The non-linear zero-differential resistance state (ZDRS) that occurs for highly mobile two-dimensional electron systems in response to a dc bias in the presence of a strong magnetic field applied perpendicular to the electron plane is suppressed and disappears gradually as the magnetic field is tilted away from the perpendicular at fixed filling factor $\nu$. Good agreement is found with a model that considers the effect of the Zeeman splitting of Landau levels enhanced by the in-plane component of the magnetic field.Comment: 4 pages, 4 figure

Transport properties of highly mobile 2D electrons are studied in symmetric GaAs quantum wells placed in titled magnetic fields. Quantum positive magnetoresistance (QPMR) is observed in magnetic fields perpendicular to the 2D layer. Application of in-plane magnetic field produces a dramatic decrease of the QPMR. This decrease correlates strongly with the reduction of the amplitude of Shubnikov–de Haas resistance oscillations due to modification of the electron spectrum via enhanced Zeeman splitting. Surprisingly no quantization of the spectrum is detected when the Zeeman energy exceeds half of the cyclotron energy suggesting an abrupt transformation of the electron dynamics. Observed angular evolution of QPMR implies strong mixing between spin subbands. Theoretical estimations indicate that in the presence of spin-orbital interaction the elastic impurity scattering provides significant contribution to the spin mixing in GaAs quantum wells at high filling factors.

Transport properties of highly mobile two-dimensional (2D) electrons in symmetric GaAs quantum wells with two populated subbands placed in tilted magnetic fields are studied at high temperatures. Quantum positive magnetoresistance (QPMR) and magneto-intersubband resistance oscillations (MISO) are observed in quantizing magnetic fields, $B_{\perp }$, applied perpendicular to the 2D layer. QPMR displays contributions from electrons with considerably different quantum lifetimes, ${\tau }_q^{(1,2)}$, confirming the presence of two subbands in the studied system. MISO evolution with $B_{\perp }$ agrees with the obtained quantum scattering times only if an additional reduction of the MISO magnitude is applied at small magnetic fields. This indicates the presence of a yet unknown mechanism leading to MISO damping. Application of an in-plane magnetic field produces a strong decrease of both QPMR and MISO magnitude. The reduction of QPMR is explained by spin splitting of Landau levels indicating a $g$ factor, $g\approx 0.4$, which is considerably less than the $g$ factor found in GaAs quantum well with a single subband populated. In contrast to QPMR, the decrease of MISO magnitude is largely related to the in-plane magnetic field induced entanglement between quantum levels in different subbands that, in addition, increases the MISO period.

Effects of temperature ${\displaystyle T}$ (6–18 K) and variable in situ static disorder on dissipative resistance of two-dimensional electrons are investigated in GaAs quantum wells placed in a perpendicular magnetic-field ${\displaystyle B_{\perp }}$. Quantum contributions to the magnetoresistance, leading to quantum positive magnetoresistance (QPMR), are separated by application of an in-plane magnetic field. QPMR decreases considerably with both the temperature and the static disorder and is in good quantitative agreement with theory. The remaining resistance ${\displaystyle R}$ decreases with the magnetic field exhibiting an anomalous polynomial dependence on ${\displaystyle B_{\perp }\text{:}[R\left(B_{\perp }\right)-R\left(0\right)]=A(T,{\tau }_q)B_{\perp }^{\eta }}$ where the power is ${\displaystyle \eta \approx 1.5\pm 0.1}$ in a broad range of temperatures and disorder. The disorder is characterized by electron quantum lifetime ${\displaystyle {\tau }_q}$. The scaling factor ${\displaystyle A(T,{\tau }_q)\sim {[\kappa \left({\tau }_q\right)+\beta \left({\tau }_q\right)T^2]}^{-1}}$ depends significantly on both ${\displaystyle {\tau }_q}$ and ${\displaystyle T}$ where the first term ${\displaystyle \kappa \sim {\tau }_q^{-1/2}}$ decreases with ${\displaystyle {\tau }_q}$. The second term is proportional to the square of the temperature and diverges with increasing static disorder. Above a critical disorder the anomalous magnetoresistance is absent, and only a positive magnetoresistance, exhibiting no distinct polynomial behavior with the magnetic field, is observed. The presented model accounts memory effects and yields ${\displaystyle \eta =3/2}$.

Magneto-intersubband resistance oscillations (MISOs) of highly mobile 2D electrons in symmetric GaAs quantum wells with two populated subbands are studied in magnetic fields tilted from the normal to the 2D electron layer at different temperatures $T$. A decrease of MISO amplitude with temperature increase is observed. At moderate tilts, the temperature decrease of MISO amplitude is consistent with a decrease of the Dingle factor due to a reduction of the quantum electron lifetime at high temperatures. At large tilts, a different regime of strong MISO suppression with the temperature is observed. The proposed model relates this suppression to magnetic entanglement between subbands, leading to beating in oscillating density of states. The model yields corresponding temperature damping factor: $A_{\text{MISO}}\left(T\right)=X/sinh\left(X\right)$, where $X=2{\pi }^{2}kT\delta f$ and $\delta f$ is the difference frequency of oscillations of density of states in two subbands. This factor is in agreement with experiments. A Fermi liquid enhancement of MISO amplitude is observed.