Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMelting of Wigner crystal in high-mobility $n$-GaAs/AlGaAs heterostructures at filling factors $0.18 > u > 0.125$: Acoustic studies
275
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Using acoustic methods the complex high-frequency conductance of high-mobility $n$-GaAs/AlGaAs heterostructures was determined in magnetic fields 12$div$18~T. Based on the observed frequency and temperature dependences we conclude that in the investigated magnetic field range and at sufficiently low temperatures, $T lesssim 200$~mK, the electron system forms a Wigner crystal deformed due to pinning by disorder. At some temperature, which depends on the electron filling factor, the temperature dependences of both components of the complex conductance get substantially changed. We have ascribed this rapid change of the conduction mechanism to melting of the Wigner crystal and study the dependence of the so-defined melting temperature on the electron filling factor.
rate research
Read More
We have measured magnetic field dependences of the attenuation and velocity of surface acoustic waves in a high-mobility $n$-GaAs/AlGaAs structure with a wide quantum well. The results allowed us to find the complex conductance, $sigma(omega)$, of the heterostructure for different frequencies, temperatures and magnetic fields near filling factors $ u=1, 2$. Observed behavior of $sigma(omega)$ versus magnetic field outside close vicinities of integer fillings reveals an oscillation pattern indicative of the rich fractional quantum Hall effect. Our result is that in very close vicinities of integer filling factors the AC response of a high-mobility two-dimensional structures behaves as that of a two-dimensional system of localized electrons. Namely, both real and imaginary parts of the complex AC conductance at low temperatures agree with the predictions for the two-site model for a two-dimensional hopping system. Another result is the specific temperature dependences of $sigma(omega)$, which are extremely sensitive to the filling factor value. These dependences indicate a sharp crossover between the localized modes and a pinned Wigner crystal.
Thermal measurements on a GaAs/AlGaAs heterostructure reveal that the state of the confined two-dimensional electrons dramatically affects the nuclear-spin diffusion near Landau level filling factor u=1. The experiments provide quantitative evidence that the sharp peak in the temperature dependence of heat capacity near u=1 is due to an enhanced nuclear-spin diffusion from the GaAs quantum wells into the AlGaAs barriers. We discuss the physical origin of this enhancement in terms the possible Skyrme solid-liquid phase transition.
High frequency (ac) conductivity in the single quantum well AlGaAs/GaAs/AlGaAs with high mobility was investigated by contactless acoustic methods in the fractional quantum Hall effect regime in perpendicular and tilted magnetic fields. We studied the dependence of ac conductivity $sigma^{ac}=sigma_1 - isigma_2$ on both the temperature and magnetic field tilt angle. Tilting the magnetic field relative to the sample surface enabled us to change the position of the conductivity oscillation minimum at $ u$=2/3. We measured the temperature dependence of ac conductivity for each tilt angle and for the 2/3 state we calculated the activation energy $Delta E$ which was derived by constructing the Arrhenius plot ln $sigma_1$ against 1/$T$. Analyzing behavior of the activation energy in total magnetic field for the filling factor 2/3 we observed a distinct minimum which can be interpreted as the spin unpolarized-polarized phase transition.
By simultaneous measurements of the attenuation and velocity of surface acoustic waves propagating in proximity to a high-quality GaAs quantum well we study the complex AC conductance of the two-dimensional electron system. Focusing on the vicinity of the filling factor $ u=1/5$ we confirm that the insulating states formed closely to this value of $ u$ are pinned Wigner crystals.
The electronic excitations at the edges of a Hall bar not much wider than a few magnetic lengths are studied theoretically at filling $ u = 2$. Both mean-field theory and Luttinger liquid theory techniques are employed for the case of a null Zeeman energy splitting. The first calculation yields a stable spin-density wave state along the bar, while the second one predicts dominant Wigner-crystal correlations along the edges of the bar. We propose an antiferromagnetic Wigner-crystal groundstate for the edge electrons that reconciles the two results. A net Zeeman splitting is found to produce canting of the antiferromagnetic order.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
