Electrical detection of spin-polarized current in topological insulator Bi1.5Sb0.5Te1.7Se1.3

황태하,김홍석,김호일,김준성,도용주 한국물리학회 2019 Current Applied Physics Vol.19 No.8

Spin-momentum locked (SML) topological surface state (TSS) provides exotic properties for spintronics applications. The spin-polarized current, which emerges owing to the SML, can be directly detected by performing spin potentiometric measurement. We observed spin-polarized current using a bulk insulating topological insulator (TI), Bi1.5Sb0.5Te1.7Se1.3, and Co as the ferromagnetic spin probe. The spin voltage was probed with varying the bias current, temperature, and gate voltage. Moreover, we observed non-local spin-polarized current, which is regarded as a distinguishing property of TIs. The spin-polarization ratio of the non-local current was larger than that of the local current. These findings could reveal a more accurate approach to determine spinpolarization ratio at the TSS.

Theoretical study on spin-polarized injection of electrical currents into polymer semiconductors

Junqing Zhao,Shizhu Qiao,Ningyu Zhang,Fuyun Xu,Yantao Pang,Ying Chen 한국물리학회 2009 Current Applied Physics Vol.9 No.5

Different from electrons and holes in traditional inorganic semiconductors, the charge carriers in polymer semiconductors are spin polarons and spinless bipolarons. In this paper, a theoretical model is presented to describe the spin-polarized injection of electrical currents from a ferromagnetic contact into a non-magnetic polymer semiconductor. In this model, a new relation of conductivity to concentration polarization for polymer semiconductors is introduced based on a three-channel model to describe the spin polarized injection of electrical currents under large electrical current densities. The calculated results of the model reveal the effects of the polaron ratio, the carrier concentration polarization, the interfacial conductance, the bulk conductivity of materials, and the electrical current density, etc. on the spin polarization of electrical currents. As conclusions, the large and matched bulk conductivity of materials, the small spin-dependent interfacial conductance, the thin polymer thickness and the large enough electrical current are critical factors for upgrading the spin polarization of electrical currents in polymer semiconductors. Particularly, when the polaron ratio in polymer semiconductors approaches the concentration polarization of the ferromagnetic contact, a modest concentration polarization is sufficient for achieving a nearly complete spin-polarized injection of electrical currents.

Manipulating edge current spin polarization in zigzag MoS2 nanoribbons

You Suejeong,Park Daehan,Kim Heesang,Kim Nammee 한국물리학회 2022 Current Applied Physics Vol.37 No.-

The electronic structure and quantum transport of a zigzag monolayer molybdenum disulfide (MoS2) nanoribbon are investigated using a six-band tight-binding model. For metallic edge modes, considering both an intrinsic spin–orbit coupling and local exchange field effects, spin degeneracy and spin inversion symmetry are broken and spin selective transport is possible. Our model is a three-terminal field effect transistor with a circular-shaped gate voltage in the middle of scattering region. One terminal measures the top edge current and the other measures the bottom edge current separately. By controlling the circular gate voltage, each terminal can detect a totally spin-polarized edge current. The radius of the circular gate and the strength of the exchange field are important, because the former determines the size of the channel in both S-terminated (top) and Mo-terminated (bottom) edges and the latter is strongly related to unbalancing of the density of spin states. The results presented here suggest that it should be possible to construct spin filters using implanted MoS2 nanoribbons.

Theoretical Approach to Spin-current Absorption at an Interface

Kazuhiro Tsutsui,Takehito Yokoyama,Kazuhiro Hosono 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12

We study the spin current induced by an inhomogeneous spin-orbit coupling due to impurities byusing the Keldysh Green’s function formalism. In particular, we focus on the diffusive contributionsand give their analytical expressions. A spin current is found to be generated in the presence ofboth a gradient in the spin-orbit strength and a gradient in the external electric field. The resultingdiffusive spin current indicates the presence of spin-current absorption at the interface between thematerials with different spin-orbit coupling strengths, which is exemplified with an experimentallyrelevantsetup.

Effects of Mechanical Rotation and Vibration on Spin Currents

Mamoru Matsuo,Jun’ichi Ieda,Sadamichi Maekawa,Eiji Saitoh 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.10

We discuss theoretically the generation of spin currents in both rotationally and linearly accelerated systems. The spin-orbit interaction modified by inertial effects is derived from the low energy limit of the generally covariant Dirac equation. It is shown that the spin-orbit interaction is responsible for the generation of spin currents by mechanical rotation and vibration. We also study effects of impurity scattering on the mechanically induced spin current, and calculate the spin accumulation by solving the spin diffusion equation with the spin-source term originating from the inertial effects.

