R. L. Oldershaw
2008-03-08
The gravitational Bohr radius (GBR) characterizes the size of a hypothetical ground state hydrogen atom wherein the binding interaction between its nucleus and its electronic structure is purely gravitational. The conventional calculation of the GBR, based on the standard Newtonian gravitational coupling constant, yields an astronomical size for the "gravitational atom". On the other hand, a discrete fractal cosmological paradigm asserts that the gravitational coupling constant that applies within Atomic Scale systems is roughly 38 orders of magnitude larger than the conventional gravitational constant. According to calculations based on predictions of this discrete fractal paradigm, the value of the GBR is actually on the order of 2 pi times the standard Bohr radius. Implications of this revised gravitational Bohr radius are discussed.
On the Bohr radius relationship to spin-orbit interaction, spin magnitude, and Thomas precession
David C. Lush
2009-03-24
The dynamics of the spin-orbit interaction in atomic hydrogen are studied in a classical electrodynamics-like setting. A Rutherfordian atomic model is used assuming a circular electron orbit, without the quantum principle as imposed arbitrarily in the Bohr model, but with an ad hoc incorporation in the electron of intrinsic spin and associated magnetic dipole moment. Analyzing the motions of the electron spin and orbital angular momenta, it is found that in the presence of Thomas precession, the total angular momentum averaged over the orbit is not generally a constant of the motion. It is noted this differs from the finding of Thomas in a similar assessment of 1927, and the reason for this difference is provided. It is found that although the total orbit-averaged angular momentum is not a constant of the motion, it precesses around a fixed axis similarly to the precession of the total angular momentum vector seen in spin-orbit coupling in quantum theory. The magnitude of the angular velocity of the total orbit-averaged angular momentum is seen to vanish only when the spin and orbital angular momenta are antiparallel and their mutual precession frequencies equate. It is then found, there is a unique radius where the mutual precession frequencies equate. Assuming the electron magnetic moment is the Bohr magneton, and an electron g-factor of two, this radius corresponds to where the orbital angular momentum is the reduced Planck's constant. The orbit radius for stationary total angular momentum for the circular orbit model with nonzero orbital angular momentum is thus the ground-state radius of the Bohr model.
R. Heyrovska; S. Narayan
2005-09-24
Sommerfeld introduced the fine-structure constant into physics, while he was taking into account the relativistic effects in the theory of the hydrogen atom. Ever since, it has puzzled many scientists like Eddington, Dirac, Feynman and others. Here the mysterious fine-structure constant, alpha = (Compton wavelength/de Broglie wavelength) = 1/137.036 = 2.627/360 is interpreted based on the finding that it is close to 2.618/360 = 1/137.508, where the Compton wavelength for hydrogen is a distance equivalent to an arc length on the circumference (given by the de Broglie wavelength) of a circle with the Bohr radius and 2.618 is the square of the Golden ratio, which was recently shown to divide the Bohr radius into two Golden sections at the point of electrical neutrality. From the data for the electron (e) and proton (p) g-factors, it is found that (137.508 - 137.036)= 0.472 = [g(p) - g(e)]/[g(p) + g(e)] (= 2/cube of the Golden ratio), and that (2.627 - 2.618)/360 = (small part of the Compton wavelength corresponding to the intrinsic radii of e and p/de Broglie wavelength) = 0.009/360 = (1- gamma)/gamma, the factor for the advance of perihilion in Sommerfeld's theory of the hydrogen atom, where gamma is the relativity factor.
Quantum dot lattice embedded in an organic medium: Hybrid exciton state and optical response
NASA Astrophysics Data System (ADS)
Huong, Nguyen Que; Birman, Joseph L.
2000-05-01
We propose a model to implement organic exciton-semiconductor exciton hybridization by embedding a semiconductor quantum dot array into an organic medium. A Wannier-Mott transfer exciton is formed when the exciton in each semiconductor dot interacts via multipole-multipole coupling with other excitons in the different dots of the array. A hybrid exciton appears in the system owing to strong dipole-dipole interaction of the Frenkel exciton of the organic molecules with the Wannier-Mott transfer exciton of the quantum dot array. This hybrid exciton has both a large oscillator strength (Frenkel-like) and a large exciton Bohr radius (Wannier-like). At resonance between these two types of excitons, the optical nonlinearity is very high and can be controlled by changing parameters of the system such as dot radius and dot spacing.
NASA Astrophysics Data System (ADS)
Heyrovska, R.; Narayan, S.
2005-10-01
Recently, the ground state Bohr radius (aB) of hydrogen was shown to be divided into two Golden sections, aB,p = aB/ø2 and aB,e = aB/ø at the point of electrical neutrality, where ø = 1.618 is the Golden ratio (R. Heyrovska, Molecular Physics 103: 877-882, and the literature cited therein). The origin of the difference of two energy terms in the Rydberg equation was thus shown to be in the ground state energy itself, as shown below: EH = (1/2)e2/(?aB) = (1/2)(e2/?) [(1/aB,p - (1/aB,e)] (1). This work brings some new results that 1) a unit charge in vacuum has a magnetic moment, 2) (e2/2?) in eq. (1) is an electromagnetic condenser constant, 3) the de Broglie wavelengths of the proton and electron correspond to the Golden arcs of a circle with the Bohr radius, 4) the fine structure constant (?) is the ratio of the Planck's constants without and with the interaction of light with matter, 5) the g-factors of the electron and proton, ge/2 and gp/2 divide the Bohr radius at the magnetic center and 6) the ``mysterious'' value (137.036) of ? -1 = (360/ø2) - (2/ø3), where (2/ø3) arises from the difference, (gp - ge).
Exciton binding energy in semiconductor quantum dots
Pokutnii, S. I., E-mail: Pokutnyi_Sergey@inbox.ru [National Academy of Sciences of Ukraine, G.V. Kurdjumov Institute for Metal Physics (Ukraine)
2010-04-15
In the adiabatic approximation in the context of the modified effective mass approach, in which the reduced exciton effective mass {mu} = {mu}(a) is a function of the radius a of the semiconductor quantum dot, an expression for the exciton binding energy E{sub ex}(a) in the quantum dot is derived. It is found that, in the CdSe and CdS quantum dots with the radii a comparable to the Bohr exciton radii a{sub ex}, the exciton binding energy E{sub ex}(a) is substantially (respectively, 7.4 and 4.5 times) higher than the exciton binding energy in the CdSe and CdS single crystals.
Exciton mapping at subwavelength scales in two-dimensional materials.
Tizei, Luiz H G; Lin, Yung-Chang; Mukai, Masaki; Sawada, Hidetaka; Lu, Ang-Yu; Li, Lain-Jong; Kimoto, Koji; Suenaga, Kazu
2015-03-13
Spatially resolved electron-energy-loss spectroscopy (EELS) is performed at diffuse interfaces between MoS2 and MoSe2 single layers. With a monochromated electron source (20 meV) we successfully probe excitons near the interface by obtaining the low loss spectra at the nanometer scale. The exciton maps clearly show variations even with a 10 nm separation between measurements; consequently, the optical band gap can be measured with nanometer-scale resolution, which is 50 times smaller than the wavelength of the emitted photons. By performing core-loss EELS at the same regions, we observe that variations in the excitonic signature follow the chemical composition. The exciton peaks are observed to be broader at interfaces and heterogeneous regions, possibly due to interface roughness and alloying effects. Moreover, we do not observe shifts of the exciton peak across the interface, possibly because the interface width is not much larger than the exciton Bohr radius. PMID:25815966
Exciton Mapping at Subwavelength Scales in Two-Dimensional Materials
NASA Astrophysics Data System (ADS)
Tizei, Luiz H. G.; Lin, Yung-Chang; Mukai, Masaki; Sawada, Hidetaka; Lu, Ang-Yu; Li, Lain-Jong; Kimoto, Koji; Suenaga, Kazu
2015-03-01
Spatially resolved electron-energy-loss spectroscopy (EELS) is performed at diffuse interfaces between MoS2 and MoSe2 single layers. With a monochromated electron source (20 meV) we successfully probe excitons near the interface by obtaining the low loss spectra at the nanometer scale. The exciton maps clearly show variations even with a 10 nm separation between measurements; consequently, the optical band gap can be measured with nanometer-scale resolution, which is 50 times smaller than the wavelength of the emitted photons. By performing core-loss EELS at the same regions, we observe that variations in the excitonic signature follow the chemical composition. The exciton peaks are observed to be broader at interfaces and heterogeneous regions, possibly due to interface roughness and alloying effects. Moreover, we do not observe shifts of the exciton peak across the interface, possibly because the interface width is not much larger than the exciton Bohr radius.
