Place
FV102
13:15
Department of Physics and Department of Materials Science and Engineering
Penn State University, USA
Properties of MgB2 Thin Films in Magnetic Field
The technique of hybrid physical-chemical vapor deposition (HPCVD) has been very successful in depositing very clean epitaxial MgB2 thin films with low residual resistivity (much smaller than 1 microOhm*cm), as well as dirty films showing very high upper critical field. One demonstration of the cleanness of the pure MgB2 films is the absence of the dendritic flux penetration due to the reduced electron scattering. In the normal state, a large anisotropic magnetoresistance is observed, which changes its angular dependence dramatically as the temperature increased. This is attributed to the multiple bands with different scattering rates, which vary differently with temperature. For high magnetic field applications, carbon is doped into the MgB2 films, which modifies the interband and intraband scattering and leads to extraordinary high Hc2 of over 60 T. Unique properties of flux pinning and vortex states in this two-band superconductor will be discussed.
Links: Web-page of Xiaoxing Xi
Store Fy
14:30
Italian National Institute for Condensed Matter Physics
Physics in the Kitchen
The lecture is devoted to the description of the physical aspects of the processes of the
preparation of tea, coffee, wine, spaghetti etc. The physical aspects of filtration processes,
heat propagation in a piece of meat, interaction of electromagnetic fields with
water molecules, NMR characterization of wine quality, the origin of the kettle noise
before boiling and dependence of its frequency on temperature, physical reasons for
the advantage of espresso coffee with respect to other methods of preparation,...
Links:
Homepage of Andrei Varlamov
Book "The Wonders of Physics"
FV102
13:15
Kavli Institute of Nanoscience Delft
Delft University of Technology
Exciting half-integer charges in a quantum point contact
We study a voltage-driven quantum point contact (QPC) strongly coupled to a qubit. We predict pronounced observable features in the QPC current that can be interpreted in terms of half-integer charge transfers. Our analysis is based on the Keldysh generating functional approach and contains general results, valid for all coherent conductors.
Links: cond-mat/0701017
FV102
14:15
SMN & Department of Chemistry, UiO
Quantitative MO imaging and MO indicator films prepared by MOD method
Our best oxygen ion and proton conducting oxides tend to exhibit high resistivities across grain boundaries, commonly assigned to charged boundary cores and resulting space charge layers in which the charge carrying ionic defect is depleted. The phenomenon is a problem for practical application of solid electrolytes, and many features are not well understood theoretically. In the talk we present theoretical models, experimental methods and results, interpretations, and current challenges.
Links: Group for Solid-State Electrochemistry
FV102
12:15
Institute of Symbiotic Science and Technology Tokyo University of Agriculture and Technology, Japan
Quantitative MO imaging and MO indicator films prepared by MOD method
Polarization modulation method widely used to measure magneto-optical (MO) spectra of magnetic materials will be reviewed. Utilizing this method allows us to obtain quantitative high-resolution MO images visualizing magnetic field spatial distribution. I will give a detailed description of the quantitative MO microscope and will discuss the properties of MO indicator films. The indicator films are fabricated by a very simple thin-film preparation technique, metal-organic decomposition (MOD) method.
FV102
16:00
Department of Physics and Astronomy, Free University, Amsterdam, The Netherlands
The dynamics of patterns in type-I superconductors
We report on patterns and their dynamics as observed in
magneto-optical experiments on type-I superconductors. We observe:
(1) A stripe-spot transition that is hysteretic, leading to two modes of stripe formation: slow continuous growth and avalanche growth. (2) A wiggling instability, similar to that in ferrimagnetic garnet films. (3) A zigzag instability when a pattern of parallel lines is rotated through a sample with low pinning. (4) Breaking and reconnection of stripes as such a pattern is rotated in a sample with strong pinning. (5) Random telegraph behavior close to the depinning of such pattern in the presence of a constant driving force. The observed patterns consist of superconducting and normal domains of macroscopic size in thin lamina of type-I superconductors and are observed by an advanced magneto-optical technique. The patterns are manipulated by changing the applied magnetic field vector or by applying an electrical transport current.
Collaboration: Mariela Menghini
Links: Phys. Rev. B 72, 172503 (2005)
FV102
13:15
Institute for Superconducting and Electronic Materials, University of Wollongong, Australia
The role of multilayering in the significant enhancement of structural and superconducting properties in high-Tc films
By introducing a multilayered structure to YBa2Cu3O7 (YBCO) films, the significant
enhancement of superconducting and structural properties in the obtained structure
has been achieved. The critical current density (Jc) is significantly larger (by a
factor of up to 3) than in monolayer YBCO films with an arbitrary thickness. This
remarkable result can be of a very high technological importance for overcoming the
well-known degradation of Jc as the function of the film thickness. The role of the
interfaces for the Jc enhancement is underlined and attributed to a larger filling
factor of the multilayer (denser structure), better grain alignment and additional
formation of dislocations at the interfaces between the layers.
