We have obtained numerically exact results for the spin-related geometric quantum phases that arise in p-type semiconductor ring structures. The interplay between gate-controllable (Rashba) spin splitting and quantum-confinement-induced mixing between hole-spin states causes a much higher sensitivity of magnetoconductance oscillations to external parameters than previously expected. Our results imply a much-enhanced functionality of hole-ring spin-interference devices and shed new light on recent experimental findings.
We show that above the critical temperature of superconductor - metal phase transitions, both the longitudinal and Hall conductivity exhibit strong temperature dependent mesoscopic fluctuations, with amplitudes much larger than the mesoscopic fluctuations in noninteracting normal metals. Such an enhancement of the mesoscopic fluctuations arises from pairing correlations and is strongly dependent on dimensions.
We propose an idea to investigate persistent current in individual arms of a multi-arm mesoscopic ring. Following a brief description of persistent current in a traditional Aharonov-Bohm (AB) ring, we examine the behavior of persistent currents in separate arms of a three-arm mesoscopic ring. Our analysis may be helpful in studying magnetic response of any complicated quantum network.
We investigate the Nernst effect in a mesoscopic two-dimensional electron system (2DES) at low magnetic fields, before the onset of Landau level quantization. The overall magnitude of the Nernst signal agrees well with semi-classical predictions. We observe reproducible mesoscopic fluctuations in the signal which diminish significantly with an increase in temperature. We also show that the Nernst effect exhibits an anomalous component which is correlated with an oscillatory Hall effect. This behavior may be able to distinguish between different spin-correlated states in the 2DES.
The persistent current in a clean mesoscopic ring with ballistic electron motion is calculated. The particle dynamics inside a ring is assumed to be chaotic due to scattering at the surface irregularities of atomic size. This allows one to use the so-called ``ballistic'' supersymmetric σmodel for calculation of the two-level correlation function in the presence of a nonzero magnetic flux.
We revisit the problem of electron transport through mesoscopic rings with spin-orbit (SO) interaction. In the well-known path-integral approach, the scattering states for a quasi-1D ring with quasi-1D leads can be expressed in terms of spinless electrons subject to a fictitious magnetic flux. We show that spin-dependent quantum-interference effects in small rings are strongest for spatially inhomogeneous SO interactions, in which case spin currents can be controlled by a small external magnetic field. Mesoscopic spin Hall effects in four-terminal rings can also be understood in terms of the f…
We present a simple phenomenological model which offers a unifying interpretation of the experimental observations on the 0.7 conductance anomaly of quantum point contacts. The model utilizes the Landauer-Buttiker formalism and involves enhanced spin correlations and thermal depopulation of spin subbands. In particular our model can account for the plateau value 0.7 and the unusual temperature and magnetic field dependence. Furthermore it predicts an anomalous suppression of shot noise at the 0.7 plateau.
We calculate the average polarisability of two dimensional mesoscopic rings in the presence of an Aharonov-Bohm flux. The screening is taken into account self-consistently within a mean-field approximation. We investigate the effects of statistical ensemble, finite frequency and disorder. We emphasize geometrical effects which make the observation of field dependent polarisability much more favourable on rings than on disks or spheres of comparable radius. The ratio of the flux dependent to the flux independent part is estimated for typical GaAs rings.
We study the spin-dependent conductance of ballistic mesoscopic ring systems in the presence of an inhomogeneous magnetic field. We show that, for the setup proposed, even a small Zeeman splitting can lead to a considerable spin polarisation of the current. Making use of a spin-switch effect predicted for such systems we propose a device of two rings connected in series that in principle allows for both creating and coherently controlling spin polarized currents at low temperatures.
We report measurements of the low temperature magnetic response of a line of 16 GaAs/GaAlAs \emph{connected} mesoscopic rings whose total length is much larger than $l_ϕ$. Using an on-chip micro-\textsc{squid} technology, we have measured a periodic response, with period $h/e$, corresponding to persistent currents in the rings of typical amplitude $0.40\pm 0.08 nA$ per ring. Direct comparison with measurements on the same rings but \emph{isolated} is presented.
We consider the effect of an oscillating potential on the single-particle spectrum and the time-averaged persistent current of a one-dimensional phase-coherent mesoscopic ring with a magnetic flux. We show that in a ring with an even number of spinless electrons the oscillating potential has a strong effect on the persistent current when the excited side bands are close to the eigen levels of a pure ring. Resonant enhancement of side bands of the Floquet state generates a sign change of the persistent current.