Excitons in monolayer transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Li, J.; Zhong, Y. L.; Zhang, Dong
2015-08-01
We theoretically investigate the exciton formed with two massive Dirac particles in monolayer \\text{Mo}{{\\text{S}}2} and other transition metal dichalcogenides as well as two layers separated by a dielectric layer. In the low-energy limit, the separation of the center-of-mass and relative motions is obtained. Analytical solutions for the exciton wave function and energy dispersion are obtained including the Coulomb interaction between electron and hole, the exciton Bohr radius, binding energy and its effective mass are obtained in monolayer transition metal dichalcogenides. In the case of two monolayers separated by a dielectric layer, we find that the exciton effective mass can be continuously tuned by the interlayer separation.
Excitons in monolayer transition metal dichalcogenides.
Li, J; Zhong, Y L; Zhang, Dong
2015-08-12
We theoretically investigate the exciton formed with two massive Dirac particles in monolayer [Formula: see text] and other transition metal dichalcogenides as well as two layers separated by a dielectric layer. In the low-energy limit, the separation of the center-of-mass and relative motions is obtained. Analytical solutions for the exciton wave function and energy dispersion are obtained including the Coulomb interaction between electron and hole, the exciton Bohr radius, binding energy and its effective mass are obtained in monolayer transition metal dichalcogenides. In the case of two monolayers separated by a dielectric layer, we find that the exciton effective mass can be continuously tuned by the interlayer separation. PMID:26190703
Exciton entanglement in two coupled semiconductor microcrystallites
Yu-xi Liu; Sahin K. Ozdemir; Adam Miranowicz; Masato Koashi; Nobuyuki Imoto
2004-04-01
Entanglement of the excitonic states in the system of two coupled semiconductor microcrystallites, whose sizes are much larger than the Bohr radius of exciton in bulk semiconductor but smaller than the relevant optical wavelength, is quantified in terms of the entropy of entanglement. It is observed that the nonlinear interaction between excitons increases the maximum values of the entropy of the entanglement more than that of the linear coupling model. Therefore, a system of two coupled microcrystallites can be used as a good source of entanglement with fixed exciton number. The relationship between the entropy of the entanglement and the population imbalance of two microcrystallites is numerically shown and the uppermost envelope function for them is estimated by applying the Jaynes principle.
Two-dimensional excitons in three-dimensional hexagonal boron nitride
Cao, X. K.; Lin, J. Y. Jiang, H. X.; Clubine, B.; Edgar, J. H.
2013-11-04
The recombination processes of excitons in hexagonal boron nitride (hBN) have been probed using time-resolved photoluminescence. It was found that the theory for two-dimensional (2D) exciton recombination describes well the exciton dynamics in three-dimensional hBN. The exciton Bohr radius and binding energy deduced from the temperature dependent exciton recombination lifetime is around 8?Å and 740?meV, respectively. The effective masses of electrons and holes in 2D hBN deduced from the generalized relativistic dispersion relation of 2D systems are 0.54m{sub o}, which are remarkably consistent with the exciton reduced mass deduced from the experimental data. Our results illustrate that hBN represents an ideal platform to study the 2D optical properties as well as the relativistic properties of particles in a condensed matter system.
Demir, Hilmi Volkan
Wannier exciton refers to a hydrogen-like bound state intrinsically with its Bohr radius exceeding the crystal homopolymer composite, and the measured energy transfer efficiencies are consistent with the analytical model lattice constant; however, in our NCs investigated in this work, such a hydrogen-like bound state cannot
Binding energy and stability of charged excitons in a semiconductor cylindrical quantum dot
NASA Astrophysics Data System (ADS)
Safwan, S. A.; Hekmat, M. H.; Asmaa, A. S.; Elmeshed, Nagwa
2008-10-01
The binding energy of full three-dimensional (3-D) charged excitons confined in a semiconductor cylindrical quantum dot (QD) is theoretically investigated using a variational procedure within the effective mass approximation. We predicted a trial wave function to not only satisfy the strong confinement regime but also yield the correct results in the weak confinement regime. The trions confinement is described by a finite square potential well. We show that the negatively charged exciton has higher binding energy than the positively charged exciton, when the QD half height is less than the effective Bohr radius (strong confinement regime). At large QD, the negatively charged exciton binding energy crosses down the positively charged exciton binding energy and becomes an unstable system. We have clarified the paradoxes existing in the previous literatures concerning the trions binding energy.
The Yellow Excitonic Series of Cu2O Revisited by Lyman Spectroscopy
NASA Astrophysics Data System (ADS)
Tayagaki, Takeshi; Mysyrowicz, Andre; Kuwata-Gonokami, Makoto
2005-05-01
We report on the observation of the yellow exciton Lyman series up to the fourth term in Cu2O by time-resolved mid-infrared spectroscopy. The dependence of oscillator strength on the principal quantum number n can be well reproduced using the hydrogenic model including an AC dielectric constant, and precise information on the electronic structure of the 1s exciton state can be obtained. A Bohr radius a1s=7.9 Å and a 1s-2p transition dipole moment ?1s--2p=4.2 e{\\AA} were found.
ERIC Educational Resources Information Center
Haendler, Blanca L.
1982-01-01
Discusses the importance of teaching the Bohr atom at both freshman and advanced levels. Focuses on the development of Bohr's ideas, derivation of the energies of the stationary states, and the Bohr atom in the chemistry curriculum. (SK)
Takagi, Hidetsugu; Kunugita, Hideyuki; Ema, Kazuhiro; Sato, Mikio; Takeoka, Yuko
2013-12-04
We have investigated experimentally excitonic properties in organic-inorganic hybrid multi quantum well crystals, (C{sub 4}H{sub 9}NH{sub 3}){sub 2}PbBr{sub 4} and (C{sub 6}H{sub 5}?C{sub 2}H{sub 4}NH{sub 3}){sub 2}PbBr{sub 4}, by measuring photoluminescence, reflectance, photoluminescence excitation spectra. In these materials, the excitonic binding energies are enhanced not only by quantum confinement effect (QCE) but also by image charge effect (ICE), since the dielectric constant of the barrier layers is much smaller than that of the well layers. By comparing the 1s-exciton and 2s-exciton energies, we have investigated the influence of ICE with regard to the difference of the Bohr radius.
REMARKS ON THE BOHR PHENOMENON CATHERINE BENETEAU, ANDERS DAHLNER, AND DMITRY KHAVINSON
Khavinson, Dmitry
REMARKS ON THE BOHR PHENOMENON CATHERINE BÂ´ENÂ´ETEAU, ANDERS DAHLNER, AND DMITRY KHAVINSON Abstract. Bohr's theorem ([10]) states that analytic functions bounded by 1 in the unit disk have power series anzn such that |an||z|n Bohr radius.) On the other hand
Exciton-exciton annihilation in organic polariton microcavities
Akselrod, G. M.; Tischler, Jonathan R.; Young, E. R.; Nocera, D.G.; Bulovic, Vladimir
2010-09-27
We investigate the incoherent diffusion of excitons in thin films (5.1±0.1?nm thick) of a highly absorbing J-aggregated cyanine dye material (10{sup 6} ?cm{sup ?1} absorption constant) as the excitonic component of a polariton microcavity. Under high-intensity pulsed laser excitation, the J-aggregated molecular films exhibit significant exciton-exciton annihilation, indicating a large exciton diffusion radius of more than 100 nm. When the material is strongly coupled to a cavity, the polaritonic structure also shows exciton-exciton annihilation, which is a competing process against the establishment of a threshold population of polaritons needed for polariton lasing. This study suggests that exciton-exciton annihilation is a loss process which can significantly increase the lasing threshold in polariton microcavities.