Quantum Kirchhoff’s Current Law and Spin Current in Mesoscopic Electronics

Sam Young Cho 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.5

We discuss a full description of electron transport that reveals an entire matrix current including both spin and charge degrees of freedoms in ideal leads attached to a ballistic quantum device. We present a Kirchhoff’s matrix current law simultaneously governing spin transport and charge transport for mesoscopic quantum circuits. We predict that spin-unpolarized electron injections can produce spin currents flowing out of quantum devices with spin-dependent potentials. Two-lead quantum devices with spin-dependent potentials, where reflected and transmitted electrons have opposite spin orientations, are shown to be a mesoscopic realization of the Stern-Gerlach apparatus with no magnetic field. Also, we discuss the spin vector conductance associated with the charge conductance in two-lead quantum devices. The quantum Kirchhoff’s current law can be applied to a wide variety of systems in mesosocopic electronics.

Current Properties in a Three-terminal Quantum-dot Ring with Spin Bias and Rashba Interaction

Chuan-Jing Yang,Wei-Jiang Gong 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.6

Electronic transport through a triple-quantum-dot ring with three terminals is theoretically studied. By introducing a local Rashba spin-orbit interaction on an individual quantum dot, we findthat the spin bias in one terminal drives apparent charge currents with the similar amplitudes andopposite directions of them in the other terminals. This means that in this structure, the spin biascan be measured by virtue of the charge current properties. Meanwhile, the spin transport inducedby the spin bias is notable. When a magnetic flux is applied through this ring, we see that it has anontrivial role in manipulating the charge and the spin transport. Based on the obtained results,we propose this structure can be used as a prototype of a charge and spin current rectifier.

Spin Current in Magnetic Tunnel Junctions

이병찬 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.4

The spin current in the free layer of magnetic tunnel junctions is investigated theoretically by using the spin-dependent drift-diffusion equations. The spin polarization and its derivative are plotted along the growth direction. The magnitudes of the spin current and its derivative are much larger for the parallel alignment of the magnetizations. The spin current is well described by the quadratic approximation. The dependence on the spin diffusion length and the thickness of the free layer is also discussed.

Spin-polarized Current Switching of Co/Cu/Py Pac-man type II Spin-valve

Andrew Lyle,Yang-Ki Hong,Byoung-Chul Choi,Gavin Abo,Seok Bae,Jeevan Jalli,Jae-jin Lee,Mun-Hyoun Park,Ryan Syslo 한국자기학회 2010 Journal of Magnetics Vol.15 No.3

We investigated spin-polarized current switching of Pac-man type Ⅱ (PM-Ⅱ) nanoelements in Pac-man shaped nanoscale spin-valves (Co/Cu/Py) using micromagnetic simulations. The effects of slot angle and antiferromag-netic (AFM) layer were simulated to obtain optimum switching in less than 2 ns. At a critical slot angle of 105˚, the lowest current density for anti-parallel to parallel (AP-P) switching was observed due to no vortex or antivortex formation during the magnetic reversal process. All other slot angles for AP-P formed a vortex or antivortex during the magnetization reversal process. Additionally, a vortex or anti-vortex formed for all slot angles for parallel to anti-parallel (P-AP) switching. The addition of an AFM layer caused the current density to decrease significantly for AP-P and P-AP at slot angles less than 90˚. However, at slot angles greater than 90˚, the current density tended to decrease by less amounts or actually increased slightly as shape anisotropy became more dominant. This allowed ultra-fast switching with 5.05 and 5.65 x 10? A/㎠ current densities for AP-P and P-AP, respectively, at a slot angle of 105˚.

Effect of Spin Memory Loss on Spin Transfer Torque

이서원,이경진 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.4

We investigate how the spin memory loss at interfaces affects the spin transfer torque in the framework of the drift-diffusion model. The spin memory loss changes the spin accumulation in the non-magnetic spacer separating the two ferromagnets in a spin valve structure and, thus, the spin transfer torque. By comparing theoretical values of the spin transfer torque with experimental results, we found that non-zero spin memory loss is essential to explain the experimental switching current densities in the current-induced magnetization switching. The spin memory loss determined by the comparison is in good agreement with the value determined by experimental measurement of giant magnetoresistance.