The existence of fractional charges carrying the current is experimentally demonstrated. Using a 2-D electron system in high perpendicular magnetic field we measure the shot noise associated with tunneling in the fractional quantum Hall regime at Landau level filling factor 1/3. The noise gives a direct determination of the quasiparticle charge, which is found to be e * = e/3 as predicted by Laughlin. The existence of e/3 Laughlin quasiparticles is unambiguously confirmed by the shot noise to Johnson-Nyquist noise cross-over found for temperature Θ = e * V ds /2kB. Can fractional charges carry the current in a conductor? Up to now, there was no evidence of such phenomenon. Usual metals are known to form Fermi liquids with quasiparticles of charge e. Low dimensional systems are believed to offer a richer spectrum of excitations. Indeed, fractional charges have been predicted for commensurate charge density waves in one dimensional systems [1], and for two-dimensional electron systems (2DES) [2] in high perpendicular magnetic field when the fractional quantum Hall effect occurs [3]. In this letter, we report experimental evidence of charges e/3 carrying the current. The observation is done in the Fractional Quantum Hall (FQH) regime at Landau level filling factor ν = 1/3.2-D electrons in high magnetic field give rise to degenerate Landau Levels (LL) with one state per flux quantum φ 0 = h/e in the plane. For integer LL filling factor ν = n s /n φ , the cyclotron or the enhanced Zeeman gap gives rise to the integer quantum Hall effect [4] IQHE (n s and n φ = eB/h are the electron and quantum flux density) [5]. The simplest elementary excitation is an electron removed from the highest occupied LL, leaving a hole having the size of a flux quantum and a unit charge e. At fractional filling factor ν = 1/q, q odd, a gap ∆ ≃ e 2 /ǫl c also opens resulting from the interactions [6] (l c = (h/eB) 1/2 ). This is the FQH effect. Laughlin has proposed [2] that an elementary excitation can be realized by introducing a flux quantum φ 0 in the collective wavefunction. As there is one electron for q flux quanta, the so-called Laughlin quasiparticle has fractional charge e * = e/q. Extensions of the Laughlin approach to higher rational fractions ν = p/q[7] explain many bulk transport properties but so far no direct experimental evidence for the bulk Laughlin quasiparticles have been found. The quasiparticles in the bulk have been mostly probed using thermal activation. The prefactor of the activated conductivity has shown a striking [8] relation to the quasiparticle charge but is not fully understood [9]. Comparison of the chemical potential jump at fractional ν obtained from capacitance measurements with the activation energy may also determine e *

We report on the electron analog of the single-photon gun. On-demand single-electron injection in a quantum conductor was obtained using a quantum dot connected to the conductor via a tunnel barrier. Electron emission was triggered by the application of a potential step that compensated for the dot-charging energy. Depending on the barrier transparency, the quantum emission time ranged from 0.1 to 10 nanoseconds. The single-electron source should prove useful for the use of quantum bits in ballistic conductors. Additionally, periodic sequences of single-electron emission and absorption generate a quantized alternating current.

What is the complex impedance of a fully coherent quantum resistance-capacitance (RC) circuit at gigahertz frequencies in which a resistor and a capacitor are connected in series? While Kirchhoff's laws predict addition of capacitor and resistor impedances, we report on observation of a different behavior. The resistance, here associated with charge relaxation, differs from the usual transport resistance given by the Landauer formula. In particular, for a single-mode conductor, the charge-relaxation resistance is half the resistance quantum, regardless of the transmission of the mode. The new mesoscopic effect reported here is relevant for the dynamical regime of all quantum devices.

The existence of the magnetic-field-induced liquid-to-solid phase transition in an extreme quantumlimit 2D electron plasma is established for electrons at a high-quality GaAs/GaAlAs heterojunction by detection of a gapless magnetophonon excitation branch with radio-frequency spectroscopy. The phase diagram, determined for Wigner-Seitz to Bohr radius ratio 1.6 <») limit. PACS numbers: 73.40.Kp, 64.70.-p, 73.20.MfA zero-temperature electron plasma confined to a plane shows unusually varied physical properties as a function of density ris and perpendicular magnetic field H, In zero field and high density, the zero-point energy arising from the Pauli exclusion principle dominates, resulting in a liquid state with Fermi energy Ef^^h^/ma^, which corresponds to the energy of confinement in the Wigner-Seitz radius, a, defined by Ka^^X/ris. As the density is reduced the Coulomb interaction Vc^e^lea in the medium of dielectric constant e gains in importance, ultimately ordering the electrons into a crystal. Wigner * predicted this quantum phase transition long ago, but it has never been seen for want of a suitable physical system.In a magnetic field, however, each single-particle state is already confined by the Lorentz force to an area --(po/H'^lKli occupied by a flux quantum ^o^hc/e Un'^ihc/eH)^^^ is the zero-point cyclotron radius] and takes on discrete energy values (n+ j)hcoc where h(Oc -h^/ml^ -heH/mc is the cyclotron energy. Each of these Landau cyclotron oscillators has an average share of v=2(////a)^ electrons. Increasing the field decreases this filling factor v, successive Landau levels empty, and, in the presence of moderate disorder, one observes the integrally quantized Hall resistance.^ When V < 1 there is spatial freedom for all the electrons for the same zero-point energy. This greatly favors Coulomb-induced correlation. The many-body ground state is a correlated liquid giving rise to the fractional quantum Hall effect^ until, below a critical filling factor estimated between y and j,^ a new ground state with long-range crystallike correlation is expected. To date, this transition, too, has eluded unambiguous observation.The present experiment gives positive evidence of this magnetically induced Wigner solid. Advances in the technology of modulation-dopedGaAs/GaAlAs heterojunctions have made available very high-quality 2D quantum electron systems. Some time ago,^ it was already suggested that the abnormal behavior observed in the dc transport for v < j could be a result of a magnetically induced Wigner solid. But to be affirmative required a much more specific type of experiment. Our experiment tests for a defining property of a solid-its rigidity to shear. An unbounded charged 2D liquid has only compressional (plasmon) excitations in zero field whose frequency-wave-vector relation is (ol^lKe^risqlem. A perpendicular magnetic field i...