Bohr-Sommerfeld quantization and meson spectroscopy
Fabian Brau
2004-12-14
We use the Bohr-Sommerfeld quantization approach in the context of constituent quark models. This method provides, for the Cornell potential, analytical formulae for the energy spectra which closely approximate numerical exact calculations performed with the Schrodinger or the spinless Salpeter equations. The Bohr-Sommerfeld quantization procedure can also be used to calculate other observables such as r.m.s. radius or wave function at the origin. Asymptotic dependence of these observables on quantum numbers are also obtained in the case of potentials which behave asymptotically as a power-law. We discuss the constraints imposed by these formulae on the dynamics of the quark-antiquark interaction.
ERIC Educational Resources Information Center
Willden, Jeff
2001-01-01
"Bohr's Atomic Model" is a small interactive multimedia program that introduces the viewer to a simplified model of the atom. This interactive simulation lets students build an atom using an atomic construction set. The underlying design methodology for "Bohr's Atomic Model" is model-centered instruction, which means the central model of the…
Special Bohr - Sommerfeld geometry
Nikolay A. Tyurin
2015-08-27
We present a new approach to special lagrangian geometry which works for Bohr - Sommerfeld lagrangian submanifolds of symplectic manifolds with integer symplectic forms. This leads to construction of finite dimensional moduli spaces of SBS lagrangian cycles over algebraic varieties.
Photoacoustic measurements of excitons in cdse nanorods
NASA Astrophysics Data System (ADS)
Awad, H.; Abdallah, T.; Mohammed, M. B.; Easawi, K.; Negm, S.; Talaat, H.
2010-03-01
Photoacoustic (PA) spectra were obtained for CdSe nanorods (NRs) of different aspect ratios, prepared via the organometallic synthesis. The second derivative spectra were used to have an accurate determination of the different excitonic transitions. Using the lowest transition energy (band gap) 1S(e)-1S1/2(h) and applying the effective mass model, the NRs diameters were determined. The obtained diameters were then compared to direct measurements of scanning tunneling microscopy (STM) and XRD. It is observed that the band gap depends on the diameter of the rods due to quantum confinement effect, since diameters are of the order of the bulk CdSe Bohr radius. The second derivative of the PA spectra for CdSe NRs also shows clearly a second excitonic transition1P(e)-1P1/2(h) in contrast to UV-Vis absorption spectra carried out for colloidal samples. The thermal parameters for samples were also measured and compared to the bulk values.
Caruso, Francisco
2008-01-01
Bohr's atomic model, its relationship to the radiation spectrum of the hydrogen atom and the inherent hypotheses are revisited. It is argued that Bohr could have adopted a different approach, focusing his analyzes on the stationary orbit of the electron and its decomposition on two harmonic oscillators and then imposing, as actually he did, Planck's quantization for the oscillators' energies. Some consequences of this procedure are examined.
NASA Astrophysics Data System (ADS)
Caruso, F.; Oguri, V.
2009-04-01
Bohr's atomic model, its relationship to the radiation spectrum of the hydrogen atom and the inherent hypotheses are revisited. It is argued that Bohr could have adopted a different approach, focusing his analyzes on the stationary orbit of the electron and its decomposition on two harmonic oscillators and then imposing, as actually he did, Planck's quantization for the oscillators' energies. Some consequences of this procedure are examined.
Francisco Caruso; Vitor Oguri
2008-06-03
Bohr's atomic model, its relationship to the radiation spectrum of the hydrogen atom and the inherent hypotheses are revisited. It is argued that Bohr could have adopted a different approach, focusing his analyzes on the stationary orbit of the electron and its decomposition on two harmonic oscillators and then imposing, as actually he did, Planck's quantization for the oscillators' energies. Some consequences of this procedure are examined.
Excitonic spectrum of the ZnO/ZnMgO quantum wells
Bobrov, M. A., E-mail: largaseal@gmail.com; Toropov, A. A.; Ivanov, S. V. [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); El-Shaer, A.; Bakin, A.; Waag, A. [TU Braunschweig, Institute of Semiconductor Technology (Germany)
2011-06-15
Excitonic spectrum of the wurtzite ZnO/Zn{sub 1-x}Mg{sub x}O quantum wells with a width on the order of or larger than the Bohr radius of the exciton has been studied; the quantum wells have been grown by the method of molecular beam epitaxy (with plasma-assisted activation of oxygen) on substrates of sapphire (0001). Low-temperature (25 K) spectra of photoluminescence excitation (PLE) have been experimentally measured, making it possible to resolve the peaks of exciton absorption in the quantum well. The spectrum of excitons in the quantum well is theoretically determined as a result of numerical solution of the Schroedinger equation by the variational method. The value of elastic stresses in the structure (used in calculations) has been determined from theoretical simulation of measured spectra of optical reflection. A comparison of experimental data with the results of calculations makes it possible to relate the observed features in the PLE spectra to excitons, including the lower level of dimensional quantization for electrons and two first levels of holes for the A and B valence bands of the wurtzite crystal. The values of the electron and hole masses in ZnO are refined, and the value of the built-in electric field introduced by spontaneous and piezoelectric polarizations is estimated.
Excited states of the A free exciton in CuInS2
NASA Astrophysics Data System (ADS)
Yakushev, M. V.; Martin, R. W.; Mudryi, A. V.; Ivaniukovich, A. V.
2008-03-01
High quality CuInS2 single crystals, grown by the traveling heater method in an indium solvent, were studied using reflectance and photoluminescence at 4.2K. The first, EA(n =2)=1.5494eV, and second, EA(n=3)=1.5532eV, excited states of the A free exciton have been observed in the photoluminescence spectra. Accurate values of the A exciton binding energy EFEA=18.5meV and Bohr radius aBA=3.8nm, bandgap Eg=1.5540eV at 4.2K and static dielectric constant ? =10.2 have been derived assuming a hydrogenic model.
Diamagnetic shift of the A free exciton in CuGaSe2 single crystals
NASA Astrophysics Data System (ADS)
Luckert, F.; Yakushev, M. V.; Faugeras, C.; Karotki, A. V.; Mudryi, A. V.; Martin, R. W.
2010-10-01
Single crystals of CuGaSe2 were studied using magnetophotoluminescence in magnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82×10-6 eV/T2. This rate was used to calculate the reduced mass as 0.115m0, the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m0 (m0 is the free electron mass) of the free A exciton using a low-field perturbation approach and the hydrogenic model.
Nondispersing Bohr Wave Packets
Maeda, H.; Gurian, J. H.; Gallagher, T. F.
2009-03-13
Long-lived, nondispersing circular, or Bohr, wave packets are produced starting from Li Rydberg atoms by exposing them first to a linearly polarized microwave field at the orbital frequency, 17.6 GHz at principal quantum number n=72, which locks the electron's motion into an approximately linear orbit in which the electron oscillates in phase with the microwave field. The microwave polarization is changed to circular polarization slowly compared to the orbital frequency, and the electron's motion follows, resulting in a nondispersing Bohr wave packet.
P. E. Georgoudis
2014-03-18
A conformal factor in the Bohr model embeds Bohr space in six dimensions, revealing the $O(6)$ symmetry and its contraction to the $E(5)$ at infinity. Phenomenological consequences are discussed after the re-formulation of the Bohr Hamiltonian in six dimensions on a five sphere.
ERIC Educational Resources Information Center
Latimer, Colin J.