We study the effect of charge discreteness in a quantum mesoscopic ring wih inductance L. The ring is pierced by a time depending external magnetic field. When the external magnetic flux varies uniformly, the current induced in the ring oscillates with a frequency proportional to the charge discreteness and the flux variation. This phenomenon is very similar to the well known Bloch's oscillation in crystals. The similitude is related to the charge discreteness in the charge-current representation, which plays the same role as the constant lattice in crystals.
Transport through a molecule sandwiched between two metallic electrodes and coupled to a mesoscopic ring that threads a magnetic flux $ϕ$ is studied. An analytic approach for the electron transport through the molecular bridge system is presented. Electronic transport properties are discussed in two aspects: (a) presence of external magnetic filed and (b) strength of molecule-to-electrode coupling.
We present a detailed theory of induced persistent current produced by hyperfine interaction in mesoscopic rings based on a 2D-electron (hole) gas in the absence of external magnetic field. The persistent current emerges due to combined action of the hyperfine interaction of charge carriers with polarized nuclei, spin-orbit interaction and Berry phase.
Persistent current in one-dimensional non-superconducting mesoscopic rings threaded by a slowly varying magnetic flux $ϕ$ is studied based on the tight-binding model. The behavior of the persistent current is discussed in three aspects: (a) single hopping impurity, (b) in-plane electric field and (c) in presence of some foreign atoms.
We present a theoretical study of spin-3/2 hole transport through mesoscopic rings, based on the spherical Luttinger model. The quasi-one-dimensional ring is created in a symmetric two-dimensional quantum well by a singular-oscillator potential for the radial in-plane coordinate. The quantum-interference contribution to the two-terminal ring conductance exhibits an energy-dependent Aharonov-Anandan phase, even though Rashba and Dresselhaus spin splittings are absent. Instead, confinement-induced heavy-hole - light-hole mixing is found to be the origin of this phase, which has ramifications for…
The calculation of the conductance of ballistic rings requires a theory that goes well beyond the Kubo-Drude formula. Assuming "mesoscopic" circumstance of very weak environmental relaxation, the conductance is much smaller compared with the naive expectation. Namely, the electro-motive-force induces an energy absorption with a rate that depends crucially on the possibility to make connected sequences of transitions. Thus the calculation of the mesoscopic conductance is similar to solving a percolation problem. The "percolation" is in energy space rather than in real space. Non-universal struc…
A tight-binding model of electron dynamics in mesoscopic normal rings is studied using boundary conformal field theory. The partition function is calculated in the low energy limit and the persistent current generated as a function of an external magnetic flux threading the ring is found. We study the cases where there are defects and electron-electron interactions separately. The same temperature scaling for the persistent current is found in each case, and the functional form can be fitted, with a high degree of accuracy, to experimental data.
The critical fluctuations in a mesoscopic superconducting ring are studied within the Ginzburg-Landau approach. The nonlocal conductivity as well as the specific heat are calculated as functions of the magnetic flux $Φ$ through the ring. At $Φ=Φ_0/2$ two low-energy eigenstates become degenerate and near this point the behavior of fluctuations-dependent quantities change dramatically: both the zero Fourier component $σ_0$ of the fluctuation conductivity and the specific heat become non-monotonic functions of $|Φ-Φ_0/2|$ with rather special resonant structure.
We develop a Luttinger liquid theory of the Coulomb drag of persistent currents flowing in concentric mesoscopic rings, by incorporating non-linear corrections to the electron dispersion relation. We demonstrate that at low temperatures, interactions between electrons in different rings generate an additional phase and thus alter the period of Aharonov-Bohm oscillations. The resulting nondissipative drag depends strongly on the relative parity of the electron numbers. We also show that interactions set a new temperature scale below which the linear response theory does not apply at certain val…
In a recent letter, Yi et al. PRL 78, 3523 (1997), have considered the stability of a Charge Density Wave in a one-dimensional ring, in the presence of an Aharonov-Bohm flux. This comment shows that, in one dimension, the stability of the Charge Density Wave depends on the parity of the number of electrons in the ring. This effect is similar to the parity effect known for the persistent current in one-dimensional rings.
Combining nonperturbative techniques with Monte Carlo simulations we demonstrate that quantum coherence effects for a particle on a ring are suppressed beyond a finite length $L_ϕ$ even at zero temperature if the particle is coupled to a diffusive electron gas by means of long range Coulomb interaction. This length is consistent with $L_ϕ$ derived from weak-localization-type of analysis.
