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Search Results: 1 - 10 of 320848 matches for " B. N. Murdin "
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Temperature dependence of the electron spin g factor in GaAs
W. Zawadzki,P. Pfeffer,R. Bratschitsch,Z. Chen,S. T. Cundiff,B. N. Murdin,C. R. Pidgeon
Physics , 2008, DOI: 10.1103/PhysRevB.78.245203
Abstract: The temperature dependence of the electron spin $g$ factor in GaAs is investigated experimentally and theoretically. Experimentally, the $g$ factor was measured using time-resolved Faraday rotation due to Larmor precession of electron spins in the temperature range between 4.5 K and 190 K. The experiment shows an almost linear increase of the $g$ value with the temperature. This result is in good agreement with other measurements based on photoluminescence quantum beats and time-resolved Kerr rotation up to room temperature. The experimental data are described theoretically taking into account a diminishing fundamental energy gap in GaAs due to lattice thermal dilatation and nonparabolicity of the conduction band calculated using a five-level kp model. At higher temperatures electrons populate higher Landau levels and the average $g$ factor is obtained from a summation over many levels. A very good description of the experimental data is obtained indicating that the observed increase of the spin $g$ factor with the temperature is predominantly due to band's nonparabolicity.
Zero-field spin-splitting and spin lifetime in n-InSb/In1-xAlxSb asymmetric quantum well heterostructures
A. M. Gilbertson,M. Fearn,J. H. Jefferson,B. N. Murdin,P. D. Buckle,L. F. Cohen
Physics , 2008, DOI: 10.1103/PhysRevB.77.165335
Abstract: The spin-orbit (SO) coupling parameters for lowest conduction subband due to structural (SIA) and bulk (BIA) inversion asymmetry are calculated for a range of carrier densities in [001]-grown delta-doped n-type InSb/In1-xAlxSb asymmetric quantum wells using the established 8 band k.p formalism [PRB 59,8 R5312 (1999)]. We present calculations for conditions of zero bias at 10 K. It is shown that both the SIA and BIA parameters scale approximately linearly with carrier density, and exhibit a marked dependence on well width when alloy composition is adjusted to allow maximum upper barrier height for a given well width. In contrast to other material systems the BIA contribution to spin splitting is found to be of significant and comparable value to the SIA mechanism in these structures. We calculate the spin lifetime for spins oriented along [11-0] based on D'yakonov-Perel mechanism using both the theory of Averkiev et al. [J. Phys.:Condens. Matter 14 (2002)] and also the rate of precession of spins about the effective magnetic field, taking into account all three SO couplings, showing good agreement.Spin lifeime for this direction is largest in the narrow wells over the range of moderate carrier densities considered, which is attributed to the reduced magnitude of the k-cubic BIA parameter in narrow wells. The inherently large BIA induced SO coupling in these systems is shown to have considerable effect on the spin lifetime, which exhibits significant reduction in the maximum spin lifetime compared to previous studies which consider systems with relatively weak BIA induced SO coupling. The relaxation rate of spins oriented in the [001] direction is dominated by the k-linear SIA and BIA coupling parameters and at least an order of magnitude greater than in the [11-0] direction.
Coherent Control of Rydberg States in Silicon
P. T. Greenland,S. A. Lynch,A. F. G. van der Meer,B. N. Murdin,C. R. Pidgeon,B. Redlich,N. Q. Vinh,G. Aeppli
Physics , 2010, DOI: 10.1038/nature09112
Abstract: We demonstrate coherent control of donor wavefunctions in phosphorous-doped silicon. Our experiments take advantage of a free electron laser to stimulate and observe photon echoes from, and Rabi oscillations between the ground and first excited state of P donors in Si.
Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures
W. Weber,L. E. Golub,S. N. Danilov,J. Karch,C. Reitmaier,B. Wittmann,V. V. Bel'kov,E. L. Ivchenko,Z. D. Kvon,N. Q. Vinh,A. F. G. van der Meer,B. Murdin,S. D. Ganichev
Physics , 2008, DOI: 10.1103/PhysRevB.77.245304
Abstract: Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.
Resonant circular photogalvanic effect in GaN/AlGaN heterojunctions
B. Wittmann,L. E. Golub,S. N. Danilov,J. Karch,C. Reitmaier,Z. D. Kvon,N. Q. Vinh,A. F. G. van der Meer,B. Murdin,S. D. Ganichev
Physics , 2008, DOI: 10.1103/PhysRevB.78.205435
Abstract: The resonant circular photogalvanic effect is observed in wurtzite (0001)-oriented GaN low-dimensional structures excited by infrared radiation. The current is induced by angular momentum transfer of photons to the photoexcited electrons at resonant inter-subband optical transitions in a GaN/AlGaN heterojunction. The signal reverses upon the reversal of the radiation helicity or, at fixed helicity, when the propagation direction of the photons is reversed. Making use of the tunability of the free-electron laser FELIX we demonstrate that the current direction changes by sweeping the photon energy through the intersubband resonance condition, in agreement with theoretical considerations.
