Article

Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes

The University of Tokyo, Tōkyō, Japan
Applied Physics Letters (Impact Factor: 3.52). 12/2007; 91(23):232105. DOI: 10.1063/1.2820445
Source: arXiv

ABSTRACT Using a laterally-fabricated quantum-dot (QD) spin-valve device, we experimentally study the Kondo effect in the electron transport through a semiconductor QD with an odd number of electrons (N). In a parallel magnetic configuration of the ferromagnetic electrodes, the Kondo resonance at N = 3 splits clearly without external magnetic fields. With applying magnetic fields (B), the splitting is gradually reduced, and then the Kondo effect is almost restored at B = 1.2 T. This means that, in the Kondo regime, an inverse effective magnetic field of B ~ 1.2 T can be applied to the QD in the parallel magnetic configuration of the ferromagnetic electrodes. Comment: 4 pages, 3 figures

Full-text

Available from: Kenji Shibata, Jun 03, 2015
0 Followers
 · 
89 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a cross-sectional transmission electron microscopy (TEM) analysis of a nanogap electrode fabricated by atomic force microscope (AFM) local oxidation. We successfully visualized a nanogap structure composed of Al | Al-oxide | Al with an Al-oxide width of less than 100 nm. We measured the composition of aluminum and oxygen by in situ energy-dispersive X-ray spectroscopy (EDX), and showed that Al is fully oxidized by AFM local oxidation. Our findings demonstrate that the depth of the Al-oxide can be precisely controlled to create a nanogap electrode without damaging the underlying substrate layer.
    Japanese Journal of Applied Physics 05/2013; 52(5):5201-. DOI:10.7567/JJAP.52.055201 · 1.06 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Andreev transport through a quantum dot coupled to two external ferromagnetic leads and one superconducting lead is studied theoretically by means of the real-time diagrammatic technique in the sequential and cotunneling regimes. We show that the tunnel magnetoresistance (TMR) of the Andreev current displays a nontrivial dependence on the bias voltage and the level detuning, and can be described by analytical formulas in the zero temperature limit. The cotunneling processes lead to a strong modification of the TMR, which is most visible in the Coulomb blockade regime. We find a zero-bias anomaly of the Andreev differential conductance in the parallel configuration, which is associated with a nonequilibrium spin accumulation in the dot triggered by Andreev processes.
    Physical Review B 03/2014; 89(11). DOI:10.1103/PhysRevB.89.115305 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We explore theoretically the density of states (LDOS) probed by a scanning tunneling microscope (STM) tip of two-dimensional systems hosting an adatom and a subsurface impurity, both capacitively coupled to atomic force microscope (AFM) tips and traversed by antiparallel magnetic fields. Two kinds of setups are analyzed, a monolayer of graphene and a two-dimensional electron gas (2DEG). The AFM tips set the impurity levels at the Fermi energy, where two contrasting behaviors emerge: The Fano factor for the graphene diverges, while in the 2DEG it approaches zero. As result, the spin degeneracy of the LDOS is lifted exclusively in the graphene system, in particular, for the asymmetric regime of Fano interference. The aftermath of this limit is a counterintuitive phenomenon, which consists of a dominant Fano factor due to the subsurface impurity even with a stronger STM-adatom coupling. Thus we find a full polarized conductance, achievable just by displacing vertically the position of the STM tip. Our work proposes the Fano effect as the mechanism to filter spins in graphene. This feature arises from the massless Dirac electrons within the band structure and allows us to employ the graphene host as a relativistic Fano spin filter.
    Physical Review B 11/2013; 88(19). DOI:10.1103/PhysRevB.88.195122 · 3.66 Impact Factor