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Observation of current-induced, long-lived persistent spin polarization in a topological insulator: A rechargeable spin battery

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ABSTRACT

We report a current-induced, persistent, long-lived, and rewritable electron spin polarization in a 3D topological insulator.

No MeSH data available.


Writing current effect on the spin signal.(A and B) Schematic four-terminal device structures and measurement setups for writing current and spin potentiometry. (C to H) Voltage detected by the FM contact as a function of in-plane magnetic field measured on device B at the relatively small Id of 0.5 μA (C, E, and G) and −0.5 μA (D, F, and H) after applying a large Iw of −40 μA for 2 hours (C and D), 50 μA for 0.5 hours (E and F), and −40 μA for 3 hours (G and H). The trend of the B field–induced voltage change, which measures the direction of the channel spin polarization, is independent of the relatively small Id but is set by the direction of the large Iw (applied at B = 0 T and before the spin potentiometric measurement). The directions of Id, Iw, channel spin polarization S as determined by the spin signal, and Py magnetization M are labeled by the corresponding arrows. All the measurements are performed at T = 1.6 K.
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Figure 2: Writing current effect on the spin signal.(A and B) Schematic four-terminal device structures and measurement setups for writing current and spin potentiometry. (C to H) Voltage detected by the FM contact as a function of in-plane magnetic field measured on device B at the relatively small Id of 0.5 μA (C, E, and G) and −0.5 μA (D, F, and H) after applying a large Iw of −40 μA for 2 hours (C and D), 50 μA for 0.5 hours (E and F), and −40 μA for 3 hours (G and H). The trend of the B field–induced voltage change, which measures the direction of the channel spin polarization, is independent of the relatively small Id but is set by the direction of the large Iw (applied at B = 0 T and before the spin potentiometric measurement). The directions of Id, Iw, channel spin polarization S as determined by the spin signal, and Py magnetization M are labeled by the corresponding arrows. All the measurements are performed at T = 1.6 K.

Mentions: We further found that the sign of δV in our device can be (re)set by applying a relatively large DC bias current for an extended time (referred to as a writing current, Iw, to distinguish from the relatively small Id in Fig. 1 that does not affect δV). In this experiment, we usually apply a large Iw between the two outside Au contacts in a four-terminal device (Fig. 2A) for an extended time at zero B field, and then the spin signal is measured by spin potentiometry (Fig. 2B; the four-terminal configuration is found to give a similar spin potentiometry signal as measured in three-terminal configurations) with a small Id. Figure 2 (C to H) shows the results measured on a 25-nm-thick BTS221 flake (device B) at T = 1.6 K. After applying a Iw = −40 μA for 2 hours, spin potentiometric measurements (Fig. 2B) were performed with Id = ±0.5 μA (shown in Fig. 2, C and D). We observe a similar step-like voltage change as that in Fig. 1, with a negative δV, for both the positive and negative Id, indicating the presence of a channel spin polarization whose direction is independent of Id. We then apply a large positive Iw = 50 μA for 0.5 hours. Afterward, spin potentiometry was performed (Fig. 2, E and F) with Id = ±0.5 μA, and the sign of the spin signal (δV) is reversed to positive, which is opposite to that in Fig. 2 (C and D) (after Iw = −40 μA), indicating that the direction of the spin polarization S has now been reversed after the application of a reversed Iw (but still independent of Id). Remarkably, the sign of δV can be reversed again and back to the case in Fig. 2 (C and D) after applying a negative Iw = −40 μA for 3 hours, as shown in Fig. 2 (G and H). Similar effects are also observed when Iw is applied during sample cooling (fig. S4) or at a higher temperature (~26 K; fig. S5). We clearly see that the sign of the spin signal and the direction of the channel spin polarization S are determined by Iw (reversing Iw reverses S) but are independent of Id (as long as Id is small enough). We find that the spin signal δV also increases with the increasing writing current Iw (fig. S6) and writing time (fig. S7). Such a current (Iw)–induced writing effect (where the induced spin polarization persists even after Iw is turned off) of spin polarization has not been previously observed in 3D TIs. We further note that the direction of S is consistent with that of the TSS spin polarization induced by Iw (see arrows indicating the directions of S and Iw in Fig. 2, C to H) according to the helicity of SML of the TSS (7, 11, 14).