1983-01-01
Discusses some lesser known examples of atomic phenomena to illustrate to students that the old quantum theory in its simplest (Bohr) form is not an antiquity but can still make an important contribution to understanding such phenomena. Topics include hydrogenic/non-hydrogenic spectra and atoms in strong electric and magnetic fields. (Author/JN)
NASA Astrophysics Data System (ADS)
Bellac, Michel Le
2014-11-01
The final form of quantum physics, in the particular case of wave mechanics, was established in the years 1925-1927 by Heisenberg, Schrödinger, Born and others, but the synthesis was the work of Bohr who gave an epistemological interpretation of all the technicalities built up over those years; this interpretation will be examined briefly in Chapter 10. Although Einstein acknowledged the success of quantum mechanics in atomic, molecular and solid state physics, he disagreed deeply with Bohr's interpretation. For many years, he tried to find flaws in the formulation of quantum theory as it had been more or less accepted by a large majority of physicists, but his objections were brushed away by Bohr. However, in an article published in 1935 with Podolsky and Rosen, universally known under the acronym EPR, Einstein thought he had identified a difficulty in the by then standard interpretation. Bohr's obscure, and in part beyond the point, answer showed that Einstein had hit a sensitive target. Nevertheless, until 1964, the so-called Bohr-Einstein debate stayed uniquely on a philosophical level, and it was actually forgotten by most physicists, as the few of them aware of it thought it had no practical implication. In 1964, the Northern Irish physicist John Bell realized that the assumptions contained in the EPR article could be tested experimentally. These assumptions led to inequalities, the Bell inequalities, which were in contradiction with quantum mechanical predictions: as we shall see later on, it is extremely likely that the assumptions of the EPR article are not consistent with experiment, which, on the contrary, vindicates the predictions of quantum physics. In Section 3.2, the origin of Bell's inequalities will be explained with an intuitive example, then they will be compared with the predictions of quantum theory in Section 3.3, and finally their experimental status will be reviewed in Section 3.4. The debate between Bohr and Einstein goes much beyond a simple controversy, which is after all almost eighty years old and has been settled today. In fact, the concept introduced in this debate, that of entanglement, lies at the heart of many very important developments of modern quantum physics, in particular all those linked to quantum information (Chapter 8). Moreover, we shall see that the phenomenon of non-local correlations compels us to revise in depth our space-time representation of quantum processes. These are the two reasons why a whole chapter is devoted to this debate.
The de Broglie-Bohr Model for the Hydrogen Atom = de Broglie's hypothesis that
Rioux, Frank
The de Broglie-Bohr Model for the Hydrogen Atom h m v = de Broglie's hypothesis that matter has -= Below the ground state energy and orbit radius of the electron in the hydrogen atom is found by plotting
The methodological lesson of complementarity: Bohr’s naturalistic epistemology
NASA Astrophysics Data System (ADS)
Folse, H. J.
2014-12-01
Bohr’s intellectual journey began with the recognition that empirical phenomena implied the breakdown of classical mechanics in the atomic domain; this, in turn, led to his adoption of the ‘quantum postulate’ that justifies the ‘stationary states’ of his atomic model of 1913. His endeavor to develop a wider conceptual framework harmonizing both classical and quantum descriptions led to his proposal of the new methodological goals and standards of complementarity. Bohr’s claim that an empirical discovery can demand methodological revision justifies regarding his epistemological lesson as supporting a naturalistic epistemology.
Reconsidering Bohr's reply to EPR
Hans Halvorson; Rob Clifton
2001-10-17
Although Bohr's reply to the EPR argument is supposed to be a watershed moment in the development of his philosophy of quantum theory, it is difficult to find a clear statement of the reply's philosophical point. Moreover, some have claimed that the point is simply that Bohr is a radical positivist. In this paper, we show that such claims are unfounded. In particular, we give a mathematically rigorous reconstruction of Bohr's reply to the \\emph{original} EPR argument that clarifies its logical structure, and which shows that it does not rest on questionable philosophical assumptions. Rather, Bohr's reply is dictated by his commitment to provide "classical" and "objective" descriptions of experimental phenomena.
A simple relativistic Bohr atom
NASA Astrophysics Data System (ADS)
Terzis, Andreas F.
2008-07-01
A simple concise relativistic modification of the standard Bohr model for hydrogen-like atoms with circular orbits is presented. As the derivation requires basic knowledge of classical and relativistic mechanics, it can be taught in standard courses in modern physics and introductory quantum mechanics. In addition, it can be shown in a class that one straightforward prediction of this relativistic version of Bohr's model is the impossibility of finding atoms in nature with atomic number larger than a critical value.
Compton wavelength, Bohr radius, Balmer's formula and g-factors
Raji Heyrovska
2004-01-11
The Balmer formula for the spectrum of atomic hydrogen is shown to be analogous to that in Compton effect and is written in terms of the difference between the absorbed and emitted wavelengths. The g-factors come into play when the atom is subjected to disturbances (like changes in the magnetic and electric fields), and the electron and proton get displaced from their fixed positions giving rise to Zeeman effect, Stark effect, etc.
EXTENSIONS OF BOHR'S INEQUALITY VERN I. PAULSEN* AND DINESH SINGH
Paulsen, Vern
EXTENSIONS OF BOHR'S INEQUALITY VERN I. PAULSEN* AND DINESH SINGH Abstract. We obtain operator-valued analogues of Bohr's inequality involving both the classical Bohr inequality. In the scalar case we extend Bohr's inequality to the case where one
Michael Carl
2007-11-19
We relate the Bohr-Sommerfeld conditions established in microlocal analysis to formal deformation quantization of symplectic manifolds by classifying star products adapted to some Lagrangian submanifold L, i.e. products preserving the classical vanishing ideal I of L up to I-preserving equivalences.
ERIC Educational Resources Information Center
Brunori, Maurizio
2012-01-01
Before the outbreak of World War II, Jeffries Wyman postulated that the "Bohr effect" in hemoglobin demanded the oxygen linked dissociation of the imidazole of two histidines of the polypeptide. This proposal emerged from a rigorous analysis of the acid-base titration curves of oxy- and deoxy-hemoglobin, at a time when the information on the…
Is Bohr challenge still relevant?
Leonardo Chiatti
2014-12-11
We argue that not all the theoretical content of the Bohr model has been captured by the definitive quantum formalism currently in use. In particular, the notion of quantum leap seems to refer to non-dynamic features, closely related to non-locality, which have not yet been formalized in a satisfactory way.
Atempts to link Quanta & Atoms before the Bohr Atom model
NASA Astrophysics Data System (ADS)
Venkatesan, A.; Lieber, M.
2005-03-01
Attempts to quantize atomic phenomena before Bohr are hardly ever mentioned in elementary textbooks.This presentation will elucidate the contributions of A.Haas around 1910. Haas tried to quantize the Thomson atom model as an optical resonator made of positive and negative charges. The inherent ambiguity of charge distribution in the model made him choose a positive spherical distribution around which the electrons were distributed.He obtained expressions for the Rydberg constant and what is known today as the Bohr radius by balancing centrifugal energy with Coulomb energy and quantizing it with Planck's relation E=h?. We point out that Haas would have arrived at better estimates of these constants had he used the virial theorem apart from the fact that the fundamental constants were not well known. The crux of Haas's physical picture was to derive Planck's constant h from charge quantum e , mass of electron m and atomic radius. Haas faced severe criticism for applying thermodynamic concepts like Planck distribution to microscopic phenomena. We will try to give a flavor for how quantum phenomena were viewed at that time. It is of interest to note that the driving force behind Haas's work was to present a paper that would secure him a position as a Privatdozent in History of Physics. We end with comments by Bohr and Sommerfeld on Haas's work and with some brief biographical remarks.
Energy Transfer of Excitons Between Quantum Wells Separated by a Wide Barrier
LYO,SUNGKWUN K.
1999-12-06
We present a microscopic theory of the excitonic Stokes and anti-Stokes energy transfer mechanisms between two widely separated unequal quantum wells with a large energy mismatch ({Delta}) at low temperatures (T). Exciton transfer through dipolar coupling, photon-exchange coupling and over-barrier ionization of the excitons through exciton-exciton Auger processes are examined. The energy transfer rate is calculated as a function of T and the center-to-center distance d between the two wells. The rates depend sensitively on T for plane-wave excitons. For located excitons, the rates depend on T only through the T-dependence of the localization radius.
Kenichiro Tanaka; Takayuki Takahashi; Takuma Ban; Takashi Kondo; Kazuhito Uchida; Noboru Miura
2003-01-01
Optical absorption and magnetoabsorption spectra of the lead-halide-based perovskite-type crystals, CH3NH3PbX3 (X=Br, I) have been investigated. The lowest-energy excitons in these crystals are normal three-dimensional Wannier-type excitons. Bohr radii, binding energies, reduced masses, effective g factors, and oscillator strengths of the excitons have been determined with satisfactory accuracy. A larger bandgap and more tightly bound nature of the excitons in
Ehrenfest's adiabatic hypothesis in Bohr's quantum theory
Pérez, Enric
2015-01-01
It is widely known that Paul Ehrenfest formulated and applied his adiabatic hypothesis in the early 1910s. Niels Bohr, in his first attempt to construct a quantum theory in 1916, used it for fundamental purposes in a paper which eventually did not reach the press. He decided not to publish it after having received the new results by Sommerfeld in Munich. Two years later, Bohr published "On the quantum theory of line-spectra." There, the adiabatic hypothesis played an important role, although it appeared with another name: the principle of mechanical transformability. In the subsequent variations of his theory, Bohr never suppressed this principle completely. We discuss the role of Ehrenfest's principle in the works of Bohr, paying special attention to its relation to the correspondence principle. We will also consider how Ehrenfest faced Bohr's uses of his more celebrated contribution to quantum theory, as well as his own participation in the spreading of Bohr's ideas.
