Strong Tilted Magnetic Field Research Articles

Disorder effects on helical edge transport in graphene under a strong tilted magnetic field

In a recent experiment, Young et al. [Nature {\bf 505}, 528 (2014)] observed a metal to insulator transition as well as transport through helical edge states in monolayer graphene under a strong, tilted magnetic field. Under such conditions, the bulk is a magnetic insulator which can exhibit metallic conduction through helical edges. It was found that two-terminal conductance of the helical channels deviates from the expected quantized value at low-temperatures ($=e^2/h$ per edge, at zero temperature). Motivated by this observation, we study the effect of disorder on the conduction through the edge channels. We show that, unlike the situation in semiconducting quantum wells, a disorder Rashba spin-orbit coupling does not lead to backscattering, at least to leading order. Instead we find the lack of perfect anti-alignment of the electron spins in the helical channels to be the most likely source for backscattering arising from scalar (i.e. spin-independent) impurities. The intrinsic spin-orbit coupling and other time-reversal symmetry breaking and/or sublattice-parity breaking potentials also lead to (sub-leading) corrections to the channel conductance.

Non-Fermi-Liquid Crossovers in a Quasi-One-Dimensional Conductor in a Tilted Magnetic Field.

We consider a theoretical problem of electron-electron scattering time in a quasi-one-dimensional (Q1D) conductor in a magnetic field, perpendicular to its conducting axis. We show that inverse electron-electron scattering time becomes of the order of characteristic electron energy, 1/τ~ε~T, in a high magnetic field, directed far from the main crystallographic axes, which indicates breakdown of the Fermi-liquid theory. In a magnetic field, directed close to one of the main crystallographic axis, inverse electron-electron scattering time becomes much smaller than characteristic electron energy and, thus, applicability of Fermi-liquid theory restores. We suggest that there exist crossovers (or phase transitions) between Fermi-liquid and some non-Fermi-liquid states in a strong enough tilted magnetic field. Application of our results to the Q1D conductor (Per)_{2}Au(mnt)_{2} shows that it has to be possible to observe the above-mentioned phenomenon in feasibly high magnetic fields of the order of H≥H^{*}≃25 T.

Fractional quantum Hall effect of topological surface states under a strong tilted magnetic field

The fractional quantum Hall effect (FQHE) of topological insulator surface state particles under a tilted strong magnetic field is theoretically studied by using the exact diagonalization method. Haldane's pseudopotentials for the Coulomb interaction are analytically obtained. The results show that by increasing the in-plane component of the tilted magnetic field, the FQHE state at n = 0 Landau level (LL) becomes more stable, while the stabilities of n = ± 1 LLs become weaker. Moreover, we find that the excitation gaps of the ν = 1/3, 1/5 and 1/7 FQHE states increase with increasing the tilt angle.

WITHDRAWN: Intersubband terahertz transitions in Landau level system of cascade GaAs/AlGaAs quantum well structures in strong tilted magnetic field

WITHDRAWN: Intersubband terahertz transitions in Landau level system of cascade GaAs/AlGaAs quantum well structures in strong tilted magnetic field

Intersubband terahertz transitions in Landau level system of cascade GaAs/AlGaAs quantum well structures in strong tilted magnetic field

The tunable terahertz intersubband Landau level transitions in resonant tunneling cascade quantum well structures are considered. The way of lifting the selection rule forbidding the inter-Landau level terahertz transitions of interest by applying a magnetic field tilted with respect to the structure layers is proposed. The importance of asymmetric structure design to achieve considerable values of transition dipole matrix elements is demonstrated.

SEQUENTIAL RESONANT TUNNELING BETWEEN LANDAU LEVELS IN GaAs\AlGaAs SUPERLATTICES IN STRONG TILTED MAGNETIC AND ELECTRIC FIELDS

The transverse resonant tunneling transport and electric field domain formation in GaAs/AlGaAs superlattices were investigated in a strong tilted magnetic field. The magnetic field component parallel to structure layers causes intensive tunneling transition between Landau levels with Δn≠0, resulting in the considerable "inhomogeneous" broadening of intersubband tunneling resonance as well as in the shift of the resonance toward higher electric fields. This leads to noticeable changes of the I-V characteristics of the superlattice, namely to smoothing of the periodic NDC structure on plateau-like regions caused by formation of the electric field domains and to the shift of the plateaus toward the higher applied voltage. The predicted behavior of the I-V characteristics of the structures in magnetic field was found experimentally.

Resonant tunneling transport through GaAs/AlGaAs superlattices in strong tilted magnetic field

An analysis is presented of the transverse resonant tunneling transport through GaAs/AlGaAs superlattices due to tunneling between Landau levels in quantum wells in a strong tilted magnetic field. A high tunneling rate is demonstrated between Landau levels with Δn ≠ 0 in a magnetic field with a nonzero in-plane component. This leads to substantial broadening and shift of the tunneling resonance and significant changes in the current-voltage characteristics of superlattices. The predicted behavior of the current-voltage characteristics of superlattices in tilted magnetic fields is demonstrated experimentally.