Observation of current-induced, long-lived persistent spin polarization in a topological insulator: A rechargeable spin battery
Writing current effect on the spin signal.(A and B) Schematic four-terminal device structures and measurement setups for writing current and spin potentiometry. (C to H) Voltage detected by the FM contact as a function of in-plane magnetic field measured on device B at the relatively small Id of 0.5 μA (C, E, and G) and −0.5 μA (D, F, and H) after applying a large Iw of −40 μA for 2 hours (C and D), 50 μA for 0.5 hours (E and F), and −40 μA for 3 hours (G and H). The trend of the B field–induced voltage change, which measures the direction of the channel spin polarization, is independent of the relatively small Id but is set by the direction of the large Iw (applied at B = 0 T and before the spin potentiometric measurement). The directions of Id, Iw, channel spin polarization S as determined by the spin signal, and Py magnetization M are labeled by the corresponding arrows. All the measurements are performed at T = 1.6 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 2: Writing current effect on the spin signal.(A and B) Schematic four-terminal device structures and measurement setups for writing current and spin potentiometry. (C to H) Voltage detected by the FM contact as a function of in-plane magnetic field measured on device B at the relatively small Id of 0.5 μA (C, E, and G) and −0.5 μA (D, F, and H) after applying a large Iw of −40 μA for 2 hours (C and D), 50 μA for 0.5 hours (E and F), and −40 μA for 3 hours (G and H). The trend of the B field–induced voltage change, which measures the direction of the channel spin polarization, is independent of the relatively small Id but is set by the direction of the large Iw (applied at B = 0 T and before the spin potentiometric measurement). The directions of Id, Iw, channel spin polarization S as determined by the spin signal, and Py magnetization M are labeled by the corresponding arrows. All the measurements are performed at T = 1.6 K.
Mentions: We further found that the sign of δV in our device can be (re)set by applying a relatively large DC bias current for an extended time (referred to as a writing current, Iw, to distinguish from the relatively small Id in Fig. 1 that does not affect δV). In this experiment, we usually apply a large Iw between the two outside Au contacts in a four-terminal device (Fig. 2A) for an extended time at zero B field, and then the spin signal is measured by spin potentiometry (Fig. 2B; the four-terminal configuration is found to give a similar spin potentiometry signal as measured in three-terminal configurations) with a small Id. Figure 2 (C to H) shows the results measured on a 25-nm-thick BTS221 flake (device B) at T = 1.6 K. After applying a Iw = −40 μA for 2 hours, spin potentiometric measurements (Fig. 2B) were performed with Id = ±0.5 μA (shown in Fig. 2, C and D). We observe a similar step-like voltage change as that in Fig. 1, with a negative δV, for both the positive and negative Id, indicating the presence of a channel spin polarization whose direction is independent of Id. We then apply a large positive Iw = 50 μA for 0.5 hours. Afterward, spin potentiometry was performed (Fig. 2, E and F) with Id = ±0.5 μA, and the sign of the spin signal (δV) is reversed to positive, which is opposite to that in Fig. 2 (C and D) (after Iw = −40 μA), indicating that the direction of the spin polarization S has now been reversed after the application of a reversed Iw (but still independent of Id). Remarkably, the sign of δV can be reversed again and back to the case in Fig. 2 (C and D) after applying a negative Iw = −40 μA for 3 hours, as shown in Fig. 2 (G and H). Similar effects are also observed when Iw is applied during sample cooling (fig. S4) or at a higher temperature (~26 K; fig. S5). We clearly see that the sign of the spin signal and the direction of the channel spin polarization S are determined by Iw (reversing Iw reverses S) but are independent of Id (as long as Id is small enough). We find that the spin signal δV also increases with the increasing writing current Iw (fig. S6) and writing time (fig. S7). Such a current (Iw)–induced writing effect (where the induced spin polarization persists even after Iw is turned off) of spin polarization has not been previously observed in 3D TIs. We further note that the direction of S is consistent with that of the TSS spin polarization induced by Iw (see arrows indicating the directions of S and Iw in Fig. 2, C to H) according to the helicity of SML of the TSS (7, 11, 14).

View Article: PubMed Central - PubMed

ABSTRACT

We report a current-induced, persistent, long-lived, and rewritable electron spin polarization in a 3D topological insulator.

No MeSH data available.