We propose a four-terminal device consisting of two parallel quantum dots with Rashba spin-orbit interaction （RSOI）, coupled to two side superconductor leads and two common ferromagnetic leads, respectively. The two...We propose a four-terminal device consisting of two parallel quantum dots with Rashba spin-orbit interaction （RSOI）, coupled to two side superconductor leads and two common ferromagnetic leads, respectively. The two ferromagnetic leads and two quantum dots form a ring threaded by Aharonov-Bohm （AB） flux. This device possesses normal quasiparticle transmission between the two ferromagnetic leads, and normal and crossed Andreev reflections providing conductive holes. For the appropriate spin polarization of the ferromagnetic leads, RSOI and AB flux, the pure spin-up （or spin-down） current without net charge current in the right lead, which is due to the equal numbers of electrons and holes with the same spin-polarization moving along the same direction, can be obtained by adjusting the gate voltage, which may be used in practice as a pure spin-current injector.展开更多
Owing to the bistable character of the single molecular magnet （SMM）, it can generate 100% spin-polarized currents even connected with normal （N） leads. In this work, we study the phonon-assisted spin current in N...Owing to the bistable character of the single molecular magnet （SMM）, it can generate 100% spin-polarized currents even connected with normal （N） leads. In this work, we study the phonon-assisted spin current in N- SMM-N systems. We mainly focus on the interplay of SMM＇s bistable character and electron-phonon coupling. It is found that when SMM is trapped in one of the lowest bistable states, it can generate phonon-assisted spin- polarized currents. At the up-spin transport channel, it is accompanied by a phonon-assisted up-spin current, while at the down-spin transport channel, it is accompanied by a phonon-assisted down-spin current.展开更多
The oscillation of tunnel splitting in Fe8 molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of instanton method with both semiclassical treatment and the effective po...The oscillation of tunnel splitting in Fe8 molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of instanton method with both semiclassical treatment and the effective potential field description of quantum spin system.The theoretical splittings of the instanton method are compared with the numerical result by diagonalization of spin Hamilton operator and experimental observations.By taking the appropriate parameters,our theory formula yields the result as the same as the experimental observation.展开更多
We use non-equilibrium Green＇s function method to analyze the shot noise spectrum of artificial single molecular magnets（ASMM） model in the strong spin–orbit coupling limit in sequential tunneling regime, mainly f...We use non-equilibrium Green＇s function method to analyze the shot noise spectrum of artificial single molecular magnets（ASMM） model in the strong spin–orbit coupling limit in sequential tunneling regime, mainly focusing on the effects of local large spin. In the linear response regime, the shot noise shows 2S ＋ 1 peaks and is strongly spin-dependent.In the nonlinear response regime, one can observe 2S ＋ 1 steps in shot noise and Fano factor. In these steps one can see the significant enhancement effect due to the spin-dependent multi-channel process of local large spin, which reduces electron correlations.展开更多
We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spinorbital interaction（RSOI） embedded in an Aharonov-Bohm interferometer connected symmetrically to leads usi...We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spinorbital interaction（RSOI） embedded in an Aharonov-Bohm interferometer connected symmetrically to leads using nonequilibrium Green＇s function method in the linear response regime.Under the appropriate configuration of magnetic flux phase and RSOI phase,the spin figure of merit can be enhanced and is even larger than the charge figure of merit.In particular,the charge and spin thermopowers as functions of both the magnetic flux phase and the RSOI phase present quadruple-peak structures in the contour graphs.For some specific configuration of the two phases,the device can provide a mechanism that converts heat into a spin voltage when the charge thermopower vanishes while the spin thermopower is not zero,which is useful in realizing the thermal spin battery and inducing a pure spin current in the device.展开更多
We study the coutrol of gate voltage over the magnetization of a single-molecule magnet （SMM） weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two el...We study the coutrol of gate voltage over the magnetization of a single-molecule magnet （SMM） weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two electrodes. It is demonstrated that the SMM＇s magnetization can change periodically with periodic gate voltage due to the driving oI the temperature gradient. Under an appropriate matching of the electrode polarization, the temperature difference and the pulse width of gate voltage, the SMM＇s magnetization can be completely reversed in a period of gate voltage. The corresponding flipping time can be controlled by the system parameters. In addition, we also investigate the tunneling anisotropic magnetoresistance （TAMFt） of the device in the steady state when the ferromagnetic electrode is noncollinear with the easy axis of the SMM, and show the jump characteristic of the TAMR.展开更多