The role of “multilayered” Ag-doping for the Jc-enhancement is also discussed.
Collaboration: Serhiy V. Pysarenko, Marie Roussel, and Shi X. Dou
Links: ISEM, University of Wollongong
FV102
13:15
Departamento de Fisica, Universidade Federal de Sao Carlos, Brazil
Fluctuation on the magnetic response of superconducting thin films of Nb and MgB2
The main results presented:M(H) curves show jumps for MgB2 films made in Pohang and Nb films made in Cambridge, but do not for MgB2 made in PennState.
AC-Susceptibility: (i) Fluctuates for measurements made in MPMS, and depends on threshold values of h, f and T. (ii) Does not fluctuate for measurements made in PPMS. (iii) When fluctuates, it depends on thickness of the sample. (iv)AC-field is able to trigger avalanches of vortices when its excitation amplitude is increasing.
Collaboration: Wilson A. Ortiz
FV102
13:15
Center for Material Science and Nanotechnology, UiO
Renewable hydrogen and solar cells: expectations and problems
Hydrogen as energy carrier, primary derived from water, can address issues of sustainability, environmental emissions, and energy security. An analysis of renewable hydrogen production pathways using solar cells and related devices will be done. Some examples of solar cell related activity at the Center for Material Science and Nanotechnology will be presented. A possible extension of such activity will be discussed.
FV102
13:15
Ioffe Physico-Technical Institute, St.Petersburg, Russia
Transport in Granular Metals
A granular metal is an array of metallic nano-particles embedded into an insulating matrix. Granular conductors combine the unique properties of individual nanocrystals and the collective properties of coupled nanocrystals thus opening a new route for novel electronic applications. A review of electronic transport properties of granular metals will be given covering both sides of the metal-insulator transition. The Hall effect in the regime of strong Coloumb blockade will also be discussed.
FV102
11:15
PGP, UiO
Spontaneous dissipation of elastic energy by self-localizing thermal runaway
Melts are often observed in the geological record as pseudotachylytes in fault
zones. Yet, apart from the fact that dissipation of energy during deformation leads
to heating above the melting temperature of rocks, little is understood of the
deformation mechanism behind the melting process. A central question is whether the
rock-melting deformation is brittle or ductile, that is, whether the dissipation of
energy is due to frictional or viscous forces. Is it at all possible to melt rocks
by viscous dissipation during ductile deformations? In this study we address the
problem of a ductile deformation process with account of viscous dissipation from a
theoretical viewpoint. Our model consists of a viscoelastic slab which is subjected
to simple shear and is in ideal thermal contact with the surroundings. The heat
conduction and momentum equations, coupled through temperature dependent viscosity,
are solved both analytically and numerically. It is demonstrated analytically that
if a generalized Brinkman number exceeds a critical value, the thermal-mechanical
interaction is inherently unstable. The critical number is a function of a
characteristic dimensionless relaxation time. Hence, the stability of the solution
is controlled by two dimensionless variables only. Numerical solution of the full
non-linear problem verifies the analytical findings. The results show that if the
Brinkman number is larger than the critical value, the stored elastic energy
spontaneously dissipates as heat in a self-localizing thermal runaway. The
deformation process thus terminates in highly localized shear zones characterized by
extreme peak temperatures. Based on our findings we propose thermal runaway as a
possible mechanism for rapid ductile deformation and generation of melts.
Collaboration: Yuri Podladchikov, Sergei Medvedev
FV102
13:15
AMCS, Dept. of Physics, UiO
High resolution thermal imaging of hotspots in superconducting films
Thermal imaging of hotspots in bridge structures of YBaCuO thin films is presented with micrometer resolution.
Hotspots formed by passing transport currents are observed using a method based on the temperature dependence in
the photoluminescence of a polymer thin film deposited on the superconductor. It is shown that, e.g., passing a
current of 10 mA in a 9 micrometer wide bridge the temperature distribution over the bridge and in its vicinity can
be observed with a resolution better than 0.1 K. The local temperature rise has a maximum of 4.5 K. In a larger
superconducting network several hotspots are observed in different branches of the network depending on the
magnitude of the applied current. In an external magnetic field the hotspots are formed at lower transport current
and at several seconds delay. It is also found that states with hotspots show hysteretic or bistable behavior, in
agreement with earlier theoretical predictions.