The possibility of making a flux qubit on nonsuperconducting mesoscopic ballistic quasi 1D ring is discussed. We showed that such ring can be effectively reduced to a two-state system with two external control parameters. The two states carry opposite persistent currents and are coupled by tunneling which leads to a quantum superposition of states. The qubit states can be manipulated by resonant microwave pulses. The flux state of the sample can be measured by a SQUID magnetometer. Two or more qubits can be coupled by the flux the circulating currents generate. The problem of decoherence is al…
We study the tunneling current through a mesoscopic two-terminal ring with spin-orbit coupling, which is threaded by a magnetic flux. The electron-electron interaction in the ring is described in terms of a Tomonaga-Luttinger model which also allows us to account for a capacitive coupling between the ring and the gate electrode. In the regime of weak tunneling, we describe how, at temperatures lower than the mean level spacing, the peak positions of the conductance depend on magnetic flux, spin-orbit coupling strength, gate voltage, charging energy, and interaction parameters (charge and spin …
We investigate parametric pumping of spin and charge currents in a mesoscopic ring interrupted by a tunnel barrier in presence of Aharonov-Casher (AC) effect and Aharonov-Bohm (AB) flux along the axis of the same ring. Generation of a dc current is achieved by tuning the tunnel barrier strength and modulating in time either a radial(transverse) electric field or the magnetic flux. A pure spin current is generated by the interplay of breaking spin reversal symmetry, due to AC effect, and time-reversal symmetry breaking, intrinsic in parametric pumping procedure. We analyze the conditions for op…
We derive non equilibrium statistical ensembles for a ballistic Aharonov-Bohm loop connected to several electrodes connected to reservoirs with different chemical potentials. A striking consequence of these non trivial ensembles is the emergence of quantum zero point fluctuations of the persistent current around the loop. Detailed predictions for the low frequency noise power are given.
We show theoretically that strong electron coupling to circularly polarized photons in non-singly-connected nanostructures results in the appearance of an artificial gauge field that changes the electron phase. The effect arises from the breaking of time-reversal symmetry and is analogous to the well-known Aharonov-Bohm phase effect. It can manifest itself in the oscillations of conductance as a function of the intensity and frequency of the illumination. The theory of the effect is elaborated for mesoscopic rings in both ballistic and diffusive regimes.
The phase of Aharonov-Bohm oscillations in mesoscopic metal rings in the presence of a magnetic field can be modulated by application of a DC-bias current I_DC. We address the question of how a variation of I_DC and hence of the microscopic phases of the electronic wave functions results in the macroscopic phase of the conductance oscillations. Whereas the first one can be varied continuously the latter has to be quantized for a ring in two-wire configuration by virtue of the Onsager symmetry relations. We observe a correlation between a phase flip by +/- pi and the amplitude of the oscillatio…
Spin accumulation generated by the anomalous Hall effects (AHE) in mesoscopic ferromagnetic Ni81Fe19 (permalloy or Py) films is detected electrically by a nonlocal method. The reciprocal phenomenon, inverse spin Hall effects (ISHE), can also be generated and detected all-electrically in the same structure. For accurate quantitative analysis, a series of nonlocal AHE/ISHE structures and supplementary structures are fabricated on each sample substrate to account for statistical variations and to accurately determine all essential physical parameters in-situ. By exploring Py thicknesses of 4 nm, …
By solving the Rashba model of mesoscopic rings, we give analytically the ground-state properties of the ring, including the spin polarization, the persistent charge and spin currents (PCC and PSC). These ground-state properties can be given based on four kinds of electron numbers in rings. The effect of the self-inductance of the ring leads to the self-sustained magnetic flux (SSMF) and the self-sustained PCC and PSC, which break spontaneously time-reversal symmetry to form orbital magnetic phase (OMP). To tune the spin-orbit coupling strength or electron number of the ring can induce the pha…
The magnetization of a system of many mesoscopic rings under non-equilibrium conditions is considered. The corresponding disorder-averaged current in a ring is shown to be a sum of the `thermodynamic' and `kinetic' contributions both resulting from the electron-electron interaction. The thermodynamic part can be expressed through the diagonal matrix elements of the current operator in the basis of exact many-body eigenstates and is a generalization of the equilibrium persistent current. The novel kinetic part is present only out of equilibrium and is governed by the off-diagonal matrix element…