Silicon as a model ion trap: time domain measurements of donor Rydberg states
N Q Vinh,P T Greenland,K Litvinenko,B Redlich,A F G van der Meer,S A Lynch,M Warner,A M Stoneham,G Aeppli,D J Paul,C R Pidgeon,B N Murdin
Physics , 2008,
Abstract: One of the great successes of quantum physics is the description of the long-lived Rydberg states of atoms and ions. The Bohr model is equally applicable to donor impurity atoms in semiconductor physics, where the conduction band corresponds to the vacuum, and the loosely bound electron orbiting a singly charged core has a hydrogen-like spectrum according to the usual Bohr-Sommerfeld formula, shifted to the far-infrared due to the small effective mass and high dielectric constant. Manipulation of Rydberg states in free atoms and ions by single and multi-photon processes has been tremendously productive since the development of pulsed visible laser spectroscopy. The analogous manipulations have not been conducted for donor impurities in silicon. Here we use the FELIX pulsed free electron laser to perform time-domain measurements of the Rydberg state dynamics in phosphorus- and arsenic-doped silicon and we have obtained lifetimes consistent with frequency domain linewidths for isotopically purified silicon. This implies that the dominant decoherence mechanism for excited Rydberg states is lifetime broadening, just as for atoms in ion traps. The experiments are important because they represent the first step towards coherent control and manipulation of atomic-like quantum levels in the most common semiconductor and complement magnetic resonance experiments in the literature, which show extraordinarily long spin lattice relaxation times key to many well-known schemes for quantum computing qubits for the same impurities. Our results, taken together with the magnetic resonance data and progress in precise placement of single impurities, suggest that doped silicon, the basis for modern microelectronics, is also a model ion trap.
Circular photogalvanic effect in HgTe/CdHgTe quantum well structures
B. Wittmann,S. N. Danilov,V. V. Bel'kov,S. A. Tarasenko,E. G. Novik,H. Buhmann,C. Brüne,L. W. Molenkamp,Z. D. Kvon,N. N. Mikhailov,S. A. Dvoretsky,N. Q. Vinh,A. F. G. van der Meer,B. Murdin,S. D. Ganichev
Physics , 2010, DOI: 10.1088/0268-1242/25/9/095005
Abstract: We describe the observation of the circular and linear photogalvanic effects in HgTe/CdHgTe quantum wells. The interband absorption of mid-infrared radiation as well as the intrasubband absorption of terahertz (THz) radiation in the QWs structures is shown to cause a dc electric current due to these effects. The photocurrent magnitude and direction varies with the radiation polarization state and crystallographic orientation of the substrate in a simple way that can be understood from a phenomenological theory. The observed dependences of the photocurrent on the radiation wavelength and temperature are discussed.
Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures
S. N. Danilov,B. Wittmann,P. Olbrich,W. Eder,W. Prettl,L. E. Golub,E. V. Beregulin,Z. D. Kvon,N. N. Mikhailov,S. A. Dvoretsky,V. A. Shalygin,N. Q. Vinh,A. F. G. van der Meer,B. Murdin,S. D. Ganichev
Physics , 2008, DOI: 10.1063/1.3056393
Abstract: We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements respectively utilise the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods our device is an easy to handle all-electric approach, which we demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.
Spin-galvanic effect due to optical spin orientation
S. D. Ganichev,Petra Schneider,V. V. Bel'kov,E. L. Ivchenko,S. A. Tarasenko,W. Wegscheider,D. Weiss,D. Schuh,B. N. Murdin,P. J. Phillips,C. R. Pidgeon,D. G. Clarke,M. Merrick,P. Murzyn,E. V. Beregulin,W. Prettl
Physics , 2003,
Abstract: Under oblique incidence of circularly polarized infrared radiation the spin-galvanic effect has been unambiguously observed in (001)-grown $n$-type GaAs quantum well (QW) structures in the absence of any external magnetic field. Resonant inter-subband transitions have been obtained making use of the tunability of the free-electron laser FELIX. It is shown that a helicity dependent photocurrent along one of the $<110>$ axes is predominantly contributed by the spin-galvanic effect while that along the perpendicular in-plane axis is mainly due to the circular photogalvanic effect. This strong non-equivalence of the [110] and [1$\bar{1}$0] directions is determined by the interplay between bulk and structural inversion asymmetries. A microscopic theory of the spin-galvanic effect for direct inter-subband optical transitions has been developed being in good agreement with experimental findings.
The XMM-Newton serendipitous ultraviolet source survey catalogue
M. J. Page,C. Brindle,A. Talavera,M. Still,S. R. Rosen,V. N. Yershov,H. Ziaeepour,K. O. Mason,M. S. Cropper,A. A. Breeveld,N. Loiseau,R. Mignani,A. Smith,P. Murdin
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21706.x
Abstract: The XMM-Newton Serendipitous Ultraviolet Source Survey (XMM-SUSS) is a catalogue of ultraviolet (UV) sources detected serendipitously by the Optical Monitor (XMM-OM) on-board the XMM-Newton observatory. The catalogue contains ultraviolet-detected sources collected from 2,417 XMM-OM observations in 1-6 broad band UV and optical filters, made between 24 February 2000 and 29 March 2007. The primary contents of the catalogue are source positions, magnitudes and fluxes in 1 to 6 passbands, and these are accompanied by profile diagnostics and variability statistics. The XMM-SUSS is populated by 753,578 UV source detections above a 3 sigma signal-to-noise threshold limit which relate to 624,049 unique objects. Taking account of substantial overlaps between observations, the net sky area covered is 29-54 square degrees, depending on UV filter. The magnitude distributions peak at 20.2, 20.9 and 21.2 in UVW2, UVM2 and UVW1 respectively. More than 10 per cent of sources have been visited more than once using the same filter during XMM-Newton operation, and > 20 per cent of sources are observed more than once per filter during an individual visit. Consequently, the scope for science based on temporal source variability on timescales of hours to years is broad. By comparison with other astrophysical catalogues we test the accuracy of the source measurements and define the nature of the serendipitous UV XMM-OM source sample. The distributions of source colours in the UV and optical filters are shown together with the expected loci of stars and galaxies, and indicate that sources which are detected in multiple UV bands are predominantly star-forming galaxies and stars of type G or earlier.
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