| 1. |
- Bergström, Lars
(författare)
-
Dark matter evidence, particle physics candidates and detection methods
- 2012
-
Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 524:9-10, s. 479-496
-
Forskningsöversikt (refereegranskat)abstract
- The problem of the dark matter in the universe is reviewed. A short history of the subject is given, and several of the most obvious particle candidates for dark matter are identified. Particular focus is given to weakly interacting, massive particles (WIMPs) of which the lightest supersymmetric particle is an interesting special case and a useful template. The three detection methods: in particle accelerators, by direct detections of scattering in terrestrial detectors, and indirect detection of products from dark matter particle annihilation in the galactic halo, are discussed and their complementarity is explained. Direct detection experiments have revealed some possible indications of a dark matter signal, but the situation is quite confusing at the moment. Very recently, also indirect detection has entered a sensitivity region where some particle candidates could be detectable. Indeed, also here there are some (presently non-conclusive) indications of possible dark matter signals, like an interesting structure at 130 GeV ?-ray energy found in publicly available data from the Fermi-LAT space detector. The future of the field will depend on whether WIMPs are indeed the dark matter, something that may realistically be probed in the next few years. If this exciting scenario turns out to be true, we can expect a host of other, complementary experiments in the coming decade. If it is not true, the time scale and methods for detection will be much more uncertain.
|
|
| 2. |
- Debbichi, Lamjed, et al.
(författare)
-
Electronic structure of In3Se4 and In3Te4 monolayers from ab-initio calculations
- 2014
-
Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 526:9-10, s. 402-407
-
Tidskriftsartikel (refereegranskat)abstract
- First principles calculations have been used to calculate the interlayer binding energy, the phonons frequencies, and the electronic structure of the In3X4 layered systems, with X = Se or Te. Using density functional theory corrected to take into account van der Waals interactions, the binding energy was found to be approximate to 41-44meV for In3Se4 and approximate to 53-58meV for In3Te4. Moreover, the absence of imaginary frequencies in the phonons bandstructures demonstrates the dynamical stability of the isolated layers. These facts suggest that isolated layers of In3Se4 and In3Te4 could be obtained by means of exfoliation from the bulk.
|
|
| 3. |
- Gabrysch, Markus, et al.
(författare)
-
XUV-induced transient phase gratings for probing ultra-fast carrier generation and recombination processes in wide-bandgap semiconductors
- 2013
-
Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 525:1-2, s. 59-65
-
Tidskriftsartikel (refereegranskat)abstract
- A method for probing the temporal evolution of ultra-fast carrier generation and recombination processes in wide-bandgap semiconductors, e.g. diamond, is described. Two extreme ultraviolet (pump) pulses produced by high-order harmonic generation in Argon gas (with a photon energy of 32 eV) are superimposed on a sample with a small angle between them, inducing periodic changes in the refractive index of the material causing it to act as a transient diffraction grating. A delayed synchronized infrared (probe) pulse gets diffracted on the induced phase grating and is detected in the first diffraction order. By varying the time-delay between pump and probe, the full temporal evolution of the free carrier generation and recombination processes can be resolved. Feasibility calculations and the first steps towards experimental implementation are presented.
|
|
| 4. |
- Granath, Mats, 1972, et al.
(författare)
-
Discretized thermal Green’s functions
- 2012
-
Ingår i: Annalen der Physik. - : Wiley - VCH Verlag GmbH. - 0003-3804 .- 1521-3889. ; 524:3-4, s. 147-152
-
Tidskriftsartikel (refereegranskat)abstract
- We present a spectral weight conserving formalism for Fermionic thermal Green's functions that are discretized in imaginary time t and thus periodic in imaginary (Matsubara) frequency i pi n. The formalism requires a generalization of the Dyson equation G (G0, S) and the Baym-Kadanoff-Luttinger-Ward functional for the free energy beta O = G (G). A conformal transformation is used to analytically continue the periodized Matsubara Green's function to real frequencies in a way that conserves the discontinuity at t = 0 of the corresponding real-time Green's function. This allows numerical Green's function calculations of very high precision and it appears to give a well controlled convergent approximation in the t discretization. The formalism is tested on dynamical mean field theory calculations of the paramagnetic Hubbard model.
|
|
| 5. |
- Maier, S. A., et al.
(författare)
-
Plasmic sensors
- 2012
-
Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 524:11, s. A155-
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 6. |
- Mårsell, Erik, et al.
