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Search Results: 1 - 10 of 809083 matches for " Erik P. A. M. Bakkers "
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Ultrafast dephasing of light in strongly scattering GaP nanowires
Martina Abb,Erik P. A. M. Bakkers,Otto L. Muskens
Physics , 2011, DOI: 10.1103/PhysRevLett.106.143902
Abstract: We demonstrate ultrafast dephasing in the random transport of light through a layer consisting of strongly scattering GaP nanowires. Dephasing results in a nonlinear intensity modulation of individual pseudomodes which is 100 times larger than that of bulk GaP. Different contributions to the nonlinear response are separated using total transmission, white-light frequency correlation, and statistical pseudomode analysis. A dephasing time of $1.2\pm 0.2$~ps is found. Quantitative agreement is obtained with numerical model calculations which include photoinduced absorption and deformation of individual scatterers. Nonlinear dephasing of photonic eigenmodes opens up avenues for ultrafast control of random lasers, nanophotonic switches, and photon localization.
Andreev reflection versus Coulomb blockade in hybrid semiconductor nanowire devices
Yong-Joo Doh,Silvano De Franceschi,Erik P. A. M. Bakkers,Leo P. Kouwenhoven
Physics , 2008, DOI: 10.1021/nl801454k
Abstract: Semiconductor nanowires provide promising low-dimensional systems for the study of quantum transport phenomena in combination with superconductivity. Here we investigate the competition between the Coulomb blockade effect, Andreev reflection, and quantum interference, in InAs and InP nanowires connected to aluminum-based superconducting electrodes. We compare three limiting cases depending on the tunnel coupling strength and the characteristic Coulomb interaction energy. For weak coupling and large charging energy, negative differential conductance is observed as a direct consequence of the BCS density of states in the leads. For intermediate coupling and charging energy smaller than the superconducting gap, the current-voltage characteristic is dominated by Andreev reflection and Coulomb blockade produces an effect only near zero bias. For almost ideal contact transparencies and negligible charging energy, we observe universal conductance fluctuations whose amplitude is enhanced due to Andreev reflection at the contacts.
Mapping the directional emission of quasi-two-dimensional photonic crystals of semiconductor nanowires using Fourier microscopy
Yannik Fontana,Grzegorz Grzela,Erik P. A. M. Bakkers,Jaime Gómez Rivas
Physics , 2013, DOI: 10.1103/PhysRevB.86.245303
Abstract: Controlling the dispersion and directionality of the emission of nanosources is one of the major goals of nanophotonics research. This control will allow the development of highly efficient nanosources even at the single photon level. One of the ways to achieve this goal is to couple the emission to Bloch modes of periodic structures. Here, we present the first measurements of the directional emission from nanowire photonic crystals by using Fourier microscopy. With this technique we efficiently collect and resolve the directional emission of nanowires within the numerical aperture of a microscope objective. The light emission from a heterostructure grown in each nanowire is governed by the photonic (Bloch) modes of the photonic crystal. We also demonstrate that the directionality of the emission can be easily controlled by infiltrating the photonic crystal with a high refractive index liquid. This work opens new possibilities for the control of the emission of sources in nanowires.
Imaging Electrical Conduction through InAs Nanowires
Ania C. Bleszynski,Floris A. Zwanenburg,Robert M. Westervelt,Aaroud L. Roest,Erik P. A. M. Bakkers,Leo P. Kouwenhoven
Physics , 2006,
Abstract: We show how a scanning probe microscope (SPM) can be used to image electron flow through InAs nanowires, elucidating the physics of nanowire devices on a local scale. A charged SPM tip is used as a movable gate. Images of nanowire conductance vs. tip position spatially map the conductance of InAs nanowires at liquid He temperatures. Plots of conductance vs. back gate voltage without the tip present show complex patterns of Coulomb-blockade peaks. Images of nanowire conductance identify multiple quantum dots located along the nanowire - each dot is surrounded by a series of concentric rings corresponding to Coulomb blockade peaks. An image locates the dots and provides information about their size. The rings around individual dots interfere with each other like Coulomb blockade peaks of multiple quantum dots in series. In this way, the SPM tip can probe complex multi-dot systems by tuning the charge state of individual dots. The nanowires were grown from metal catalyst particles and have diameters ~ 80 nm and lengths 2 to 3 um.
Diameter-dependent conductance of InAs nanowires
Marc Scheffler,Stevan Nadj-Perge,Leo P. Kouwenhoven,Magnus T. Borgstr?m,Erik P. A. M. Bakkers
Physics , 2009, DOI: 10.1063/1.3270259
Abstract: Electrical conductance through InAs nanowires is relevant for electronic applications as well as for fundamental quantum experiments. Here we employ nominally undoped, slightly tapered InAs nanowires to study the diameter dependence of their conductance. Contacting multiple sections of each wire, we can study the diameter dependence within individual wires without the need to compare different nanowire batches. At room temperature we find a diameter-independent conductivity for diameters larger than 40 nm, indicative of three-dimensional diffusive transport. For smaller diameters, the resistance increases considerably, in coincidence with a strong suppression of the mobility. From an analysis of the effective charge carrier density, we find indications for a surface accumulation layer.
