Andreev reflection

Ancymidol, 13 40t, 306 Anderson and McLean experimental design text, versus other texts, 8 395t Andgemifloxacin, 21 222 Andreason sedimentation pipette, 8 720 Andreev reflection, 23 821 Androgens, synthetic, 13 3 Anemia... 

The process of Andreev reflection involves a spin-up electron of energy E coupling with a spin-down electron of energy —E to form a Cooper pair in the superconductor. If the normal metal is replaced by a ferromagnet with a finite polarization P, not all electrons of one spin species will be able to find a corresponding electron of the opposite spin species in order to form Cooper pair. Hence, the probability of Andreev reflection will be reduced by a factor of (l-P), where we define the polarization P by... 

In order to get a physical understanding of this effect, one has to consider the microscopic mechanism of the Andreev reflection at the N-S interface [1]. An electron arriving on the interface from the normal metal side cannot... 

At subgap voltage, eV < A,p, when the charge transport at T = 0 is only due to the Andreev reflection, the current I, the shot noise power Pi, and the third cumulant 63 read... 

Usually, the electronic thermal conductance re can be calculated from the Wiedemann - Franz law, re TG/e2. However, as shown in Ref. [8, 9] for the ballistic limit f > d, this law gives a wrong result for Andreev wires if one uses an expression for G obtained for a wire surrounded by an insulator. Andreev processes strongly suppress the single electron transport for all quasiparticle trajectories except for those which have momenta almost parallel to the wire thus avoiding Andreev reflection at the walls. The resulting expression for the thermal conductance... 

The counter-intuitive behavior of the single-particle conductance Eq. (3) which increases with decreasing was first predicted by Andreev [10]. Comparing Eq. (3) with the ballistic ( d) expression Eq. (1) we see that disorder with d stimulates the single-particle transport by opening of new single-particle conducting modes that are blocked by Andreev reflections in the ballistic limit. The conductance reaches its maximum when the mean free path decreases down to a, after which the distinction between the usual and the Andreev diffusion is lost and Eq. (3) transforms into Eq. (4) for a dirty wire (see [11] for the particular case of vortex lines). 

In conclusion, we mention that the effects of disorder on the kinetics of quasiparticles confined in an insulator/normal-metal/superconductor (INS) hybrid structure due to Andreev reflections was first considered in Ref. [12] within a model where the disorder is provided by irregularities on the I/N boundary through the normal scattering of quasiparticles. 

In the SC state the excess current Iexc (1), which is due to the Andreev reflection of electron quasiparticles from the N — S boundary inaW-c — S contact (c stands for constriction ), can be written as... 

The physics of appearance of long range proximity effect in SF systems can be understood in terms of Andreev reflection. In the absence of spin active scattering or magnetization inhomogeneity Cooper pairs composed of minority or majority electrons do not mix with each other and there is no long range... 

Keywords Coherent transport, quantum dots, Andreev reflection... 

We analyze theoretically the phenomenon of photon-assisted quantum transport in superconductor(S)- semiconductorfN) mesoscopic system. Sub-gap structures in the I-V characteristics could be explained by multiple Andreev reflections. The electrical properties are strongly determined by the interface between superconductor and semiconductor. The current - voltage characteristics were found to be very sensitive to the photon frequency. 

In the present paper, a sandwich type model for the transport characteristics of the S-N-S junction is developed. The role of the Andreev reflection at the S-N interface is taken into account. We analyze the photon-assisted transport process due to both intersubband transitions (when the radiation field is in that transverse polarization) and to intrasubband transition (when the ac field is in the longitudinal polarization). 

The Andreev reflection is the second-order quantum mechanical process by which an electron-like particle incident on a superconductor with a quasi-particle excitation energy E above the Fermi energy may be transmitted as a Cooper pair in the superconductor, if a hole-like particle (-E) is reflected along the path of the incoming electron [12], For a superconductor-semiconductor interface with low contact resistance (high transparency) and with a negligible Schottky barrier, the Andreev scattering leads to an increased conductance. 

The current density, J2, due to Andreev reflection processes is given by [17] ... 

It might be seen that this expression for A E) gives a quite fair description for the process of Andreev reflection occuning at the junction interface. Substituting eq. (7) into eq. (6) and performing the integration we get ... 

Fig. 1 exhibits sub-gap structures in the I-V characteristics. A sub-gap structure can be explained by multiple Andreev reflections [8] at the interface between the semiconductor and the superconductor [7,12,13], where an electron in the semiconductor can be transmitted as a Cooper pair into the superconductor if a hole is reflected along the time-reversed path of the electron. 

Andreev reflection A process occurring at the interface between a normal conductor of electricity and a "superconductor, in which charge is transferred from the normal conductor to the superconductor. This results in the formation of a Cooper pair in the superconductor and a reflected hole in the normal conductor. The process was first described by the Russian physicist Alexander Andreev in 1964. It has possible applications in spintronics and quantum computing. 

---