(författare)
-
Secondary electron imaging of nanostructures using Extreme Ultra-Violet attosecond pulse trains and Infra-Red femtosecond pulses
- 2013
-
Ingår i: Annalen der Physik. - : Wiley. - 0003-3804. ; 525:1-2, s. 162-170
-
Tidskriftsartikel (refereegranskat)abstract
- Surface electron dynamics unfold at time and length scales down to attoseconds and nanometres, making direct imaging with extreme spatiotemporal resolution highly desirable. However, this has turned out to be a major challenge even with the advent of reliable attosecond light sources. In this paper, photoelectrons from Ag nanowires and nanoparticles excited by extreme ultraviolet (XUV) attosecond pulse trains and infrared femtosecond pulses using a PhotoEmission Electron Microscope (PEEM) are imaged. In addition, the samples were investigated using Scanning Electron Microscopy (SEM) and synchrotron based X-ray photoelectron spectroscopy (XPS). To achieve contrast between the nanostructures and the substrate in the XUV images, three different substrate materials were investigated: Cr, ITO and Au. While plasmonic field enhancement can be observed on all three substrates, only on Au substrates do the Ag nanowires appear significantly brighter than the substrate in XUV-PEEM imaging. 3-photon photoemission imaging of plasmonic hot-spots was performed where the autocorrelation trace is observed in the interference signal between two femtosecond Infra-Red (IR) beams with sub-cycle precision. Finally, using Monte Carlo simulations, it is shown how the secondary electrons imaged in the XUV PEEM can potentially reveal information on the attosecond time scale from the near surface region of the nanostructures.
|
|
| 7. |
- Rammer, Jörgen, et al.
(författare)
-
Counting quantum fluctuations of particle density
- 2012
-
Ingår i: Annalen der Physik. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 0003-3804 .- 1521-3889. ; 524:3-4, s. 163-174
-
Tidskriftsartikel (refereegranskat)abstract
- Methods of charge projectors using special gauge transformations for tagging particles are presented. Such engineering of a many-body wave function allows extracting information regarding properties of a physical system beyond average values. The method is first used to establish under which circumstances the properties of particle currents can be understood as discrete transfers of particles from one region to another. Next, the method is extended to show that in a tunnel junction coupled to a two-level system, the transmission of electrical noise causes decoherence and thereby a projective measurement of the two-level system as encoded by the amount of tunnelled charge. Finally the method is extended to deal with the exceptional circumstance where a measurement on a system with a large number of particles gives macroscopically distinguishable outcomes that are unpredictable, the observed interference pattern of interfering BEC's.
|
|
| 8. |
- Shen, Jian Qi
(författare)
-
A three-level dark state and double-control single-photon logic gates via quantum coherent control
- 2012
-
Ingår i: Annalen der Physik. - : Wiley-Blackwell. - 0003-3804 .- 1521-3889. ; 524:2, s. 85-96
-
Tidskriftsartikel (refereegranskat)abstract
- Multilevel quantum coherence and its quantum-vacuum counterpart, where a three-level dark state is involved, are suggested in order to achieve new photonic and quantum optical applications. It is shown that such a three-level dark state in a four-level tripod-configuration atomic system consists of three lower levels, where constructive and destructive quantum interference between two control transitions (driven by two control fields) arises. We point out that the controllable optical response due to the double-control tunable quantum interference can be utilized to design some fascinating new photonic devices such as logic gates, photonic transistors and switches at quantum level. A single-photon two-input XOR logic gate (in which the incident gate photons are the individual light quanta of the two control fields) based on such an effect of optical switching control with an EIT (electromagnetically induced transparency) microcavity is suggested as an illustrative example of the application of the dark-state manipulation via the double-control quantum interference. The present work would open up possibility of new applications in both fundamental physics (e.g., field quantization and relevant quantum optical effects in artificial systems that can mimic atomic energy levels) and applied physics (e.g., photonic devices such as integrated optical circuits at quantum level).
|
|
| 9. |
- Zheltukhin, Aleksandr, 1946-
(författare)
-
Dmitrij Volkov, super-Poincare group and Grassmann variables
- 2010
-
Ingår i: Annalen der Physik. - Berlin : Wiley-VCH. - 0003-3804 .- 1521-3889. ; 19:3-5, s. 177-185
-
Tidskriftsartikel (refereegranskat)abstract
- A fundamental role of the Hermann Grassmann anticommuting variables both in physics and mathematics is discussed on the example of supersymmetry. The talk describes how the D. Volkov question about possibility of the existence of Nambu-Goldstone fermions, realized by the Grassmannian variables, resulted in the discovery of the super-Poincaré group, its spontaneous breaking and gauging.
|
|
