Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCompressibility stripes for mesoscopic quantum Hall samples
53
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We numerically investigate the interplay of disorder and electron-electron interactions in the integer quantum Hall effect. In particular, we focus on the behaviour of the electronic compressibility as a function of magnetic field and electron density. We find manifestations of non-linear screening and charging effects around integer filling factors, consistent with recent imaging experiments. Our calculations exhibit $g$-factor enhancement as well as strong overscreening in the centre of the Landau bands. Even though the critical behaviour appears mostly unaffected by interactions, important implications for the phase diagram arise. Our results are in very good agreement with the experimental findings and strongly support the relevance of electron-electron interactions for understanding integer quantum Hall physics.
rate research
Read More
Time-reversal invariant two-dimensional topological insulators, often dubbed Quantum Spin Hall systems, possess helical edge modes whose ballistic transport is protected by physical symmetries. We argue that, though the time-reversal symmetry (TRS) of the bulk is needed for the existence of helicity, protection of the helical transport is actually provided by the spin conservation on the edges. This general statement is illustrated by specific examples. One example demonstrates the ballistic conductance in the setup where the TRS on the edge is broken. It shows that attributing the symmetry protection exclusively to the TRS is not entirely correct. Another example reveals weakness of the protection in the case where helical transport is governed by a space-fluctuating spin-orbit interaction. Our results demonstrate the fundamental importance of the spin conservation analysis for the identification of mechanisms which may (or may not) lead to suppression of the ballistic helical transport.
Our magnetotransport measurements of quantum Hall stripes in a high-quality GaAs quantum well in a slightly tilted magnetic field reveal that the orientation of stripes can be changed by temperature. Field-cooling and field-warming measurements, as well as observation of hysteresis at intermediate temperatures allow us to conclude that the observed temperature-induced reorientation of stripes is owing to the existence of two distinct minima in the symmetry-breaking potential. We also find that the native symmetry-breaking mechanism does not depend on temperature and that low-temperature magnetotransport data should be treated with caution as they do not necessarily reveal the true ground state, even in the absence of hysteresis.
We use the Kubo-Landauer formalism to compute the longitudinal (two-terminal) conductance of a two dimensional electron system placed in a strong perpendicular magnetic field, and subjected to periodic modulations and/or disorder potentials. The scattering problem is recast as a set of inhomogeneous, coupled linear equations, allowing us to find the transmission probabilities from a finite-size system computation; the results are exact for non-interacting electrons. Our method fully accounts for the effects of the disorder and the periodic modulation, irrespective of their relative strength, as long as Landau level mixing is negligible. In particular, we focus on the interplay between the effects of the periodic modulation and those of the disorder. This appears to be the relevant regime to understand recent experiments [S. Melinte {em et al}, Phys. Rev. Lett. {bf 92}, 036802 (2004)], and our numerical results are in qualitative agreement with these experimental results. The numerical techniques we develop can be generalized straightforwardly to many-terminal geometries, as well as other multi-channel scattering problems.
We report on quantum Hall stripes (QHSs) formed in higher Landau levels of GaAs/AlGaAs quantum wells with high carrier density ($n_e > 4 times 10^{11}$ cm$^{-2}$) which is expected to favor QHS orientation along unconventional $left < 1bar{1}0 right >$ crystal axis and along the in-plane magnetic field $B_{||}$. Surprisingly, we find that at $B_{||} = 0$ QHSs in our samples are aligned along $left < 110 right >$ direction and can be reoriented only perpendicular to $B_{||}$. These findings suggest that high density alone is not a decisive factor for either abnormal native QHS orientation or alignment with respect to $B_{||}$, while quantum confinement of the 2DEG likely plays an important role.
Using the random matrix theory, we investigate the ensemble statistics of edge transport of a quantum spin Hall insulator with multiple edge states in the presence of quenched disorder. Dorokhov-Mello-Pereyra-Kumar equation applicable for such a system is established. It is found that a two-dimensional quantum spin Hall insulator is effectively a new type of one-dimensional (1D) quantum conductor with the different ensemble statistics from that of the ordinary 1D quantum conductor or the insulator with an even number of Kramers edge pairs. The ensemble statistics provides a physical manifestation of the Z2-classification for the time-reversal invariant insulators.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
