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Quantum Electron Lifetime
The quantum lifetime of two dimensional electrons in GaAs quantum wells, placed in weak quantizing magnetic fields, is determined from quantum positive magnetoresistance (QPMR) observed in the studied system. In broad range of temperatures from 0.3 K to 20 K the temperature variations of the electron lifetime are found to be in good agreement with conventional theory of electron-electron scattering in 2D systems.
"Quantum lifetime of two-dimensional electrons in a magnetic field" ; Scott Dietrich, Sergey Vitkalov, D. V. Dmitriev, and A. A. Bykov; Phys. Rev. B 85, 115312 (2012)
Quantum SdH Oscillations and DC Bias
Oscillations of dissipative resistance of two-dimensional electrons in GaAs quantum wells with one subband populated are observed in response to an electric current I and a strong magnetic field applied perpendicular to the 2D systems. Period of the current-induced oscillations does not depend on the magnetic field and temperature. At a fixed current the oscillations are periodic in inverse magnetic fields with a period that does not depend on dc bias. Proposed model considers spatial variations of electron filling factor, which are induced by the electric current, as the origin of the resistance oscillations.
Quantum oscillations of dissipative resistance in crossed electric and magnetic fields; Scott Dietrich, Sean Byrnes, Sergey Vitkalov, D. V. Dmitriev and A. A. Bykov; Phys. Rev. B 85, 155307 (2012)
Quantum oscillations of nonlinear response in electron systems with variable density; Scott Dietrich, Sean Byrnes, Sergey Vitkalov, A. V. Goran and A. A. Bykov; J. Appl. Phys. 113, 053709 (2013)
The proposed mechanism considers a spatial charge separation caused by the Hall field generated by the bias current (IDC). The transfer of electrons across the sample and thereby a spatial variation of the Fermi energy leads to varying conductivity. Areas with completely filled Landau bands (EF between bands) do not conduct while those with partially filled bands provide dissipative conductivity. Oscillations in the differential resistance occur as EF passes through the bands.
FIG. A
Quantum Intersubband Oscillations and DC Bias.
In comparison with the single band results (above), a different type of resistance oscillations occur when two subbands are populated. By varying the Landau level spacing at a fixed subband energy separation, additional electron transitions become possible between simultaneously aligned Landau levels in different subbands. This inter-subband spectral overlap leads to an enhancement of electron scattering and, thus, the dissipative resistance . In the case when two sets of Landau levels are misaligned as shown in the figure B the scattering enhancement is suppressed. The alternating overlap between two spectra leads to oscillations of dissipative resistance called magneto-intersubband oscillations (MISO) of resistance. In right panel of Fig.A blue curve presents MISO at zero dc bias. Red curve presents MISO, which are modified by a dc bias.
FIG. B
FIG. C
The upper panel of Fig.A presents the resistance along the horizontal cuts shown in green and black of the main R(B,I) plot. A comparison indicates a phase shift between oscillations taken at MISO minima (black curve) and MISO maxima (green curve). To facilitate analysis of the oscillating content we have labeled the important features of observed bias induced oscillations. The processed data are shown in Fig.C.
Fig.C shows resistance oscillations at small magnetic field (B<0.2T). These oscillations are due Landau-Zener (LZ) transitions between different Landau levels, which occur during electron scattering on impurities in crossed electric and magnetic fields. Position of these LZ oscillations depends on both magnetic field and dc bias J. Index j=1,23 labels maximum of different LZ transitions. At larger magnetic field (B>0.2T) a new kind of resistance oscillations is observed. In contrast to LZ oscillations the period of these novel oscillations does depend on the magnetic field. In this respect these oscillations are similar to one observed above in 2D systems with one subband populated. The main difference, however, is that in the single subband system the quantum oscillations (SdH oscillations) induced by a mechanism, which is sensitive to the position of Fermi energy and, thus, to the electron density, while MISO are related to the intersubband correlations of the spectra and resilient to the particular value of Fermi energy. Proposed model relates these novel quantum oscillations to a spatial modification of the electron spectrum due to electron re-distribution in response to the dc bias. The main affected parameter is the gap between bottoms of two subbands, which is assumed to be density dependent quantity.
Intersubband resistance oscillations in crossed electric and magnetic fields; Scott Dietrich, Sean Byrnes, Sergey Vitkalov, A. V. Goran and A. A. Bykov; Phys. Rev. B 86, 075471 (2012)
Transport in Tilted Magnetic Fields
All the phenomena discussed above can be further modified by applying a magnetic field parallel to the sample in addition to the perpendicular magnetic field. In systems with multiple populated subbands significant modification of electron spectra, including a magnetic breakdown of the spectrum, is observed. Left figure below presents positions of MISO maxima (white regions) and minima (black regions) for different parallel and perpendicular magnetic fields fields. In this map quantum states with odd index K are topologically distinct while all states with even K are topologically equivalent. Here index K labels MISO maxima and equals to number of Landau levels (quantum states) within the subband gap (the energy interval between the subbands bottoms).
Magnetointersubband resistance oscillations in GaAs quantum wells placed in a tilted magnetic field; W. Mayer, J. Kanter, J. Shabani, S. Vitkalov, A. K. Bakarov and A. A. Bykov; Phys. Rev. B 93, 115309 (2016).
Upon the application of DC bias to this system in the magnetic breakdown regime Landau-Zener oscillations of the resistance are observed at different parallel magnetic fields. Right upper panel presents these LZ oscillation of the resistance. At zero parallel magnetic field the oscillations are similar to one presented above on Fig. A. Maxima of the oscillations occurs at integer values (j=0,1,2...) of normalized dc bias. At parallel magnetic field 0.028T the oscillations are inverted and the LZ maxima follow a half integer pattern: (j=1/2,3/2/, 5/2...). We found that these novel pattern is due to new quantum selection rules for the electron backscattering on impurities, which occurs in systems with several subbands populated placed in a titled magnetic field.
Resistance oscillations of two-dimensional electrons in crossed electric and tilted magnetic fields; W. Mayer, S. Vitkalov and A. A. Bykov; Phys. Rev. B 93, 245436 (2016)
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