Supercurrent reversal in quantum dots
Jorden A. van Dam,Yuli V. Nazarov,Erik P. A. M. Bakkers,Silvano De Franceschi,Leo P. Kouwenhoven
Physics , 2006, DOI: 10.1038/nature05018
Abstract: When two superconductors become electrically connected by a weak link a zero-resistance supercurrent can flow. This supercurrent is carried by Cooper pairs of electrons with a combined charge of twice the elementary charge, e. The 2e charge quantum is clearly visible in the height of Shapiro steps in Josephson junctions under microwave irradiation and in the magnetic flux periodicity of h/2e in superconducting quantum interference devices. Several different materials have been used to weakly couple superconductors, such as tunnel barriers, normal metals, or semiconductors. Here, we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Due to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, i.e. in a normal or a pi-junction, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions.
Quantum Interference Effects in InAs Semiconductor Nanowires
Yong-Joo Doh,Aarnoud L. Roest,Erik P. A. M. Bakkers,Silvano De Franceschi,Leo P. Kouwenhoven
Physics , 2007,
Abstract: We report quantum interference effects in InAs semiconductor nanowires strongly coupled to superconducting electrodes. In the normal state, universal conductance fluctuations are investigated as a function of magnetic field, temperature, bias and gate voltage. The results are found to be in good agreement with theoretical predictions for weakly disordered one-dimensional conductors. In the superconducting state, the fluctuation amplitude is enhanced by a factor up to ~ 1.6, which is attributed to a doubling of charge transport via Andreev reflection. At a temperature of 4.2 K, well above the Thouless temperature, conductance fluctuations are almost entirely suppressed, and the nanowire conductance exhibits anomalous quantization in steps of e^{2}/h.
Avalanche amplification of a single exciton in a semiconductor nanowire
Gabriele Bulgarini,Michael E. Reimer,Mo?ra Hocevar,Erik P. A. M. Bakkers,Leo P. Kouwenhoven,Val Zwiller
Physics , 2012, DOI: 10.1038/nphoton.2012.110
Abstract: Interfacing single photons and electrons is a crucial ingredient for sharing quantum information between remote solid-state qubits. Semiconductor nanowires offer the unique possibility to combine optical quantum dots with avalanche photodiodes, thus enabling the conversion of an incoming single photon into a macroscopic current for efficient electrical detection. Currently, millions of excitation events are required to perform electrical read-out of an exciton qubit state. Here we demonstrate multiplication of carriers from only a single exciton generated in a quantum dot after tunneling into a nanowire avalanche photodiode. Due to the large amplification of both electrons and holes (> 10^4), we reduce by four orders of magnitude the number of excitation events required to electrically detect a single exciton generated in a quantum dot. This work represents a significant step towards single-shot electrical read-out and offers a new functionality for on-chip quantum information circuits.
Giant optical birefringence of semiconductor nanowire metamaterials
Otto L. Muskens,Maarten H. M. van Weert,Magnus T. Borgstrom,Erik P. A. M. Bakkers,Jaime Gomez Rivas
Physics , 2006, DOI: 10.1063/1.2402906
Abstract: Semiconductor nanowires exhibit large polarization anisotropy for the absorption and emission of light, making them ideal building blocks for novel photonic metamaterials. Here, we demonstrate that a high density of aligned nanowires exhibits giant optical birefringence, a collective phenomenon observable uniquely for collections of wires. The nanowire material was grown on gallium phosphide (GaP) (111) in the form of vertically standing GaP nanowires. We obtain the largest optical birefringence to date, with a difference between the in-plane and out-of-plane refractive indices of 0.80 and a relative birefringence of 43%. These values exceed by a factor of 75 the natural birefringence of quartz and a by more than a factor of two the highest values reported so far in other artificial materials. By exploiting the specific crystallographic growth directions of the nanowires on the substrate, we further demonstrate full control over the orientation of the optical birefringence effect in the metamaterial.
Tunable Supercurrent Through Semiconductor Nanowires
Yong-Joo Doh,Jorden A. van Dam,Aarnoud L. Roest,Erik P. A. M. Bakkers,Leo P. Kouwenhoven,Silvano De Franceschi
Physics , 2005, DOI: 10.1126/science.1113523
Abstract: Nanoscale superconductor-semiconductor hybrid devices are assembled from InAs semiconductor nanowires individually contacted by aluminum-based superconductor electrodes. Below 1 K, the high transparency of the contacts gives rise to proximity-induced superconductivity. The nanowires form superconducting weak links operating as mesoscopic Josephson junctions with electrically tunable coupling. The supercurrent can be switched on/off by a gate voltage acting on the electron density in the nanowire. A variation in gate voltage induces universal fluctuations in the normal-state conductance which are clearly correlated to critical current fluctuations. The ac Josephson effect gives rise to Shapiro steps in the voltage-current characteristic under microwave irradiation.
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