H. BOHR'S THEOREM FOR BOUNDED SYMMETRIC Abstract. A theorem of H. Bohr (1914) states that if f(z) =
1914-01-01
H. BOHR'S THEOREM FOR BOUNDED SYMMETRIC DOMAINS GUY ROOS Abstract. A theorem of H. Bohr (1914 on classification. Introduction The following theorem was proved by Harald Bohr [Bohr 1914] for |z| circled symmetric domain. In the above generalization of Bohr's theorem, one considers the Taylor
Corda, Christian
2015-01-01
The idea that black holes (BHs) result in highly excited states representing both the "hydrogen atom" and the "quasi-thermal emission" in quantum gravity is today an intuitive but general conviction. In this paper it will be shown that such an intuitive picture is more than a picture. In fact, we will discuss a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. The model is completely consistent with existing results in the literature, starting from the celebrated result of Bekenstein on the area quantization.
Christian Corda
2015-03-11
The idea that black holes (BHs) result in highly excited states representing both the "hydrogen atom" and the "quasi-thermal emission" in quantum gravity is today an intuitive but general conviction. In this paper it will be shown that such an intuitive picture is more than a picture. In fact, we will discuss a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. The model is completely consistent with existing results in the literature, starting from the celebrated result of Bekenstein on the area quantization.
Vibrating Wire Loop and the Bohr Model
NASA Astrophysics Data System (ADS)
Bloom, Danning; Bloom, Dan W.
2003-05-01
PASCO scientific has designed a vibration apparatus that includes a mechanical driver used to excite vibrations in various systems. One of these is a circular wire loop, which PASCO suggests can be used as a visual representation of the Bohr model of the hydrogen atom. In this paper we investigate the similarity between the wire loop and the Bohr atom.
Porter, Mason A.
GroundControl toNielsBohr: ExploringOuterSpace withAtomicPhysics Mason A. Porter and Predrag the theory of dy- namical systems, NASA launched the spacecraft Genesis towards the Sun to collect pieces. In a turn of events that would have astonished anyone but N. Bohr, we now know that chaotic tra- jectories
Rutherford and Bohr describe atomic structure 1913
NSDL National Science Digital Library
1998-01-01
This page is from PBS A Science Odyssey: People and Discoveries. It describes Bohr's contribution to theories of the atom and its relationship to others' such as Rutherford's. Links to relevant pages are provided. An image of Bohr's conception drawn in his notebook is included.
What classicality? Decoherence and Bohr's classical concepts
Maximilian Schlosshauer; Kristian Camilleri
2012-03-12
Niels Bohr famously insisted on the indispensability of what he termed "classical concepts." In the context of the decoherence program, on the other hand, it has become fashionable to talk about the "dynamical emergence of classicality" from the quantum formalism alone. Does this mean that decoherence challenges Bohr's dictum -- for example, that classical concepts do not need to be assumed but can be derived? In this paper, we'll try to shed some light down the murky waters where formalism and philosophy mingle. To begin, we'll clarify the notion of classicality in the decoherence description. We'll then discuss Bohr's and Heisenberg's takes on the quantum-classical problem and reflect on the different meanings of the terms "classicality" and "classical concepts" in the writings of Bohr and his followers. This analysis will allow us to put forward some tentative suggestions for how we may better understand the relation between decoherence-induced classicality and Bohr's classical concepts.
Analytical method for determining quantum well exciton properties in a magnetic field
NASA Astrophysics Data System (ADS)
Stépnicki, Piotr; Piétka, Barbara; Morier-Genoud, François; Deveaud, Benoît; Matuszewski, Micha?
2015-05-01
We develop an analytical approximate method for determining the Bohr radii of Wannier-Mott excitons in thin quantum wells under the influence of magnetic field perpendicular to the quantum well plane. Our hybrid variational-perturbative method allows us to obtain simple closed formulas for exciton binding energies and optical transition rates. We confirm the reliability of our method through exciton-polariton experiments realized in a GaAs/AlAs microcavity with an 8 nm InxGa1 -xAs quantum well and magnetic field strengths as high as 14 T.
Excitonic Spectra in Semiconductor Nanostructures Roland Zimmermann
Zimmermann, Roland
Âhole bound state is a rescaled version of the Hydrogen atom, with Bohr radius a \\Lambda = Â¯h 2 ffl S =Â¯e 2 for dipoleÂallowed optical transitions is given by 1) Ã? 3D 2 (!) = 1 X n=1 2 n 3 ffi (E + n \\Gamma2 ) + \\Theta(E) 1 \\Gamma exp(\\Gamma2Ã?= p E) (1) with energy variable E = (Â¯h! \\Gamma E g )=Ry \\Lambda
Bohr Compacti cations of Discrete Structures Joan E. Hart
Kunen, Ken
Bohr Compacti#12;cations of Discrete Structures Joan E. Hart #3; Union College, Schenectady, NY.S.A. kunen@math.wisc.edu March 22, 1999 Abstract The Bohr compacti#12;cation and the Bohr topology are well Bohr topologies in this general setting. Some of these results are new even for groups; for example
Generalized Bohr compactication and model-theoretic connected components
KrupiÃ±ski, Krzysztof
Generalized Bohr compactication and model-theoretic connected components Krzysztof Krupi a direct description in the paper; the [externally denable] generalized Bohr compactcation of G/(G)000 M lies in between the externally denable generalized Bohr compactication and the denable Bohr
NIL BOHR0-SETS, POINCARE RECURRENCE AND GENERALIZED POLYNOMIALS
Shao, Song
NIL BOHR0-SETS, POINCARÂ´E RECURRENCE AND GENERALIZED POLYNOMIALS WEN HUANG, SONG SHAO concerning Bohr sets is investigated: for any d N does the collection of {n Z : S (S - n) . . . (S - dn) = } with S syndetic coincide with that of Nild Bohr0-sets? In this paper it is proved that Nild Bohr0-sets could
Zur Geschichte der Bohr-Sommerfeldschen Quantentheorie
NASA Astrophysics Data System (ADS)
Schöpf, Hans-Georg
In der vorliegenden Arbeit werden Artikel von N. Bohr, P. Ehrenfest, A. Sommerfeld, P. Epstein und K. Schwarzschild im Hinblick auf die wesentlichen Konzeptiontionen in der Geschichte der älteren Quantentheorie im Zeitraum von 1914 bis 1918 besprochen.Translated AbstractOn the History of Bohr-Sommerfeld Quantum TheoryIn the present paper articles of N. Bohr, P. Ehrenfest, A. Sommerfeld, P. Epstein and K. Schwarzschild are reviewed with respect to the conceptual essentials in the history of the early quantum theory during the period from 1914 to 1918.
Bohr Hamiltonian with deformation-dependent mass
NASA Astrophysics Data System (ADS)
Bonatsos, Dennis; Minkov, N.; Petrellis, D.; Quesne, C.
2015-04-01
The Bohr Hamiltonian with a mass depending on the nuclear deformation is solved using the techniques of supersymmetric quantum mechanics (SUSYQM). Analytical expressions for spectra and wave functions are obtained. Spectra and B(E2) transition rates are calculated for more than 50 ?-unstable nuclei and more than 60 prolate deformed nuclei using the Davidson potential and the Kratzer potential. In addition to solving the long standing problem of the too rapid increase of the moment of inertia with deformation, the method reveals a conformal factor in the Bohr Hamiltonian, embedding the Bohr space in six dimensions.
Bohr model as an algebraic collective model
Rowe, D. J.; Welsh, T. A.; Caprio, M. A.