FV102
14:15
AMCS, Dept. of Physics, UiO
Introduction to Magnetic Garnets thin films
The talk is devoted to thin films of the magnetic Garnet-structure. This kind of films is used for
magneto-optical imaging and for optical isolation. The general overview about structures and optical properties
will be given. The talk will cover
YIG (Ytterium Iron Garnet) films, FGF (Ferrite Garnet Films) as well as description of their growth techniques
(liquid phase epitaxy and pulsed laser deposition). The most important optical properties
of the garnets to be discussed include the Faraday rotation,
reflectance, transmittance and absorption spectra.
FV102
13:15
AMCS, Dept. of Physics, UiO
Small thermal avalanches of vortices in superconductors
The critical state of type-II superconductors is a metastable state characterized by a certain gradient of flux
density. In many respects it is similar to a sandpile, where the role of sand grains is played by vortices that
get pinned by microscopic defects, which prevents them from reaching the equilibrium uniform distribution. If the
flux density gradient exceeds the critical value, the vortices are set in motion and continue moving until the
critical gradient is restored. We study small avalanches of vortices occurring when the external magnetic field is
increased. The avalanches in superconducting films are visualized using magneto-optical imaging and their size
distribution is found to have a peak. We propose a model of vortex avalanches that takes into account local
heating due to energy released by moving vortices.
Links:
Phys. Rev. B 72, 024541 (2005)
Vortex avalanches in superconductors
FV102
13:15
AMCS, Dept. of Physics, UiO
Spin echo in an arbitrary field: How to undo an unknown rotation
Spin echo is a well known technique in Nuclear Magnetic Resonance (NMR). By applying a control pulse, one can
make a nuclear spin return to its starting point, even if the rate of precession is unknown. However, the method
is limited by the fact that you have to know the direction of the external magnetic field, but not its magnitude.
Motivated by recent
experiments with electron spins in quantum dots, were the nuclear field provides magnetic field that is unknown
both in magnitude and direction we have studied the possibility of making echo experiments in this situation.
Collaboration: Leonid Glazman, University of Minnesota
Links: Joakim Bergli's homepage
FV102
13:15
Physical Electronics, Dept. of Physics, UiO
Ion induced electronic nanochannels in Si
During penetration of an ion into a solid it induces electrically active
point defects. It has been proposed that for implantation of heavy ions in
semiconductors, e.g. Si, electrically active point defects are generated
predominantly along the ion trajectory. This can result in a local
modification of the Fermi-level, creating “electronic nanochannels” along
the ion track. The technological advantage of such nanochannels is that,
unlike the “traditional” nanowires, the ion induced nanochannels are
readily embedded into the Si crystal by conventional ion implantation.
However, no observation of such nanochannels has been reported in
elemental semiconductors by conventional techniques measuring structurally
(transmission electron microscopy) or topographically (atomic force
microscopy) related techniques.
In an ongoing project at the physical electronics group in MiNa lab, the
ion induced nanochannels are studied using scanning capacitance microscopy
(SCM) and deep level transient spectroscopy (DLTS). In particular, SCM
studies show a pattern of increased charge concentration in regions of
150-600nm after 3 and 5 MeV Au2+ implantations in Si. The pattern shows a
distinct dose and temperature dependence, in accordance with measured
energy levels in the forbidden band gap, and has been ascribed the ion
induced nanochannels.
Links: Semiconductror nanostructure research at Microtechnology Lab
FV102
12:15
Dept. of Physics, University of Houston, TX, USA
The Self-Organized Evolution of Canalization
Canalization, which is a form of robustness in complex networks, has long been recognized to be an important
property of evolving biological systems. The mechanism for the evolution of canalization, however, remains
controversial. In this colloquium, a novel mechanism that produces canalization by selecting for diversity of
expression patterns based on a frustrated competition between nodes (genes) will be presented. It will be shown
that the mechanism produces a canalized, critical steady state that retains a capacity for further evolution in a
simple model of a genetic regulatory network. Recent results that suggest small networks may evolve in a
fundamentally different way than large networks will also be presented.
Links: Phys. Rev. Lett. 93, 038101 (2004)
FV102
13:15
Department of Physics, University of Oslo
&
Institute of Physics AS CR, Prague
Interaction of Vortices with Artificial Defects in Type-II Superconductors
In the talk I will highlight the most important
features of large cylinder cavities, i.e. antidots, in superconductors
in the context of their interaction with vortex medium. Technology of
antidots production, energy of interaction between the holes and
vortices (theory and effective experimental values), principles of
flux localization in perforated samples, possible mechanisms of vortex
guidance along the arrays of antidots are the subjects to be discussed.