We propose an all-electrical nanoscopic structure where {\em pure} spin current is induced in the transverse voltage probes attached to {\em quantum-coherent} one-dimensional ring when conventional unpolarized charge current is injected through its longitudinal leads. Tuning of the Rashba spin-orbit coupling in semiconductor heterostructure hosting the ring generates quasi-periodic oscillations of the predicted spin Hall current due to {\em spin-sensitive quantum-interference effects} caused by the difference in Aharonov-Casher phase acquired by opposite spins states traveling clockwise and co…
We study a mesoscopic ring with an in-line quantum dot threaded by an Aharonov-Bohm flux. Zero-point fluctuations of the electromagnetic environment capacitively coupled to the ring, with $ω^s$ spectral density, can suppress tunneling through the dot, resulting in a quantum phase transition from an unpolarized to a polarized phase. We show that robust signatures of such a transition can be found in the response of the persistent current in the ring to the external flux as well as to the bias between the dot and the arm. Particular attention is paid to the experimentally relevant cases of ohmic…
We study the spin-dependent geometric phase effect in mesoscopic rings of charge-density-wave(CDW) materials. When electron spin is explicitly taken into account, we show that the spin-dependent Aharonov-Casher phase can have a pronounced frustration effects on such CDW materials with appropriate electron filling. We show that this frustration has observable consequences for transport experiment. We identify a phase transition from a Peierls insulator to metal, which is induced by spin-dependent phase interference effects. Mesoscopic CDW materials and spin-dependent geometric phase effects, an…
Spin states and persistent currents are investigated theoretically in a mesoscopic ring with an embedded magnetic ion under a uniform magnetic field including the spin-orbit interactions. The magnetic impurity acts as a spin-dependent $δ$-potential for electrons and results in gaps in the energy spectrum, consequently suppresses the oscillation of the persistent currents. The competition between the Zeeman splittings and the $s$-$d$ exchange interaction leads to a transition of the electron ground state in the ring. The interplay between the periodic potential induced by the Rashba and Dressel…
Based on the finite $U$ slave boson method, we have investigated the effect of Rashba spin-orbit(SO) coupling on the persistent charge and spin currents in mesoscopic ring with an Anderson impurity. It is shown that the Kondo effect will decrease the magnitude of the persistent charge and spin currents in this side-coupled Anderson impurity case. In the presence of SO coupling, the persistent currents change drastically and oscillate with the strength of SO coupling. The SO coupling will suppress the Kondo effect and restore the abrupt jumps of the persistent currents. It is also found that a …
We present a detailed study of persistent current and low-field magnetic susceptibility in single isolated normal metal mesoscopic rings and cylinders in the tight-binding model with higher order hopping integral in the Hamiltonian. Our exact calculations show that order of magnitude enhancement of persistent current takes place even in presence of disorder if we include higher order hopping integral in the Hamiltonian. In strictly one-channel mesoscopic rings the sign of the low-field currents can be predicted exactly even in presence of impurity. We observe that perfect rings with both odd a…
Electronic transport in a one-dimensional mesoscopic ring threaded by a magnetic flux is studied in presence of Rashba and Dresselhaus spin-orbit interactions. A completely analytical technique within a tight-binding formalism unveils the spin-split bands in presence of the spin-orbit interactions and leads to a method of determining the strength of the Dresselhaus interaction. In addition to this, the persistent currents for ordered and disordered rings have been investigated numerically. It is observed that, the presence of the spin-orbit interaction, in general, leads to an enhanced amplitu…
We re-examine the effect of electron-electron interactions on the persistent current in mesoscopic metal rings threaded by an Aharonov-Bohm flux. The exchange contribution to the current is shown to be determined by the weak localization correction to the polarization. We explicitly calculate the contribution from exchange interactions with momentum transfers smaller than the inverse elastic mean free path to the average current, and find that it has the same order of magnitude as the {\it{canonical}} current without interactions. \\
The present work proposes an idea to remove the long standing controversy between the calculated and measured current amplitudes carried by a small conducting ring upon the application of an Aharonov-Bohm (AB) flux $ϕ$. Within a mean field Hartree-Fock (HF) approximation we numerically calculate persistent current, Drude weight, low-field magnetic susceptibility and related issues. Our analysis may be inspiring for studying magnetic response in nano-scale loop geometries.
