[Show abstract][Hide abstract] ABSTRACT: Studies of non-equilibrium current fluctuations enable assessing correlations involved in quantum transport through nanoscale conductors. They provide additional information to the mean current on charge statistics and the presence of coherence, dissipation, disorder, or entanglement. Shot noise, being a temporal integral of the current autocorrelation function, reveals dynamical information. In particular, it detects presence of non-Markovian dynamics, i.e., memory, within open systems, which has been subject of many current theoretical studies. We report on low-temperature shot noise measurements of electronic transport through InAs quantum dots in the Fermi-edge singularity regime and show that it exhibits strong memory effects caused by quantum correlations between the dot and fermionic reservoirs. Our work, apart from addressing noise in archetypical strongly correlated system of prime interest, discloses generic quantum dynamical mechanism occurring at interacting resonant Fermi edges.
[Show abstract][Hide abstract] ABSTRACT: The shot noise of a single parameter quantized charge pump is studied. The pumped current can be varied using a control gate. Quantized current plateaus I = ne fp with fp the pumping frequency and e the electron charge are observed. The shot noise is minimal for each current plateau and maximal in between. Interestingly the first expected quantized current plateau at n = 1 is missing for certain control gate voltages. We use the measured shot noise to extract the probabilities for pumping none, one or two electrons at the position of the missing step. These probabilities can be used to characterize the dynamics of the non-adiabatic pumping process.
[Show abstract][Hide abstract] ABSTRACT: We study the noise properties of a gate controlled single electron pump at a driving frequency fp=400 MHz. We observe a significant reduction of the noise power on the current plateaus. This is a strong indication for true quantized charge pumping. We furthermore observe a small level of low frequency fluctuations which indicates a good frequency stability of the pump.
[Show abstract][Hide abstract] ABSTRACT: Measuring shot noise and electron counting are both methods for accessing information about the dynamics of electronic transport through a system of interest. Here we apply these tools to examine electronic transport through coupled quantum dot systems. In the first part of the paper we show temperature dependent shot noise measurements for a strongly coupled double-quantum-dot system. We observe super-Poissonian shot noise as expected for coherent inter-dot coupling and asymmetric lead tunnelling rates. In the second part we apply direct electron counting to examine a weakly coupled triple-dot system. A quantum point contact placed near the triple dot allows us to monitor electron hops between the dots and the leads. This allows us to, e.g., individually characterize different tunnelling rates relevant in the system.
[Show abstract][Hide abstract] ABSTRACT: We present noise measurements of self-assembled InAs quantum dots at
high magnetic field. In comparison to I-V characteristics at zero
magnetic field, we notice a strong current overshoot that is due to a
Fermi-edge singularity. We observe an enhanced suppression in the shot
noise power simultaneous to the current overshoot that is attributed to
the electron-electron interaction at the Fermi-edge singularity.
[Show abstract][Hide abstract] ABSTRACT: We apply an external bias voltage to vertically coupled self-assembled InAs quantum dots. We observe pronounced peaks in the I-V characteristic due to resonant transport through a stack of coupled quantum dots. We investigate the noise properties at these peaks and we find an astonishing enhancement of the shot noise at low temperatures with a distinct double-peak structure.
[Show abstract][Hide abstract] ABSTRACT: Quantum dots are quasi zero-dimensional systems in semiconductors and they represent promising candidates for future applications in quantum information processing. Their electronic properties are influenced by interaction and correlation effects, which are not clearly revealed in simple transport experiments. Shot noise measurements allow to investigate such interaction and correlation effects in detail and can lead to astonishing results. We studied shot noise in electrical transport through single and coupled quantum dots and found for single quantum dots suppressed shot noise in respect to Poissonian noise as, e.g. is assumed in the recently developed technique of spin noise spectroscopy. Whereas the suppressed shot noise in single dots weakly coupled to the leads can be explained in simple models using emitter and collector tunnelling rates, for strong coupling an additional suppression is observed where interaction effects have to be taken into account. In recent measurements on coupled quantum dots an astonishing enhancement of shot noise, i.e. super-Poissonian noise, was found being in stark contrast to the suppression of shot noise found for single quantum dots. This enhancement of shot noise cannot be understood in a single-particle picture neglecting interactions. An enhanced shot noise could result from a coupling to other stacks of coupled quantum dots or from interaction and coherence effects within one stack.
[Show abstract][Hide abstract] ABSTRACT: We have investigated the noise properties of the tunneling current through vertically coupled self-assembled InAs quantum dots. We observe super-Poissonian shot noise at low temperatures. For increased temperature this effect is suppressed. The super-Poissonian noise is explained by capacitive coupling between different stacks of quantum dots.
[Show abstract][Hide abstract] ABSTRACT: We study the Fermi-edge singularity appearing in the current-voltage characteristics for resonant tunneling through a localized level at finite temperature. An explicit expression for the current at low temperature and near the threshold for the tunneling process is presented which allows to coalesce data taken at different temperatures to a single curve. Based on this scaling function for the current we analyze experimental data from a GaAs-AlAs-GaAs tunneling device with embedded InAs quantum dots obtained at low temperatures in high magnetic fields.
[Show abstract][Hide abstract] ABSTRACT: The noise properties of self-assembled InAs quantum dots were measured at high magnetic fields and for varying temperatures. We see a high current overshoot which we ascribe to a Coulomb interaction effect between a localized electron on the dot and the electrons at the Fermi edge of the emitter, a so-called Fermi edge singularity (FES) effect. We measure the shot noise at this point in detail for different temperatures.
Physica E Low-dimensional Systems and Nanostructures 01/2006; 34:508-510. · 1.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the noise properties of a zero-dimensional InAs quantum dot (QD) embedded in a GaAs-AlAs-GaAs tunneling structure. We observe an approximately linear dependence of the Fano factor and the current as function of bias voltage. Both effects can be linked to the scanning of the 3-dimensional emitter density of states by the QD. At the current step the shape of the Fano factor is mainly determined by the Fermi function of the emitter electrons. The observed voltage and temperature dependence is compared to the results of a master equation approach.