Collaboration:
M. Jirsa, A. Stupakov, Institute of Physics AS CR, Prague
R. Wordenweber, Research Centre of Julich, Germany
FV102
13:15
Department of Physics, University of Oslo
Phonon-vortex interaction in superfluid helium II
- Description of the two-fluid model, quantized vortices, and phonon
excitations in helium II.- Outline of how phonons are scattered on a vortex, and how the transverse force on the quantized vortex from the phonons can be found.
- Finally, I present a controversy about the existence of the force based on other results.
Collaboration:
Jon Magne Leinaas, Department of Physics, UiO
FV102
13:15
Department of Physics, University of Oslo
&
State Research Center of Virology and Biotechnology VECTOR, Kolcovo, Russia
Interaction of biological cells with nonuniform AC electric field
The method of cell destruction by AC electric field and experimental
data on investigation of virus-cell interaction by dielectrophoresis
(motion of cells in inhomogeneous AC electric field) will be introduced.
The following virus-cell pairs were studied: tick-borne
encephalitis-goose erythrocytes, influenza virus-chicken erythrocytes,
virus-Vero cells. The performed studies have revealed that the
amplitude-frequency characteristics of the erythrocyte polarization and
the equilibrium frequency change considerably at the stage of the virus
adsorption to the erythrocyte membrane. The higher concentration of
viruses in cell suspension, the more considerable changes occur. At the
same time in case of low virus concentration the cells with
characteristics similar to that of intact ones were observed along with
infected cells.
Links: State Research Center of Virology and Biotechnology VECTOR
FV102
13:15
Department of Physics, University of Oslo
&
Linkoping University, Sweden
Ni/V multilayer X-ray mirrors for the Water Window
Carbon and nitrogen have a high absorption, compared to oxygen and hydrogen, in the region of soft X-ray wavelengths. One can take advantage of this to study biological specimens using a microscope operating in this wavelength range. The region is called the water window, 2.4 - 4.4 nm. Nickel (Ni) and Vanadium (V) multilayers have been designed to obtain the highest reflectivity for the normal incident of the X-ray wavelength at 2.48 nm. The optimal parameters, which are predicted to give highest reflectivity for Ni/V at 2.48 nm, was determined to be L=1.242 nm and G=0.411. Ni/V multilayer films were deposited on Silicon (100) substrates by magnetron D.C. sputtering with Argon as the sputtering gas. Furthermore, hard X-rays with wavelength 0.154 nm were used in the structural characterisation and compared with computer simulations. It was found that a substrate bias of -33 volts was required during deposition in order to achieve the highest peak reflectivity and the lowest diffuse scattering.
Collaboration:
Fredrik Eriksson, Linkoping University, Sweden
FV102
13:15
Department of Physics, University of Oslo
&
Ioffe Physico-Technical Institute, St.Petersburg, Russia
Negative-U centers model. Similarity in the superconducting properties of chalcogenides and cuprate oxides
The idea of Anderson pairs has been put forward for explanation of many extraordinary properties of chalcogenides glassy semiconductors. Recent decades made obvious that these pairs localized on the centers with negative effective correlation energy (negative-U centers) really exist in chalcogenides. If the concentration of negative-U centers is enough to create the pair band states, this can lead to superconductivity because Anderson pairs are Bose particles. Several properties of chalcogenides and HTSC cuprates in normal and superconducting states are similar for these groups of materials and can be naturally explained in the frame of negative U centers model of superconductivity.
Collaboration:
Konstantin D. Tsendin, Boris P. Popov, Ioffe Physico-Technical Institute, St.Petersburg, Russia
Links: Supercond. Sci. Techn. 16 80, 2003
FV102
13:15
Department of Physics, University of Oslo
&
Princeton University, USA
Dephasing of superconducting qubits
I will discuss recent experiments on superconducting
qubits. In particular I will explain how to understand the change in
dephasing and decoherence rates as the working point of the qubit is
changed. Also I will discuss the effect of low frequency noise that gives
a non-Gaussian distribution of the phase and contrast it to the
conventional Gaussian description.
Links: Phys. Rev. Lett. 87, 246601 (2001).
FV102
10:15
A. Ya. Usikov Institute for Radiophysics and Electronics, Kharkov, Ukraine
Symbolic stochastic dynamical systems viewed as binary N-step Markov chains and the Zipf law
A theory of systems with long-range correlations based on the consideration of binary N-step Markov chains is developed. In the model, the conditional probability that the ith symbol in the chain equals zero or unity is a linear function of the number of unities among the preceding N symbols. The correlation and distribution functions as well as the variance of the number of symbols in the words of arbitrary length L are obtained analytically and numerically. A self-similarity of the studied stochastic process is revealed and the similarity group transformation of the chain parameters is presented. The diffusion Fokker-Planck equation governing the distribution function of the L words is explored. If the persistent correlations are not extremely strong, the distribution function is shown to be the Gaussian with the variance being nonlinearly dependent on L.