A time-dependent electric field gives rise to a stationary non-equilibrium current I^{(2)} around a mesoscopic metal ring threaded by a magnetic flux. We show that this current, which is proportional to the intensity of the field, is closely related to the exchange part of the interaction contribution to the equilibrium persistent current, and that the corresponding non-linear conductivity directly measures the weak localization correction to the polarization. We explicitly calculate the disorder average of I^{(2)} in the diffusive regime as function of the frequency of the electric field and …
We have studied the current magnification effect in a multi-channel open mesoscopic ring. We show that the current magnification effect is robust even in the presence of several propagating modes inspite of mode mixing and cancellation effects. The magnitude of circulating currents in the multi-channel regime can be much larger than that in a single channel case. Impurities can enhance or degrade the current magnification effect depending sensitively on the system parameters. Circulating currents are mostly associated with Fano resonances in the total transport current. We further show that sy…
We report measurements of the amplitude of the Aharonov-Bohm oscillations in a mesoscopic diffusive gold ring as a function of the DC bias voltage V. The amplitude of the h/e oscillations increases with V once the Thouless energy Ec and thermal energy are exceeded, and decreases at higher values of V. The increase of the amplitude is interpreted in terms of a superposition of the statistically independent contributions of eV/Ec energy intervals, whereas its decrease at high V could be attributed to enhanced inelastic scattering processes.
In the present review we make a comprehensive analysis of our understanding on electron transport in mesoscopic single-channel rings and multi-channel cylinders within a tight-binding framework. A spectacular mesoscopic phenomenon where a non-decaying current circulates in a small conducting loop is observed upon the application of an Aharonov-Bohm flux $ϕ$. To understand its behavior one has to focus attention on the interplay of quantum phase coherence, electron-electron correlation and disorder. This is a highly challenging problem and here we address it for some simple loop geometries with…
Kinetic theory of nonlinear current response to an external field is developed for mesoscopic normal metal rings threaded by a magnetic flux. General expressions for direct current (DC) are derived for a non-equilibrium regime. These expressions describe simultaneously a contribution to DC made by a non-equilibrium (external) field, as well as the contribution caused by interaction with intrinsic fields. Contributions of electron-electron and electron-phonon interactions to the direct current in a non-equilibrium systems are studied. The kinetic equation for electrons in a disordered metal rin…
We study the current magnification effect in presence of exchange scattering of electron from a magnetic impurity placed in one arm of an open mesoscopic ring. The exchange interaction causes entanglement of electron spin and impurity spin. Earlier studies have shown that such an entanglement causes reduction or loss of interference in the Aharonov-Bohm oscillations leading to decoherence. We find however, that this entanglement, in contradiction to the naive expectation of a reduction of current magnification, leads to enhancement as well as suppression of the effect. We also observe addition…
The presence of spin-orbit coupling affects the spontaneously flowing persistent currents in mesoscopic conducting rings. Here we analyze their dependence on magnetic flux with emphasis on identifying possibilities to prove the presence and extract the strength of Rashba spin splitting in low-dimensional systems. Effects of disorder and mixing between quasi-onedimensional ring subbands are considered. The spin-orbit coupling strength can be inferred from the values of flux where sign changes occur in the persistent charge current. As an important consequence of the presence of spin splitting, …
We present a detailed analysis of the Aharonov-Bohm interference oscillations manifested through transmission of an electron in a mesoscopic ring with a magnetic impurity atom inserted in one of its arms. The electron interacts with the impurity through the exchange interaction leading to exchange spin-flip scattering. Transmission in the spin-flipped and spin-unflipped channels are explicitly calculated. We show that the spin-flipper acts as a dephasor in spite of absence of any inelastic scattering. The spin-conductance (related to spin-polarized transmission coefficient) is asymmetric in th…
In normal mesoscopic metals of a ring topology persistent currents can be induced by threading the center of the ring with a magnetic flux. This phenomenon is an example of the famous Aharonov-Bohm effect. In the paper we study the current {\it vs} the external constant magnetic flux characteristics of the system driven by both the classical and the quantum thermal fluctuations. The problem is formulated in terms of Langevin equations in classical and quantum Smoluchowski regimes. We analyze the impact of the quantum thermal fluctuations on the current-flux characteristics. We demonstrate that…
