Spin and charge transport through a helical Aharonov-Bohm interferometer with a strong magnetic impurity

Abstract

We discuss transport through an interferometer formed by helical edge states of the quantum spin Hall insulator. Focusing on effects induced by a strong magnetic impurity placed in one of the arms of interferometer, we consider the experimentally relevant case of relatively high temperature as compared to the level spacing. We obtain the conductance and the spin polarization in the closed form for arbitrary tunneling amplitude of the contacts and arbitrary strength of the magnetic impurity. We demonstrate the existence of quantum effects which do not show up in previously studied case of weak magnetic disorder. We find optimal conditions for spin filtering and demonstrate that the spin polarization of outgoing electrons can reach 100%.

Shot Noise in Helical Edge States in Presence of a Static Magnetic Defect

“…Using the expressions ( 3), ( 6), (15) and averaging over energy, we find that the FF does not depend on the magnetic flux and is related by a simple formula to the transmission coefficient: (16) Here, Equation ( 16) is shown by the blue line in Fig. 3.…”

“…Such scattering can be caused, for example, by a MD or a charged island tunnel-coupled to the HES. It is worth noting that interference effects in a helical interferometer are not reduced to AB oscillations (examples of interference Δ ( , ) T eV Δ T processes independent of the magnetic field are given in [16], see Section 4).…”

“…Typically, interference is suppressed when T becomes larger than the distance, , between levels of the system. As was recently shown theoretically [14][15][16][17], for AB interferometers based on helical edge states (HES), this is not the case, and the interference effects "survive" even in the case where are the lengths of the interferometer arms, and is the Fermi velocity. For typical of order of 10 7 cm/s and typical system sizes (>1 micron), the value of does not exceed a few Kelvin.…”

“…Since the sample boundary can be bypassed in two direc-tions, such a system is an interferometer. Accordingly, both the average current and its noise depend on interference effects and, as a consequence, the observed quantities in such systems can be controlled due to the Aharonov-Bohm (AB) effect [11][12][13][14][15][16][17]: they periodically depend on the magnetic flux penetrating the region encompassed by electronic states.…”

“…We recently discussed the conductance of the AB helical interferometers [14][15][16][17] and the properties of the tunnel chain of the AB helical rings [18,19]. Here we will discuss another observable quantity-the current shot noise.…”