diffusive ferromagnet-superconductor structures[J].Europhys Lett,2001,54(3):394-400.
[7]RICHARD C,HOUZET M,MEYER J S.Superharmonic Long-Range Triplet Current in a Diffusive Josephson Junction[J].Phys Rev Lett,2013,110(21):217004[5pages].
[8]BERGERET F S,VOLKOV A F,EFETOV K B.Manifestation of triplet superconductivity in superconductor-ferromagnet structures[J].Phys Rev B,2003,68(6):064513[11 pages].
[9]GREIN R,LFWANDER T,METALIDIS G,et al.Theory of superconductor-ferromagnet point-contact spectra:The case of strong spin polarization[J].Phys Rev B,2010,81(9):094508[17 pages].
[10]GENNES P G.Superconductivity of Metals and Alloys[M].New York:Benjamin,1999:137-170.
[11]HALTERMAN K,VALLS O T,BARSIC P H.Induced triplet pairing in clean s-wave superconductor/ferromagnet layered structures[J].Phys Rev B,2008,77(17):174511[14 pages].
[12]ESCHRIG M,KOPU J,CUEVAS J C,et al.Theory of Half-Metal/Superconductor Heterostructures[J].Phys Rev Lett,2003,90(13):137003[4 pages].
[13]ASANO Y,TANAKA Y,GOLUBOV A A.Josephson Effect due to Odd-Frequency Pairs in Diffusive Half Metals[J].Phys Rev Lett,2007,98(10):107002[4 pages].
[14]ASANO Y,SAWA Y,TANAKA Y,et al.Odd-frequency pairs and Josephson current through a strong ferromagnet[J].Phys Rev B,2007,76(22):224525[11 pages].
[15]BRAUDE V,NAZAROV Y V.Fully Developed Triplet Proximity Effect[J].Phys Rev Lett,2007,98(7):077003[4 pages].
[16]ESCHRIG M,LFWANDER T.Triplet supercurrents in clean and disordered half-metallic ferromagnets[J].Nature Physics,2008,4(2):138-143.