The binary many-step Markov chain with the step-like memory function is considered as a model for the analysis of rank distributions of words in stochastic symbolic dynamical systems. We prove that the envelope curve for this distribution obeys the power law with the exponent of the order of unity in the case of rather strong persistent correlations. The Zipf law is shown to be valid for the rank distribution of words with lengths about and shorter than the correlation length in the Markov sequence. A self-similarity in the rank distribution with respect to the decimation procedure is observed. The applicability of the developed theory to the coarse-grained written and DNA texts is discussed.
Collaboration:
O. V. Usatenko, Institute for Radiophysics and Electronics, Kharkov, Ukraine
K. E. Kechedzhy and S. S. Mel'nyk, Kharkov National University, Kharkov, Ukraine
Links: Phys. Rev. Lett. 90, 110601 (2003), Phys. Rev. E 68, 061107 (2003).
FV102
13:15
Physical electronics, Physics Dept, University of Oslo
Impurities in SiC
Silicon Carbide (SiC) is a wide band gap semiconductor attracting
great interest because it is expected to replace Si or GaAs in
high-temperature, high-power, and high-frequency devices. Intrinsic
defects and impurities in the crystal may create energy levels in the
band gap and are therefore crucial for the functionality of any
semiconductor device. Consequently, it is of high technological
interest to establish a correlation between band gap states and a
certain defect structure. Within extensive studies in the last years,
the electronic properties of transition metals in SiC were revealed by
means of radiotracer Deep Level Spectroscopy (DLTS-RI). In each case a
definite chemical assignment of band gap states was established and in
some cases the defect structure could be clarified. The radiotracer
DLTS experiments have lead to the most extensive and reliable dataset
about impurity atoms in SiC available.
Links: Physical Electronics at UiO
FV102
13:15
Physics of Geological Processes, University of Oslo
Reverse Modelling of Geological Phenomena
The talk is about mathematical and numerical aspects of geological "restorations". Geological past is reconstructed using present day observations. It is an inverse problem known to be ill posed. Several cases (gravity, seismic) are treated in classical geophysics. Numerous new modeling directions became feasible due to growth of computer power. Most of these new modeling attempts are "forward" in time because they deal with irreversible processes. However, geological structures often formed by instabilities. Amazingly, instabilities are often easier to simulate inverse (reverse) in time. Case studies on inversion of several instabilities will be reported (folding, Rayleigh-Taylor).
Links: Yuri Podladchikov homepage
FV102
13:15
Imperial College, London, United Kingdom
Universal Fluctuations in Critical Phenomena
Systems displaying critical phenomena are often distinguished by the
"universality classes" they belong to. Traditionally, the assignment
of a universality class is made on the basis of the critical exponents
for a system at the critical point. Alternatively, the probability
distribution for the order parameter can be used instead. I will give
examples of this latter approach in both equilibrium and
non-equilibrium systems.
Collaboration:
Z.Racz, G.Gyorgyi, ELTE, Budapest
Links: Nicholas R. Moloney homepage
Store fysiske
13:00
Argonne National Laboratory, USA
Superconductivity: History and present state
The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2003 "for pioneering contributions to the theory of superconductors and superfluids" jointly to
Alexei A. Abrikosov, Vitaly L. Ginzburg, and
Anthony J. Leggett.Landau's pupil, Alexei Abrikosov, realised almost immediately that Ginzburg and Landau's theory can also describe those superconductors (type II) that can coexist with strong magnetic fields. According to Abrikosov's theory this occurs because the superconductor allows the magnetic field to enter through vortices in the electron superfluid. These vortices can form regular structures, Abrikosov lattices, but disordered structures can also occur.
Links: Press Release and Illustrated presentation from The Royal Swedish Academy of Sciences; Gallery of Abrikosov Lattices in Superconductors
FV102
13:15
AMCS group, Department of Physics, University of Oslo
Quantum bit in dynamic disorder
With the growing efforts in isolating solid-state qubits from
external decoherence sources, the material-inherent sources of
noise start to play crucial role. One representative example is
electron traps in the device material or substrate. Electrons can
tunnel or hop between a charged and an empty trap, or between a
trap and a gate electrode. A single trap typically produces
telegraph noise and can hence be modeled as a bistable fluctuator.
Since the distribution of hopping rates is exponentially broad,
many traps produce flicker-noise with spectrum close to 1/f.