2009-05-15
Developments and applications are presented of an algebraic version of Bohr's collective model. Illustrative examples show that fully converged calculations can be performed quickly and easily for a large range of Hamiltonians. As a result, the Bohr model becomes an effective tool in the analysis of experimental data. The examples are chosen both to confirm the reliability of the algebraic collective model and to show the diversity of results that can be obtained by its use. The focus of the paper is to facilitate identification of the limitations of the Bohr model with a view to developing more realistic, computationally tractable models.
Frenkel-like Wannier-Mott excitons in few-layer Pb I2
NASA Astrophysics Data System (ADS)
Toulouse, Alexis S.; Isaacoff, Benjamin P.; Shi, Guangsha; Matuchová, Marie; Kioupakis, Emmanouil; Merlin, Roberto
2015-04-01
Optical measurements and first-principles calculations of the band structure and exciton states in direct-gap bulk and few-layer Pb I2 indicate that the n =1 exciton is Frenkel-like in nature in that its energy exhibits a weak dependence on thickness down to atomic-length scales. Results reveal large increases in the gap and exciton binding energy with a decreasing number of layers and a transition of the fundamental gap, which becomes indirect for one and two monolayers. Calculated values are in reasonable agreement with a particle-in-a-box model relying on the Wannier-Mott theory of exciton formation. General arguments and existing data suggest that the Frenkel-like character of the lowest exciton is a universal feature of wide-gap layered semiconductors whose effective masses and dielectric constants give bulk Bohr radii that are on the order of the layer spacing.
Anion Bohr effect of human hemoglobin.
Bucci, E; Fronticelli, C
1985-01-15
The pH dependence of oxygen affinity of hemoglobin (Bohr effect) is due to ligand-linked pK shifts of ionizable groups. Attempt to identify these groups has produced controversial data and interpretations. In a further attempt to clarify the situation, we noticed that hemoglobin alkylated in its liganded form lost the Bohr effect while hemoglobin alkylated in its unliganded form showed the presence of a practically unmodified Bohr effect. In spite of this difference, analyses of the extent of alkylation of the two compounds failed to identify the presence of specific preferential alkylations. In particular, the alpha 1 valines and beta 146 histidines appeared to be alkylated to the same extent in the two proteins. Focusing our attention on the effect of the anions on the functional properties of hemoglobin, we measured the Bohr effect of untreated hemoglobin in buffers made with HEPES [N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid], MES [2-(N-morpholino)ethanesulfonic acid], and MOPS [3-(N-morpholino)propanesulfonic acid], which being zwitterions do not need addition of chlorides or other anions for reaching the desired pH. The shape acquired by the Bohr effect curves, either as pH dependence of oxygen affinity or as pH dependence of protons exchanged with the solution, was irreconcilable with that of the Bohr effect curves in usual buffers. This indicated the relevance of solvent components in determining the functional properties of hemoglobin. A new thermodynamic model is proposed for the Bohr effect that includes the interaction of hemoglobin with solvent components. The classic proton Bohr effect is a special case of the new theory. PMID:3978079
Nonlocality and Bohr's reply to EPR
N. David Mermin
1997-12-01
Henry Stapp's commentary (quant-ph/9711060) does not capture the point I was trying to make in my essay (quant-ph/9711052) on how a subtle flaw in his ``proof of quantum nonlocality'' clearly illustrates a central issue in Bohr's reply to EPR. I therefore wish to emphasize what I do and do not say in that essay and even, with some trepidation, what Bohr did and did not say in his reply to EPR.
Alkaline Bohr effect of human hemoglobin Ao.
Di Cera, E; Doyle, M L; Gill, S J
1988-04-01
Differential oxygen binding measurements obtained over the pH range 6.95 to 9.10 at 25 degrees C have allowed a detailed description of the alkaline Bohr effect of human hemoglobin Ao. Phenomenological analysis of the data in terms of the Adair equation shows that: (1) the oxygen binding curves are asymmetrical with the population of the triply oxygenated species being negligible throughout the pH range studied: (2) the shape of the oxygen binding curve is affected by pH, especially at low saturation; and (3) the maximum O2-proton linkage is -0.52 mole of proton per mole of oxygen at pH 7.4. A possible molecular mechanism of the Bohr effect is proposed within the framework of an allosteric model which accounts for the low population of triply oxygenated hemoglobin species. At least three Bohr groups are necessary for a quantitative description of the alkaline Bohr effect. Two of these groups titrate in the range of the His146 beta and Vall alpha residues, which have long been identified as the main alkaline Bohr groups, and altogether contribute 84% of the alkaline Bohr effect at physiological pH. A third ionizable group, linked to oxygenation presumably at the beta chains, is implicated and is titrated in a pH range characteristic of a surface histidyl residue. PMID:2840510
[Current conception of the Bohr effect].
Poyart, C F; Bursaux, E
1975-01-01
The molecular mechanism of the Bohr effect is explained according to the molecular model proposed by Perutz et al. The Bohr effect is due to changes in the pK of specific carboxyl and amino groups of the four globin chains following the transition between the deoxy and oxy conformations of the molecule. Carbon dioxide binds to the N terminal valine of the 4 monomers to form carbamino compounds. This carbaminoformation depends upon pH, PCO2 and predominates on deoxygenated haemoglobin. It is lowered when O2 binds to the heme groups (O2 linked carbamino compounds). Through the carbamino compounds Carbon dioxide lowers both the affinity of haemoglobin for O2 and the Bohr effect. Diphosphoglycerate also binds to the haemoglogin molecule. This organophosphate lowers the affinity for O2 but increases the Bohr effect. In whole blood, the Bohr effect is therefore dependent upon pH, O2 saturation, PCO2 and DPG concentration into the red blood cells. PMID:1718
Kristian Camilleri; Maximilian Schlosshauer
2015-02-23
Niels Bohr's doctrine of the primacy of "classical concepts" is arguably his most criticized and misunderstood view. We present a new, careful historical analysis that makes clear that Bohr's doctrine was primarily an epistemological thesis, derived from his understanding of the functional role of experiment. A hitherto largely overlooked disagreement between Bohr and Heisenberg about the movability of the "cut" between measuring apparatus and observed quantum system supports the view that, for Bohr, such a cut did not originate in dynamical (ontological) considerations, but rather in functional (epistemological) considerations. As such, both the motivation and the target of Bohr's doctrine of classical concepts are of a fundamentally different nature than what is understood as the dynamical problem of the quantum-to-classical transition. Our analysis suggests that, contrary to claims often found in the literature, Bohr's doctrine is not, and cannot be, at odds with proposed solutions to the dynamical problem of the quantum-classical transition that were pursued by several of Bohr's followers and culminated in the development of decoherence theory.
The Influence of Bohr on Delbruck
NASA Astrophysics Data System (ADS)
Holladay, Wendell
2000-11-01
The book by Robert Lagemann on the history of physics and astronomy at Vanderbilt University contains a chapter on Max Delbruck, a member of the Vanderbilt physics department from 1940 - 1947, where he did seminal work in establishing microbial genetics, for which he received the Nobel prize in physiology in 1969. Delbruck, a Ph.D. in physics for work with Max Born in Gottingen, had been inspired by Niels Bohr's suggestion of a complementary relation between biology and atomic physics to work in biology. We will explore exactly what Bohr said in this connection and argue that Delbruck's own work leads to a conclusion in opposition to Bohr's suggestion, namely that the existence of life is reducible to molecular physics, through the remarkable properties of DNA. The lesson for scientific methodology to be learned from this example is that science can lead to truth even if motivated by an ideology pushing in the opposite direction.
HOMOLOGY COBORDISM AND CLASSICAL KNOT CHRISTIAN BOHR, RONNIE LEE
Bohr, Christian
HOMOLOGY COBORDISM AND CLASSICAL KNOT INVARIANTS CHRISTIAN BOHR, RONNIE LEE Abstract. In this paper examples of 3{manifolds which cannot be obtained by integral surgery on a knot. 1 #12; 2 CHRISTIAN BOHR
A deBroglie-Bohr Model for Positronium Frank Rioux
Rioux, Frank
A deBroglie-Bohr Model for Positronium Frank Rioux Positronium is a metastable bound state, to be determined. The purpose of this tutorial is to calculate this value using the Bohr model for positronium
EMBEDDED SPHERES AND 4{MANIFOLDS WITH SPIN CHRISTIAN BOHR
Bohr, Christian
EMBEDDED SPHERES AND 4{MANIFOLDS WITH SPIN COVERINGS CHRISTIAN BOHR Abstract. A strategy Forschungsgemeinschaft. 1 #12; 2 CHRISTIAN BOHR embeddings, although there are topological versions of most of our
ON THE SIGNATURES OF EVEN 4--MANIFOLDS CHRISTIAN BOHR
Bohr, Christian
ON THE SIGNATURES OF EVEN 4--MANIFOLDS CHRISTIAN BOHR Abstract. In this paper, we prove a number by the Graduiertenkolleg ``Mathematik im Bereich ihrer Wechselwirkung mit der Physik''. 1 #12; 2 CHRISTIAN BOHR
Linearity of the hemoglobin oxidation bohr effect.