We investigate theoretically electron spin states in one dimensional (1D) and two dimensional (2D) hard-wall mesoscopic rings in the presence of both the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI) in a perpendicular magnetic field. The Hamiltonian of the RSOI alone is mathematically equivalent to that of the DSOI alone using an SU(2) spin rotation transformation. Our theoretical results show that the interplay between the RSOI and DSOI results in an effective periodic potential, which consequently leads to gaps in the energy spectrum. This periodic p…
The time reversal Aharonov-Casher (AC) interference effect in the mesoscopic ring structures, based on the experiment in Phys. Rev. Lett. \textbf{97}, 196803 (2006), is studied theoretically. The transmission curves are calculated from the scattering matrix formalism, and the time reversal AC interference frequency is singled out from the Fourier spectra in numerical simulations. This frequency is in good agreement with analytical result. It is also shown that in the absent of magnetic field, the Altshuler-Aronov-Spivak type (time reversal) AC interference retains under the influence of strong…
We study the amplitude of mesoscopic Aharonov-Bohm oscillations in quasi-one-dimensional (Q1D) diffusive rings. We consider first the low-temperature limit of a fully coherent sample. The variance of oscillation harmonics is calculated as a function of the length of the leads attaching the ring to reservoirs. We further analyze the regime of relatively high temperatures, when the dephasing due to electron-electron interaction suppresses substantially the oscillations. We show that the dephasing length L_phi^AB governing the damping factor exp(-2pi R /L_phi^AB) of the oscillations is parametric…
We investigate the persistent current in a hybrid Aharonov-Bohm ring - quantum dot system coupled to a reservoir which provides spin fluctuations. It is shown that the spin exchange interaction between the quantum dot and the reservoir induces dephasing in the absence of direct charge transfer. We demonstrate an anomalous nature of this spin-fluctuation induced dephasing which tends to enhance the persistent current. We explain our result in terms of the separation of the spin from the charge degree of freedom. The nature of the spin fluctuation induced dephasing is analyzed in detail.
The effect of the Coulomb-interaction on persistent currents in disordered mesoscopic metal rings threaded by a magnetic flux $ϕ$ is studied numerically. We use the simplest form of ``self-consistent'' Hartree theory, where the spatial variations of the self-consistent Hartree potential are ignored. In this approximation the self-consistent Hartree energies are simply obtained by diagonalizing the non-interacting system via the Lanczos method and then calculating the (disorder-dependent) particle number on the ring self-consistently. In the diffusive regime we find that the variance of the tot…
The behavior of the dc-component of the current along a quantum loop of tight-binding electrons threaded by a magnetic flux that varies linearly in time Phi_M(t)= Phi t is investigated. We analize the electron transport in different kinds of one-dimensional structures bended into a ring geometry: a clean one-dimensional metal, a chain with a two-band structure and a disordered chain. Inelastic scattering events are introduced through the coupling to a particle reservoir. We use a theoretical treatment based in Baym-Kadanoff-Keldysh non-equilibrium Green functions, which allows us to solve the …
In the present work the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designin…
Geometric phases of scattering states in a ring geometry are studied based on a variant of the adiabatic theorem. Three time scales, i.e., the adiabatic period, the system time and the dwell time, associated with adiabatic scattering in a ring geometry plays a crucial role in determining geometric phases, in contrast to only two time scales, i.e., the adiabatic period and the dwell time, in an open system. We derive a formula connecting the gauge invariant geometric phases acquired by time-reversed scattering states and the circulating (pumping) current. A numerical calculation shows that the …
We investigate the properties of persistent charge current driven by magnetic flux in a quasi-periodic mesoscopic Fibonacci ring with Rashba and Dresselhaus spin-orbit interactions. Within a tight-binding framework we work out individual state currents together with net current based on second-quantized approach. A significant enhancement of current is observed in presence of spin-orbit coupling and sometimes it becomes orders of magnitude higher compared to the spin-orbit interaction free Fibonacci ring. We also establish a scaling relation of persistent current with ring size, associated wit…
We study electron decoherence by measuring the temperature dependence of Aharonov-Bohm (AB) oscillations in quasi-1D rings, etched in a high-mobility GaAs/GaAlAs heterostructure. The oscillation amplitude is influenced both by phase-breaking and by thermal averaging. Thermal averaging is important when the temperature approaches the energy scale, on which the AB oscillations shift their phase. For the phase-breaking, it is demonstrated that the damping of the oscillation amplitude is proportional to the length of the interfering paths. For temperatures $T$ from 0.3 to 4 $\rm K$ we find the pha…