Here we develop a theory of decoherence of a qubit in the
environment consisting of two-state fluctuators, which experience
transitions between their states induced by interaction with
thermal bath. Due to interaction with the qubit the fluctuators
produce 1/f-noise in the qubit's eigenfrequency. We calculate
the results of qubit manipulations - free induction and echo
signals - in such environment. The main problem is that in many
important cases the relevant random process is both non-Markovian
and non-Gaussian. Consequently the results in general cannot be
represented by pair correlation function of the qubit
eigenfrequency fluctuations. Our calculations are based on
analysis of the density matrix of the qubit using methods
developed for stochastic differential equations. The proper
generating functional is then averaged over different fluctuators
using the so-called Holtsmark procedure. The analytical results
are compared with simulations allowing checking accuracy of the
averaging procedure and evaluating mesoscopic fluctuations. The
results allow understanding some observed features of the echo
decay in Josephson qubits.
Collaboration:
Boris Altshuler, Princeton University
Daniel Shantsev, University of Oslo
Links: Boris Altshuler homepage
FV102
13:15
AMCS group, Department of Physics, University of Oslo
&
University of Arizona
Near-Field Modeling
Near-Field systems can produce sub-wavelength diameter optical spots
used for data recording and reading. The purpose of this talk is
to introduce XFDTD, a finite difference time domain program used
to calculate electro-magnetic phenomena in Near-Field Optical Data Storage.
The talk will discuss several geometries studied using XFDTD and
their applications to Data Storage.
Links: Optical Data Storage Center, University of Arizona
FV102
13:15
AMCS group, Department of Physics, University of Oslo
&
SINTEF
Downhole instrumentation in oil wells
Part 1: Signal analysis and sensors for measuring flow rates of oil,
water and gas in an oil producing well.
Part 2: Acoustic sensor for flow rates, gauge level sensor for water separation in the well, wireless communication in oil wells and ultra sound imaging in oil wells.
Part 3: Other projects like estimating airplane brake distance on icy Norwegian air fields
Part 4: New project: thermo-optical imaging of superconductors.
Links: SINTEF
FV146C
12:15
University of Jyvaskyla, Finland
Heat transport along mesoscopic dielectric bridges
Thermodynamic properties, including heat transport, of thin, isotropic
free standing membranes, have been studied. The dispersion relation in
this geometry is different from the disperion relation
of an infinite solid and, due to that, thermodynamics differ as well.
Further we cut the membrane into a narrow bridge. We are especially
interested in the heat transport along the bridge. Due to the small width
of the bridge, the scattering on its edges may become the dominant
scattering process and the mean free path of the phonons should become a
constant that depends on the width of the bridge
Collaboration:
Dragos-Victor Anghel, University of Oslo
Links: Department of Physics, University of Jyvaskyla, Dragos Anghel
FV146C
12:15
Theoretical Division, Los Alamos National Laboratory, USA
Tunneling measurement of quantum spin oscillations
The problem of tunneling between two leads via a localized spin 1/2 or any
other microscopic system (e.g., a quantum dot) which can be modeled by
a two-level Hamiltonian is considered.
We assume that a constant magnetic field acts on the spin, that electrons in the leads are in a voltage driven thermal equilibrium and that the tunneling electrons are coupled to the spin through exchange interaction. Using the non-equilibrium Keldysh formalism we find the dependence of the spin-spin and current-current correlation functions on the applied voltage between leads, temperature, and on the degree and orientation of spin polarization of the electrons in the right and left leads. We found conditions under which both the spin-spin and current-current correlation functions exhibit a peak at the Larmor frequency corresponding to the effective magnetic field acting upon the spin.
We compare our results of a full quantum-mechanical treatment of the
tunneling-via-spin model with those previously obtained in the
quasi-classical approach, and discuss the experimental results observed
using STM dynamic probes of the localized spin.
Collaboration:
M. Hruska, G. Ortiz, Los Alamos National Laboratory
Links: cond-mat/0212049
FV146C
12:15
Department of Chemistry, University of Oslo
Exited state properties from density functional calculation
The density functional theory (DFT) is originally deviced to describe the
ground state properties of materials. But, recent years it has been shown
that it can be used to study the excited state properties of the materials
also. We have recently calcualted the linear optical properties such as
optical dielectric functions, reflectivity, absorption coefficient,
refractive index, electron energy loss function etc. for a series of
LaXO3 (X=Sc-Cu) type oxides. We found that gradient corrected DFT
describe correctly the semiconducting behavior of ionic insulators
LaScO3 and CT insulators such as LaCrO3, LaFeO3 and LaMnO3 though it
underestimate the bandgap. But it failed to describe the insulating
behavior for Mott insulators such as LaTiO3 and LaVO3.