The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal m...The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with（2S＋1） sublevels.In the sequential tunneling regime,the differential conductance exhibits（2S＋1） possible peaks,corresponding to resonance tunneling via（2S＋1） sublevels.At low temperature,Kondo physics dominates transport and（2S＋1） Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.展开更多
We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localiza...We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localization. We found that when the ratio of the magnetic flux to the total quantum dots number is a root of the zeroth order Bessel function, dynamical localization and collapse of quasi-energy occurs and importantly~ the transport current displays a dip which is the signal of dynamical localization. The dynamical localization effect is strengthened as a result of the increase of the quantum dot number, and it is weakened on account of the increase of the dots-lead hopping rate.展开更多
The quantum-classical transitions of the escape rates in the molecular magnet Mnl2Ac and a biaxial anisotropic ferromagnetic spin model are investigated by applying the periodic instanton method.The effective free ene...The quantum-classical transitions of the escape rates in the molecular magnet Mnl2Ac and a biaxial anisotropic ferromagnetic spin model are investigated by applying the periodic instanton method.The effective free energies are expanded around the top of the potential barrier in analogy to the Landau theory of phase transitions.We show that the first-order transitions occur below the critical external magnetic field h_(x)=1/4 for Mnl2Ac and beyond the critical anisotropy constant ratioλ=1/2 for the biaxial ferromagnetic grains,which is in good agreement with earlier studies.展开更多
We have investigated theoretically the field-driven electron-transport through a double-quantum-well semiconductor-heterostructure with spin-orbit coupling. The numerical results demonstrate that the transmission spec...We have investigated theoretically the field-driven electron-transport through a double-quantum-well semiconductor-heterostructure with spin-orbit coupling. The numerical results demonstrate that the transmission spectra are divided into two sets due to the bound-state level-splitting and each set contains two asymmetric resonance peaks which may be selectively suppressed by changing the difference in phase between two driving fields. When the phase difference changes from 0 to π, the dip of asymmetric resonance shifts from one side of resonance peak to the other side and the asymmetric Fano resonance degenerates into the symmetric Breit-Wigner resonance at a critical value of phase difference. Within a given range of incident electron energy, the spin polarization of transmission current is completely governed by the phase difference which may be used to realize the tunable spin filtering.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10775091,10774094,10974124,and 11047172)the Excellent Youth and Midlife Scientist Scientific Research Encouragement Foundation of Shandong Province,China(Grant No. BS2010DS006)the Doctor Research Startup Foundation of Linyi University,China (Grant No. BS201023)
文摘We propose a four-terminal device consisting of two parallel quantum dots with Rashba spin-orbit interaction （RSOI）, coupled to two side superconductor leads and two common ferromagnetic leads, respectively. The two ferromagnetic leads and two quantum dots form a ring threaded by Aharonov-Bohm （AB） flux. This device possesses normal quasiparticle transmission between the two ferromagnetic leads, and normal and crossed Andreev reflections providing conductive holes. For the appropriate spin polarization of the ferromagnetic leads, RSOI and AB flux, the pure spin-up （or spin-down） current without net charge current in the right lead, which is due to the equal numbers of electrons and holes with the same spin-polarization moving along the same direction, can be obtained by adjusting the gate voltage, which may be used in practice as a pure spin-current injector.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11504210,11504211,11504212,11274207,11274208,11174115 and 11325417the Key Program of the Ministry of Education of China under Grant No 212018+2 种基金Shanxi Provincial Scientific and Technological Project(2015031002-2)Shanxi Provincial Natural Science Foundation under Grant Nos2013011007-2 and 2013021010-5Outstanding Innovative Teams of Higher Learning Institutions of Shanxi Province
文摘Owing to the bistable character of the single molecular magnet （SMM）, it can generate 100% spin-polarized currents even connected with normal （N） leads. In this work, we study the phonon-assisted spin current in N- SMM-N systems. We mainly focus on the interplay of SMM＇s bistable character and electron-phonon coupling. It is found that when SMM is trapped in one of the lowest bistable states, it can generate phonon-assisted spin- polarized currents. At the up-spin transport channel, it is accompanied by a phonon-assisted up-spin current, while at the down-spin transport channel, it is accompanied by a phonon-assisted down-spin current.
基金Supported by the National Natural Science Foundation of China under Grant No.19775033.
