Interplay of spin and orbital magnetogyrotropic photogalvanic effects in InSb/(Al,In)Sb quantum well structures

We report on the observation of linear and circular magnetogyrotropic photogalvanic effects in InSb/(Al,In)Sb quantum well structures. We show that intraband (Drude-type) absorption of terahertz radiation in the heterostructures causes a dc electric current in the presence of an in-plane magnetic field. The photocurrent behavior upon variation of the magnetic field strength, temperature, and wavelength is studied. We show that at moderate magnetic fields, the photocurrent exhibits a typical linear field dependence. At high magnetic fields, however, it becomes nonlinear and inverses its sign. The experimental results are analyzed in terms of the microscopic models based on asymmetric relaxation of carriers in the momentum space. We demonstrate that the observed nonlinearity of the photocurrent is caused by the large Zeeman spin splitting in InSb/(Al,In)Sb structures and an interplay of the spin-related and spin-independent roots of the magnetogyrotropic photogalvanic effect.

Figure 1

(a) Conduction-band profile and electron wave function of QW structure with $L_W=$ 20 nm calculated within a self-consistent Schrödinger-Poisson model (Ref. 13). (b) Temperature dependences of mobility ${\mu }_e$ and carrier density $N_s$ obtained by the low-field Hall measurements in 20-nm QW sample.

Figure 2

Magnetic field dependence of $J_y/P$ for $\lambda =118$ $\mu$m and $T=35$ K. Lines are fit after Eq. (15). The left inset shows the experimental geometry. The right inset shows the photocurrent as a function of the azimuth angle $\alpha$ measured for $T=4.2$ and 35 K at fixed $B_x$ $=$ $+$5 T. Triangle symbols correspond to 30-nm, and circle and squared symbols to 20-nm QW structures.

Figure 3

Magnetic field dependence of $J_y/P$ for $\lambda =148$ $\mu$m and different temperatures. Lines are fit after Eq. (15).

Figure 4

Dependence of the LMPGE on the magnetic field at $T=4.2$ K for wavelengths of $\lambda =148$ and $280\mu$m obtained for the 20-nm QW structure. The inset shows the LMPGE for the 30-nm QW sample. Lines are fit after Eq. (15).

Figure 5

Relative change in conductivity $\Delta \sigma /{\sigma }_0=({\sigma }_i-{\sigma }_0)/{\sigma }_0$ in QW structure with $L_W=20$ nm measured versus radiation power $P$ at $T=4.2$ K and $B=0$. The ratio of conductivity under illumination ${\sigma }_i$ and dark conductivity ${\sigma }_0$ is determined from the photoconductive signals measured in the circuit sketched in the inset of the upper plate. (a) Photoconductive signal measured applying cw radiation with wavelength $\lambda =118$ $\mu$m. (b) $\Delta \sigma /{\sigma }_0$ measured applying pulsed laser radiation with $\lambda =148$ and $280$$\mu$m. The inset shows a section of the temperature dependence of the relative mobility $\Delta {\mu }_e/{\mu }_{e,0}$, where ${\mu }_{e,0}$ is the mobility at $T_0=4.2$ K.

Figure 6

Helicity dependence of the photocurrent $J_x$ measured for $B_x=-6$ T and $\lambda =280$ $\mu$m with subtracted offset $\xi$. The inset shows the experimental geometry. The ellipses on top illustrate the polarization states for various $\varphi$.

Figure 7

Magnetic field dependence of $J_x/P$ for wavelengths of $\lambda =90.5$, 148, and 280 $\mu$m at $T=270$ K.

Figure 8

Models of magnetogyrotropic photogalvanic currents: (a) spin-dependent LMPGE; (b) orbital LMPGE.

Figure 9

Average spin in 20-nm QW structures obtained by self-consistent calculations of Eqs. (7) and (9) as a function of the magnetic field. For calculation, we used $g_0=-25$ and an effective mass $m^{*}=0.02m_0$. Average spin calculated for (a) fixed temperature but for various values of the exchange interaction given by the parameter $g^{**}$ indicated by numbers next to the curves; (b) fixed exchange interaction $g^{**}=-30$ but various electron temperatures $T_e$.

Figure 10

Model for the spin-related CMPGE. The excitation with circularly polarized light yields a spin orientation $S_{0z}$. An in-plane component $S_y$ of the nonequilibrium spin is generated by the Larmor precession.