In order to probe the occupied and unoccupied electronic structure of the semiconductors we have calculated the XPS, BIS and UPS spectra for the semiconducting oxides. Another experimental technique that provides information about CB is XANES. I will present some examples where comparision is made between experimental and theoretical spectra. The investigation of compounds with high magneto-optical activity is of great importance both for applications (the search for potential materials for magneto-optical disks) and for achieving a deeper understanding of the electronic structure and magnetic properties of solids. We have calculated the MO properties such as Kerr and Faraday spectra for series of ferromagnetic materials.
From these study I will show that from the density functional calculations
we can predict the excited state properties of the materials and also
explain the features of experimentally observed spectra.
Links: Theory group in solid state chemistry
FV146C
12:15
Condensed matter physics, Department of Physics, University of Oslo
Front scaling: from capillary fingering to viscous fingering
When one fluid phase displace another in a porous media the
displacement is stable or unstable depending on wetting properties
(capillary effects), gravity, viscous contrast and invasion speed.
We have experimentally studied the transition between two unstable
regimes. One controlled by "pore scale forces" (capillary fingering) the
other controlled by the viscous pressure field (viscous fingering). The
experiments are performed by injecting a low viscous non-wetting liquid
(air) into a quasi two dimensional porous medium saturated with a high
viscous liquid (glycerol/water) at various injection speeds
Collaboration:
Knut Jørgen Måløy, Dep. of Physics, UiO
Yves Méheust, Dep. of Physics, NTNU
Jean Schmittbuhl, Dep. of Geology ENS, Paris
Links: Grunde Løvoll homepage,
Complex Systems group
FV146C
12:15
Physical Electronics, Department of Physics, University of Oslo
Observation of a "new" double acceptor center in silicon
This work has been initiated within the CERN collaboration on
Radiation
hard semiconductor devices for very high luminosity colliders.
A considerable part of this collaboration is aimed to improvement of
radiation hardness of silicon by means of defect engineering.
During our studies of radiation-induced defects we have observed formation
of a new double acceptor center (a defect with singly negative and
doubly negative charge states, so it can capture up to 2 additional electrons)
[Monakhov et al., Phys. Rev. B 65, 233207 (2002)].
After additional studies and independent theoretical works, it is believed now
that we have observed a previously unknown second negative charge state
of the divacancy-oxygen (V2O) complex. The V2O complex is considered
one of the most important center with respect to radiation stability of silicon.
Some believe that it is responsible for the radiation-induced degradation of
silicon devices. Our studies will also help to resolve the mystery of divacancy
annealing that persists despite of decades of silicon-based technology.
Collaboration:
G. Alfieri, B. Svensson, Dept. of Physics, UiO
B. S. Avset, SINTEF
A. Hallén, Royal Institute of Technology, Stockholm
Links: Physical Electronics at UiO
FV102
12:15
Condensed-matter physics, Department of Physics, University of Oslo
&
Institute of Nutrition Research, University of Oslo
Protein Folding
An introduction to the protein folding problem is given by a physicist
making his first steps in biology. The talk is focused on review
of the protein folding simulations, and related experiments.
For more information see:
Geometrical approach to protein folding: a tube picture, Banavar et al, Rev. Mod. Phys. 75 , 23 (2003).
Absolute comparison of simulated and experimental protein-folding dynamics, Snow et al., Nature 420, 102 (07 Nov 2002).
Mathematical Analysis of Coupled Parallel Simulations, Shirts et al., Phys. Rev. Lett. 86, 4983 (2001).
A surprising simplicity to protein folding, Baker, Nature 405, 39 (04 May 2000).
Heteropolymer freezing and design: Towards physical models of protein folding, Pande et al., Rev. Mod. Phys. 72, 259 (2000).
Links: Folding simulations @ Stanford, Searchable on-line textbooks on molecular cell biology
FV102
12:15
Theory group, Department of Physics, University of Oslo
A Carbon Nanotube Based Nanorelay
We investigate the operational characteristics of a nanorelay based on a conducting carbon nanotube placed on a terrace in a silicon substrate. The nanorelay is a three terminal device that acts as a switch in the GHz regime. Potential applications include logic devices,
memory elements, pulse generators, and current or voltage amplifiers.
Collaboration:
J.M. Kinaret, T. Nord.
Chalmers University of Technology, Sweden
Links: cond-mat/0208427
FV102
12:15
Condensed-matter physics, Department of Physics, University of Oslo
Coherent "shuttle" transfer of Cooper pairs by a movable superconducting grain
We consider coherent transfer of Cooper pairs between two bulk
superconductors by a movable superconductor grain. It is assumed that
the grain commutes between the leads by some external driving system
(nano-pendulum). Devices of such type made of normal metals were
recently studied experimentally. The main feature of the system under
consideration is that by proper choice of the gates the states with N
and N+1 Cooper pairs on the grain are made degenerate. As a result,
during the time between contacts with the leads the grain persists in
a hybrid quantum state as a movable quantum bit.