Spin-dependent Hall effect in a parabolic well with a quasi-three-dimensional electron gas

We study the Hall effect in wide ${\mathrm{Al}}_{c}{\mathrm{Ga}}_{c\ensuremath{-}1}\mathrm{As}$ parabolic wells in the presence of the tilted magnetic field. The Hall resistance is described by equations ${R}_{xy}∕\mathrm{cos}\phantom{\rule{0.2em}{0ex}}\ensuremath{\Theta}=\ensuremath{-}B∕e{n}_{s}$ at $B<4\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, and ${R}_{xy}∕\mathrm{cos}\phantom{\rule{0.2em}{0ex}}\ensuremath{\Theta}=\ensuremath{-}A\ifmmode\times\else\texttimes\fi{}(B\ensuremath{-}{B}_{0})∕e{n}_{s}$ at $B>4\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, where ${n}_{s}$ is the electron density, ${B}_{0}=2--2.6\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, $A$ is the temperature dependent coefficient, and $\ensuremath{\Theta}$ is the angle between the magnetic field and the normal to the well plane. The effective $g$ factor in such materials depends on the Al composition and changes the sign along the well width. In the presence of the strong tilted magnetic field electron moving along the $z$ direction acquires a spin flip process, which is strongly suppressed at low temperatures, and leads to the change of the Hall effect slope.

Diophantine equation for the 3D transport coefficients of Bloch electrons in a strong tiltedmagnetic field with quantum Hall effect

We study the 3D integer transport coefficients of the electron gas in a tilted magnetic fieldwith the model of Bloch electrons. Calculations without any approximation of the relevantbasis functions and matrix elements yield the topologically invariant conductances andtheir Diophantine equation.

SPECTRUM OF CARRIERS AND OPTICAL PROPERTIES OF 2D HETEROSTRUCTURES IN TILTED MAGNETIC FIELD

The structure and features of spatially-confined states in the presence of a tilted magnetic field are theoretically investigated. The electron states in single- and double-quantum wells are described using the variational method. It is shown that the finite ratio of magnetic length to the width of heterostructure could not be neglected in the strong tilted magnetic field. The electronic structure of broken-gap heterostructures is considered similar to the case of usual double-quantum-well with the high narrow barrier. It is shown that tilted magnetic field can eliminate the strong coupling between two degenerated electron states or those of the electron and hole. The existence of such an effect is in accordance with cyclotron resonance studies of InAs / GaSb heterostructures.

Dynamic magnetic susceptibility of a two-layer film in a strong magnetic field

A theoretical study is reported of the effect of interlayer exchange coupling on the resonance properties of a two-layer magnetic film with “easy-axis” and “easy-plane” anisotropic layers in a strong tilted magnetic field. The dependence of the resonance fields on the tilting angle of the external magnetic field to the film has been obtained, the tensor of integrated high-frequency film susceptibility has been found, and its dependence on the strength and orientation of the external field, as well as on layer thickness, has been analyzed. The results obtained agree with the available experimental data.

Crossing of cyclotron and spin resonances in a 2D electron gas

We compare anticrossing of the cyclotron and spin resonances in spin-polarized and non-polarized phases of the degenerate two-dimensional Coulomb gas subjected to a strong tilted magnetic field. The spin-orbit coupling splits these resonances into three lines with the gaps between them exactly equal to δ 2 n+1 = v so P F and δ 2n = V soP F √2 at odd- and even- integer filling factors, respectively. The 1 √2 difference between δ 2 n and δ 2 n+1 comes from the existence of an additional spin-density wave excitation in the polarized phase of interacting electrons at v = 2 n and can be treated as a means to indicate the re-entrance of the system into it.

The fine structure of cyclotron and spin resonances at their crossing: interplay between spin-orbit and Coulomb interactions

We compare the anticrossing of the spin and cyclotron resonances in spin-polarized and non-polarized phases of a two-dimensional electron gas subjected to a strong tilted magnetic field. The spin-orbit coupling splits these resonances into three lines with the gaps between them exactly equal to delta 2n+1=Vso rho F and delta 2n=vso rho F/ square root 2 at odd- and even-integer factors, respectively. The 1/ square root 2 factor difference between the gaps delta 2n and delta 2n+1 arises from the existence of two collective spin-wave-density modes in the polarized phase of interacting electrons in the system with two filled Landau levels. This allows us to predict a new type of spectral Shubnikov-de Haas oscillations, which indicates the re-entrance of the system into the spin-polarized state.

Crossing of cyclotron and spin resonances in two-dimensional Coulomb gas.

We predict the Shubnikov--de Haas oscillations of the fine structure of the cyclotron resonance near its crossing with the spin resonance in the degenerate two-dimensional Coulomb gas subjected to a strong tilted magnetic field. The spin-orbit coupling splits these resonances into three lines with the splitting gaps varying with the filling factor from ${\mathit{v}}_{\mathrm{so}}$${\mathit{p}}_{\mathit{F}}$ to ${\mathit{v}}_{\mathrm{so}}$${\mathit{p}}_{\mathit{F}}$/ \ensuremath{\surd}2 at odd- and even-integer filling, respectively. This indicates re-entrance of the system into a partially spin-polarized state and can be treated as manifestation of a new spin-density wave mode in it.