Effects of nonequilibrium electron distribution and electron-electron interaction observed in spin-split cyclotron resonance of InAs/AlSb single quantum wells at high magnetic fields

Abstract

We have observed two remarkable phenomena in spin-split cyclotron resonance of InAs/AlSb single quantum wells under short-pulse high magnetic fields produced by the single-turn coil technique. The first phenomenon is a hysteretic phenomenon, which was observed with a rapid sweep of the magnetic field in increasing and decreasing directions ͑ϳ100 T in a few microseconds͒. The sweep-rate dependence of the cyclotron resonance spectra revealed that the hysteretic phenomenon is attributable to the nonequilibrium electron distribution in the lowest Landau levels (Nϭ0) with plus and minus spins induced by short-pulse high magnetic fields. At low temperatures of around 15 K, a disagreement in intensity between the two different spins is observed in such a way that the total intensity is conserved. The hysteresis is attributed to a slow spin-flip relaxation between the two spin states of the Nϭ0 Landau level with a time constant of 1 s comparable with the field pulse duration. At high temperatures of around 100 K, a different type of hysteresis is found, where the absorption intensity of the minus spin is smaller in the down sweep than in the up sweep. The sweep-rate dependence shows that the up sweep does not change significantly, but the minus spin decreases with increasing the sweep rate in the down sweep. This is attributed to a slow electron transfer from donor levels in AlSb to a Landau level in InAs. The second phenomenon is the electron-electron interaction effect on the spin-split cyclotron resonance, which displays an intriguing dependence on the filling factor and the temperature at around 45 T, where 0.3рр1.2. With increasing temperature, the absorption intensity of the down spin increases, exceeding the amount expected from the Boltzmann distribution, while that of the up spin shows the opposite behavior. For samples with different carrier concentrations, the spin splitting at ϭ0.7 is smaller than that at ϭ0.4 by 1 T at around 50 K. These features can be explained qualitatively by a recent theory by Asano and Ando that calculates the effect of the electron-electron interaction on cyclotron resonance spectra by numerical diagonalization for a finite-size system with a finite number of electrons.

Effect of electron-electron interaction on cyclotron resonance in high-mobility InAs/AlSb quantum wells

“…This paper presents experimental results, obtained by CR technique in InAs/AlSb QWs with electron mobility up to 5.5 Â 10 5 cm 2 /V s, which significantly exceed the mobility values in the samples of InAs/AlSb QWs studied previously. [24][25][26][27][28][29][30][31][32][33] The top quality of our samples was also confirmed by observing pronounced triple splitting of CR line for transitions with partially filled LLs. In the range of filling factors 3 < < 4, the samples with different QW widths and electron concentrations demonstrate similar "enhanced" splitting of CR lines.…”

“…It should be emphasized that the prediction of Asano and Ando, 6 according to which the behaviour of CR modes at noninteger should be close to HFA results, could be valid at more high temperature than we have. 24 In our opinion, this is attributed to different phases of 2DEG (Refs. 51, 54, and 55) that realized at low and high temperatures.…”

“…Arimoto et al 24 observed a very large effect of CR mode coupling in InAs/AlSb QWs at 0.3 < < 1.2. Splitting of absorption line, corresponding to CR transitions from the lowest pair of the spin-split LLs, was studied at different temperatures in magnetic fields up 50 T. The energy transition from the upper state of the split LL was shifted towards the weak magnetic fields when the temperature was decreased from 300 K to 13 K, while electron concentration was reduced to about a half.…”

Cyclotron Resonance in High Magnetic Fields

“…Here, we present two examples: a hysteresis effect in the cyclotron resonance in fast pulsed magnetic fields (in this subsection), and electron-electron interaction effects (in the next subsection). Figure 14 shows CR spectra for a 15-nm InAs/AlSb quantum well taken in pulsed magnetic fields with different peak fields 31 . The experiments were performed in high magnetic fields produced by the single-turn coil technique.…”

“…In megagauss fields, the quantum limit is achieved in most cases, so that information on the lowest few Landau levels is obtained. A variety of physical phenomena have been investigated using megagauss CR, including resonant polaron effects in II-VI compounds 28 , field-induced structural phase transitions 29 , a semimetal-semiconductor transition 30 , electron-electron interaction effects 31 , spin-relaxation phenomena 31 , and a new type of combined cyclotron resonance 32 . Furthermore, CR experiments are possible even for "dirty" or low mobility samples, such as diamond 33 or diluted magnetic semiconductors 34 , since the condition ω c τ > 1 can be readily achieved in megagauss fields.…”