Hoffman, B M; Bull, C
1976-03-01
The hemoglobin oxidation Bohr effect below pH 7 is essentially proportional to the fraction of hemes oxidized, just as the ligation Bohr effect is proportional to fractional heme ligation. The reported nonlinear proton release during oxidation [(1965) J. Biol. Chem. 240, 3317-3324] is shown to be an artifact resulting from the use of ferricyanide as oxidant. Published forms of the two-state allosteric transition model for hemoglobin function have used several proton linkage schemes, and none are compatible with a linear proton release upon oxidation. PMID:1062790
Exciton states in quasi-zero-dimensional semiconductor nanosystems
Pokutnyi, S. I., E-mail: Pokutnyi_Sergey@inbox.ru [National Academy of Sciences of Ukraine, Kurdyumov Institute for Metal Physics (Ukraine)
2012-02-15
The variational method in the context of the modified effective mass approximation is used to calculate the dependence of exciton ground-state energy for a quantum dot embedded in a borosilicate glassy matrix on the quantum dot radius. It is shown that the peaks in the absorption and low-temperature luminescence spectra of such a nanosystem are shifted to shorter wavelengths due to size quantization of the exciton ground-state energy in the quantum dot.
Bohr Model Calculations for Atoms and Ions Frank Rioux
Rioux, Frank
Bohr Model Calculations for Atoms and Ions Frank RiouxBroglie Bohr model is described that can be used to calculate the electronic energies of atoms or ions extending the Bohr model to two and threeelectron atoms and ions could be used to enhance student
Lamprey Hemoglobin STRUCTURAL BASIS OF THE BOHR EFFECT*
Riggs, Austen
Lamprey Hemoglobin STRUCTURAL BASIS OF THE BOHR EFFECT* Received for publication, July 23, 1999 indicate that Glu75 is one of two groups responsible for the Bohr effect. Changing the distal histidine 73 (Petromyzon marinus) Hb were strongly pH-dependent (Bohr effect), a surprising result at the time because
QUASIMODES AND BOHR-SOMMERFELD CONDITIONS FOR THE TOEPLITZ OPERATORS
Charles, Laurent
QUASIMODES AND BOHR-SOMMERFELD CONDITIONS FOR THE TOEPLITZ OPERATORS L. CHARLES Abstract theory. We apply this to construct quasimodes for the Toeplitz operators and we state the Bohr-Sommerfeld conditions under the usual regularity assumption. To compare with the Bohr-Sommerfeld conditions
Bohr--Sommerfeld Quantization Rules in the Semiclassical Limit
Bohr--Sommerfeld Quantization Rules in the Semiclassical Limit George A. Hagedorn Department H(~) when the energy E and Planck's constant ~ satisfy the appropriate BohrÂSommerfeld conditions--dependent methods. The Bohr--Sommerfeld quantization rules arise as a sufficient conÂ dition under which our
SINGULAR BOHR-SOMMERFELD RULES FOR 2D INTEGRABLE SYSTEMS
SINGULAR BOHR-SOMMERFELD RULES FOR 2D INTEGRABLE SYSTEMS Yves Colin de Verdi#18;ere #3;; #3://www-fourier.ujf-grenoble.fr/prepublications.html Abstract In this paper, we describe Bohr-Sommerfeld rules for semi-classical completely integrable systems-classical Bohr-Sommerfeld rules match very accurately the \\purely quantum" computations. Keywords: eigenvalues
Bohr Topologies and Partition Theorems for Vector Spaces \\Lambda
Kunen, Ken
Bohr Topologies and Partition Theorems for Vector Spaces \\Lambda Kenneth Kunen y University. As an application of this theorem, we prove that there are countably infinite Abelian groups whose Bohr topologies of vectors in a vector space. Second, we apply this theorem to study the Bohr topologies for these vector
NASA Astrophysics Data System (ADS)
Ciuti, C.; La Rocca, G. C.
1997-11-01
We have calculated the nonlinear optical properties of a double QW structure, where it is possible to achieve a resonance between a real space direct exciton |dir (electron and hole both confined in the same well) and a real space indirect exciton |ind (electron and hole confined in separated wells). |dir and |ind are coupled by electron tunneling between the two QWs, so that the true excitonic eigenstates are the hybrid direct-indirect excitons. Because of the reduced electron-hole overlap, the |ind oscillator strength is negligible compared to |dir, but owing to the electron-hole charge separation, it does have large nonlinear properties. Apart from the above electro-optic effect, many-body nonlinearities (due to large two-dimensional Bohr radii) are significant. We have applied our model to the realistic polytype AlSb/InAs/AlSb/GaSb/AlSb structure.
Exciton-exciton annihilation in organic polariton microcavities
Bulovic, Vladimir
Sublinear intensity dependence of photoluminescence from organic exciton-polariton microcavities under non-resonant excitation in two power regimes is shown. The sublinearity is attributed to exciton-exciton annihilation, ...
Uncertainty rescued: Bohr's complementarity for composite systems
Ilki Kim; Guenter Mahler
2000-04-12
Generalized uncertainty relations may depend not only on the commutator relation of two observables considered, but also on mutual correlations, in particular, on entanglement. The equivalence between the uncertainty relation and Bohr's complementarity thus holds in a much broader sense than anticipated.
Quadrupole collective states within the Bohr collective Hamiltonian
L. Prochniak; S. G. Rohozinski
2009-11-02
The article reviews the general version of the Bohr collective model for the description of quadrupole collective states, including a detailed study the model's kinematics. The general form of the classical and quantum Bohr Hamiltonian is presented together with a discussion of the tensor structure of the collective wave functions and with a short review of various methods of solving the Bohr Hamiltonian eigenvalue equation.The methods of derivation of the classical and quantum Bohr Hamiltonian from the microscopic many-body theory are recalled and the microscopic approach to the Bohr Hamiltonian is applied to interpret collective properties of 12 heavy even-even nuclei in the Hf-Hg region.
Analytical Special Solutions of the Bohr Hamiltonian
D. Bonatsos; D. Lenis; D. Petrellis; P. A. Terziev; I. Yigitoglu
2005-12-13
The following special solutions of the Bohr Hamiltonian are briefly described: 1) Z(5) (approximately separable solution in five dimensions with gamma close to 30 degrees), 2) Z(4) (exactly separable gamma-rigid solution in four dimensions with gamma = 30 degrees), 3) X(3) (exactly separable gamma-rigid solution in three dimensions with gamma =0). The analytical solutions obtained using Davidson potentials in the E(5), X(5), Z(5), and Z(4) frameworks are also mentioned.
Bohr-Sommerfeld Quantization of Periodic Orbits
Gabor Vattay
1995-11-17
We show, that the canonical invariant part of $\\hbar$ corrections to the Gutzwiller trace formula and the Gutzwiller-Voros spectral determinant can be computed by the Bohr-Sommerfeld quantization rules, which usually apply for integrable systems. We argue that the information content of the classical action and stability can be used more effectively than in the usual treatment. We demonstrate the improvement of precision on the example of the three disk scattering system.
Spreading the gospel: The Bohr atom popularised
Kragh, Helge
2011-01-01
The emergence of quantum theory in the early decades of the twentieth century was accompanied by a wide range of popular science books, all of which presented in words and in images new scientific ideas about the structure of the atom. The work of physicists such as Ernest Rutherford and Niels Bohr, among others, was pivotal to the so-called planetary model of the atom, which, still today, is used in popular accounts and in science textbooks. In an attempt to add to our knowledge about the popular trajectory of the new atomic physics, this paper examines one book in particular, coauthored by Danish science writer Helge Holst and Dutch physicist and close collaborator of Niels Bohr, Hendrik A. Kramers. Translated from Danish into four European languages, the book not only presented contemporary ideas about the quantum atom, but also went into rather lengthy discussions about unresolved problems. Moreover, the book was quite explicit in identifying the quantum atom with the atom as described by Bohr's theory. W...