Two situations are discussed: (i) the phase different between the leads
is kept constant, and DC current is measured. In this situation the
movable grain stimulates DC Josephson effect, the critical current
being dependent on the shuttle parameters
Nature 411, 454 (2001); (ii)
The leads are isolated, and the distribution of the phase difference
between them is studied as a function of the number of the grain's
excursions
Phys. Rev. Lett. 89, 277002 (2002).
In the talk I will
concentrate on the role of interaction with environment which leads to
decoherence.
Collaboration:
A. Isacsson, L. Y. Gorelik, R. I. Shekhter, and M. Jonson.
Chalmers University of Technology, Sweden
Links: homepage of Y.M. Galperin
FV102
13:00
Nuclear and energy physics, Department of Physics, University of Oslo
Can we classify phase transitions in small systems of interacting fermions?
Links: homepage of M. Hjorth-Jensen
FV102
12:15
Oak Ridge National Lab, Oak Ridge
Department of Physics, University of Tennessee, Knoxville, Tennessee, USA
Computational chemistry for molecular electronics and related topics
Current through a benzine molecule between gold layers.
Phase transitions in a quantum dot in a strong magnetic field.
Review of computational methods.
Links: homepage of David J. Dean
FV102
12:15
Nuclear and energy physics, Department of Physics, University of Oslo
Quantum mechanical modelling of hydrogen in metals
Links: folk.uio.no/olem/
FV102
12:15
Department of Chemistry, University of Oslo
Theoretical investigations on metal hydrides from density functional calculations
I will present some of our recent work on metal hydrides
which violate the "2 A rule" and also pressure induced strcutural
transition in MgH2". More details about my presentation will be
found in the following two references:Violation of the "2 Å rule" for Metal Hydrides, Phys. Rev.Lett. 89, 106403 (2002).
Pressure-induced structural transitions in MgH2, Phys. Rev. Lett. 89, 175506 (2002).
Collaboration:
P.Ravindran, R.Vidya, A. Kjekshus, H. Fjellvåg. Department of Chemistry, University of Oslo
Links: folk.uio.no/ravi
FV102
12:15
Condensed-Matter Physics Group, Department of Physics, University of Oslo
Universality and first order phase transitions in systems of generalized statistics
I make a brief introduction to the first order phase
transitions,
by showing the main aspects of Yang & Lee theory [Phys. Rev. 87, 404
(1952),
Phys. Rev. 87, 410 (1952)] and Landau's phenomenological model (Landau and
Lifshitz, Stat. Mech.). Nonanalyticity of the thermodynamic potential may
be due to multiple, competing peaks of the probability distribution in the
phase-space of a system. I show a concrete example of such a system:
2D interacting gas of generalized statistics (i.e. Bose, Fermi, or
Haldane's fractional exclusion statistics).
I turn off the interaction, and emphasize the universal thermodynamics of
quantum gases in 2D. The paper is published in J. Phys. A
(Abstract)
Links: folk.uio.no/dragos/
FV102
12:15
Condensed-Matter Physics Group, Department of Physics, University of Oslo
Thermomagnetic instability in type-II superconductors
Magnetic flux penetrates in type-II superconductors in form of
quantized flux lines or vortices. The vortices can be pinned by tiny
material inhomogeneities, which prevents their motion. When votices
are moving, a heat is dissipated, and the resulting temperature rise
weakens the pinning. This can lead to a thermomagnetic instability
accompanied by abundant heating and macroscopic redistribution of
magnetic flux. Development of the instability is very sensitive to
the material, sample geometry and external conditions. Theoretical
efforts, both analytical and simulations, to understand the phenomenon
are reviewed. MD simulations reproducing dendritic instability,
found experimentally in thin superconducting films, are discussed in detail.Collaboration:
T. H. Johansen, Y. M. Galperin, S. Braeck, M. Baziljevich, P. E. Goa.
Condensed-Matter Physics Group, Department of Physics, University of Oslo
Links: www.fys.uio.no/super/dend
FV102
14:15
Material Physics and Semiconductors, Royal Institute of Technology, Stockholm, Sweden
Formation and stability of radiation defect complexes in Si and Si:Ge: Pressure effects
Collaboration:
A.Yu. Kuznetsov.
Material Physics and Semiconductors, Royal Institute of Technology, Stockholm, Sweden
Physical Electronics, Department of Physics, University of Oslo, Oslo, Norway
A.V.Nazarov.
Department of Material Science, Moscow State Engineering-Physics Institute, Moscow, Russia
R.M.Nieminen.
Helsinki University of Technology, Department of Engineering Physics and Mathematics, Espoo,
Finland