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We demonstrate by Raman scattering that the spin splitting in the conduction band of a GaAs/ Ga, "Al As asymmetric quantum well is anisotropic and inequivalent along the [11]and [11]directions. This agrees with the results of tight-binding calculations. The Rashba contribution to the spin orientation induced by the asymmetric potential is of comparable magnitude to the bulk inversion-asymmetry-induced term. Hence, we obtain quantitative information on the origin of the spin orientation at the GaAsiGa& Al As interface.

The 2D quantum system of electrons at a GaAs/GaAlAs heterojunction in high magnetic field at low temperature is shown to exhibit conduction typical of pinned charge-density waves. Crossover from Ohmic conduction occurs on the same boundary at which radio-frequency resonances signal the onset of transverse elasticity. A further small non-Ohmic region is isolated from the main area by a v-j quantum-Hall-effect phase. The relationship found between the threshold conduction field and the resonance frequency is well accounted for by a model of a pinned electron crystal.

We report measurements of the low temperature magnetic response of a line of 16 GaAs/GaAlAs connected mesoscopic rings whose total length is much larger than l φ . Using an on-chip micro-squid technology, we have measured a periodic response, with period h/e, corresponding to persistent currents in the rings of typical amplitude 0.40 ± 0.08 nA per ring. Direct comparison with measurements on the same rings but isolated is presented.PACS numbers: 73.20.Dx, 72.20.My In a mesoscopic metallic sample, quantum coherence of the electronic wave functions can affect drastically the equilibrium properties of the system. In the case of a metallic ring in a magnetic field, the new boundary conditions imposed by the magnetic flux [1] lead the wave functions and therefore all the thermodynamic properties of the system to be periodic with flux, with periodicity Φ 0 = h/e, the flux quantum. One of the most striking consequences of this, first pointed out by Büttiker, Imry and Landauer [2] for the 1D case, is that a mesoscopic normal-metal ring pierced by a magnetic flux carries a persistent non-dissipative current: this is a consequence of the periodicity of the free energy F (Φ) with flux, implying the existence of an equilibrium current I(Φ) = −∂F (Φ)/∂Φ. Subsequently, much theoretical effort has been devoted to the description of a realistic 3D disordered ring [3][4][5][6][7]. Both the sign and the amplitude of this current depend on the number of electrons in the ring and on the microscopic disorder configuration: thus this current, like other mesoscopic phenomena such as Aharonov-Bohm conductance oscillations [8], is sample specific. However, the order of magnitude of the current for a single, isolated ring can be characterized by its typical value I typ = I 2 , denoting the average over disorder configurations. It is given [6,7] by I typ = 1.56 I 0 l e /L. In this formula, I 0 = ev F /L where v F is the Fermi velocity and L the perimeter of the ring, and l e is the elastic mean free path: the current varies as the inverse of the diffusion time τ D = L 2 /D where D = v F l e is the diffusion constant. When measuring an ensemble of rings, the typical current per ring decreases as 1/ √ N R , where N R is the number of rings. At finite temperature [6,7,9], mixing of the energy levels reduces the current on the scale of the Thouless energy E c , the energy scale for energy correlations. Further reduction arises when temperature reduces the phase coherence length l φ down to values lower than L.For a long time, persistent currents were believed to be a specific property of isolated systems [2]. However, recent theoretical predictions suggest that persistent currents should exist even in connected rings. Using a semi-classical model in the diffusive limit, ref.[10] calculated persistent currents in various networks of connected rings, showing that the amplitude of the persistent currents should be reduced only weakly as compared to its value in the same network of isolated rings, whereas all the other properties, like temper...