We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to twoferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach.We first developa B1oc...We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to twoferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach.We first developa B1och-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics,and then developexplicit analytical expressions for the local magnetization,current,and its fluctuations.On this basis,we predict a novelzero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration,and asymmetric peak splitting in a magnetic field.Also,for the same system with large polarization,we find a negativezero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapidspin-reversal due to underlying spin-flip cotunneling.展开更多
The nanocrystalline samples of Nd1-xSrxMnO3 （NSMO） （x=0.5, 0.55, 0.60, 0.63） were synthesized by sol-gel based polymeric pre-cursor route. Structural, magnetic and magnetotransport properties were studied systemat...The nanocrystalline samples of Nd1-xSrxMnO3 （NSMO） （x=0.5, 0.55, 0.60, 0.63） were synthesized by sol-gel based polymeric pre-cursor route. Structural, magnetic and magnetotransport properties were studied systematically. It was found that in the composition range （x=0.50-0.63）, Nd1-xSrxMnO3 showed paramagnetic to ferromagnetic （PM-FM） transition in the vicinity of TC～270 K but the FM phase was weakened as the Sr concentration increased. The appearance of weak ferromagnetism was explained in terms of the core-shell model. More-over, for x=0.63 sample, a second transition is observed below TC at T=185 K, which is possibly due to the appearance of A-AFM/ C-AFM or a mixture of both the phases. Resistivity vs temperature （ρ-T） curve showed that the resistivity of all the samples was much larger than the sin-gle crystals of corresponding compositions due to large contribution of the grain boundaries in the present nanocrystalline samples. In all samples, extrinsic kind of MR behavior dominated because of nanocrystalline nature of the samples, which was nearly of the same order （～10%） in all samples. However, the intrinsic kind of MR behavior was also significant in x=0.50 sample, because of the strongest FM feature in this sample.展开更多
基金The project supported by National Natural Science Foundation of Chinathe Shanghai Municipal Commission of Science and Technology+2 种基金the Shanghai Pujiang Programthe Program for New Century Excellent Talents in Universities (NCET)NJMH is supported by the DURINT program administered by the US Army Research Office, DAAD Grant No. 19-O1-1-0592
文摘We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to twoferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach.We first developa B1och-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics,and then developexplicit analytical expressions for the local magnetization,current,and its fluctuations.On this basis,we predict a novelzero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration,and asymmetric peak splitting in a magnetic field.Also,for the same system with large polarization,we find a negativezero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapidspin-reversal due to underlying spin-flip cotunneling.
文摘The nanocrystalline samples of Nd1-xSrxMnO3 （NSMO） （x=0.5, 0.55, 0.60, 0.63） were synthesized by sol-gel based polymeric pre-cursor route. Structural, magnetic and magnetotransport properties were studied systematically. It was found that in the composition range （x=0.50-0.63）, Nd1-xSrxMnO3 showed paramagnetic to ferromagnetic （PM-FM） transition in the vicinity of TC～270 K but the FM phase was weakened as the Sr concentration increased. The appearance of weak ferromagnetism was explained in terms of the core-shell model. More-over, for x=0.63 sample, a second transition is observed below TC at T=185 K, which is possibly due to the appearance of A-AFM/ C-AFM or a mixture of both the phases. Resistivity vs temperature （ρ-T） curve showed that the resistivity of all the samples was much larger than the sin-gle crystals of corresponding compositions due to large contribution of the grain boundaries in the present nanocrystalline samples. In all samples, extrinsic kind of MR behavior dominated because of nanocrystalline nature of the samples, which was nearly of the same order （～10%） in all samples. However, the intrinsic kind of MR behavior was also significant in x=0.50 sample, because of the strongest FM feature in this sample.
