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Zero field spin polarization in a 2D paramagnetic resonant tunneling diode

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 Added by Charles Gould
 Publication date 2010
  fields Physics
and research's language is English




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We study I-V characteristics of an all-II-VI semiconductor resonant tunneling diode with dilute magnetic impurities in the quantum well layer. Bound magnetic polaron states form in the vicinity of potential fluctuations at the well interface while tunneling electrons traverse these interface quantum dots. The resulting microscopic magnetic order lifts the degeneracy of the resonant tunneling states. Although there is no macroscopic magnetization, the resulting resonant tunneling current is highly spin polarized at zero magnetic field due to the zero field splitting. Detailed modeling demonstrates that the local spin polarization efficiency exceeds 90% without an external magnetic field.



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A spin-dependent quantum transport is investigated in a paramagnetic resonant tunneling diode (RTD) based on a Zn$_{1-x}$Mn$_x$Se/ZnBeSe heterostructure. Using the Wigner-Poisson method and assuming the two-current model we have calculated the current-voltage characteristics, potential energy profiles and electron density distributions for spin-up and spin-down electron current in an external magnetic field. We have found that -- for both the spin-polarized currents -- two types of the current hysteresis appear on the current-voltage characteristics. The current hysteresis of the first type occurs at the bias voltage below the resonant current peak and results from the accumulation of electrons in the quantum well layer. The current hysteresis of the second type appears at the bias voltage above the resonant current peak and is caused by the creation of the quasi-bound state in the left contact region and the resonant tunneling through this quasi-bound state. The physical interpretation of both the types of the current hysteresis is further supported by the analysis of the calculated self-consistent potential profiles and electron density distributions. Based on these results we have shown that -- in certain bias voltage and magnetic field ranges -- the spin polarization of the current exhibits the plateau behavior with the nearly full spin polarization. This property is very promising for possible applications in spintronics.
We investigate the current-voltage characteristics of a II-VI semiconductor resonant-tunneling diode coupled to a diluted magnetic semiconductor injector. As a result of an external magnetic field, a giant Zeeman splitting develops in the injector, which modifies the band structure of the device, strongly affecting the transport properties. We find a large increase in peak amplitude accompanied by a shift of the resonance to higher voltages with increasing fields. We discuss a model which shows that the effect arises from a combination of three-dimensional incident distribution, giant Zeeman spin splitting and broad resonance linewidth.
We report on the realization of a double barrier resonant tunneling diode for cavity polaritons, by lateral patterning of a one-dimensional cavity. Sharp transmission resonances are demonstrated when sending a polariton flow onto the device. We use a non-resonant beam can be used as an optical gate and control the device transmission. Finally we evidence distortion of the transmission profile when going to the high density regime, signature of polariton-polariton interactions.
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A mesoscopic ring subject to the Rashba spin-orbit interaction and sequentially coupled to an interacting quantum dot, in the presence of Aharonov-Bohm flux, is proposed as a flux tunable tunneling diode. The analysis of the conductance by means of the nonequilibrium Greens function technique, shows an intrinsic bistability at varying the Aharonov-Bohm flux when 2U > pi Gamma, U being the charging energy on the dot and Gamma the effective resonance width. The bistability properties are discussed in connection with spin-switch effects and logical storage device applications.
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