文摘The oscillation of tunnel splitting in Fe8 molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of instanton method with both semiclassical treatment and the effective potential field description of quantum spin system.The theoretical splittings of the instanton method are compared with the numerical result by diagonalization of spin Hamilton operator and experimental observations.By taking the appropriate parameters,our theory formula yields the result as the same as the experimental observation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.1150421011504211+11 种基金11504212112742071127420811174115and11325417)the Key Program of the Ministry of Education of China(Grant No.212018)the Scientific and Technological Project of Shanxi ProvinceChina(Grant No.2015031002-2)the Natural Science Foundation of Shanxi ProvinceChina(Grant Nos.2013011007-2 and 2013021010-5) the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi ProvinceChina
文摘We use non-equilibrium Green＇s function method to analyze the shot noise spectrum of artificial single molecular magnets（ASMM） model in the strong spin–orbit coupling limit in sequential tunneling regime, mainly focusing on the effects of local large spin. In the linear response regime, the shot noise shows 2S ＋ 1 peaks and is strongly spin-dependent.In the nonlinear response regime, one can observe 2S ＋ 1 steps in shot noise and Fano factor. In these steps one can see the significant enhancement effect due to the spin-dependent multi-channel process of local large spin, which reduces electron correlations.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274208 and 11447170)
文摘We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spinorbital interaction（RSOI） embedded in an Aharonov-Bohm interferometer connected symmetrically to leads using nonequilibrium Green＇s function method in the linear response regime.Under the appropriate configuration of magnetic flux phase and RSOI phase,the spin figure of merit can be enhanced and is even larger than the charge figure of merit.In particular,the charge and spin thermopowers as functions of both the magnetic flux phase and the RSOI phase present quadruple-peak structures in the contour graphs.For some specific configuration of the two phases,the device can provide a mechanism that converts heat into a spin voltage when the charge thermopower vanishes while the spin thermopower is not zero,which is useful in realizing the thermal spin battery and inducing a pure spin current in the device.
基金Supported by the National Natural Science Foundation of China under Grant No 11274208
文摘We study the coutrol of gate voltage over the magnetization of a single-molecule magnet （SMM） weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two electrodes. It is demonstrated that the SMM＇s magnetization can change periodically with periodic gate voltage due to the driving oI the temperature gradient. Under an appropriate matching of the electrode polarization, the temperature difference and the pulse width of gate voltage, the SMM＇s magnetization can be completely reversed in a period of gate voltage. The corresponding flipping time can be controlled by the system parameters. In addition, we also investigate the tunneling anisotropic magnetoresistance （TAMFt） of the device in the steady state when the ferromagnetic electrode is noncollinear with the easy axis of the SMM, and show the jump characteristic of the TAMR.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10974124 and 11004124)the Natural Science Foundation of Shanxi Province of China (Grant No. 2009011001-1)
文摘The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with（2S＋1） sublevels.In the sequential tunneling regime,the differential conductance exhibits（2S＋1） possible peaks,corresponding to resonance tunneling via（2S＋1） sublevels.At low temperature,Kondo physics dominates transport and（2S＋1） Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.
文摘We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localization. We found that when the ratio of the magnetic flux to the total quantum dots number is a root of the zeroth order Bessel function, dynamical localization and collapse of quasi-energy occurs and importantly~ the transport current displays a dip which is the signal of dynamical localization. The dynamical localization effect is strengthened as a result of the increase of the quantum dot number, and it is weakened on account of the increase of the dots-lead hopping rate.
基金Supported by the National Natural Science Foundation of China under Grant Nos.19677101 and 19775033.
文摘The quantum-classical transitions of the escape rates in the molecular magnet Mnl2Ac and a biaxial anisotropic ferromagnetic spin model are investigated by applying the periodic instanton method.The effective free energies are expanded around the top of the potential barrier in analogy to the Landau theory of phase transitions.We show that the first-order transitions occur below the critical external magnetic field h_(x)=1/4 for Mnl2Ac and beyond the critical anisotropy constant ratioλ=1/2 for the biaxial ferromagnetic grains,which is in good agreement with earlier studies.
基金supported by the National Natural Science Foundation of China (Grant Nos 10475053,10775091 and 10774094)the Shanxi Natural Science Foundation,China (Grant No 20051002)
文摘We have investigated theoretically the field-driven electron-transport through a double-quantum-well semiconductor-heterostructure with spin-orbit coupling. The numerical results demonstrate that the transmission spectra are divided into two sets due to the bound-state level-splitting and each set contains two asymmetric resonance peaks which may be selectively suppressed by changing the difference in phase between two driving fields. When the phase difference changes from 0 to π, the dip of asymmetric resonance shifts from one side of resonance peak to the other side and the asymmetric Fano resonance degenerates into the symmetric Breit-Wigner resonance at a critical value of phase difference. Within a given range of incident electron energy, the spin polarization of transmission current is completely governed by the phase difference which may be used to realize the tunable spin filtering.
