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Register a new userAnomalous Decay of Quantum Resistance Oscillations of Two Dimensional Helical Electrons in Magnetic Field
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Shubnikov de Haas resistance oscillations of highly mobile two dimensional helical electrons propagating on a conducting surface of strained HgTe 3D topological insulator are studied in magnetic fields B tilted by angle $theta$ from the normal to the conducting layer. Strong decrease of oscillation amplitude A is observed with the tilt: $A sim exp(-xi/cos(theta))$, where $xi$ is a constant. Evolution of the oscillations with temperature T shows that the parameter $xi$ contains two terms: $xi=xi_1+xi_2 T$. The temperature independent term, $xi_1$, describes reduction of electron mean free path in magnetic field B pointing toward suppression of the topological protection of the electron states against impurity scattering. The temperature dependent term, $xi_2 T$, indicates increase of the reciprocal velocity of 2D helical electrons suggesting modification of the electron spectrum in magnetic fields.
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Effect of dc electric field on transport of highly mobile 2D electrons is studied in wide GaAs single quantum wells placed in titled magnetic fields. The study shows that in perpendicular magnetic field resistance oscillates due to electric field induced Landau-Zener transitions between quantum levels that corresponds to geometric resonances between cyclotron orbits and periodic modulation of electron density of states. Magnetic field tilt inverts these oscillations. Surprisingly the strongest inverted oscillations are observed at a tilt corresponding to nearly absent modulation of the electron density of states in regime of magnetic breakdown of semiclassical electron orbits. This phenomenon establishes an example of quantum resistance oscillations due to Landau quantization, which occur in electron systems with a constant density of states.
The low-temperature($4.2<T<12.5$ K) magnetotransport ($B<2$ T) of two-dimensional electrons occupying two subbands (with energy $E_1$ and $E_2$) is investigated in GaAs single quantum well with AlAs/GaAs superlattice barriers. Two series of Shubnikov-de Haas oscillations are found to be accompanied by magnetointersubband (MIS) oscillations, periodic in the inverse magnetic field. The period of the MIS oscillations obeys condition $Delta_{12}=(E_2-E_1)=k cdot hbar omega_c$, where $Delta_{12}$ is the subband energy separation, $omega_c$ is the cyclotron frequency, and $k$ is the positive integer. At $T$=4.2 K the oscillations manifest themselves up to $k$=100. Strong temperature suppression of the magnetointersubband oscillations is observed. We show that the suppression is a result of electron-electron scattering. Our results are in good agreement with recent experiments, indicating that the sensitivity to electron-electron interaction is the fundamental property of magnetoresistance oscillations, originating from the second-order Dingle factor.
Magnetic barriers in two-dimensional electron gases are shifted in B space by homogeneous, perpendicular magnetic fields. The magnetoresistance across the barrier shows a characteristic asymmetric dip in the regime where the polarity of the homogeneous magnetic field is opposite to that one of the magnetic barrier. The measurements are in quantitative agreement with semiclassical simulations, which reveal that the magnetoresistance originates from the interplay of snake orbits with E x B drift at the edges of the Hall bar and with elastic scattering.
The magnetotransport of highly mobile 2D electrons in wide GaAs single quantum wells with three populated subbands placed in titled magnetic fields is studied. The bottoms of the lower two subbands have nearly the same energy while the bottom of the third subband has a much higher energy ($E_1approx E_2<<E_3$). At zero in-plane magnetic fields magneto-intersubband oscillations (MISO) between the $i^{th}$ and $j^{th}$ subbands are observed and obey the relation $Delta_{ij}=E_j-E_i=kcdothbaromega_c$, where $omega_c$ is the cyclotron frequency and $k$ is an integer. An application of in-plane magnetic field produces dramatic changes in MISO and the corresponding electron spectrum. Three regimes are identified. At $hbaromega_c ll Delta_{12}$ the in-plane magnetic field increases considerably the gap $Delta_{12}$, which is consistent with the semi-classical regime of electron propagation. In contrast at strong magnetic fields $hbaromega_c gg Delta_{12}$ relatively weak oscillating variations of the electron spectrum with the in-plane magnetic field are observed. At $hbaromega_c approx Delta_{12}$ the electron spectrum undergoes a transition between these two regimes through magnetic breakdown. In this transition regime MISO with odd quantum number $k$ terminate, while MISO corresponding to even $k$ evolve $continuously$ into the high field regime corresponding to $hbaromega_c gg Delta_{12}$
Oscillations of dissipative resistance of two-dimensional electrons in GaAs quantum wells are observed in response to an electric current I and a strong magnetic field applied perpendicular to the two-dimensional 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. The proposed model considers spatial variations of electron filling factor, which are induced by the electric current, as the origin of the resistance oscillations.
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