Optically programmable excitonic traps
Alloing, Mathieu; Lemaître, Aristide; Galopin, Elisabeth; Dubin, François
2013-01-01
With atomic systems, optically programmed trapping potentials have led to remarkable progress in quantum optics and quantum information science. Programmable trapping potentials could have a similar impact on studies of semiconductor quasi-particles, particularly excitons. However, engineering such potentials inside a semiconductor heterostructure remains an outstanding challenge and optical techniques have not yet achieved a high degree of control. Here, we synthesize optically programmable trapping potentials for indirect excitons of bilayer heterostructures. Our approach relies on the injection and spatial patterning of charges trapped in a field-effect device. We thereby imprint in-situ and on-demand electrostatic traps into which we optically inject cold and dense ensembles of excitons. This technique creates new opportunities to improve state-of-the-art technologies for the study of collective quantum behavior of excitons and also for the functionalisation of emerging exciton-based opto-electronic circuits. PMID:23546532
Cation influence on exciton localization in homologue scheelites.
Laasner, R; Nagirnyi, V; Vielhauer, S; Kirm, M; Spassky, D; Sirutkaitis, V; Grigonis, R; Vasil'ev, A N
2015-09-30
Homologue scheelite crystals CaWO4, SrWO4, and BaWO4 possess similar crystal and electronic structure, but their luminescence exhibits drastically different thermal stabilities. By measuring the temperature dependence of the decay time of the intrinsic luminescence and fitting it to a three level model, we have qualitatively shown the effective exciton radius to increase in the order CaWO4 [Formula: see text] SrWO4 [Formula: see text] BaWO4, which explains the differences in the thermal stability. The origin of the variation in the exciton radii is suggested to be related to differences in the excited state dynamics in these crystals. From the decay kinetics measured under conditions of high excitation density, the efficiency of dipole-dipole interaction between excitons is shown to grow with exciton delocalization. PMID:26354042
Neutral and positively charged excitons in narrow quantum ring
Porras Monroy, L. C.; Rodríguez-Prada, F. A.; Mikhailov, I. D.
2014-05-15
We study theoretically quantized states of a neutral and a positively charged exciton (trion X{sup +}) confined in a heterostructure with the ring-like geometry. In order to assess the experimentally relevant domain of parameters, we adopt a simple model of a narrow ring when 3D wave equations for the neutral and positively charged excitons can be separated. By using the Fourier series method, we have calculated the energy spectra of excitons complexes in a quantum ring as a function of the electron-to-hole mass ratio, the ring radius, and the magnetic field strength. The quantum-size effect and the size-dependent magnetic oscillations of energy levels of excitons' complexes spectra have been revealed.
Anomalous magnetization of a carbon nanotube as an excitonic insulator
NASA Astrophysics Data System (ADS)
Rontani, Massimo
2014-11-01
We show theoretically that an undoped carbon nanotube might be an excitonic insulator—the long-sought phase of matter proposed by Keldysh, Kohn, and others fifty years ago. We predict that the condensation of triplet excitons, driven by intervalley exchange interaction, spontaneously occurs at equilibrium if the tube radius is sufficiently small. The signatures of exciton condensation are its sizable contributions to both the energy gap and the magnetic moment per electron. The increase of the gap might have already been measured, albeit with a different explanation [V. V. Deshpande, B. Chandra, R. Caldwell, D. S. Novikov, J. Hone, and M. Bockrath, Science 323, 106 (2009), 10.1126/science.1165799]. The enhancement of the quasiparticle magnetic moment is a pair-breaking effect that counteracts the weak paramagnetism of the ground-state condensate of excitons. This property could rationalize the anomalous magnitude of magnetic moments recently observed in different devices close to charge neutrality.
Epistemological Dimensions in Niels Bohr's Conceptualization of Complementarity
NASA Astrophysics Data System (ADS)
Derry, Gregory
2008-03-01
Contemporary explications of quantum theory are uniformly ahistorical in their accounts of complementarity. Such accounts typically present complementarity as a physical principle that prohibits simultaneous measurements of certain dynamical quantities or behaviors, attributing this principle to Niels Bohr. This conceptualization of complementarity, however, is virtually devoid of content and is only marginally related to Bohr's actual writing on the topic. Instead, what Bohr presented was a subtle and complex epistemological argument in which complementarity is a shorthand way to refer to an inclusive framework for the logical analysis of ideas. The important point to notice, historically, is that Bohr's work involving complementarity is not intended to be an improvement or addition to a particular physical theory (quantum mechanics), which Bohr regarded as already complete. Bohr's work involving complementarity is actually an argument related to the goals, meaning, and limitations of physical theory itself, grounded in deep epistemological considerations stemming from the fundamental discontinuity of nature on a microscopic scale.
Mapping donor electron wave function deformations at sub-Bohr orbit resolution
Seung H. Park; Rajib Rahman; Gerhard Klimeck; Lloyd C. L. Hollenberg
2009-08-25
Quantum wave function engineering of dopant-based Si nano-structures reveals new physics in the solid-state, and is expected to play a vital role in future nanoelectronics. Central to any fundamental understanding or application is the ability to accurately characterize the deformation of the electron wave functions in these atom-based structures through electromagnetic field control. We present a method for mapping the subtle changes that occur in the electron wave function through the measurement of the hyperfine tensor probed by 29Si impurities. Our results show that detecting the donor electron wave function deformation is possible with resolution at the sub-Bohr radius level.
Exciton hybridization states in organic–semiconductor heterostructures containing quantum dots
NASA Astrophysics Data System (ADS)
Huong, Nguyen Que
2011-03-01
The formation of a hybridization state of Wannier Mott and Frenkel excitons is theoretically studied for different heterostructure configurations involving quantum dots. At the interfaces of the semiconductor quantum dots and the organic medium, the hybridization states are formed, having complimentary properties of both kinds of excitons as well as large optical nonlinearities. The coupling at resonance is very strong, depending on the parameters of the systems (dot radius, dot separation, generation of the organic dendrites and the materials of the systems, etc). The hybrid excitons are as sensitive to external perturbation as Wannier–Mott excitons. Upon the application of magnetic and electric fields, the coupling term between the two kinds of excitons increases. The most important feature of this system is that by adjusting the system parameters as well as the external fields and their orientation, one can tune the resonance between the two kinds of excitons to get different regions of mixing to obtain the expected high nonlinearity.
Electrostatic conveyer for excitons.
Winbow, A G; Leonard, J R; Remeika, M; Kuznetsova, Y Y; High, A A; Hammack, A T; Butov, L V; Wilkes, J; Guenther, A A; Ivanov, A L; Hanson, M; Gossard, A C
2011-05-13
We report on the study of indirect excitons in moving lattices-conveyers created by a set of ac voltages applied to the electrodes on the sample surface. The wavelength of this moving lattice is set by the electrode periodicity, the amplitude is controlled by the applied voltage, and the velocity is controlled by the ac frequency. We found the dynamical localization-delocalization transition for excitons in the conveyers and determined its dependence on exciton density and conveyer amplitude and velocity. PMID:21668190
Bohr-Sommerfeld quantization of periodic orbits
Vattay, G. [Division de Physique Theorique, Institut de Physique Nucleaire, F-91406 Orsay Cedex (France)] [Division de Physique Theorique, Institut de Physique Nucleaire, F-91406 Orsay Cedex (France)
1996-02-01
We show that the canonical invariant part of {h_bar} corrections to the Gutzwiller trace formula and the Gutzwiller-Voros spectral determinant can be computed by the Bohr-Sommerfeld quantization rules, which usually apply for integrable systems. We argue that the information content of the classical action and stability can be used more effectively than in the usual treatment. We demonstrate the improvement of precision on the example of the three disk scattering system. {copyright} {ital 1996 The American Physical Society.}
The operation : The interview of Niels Bohr
NASA Astrophysics Data System (ADS)
Terletskij, Yakov P.
The article represents a stenogramme of the recollections of professor Yakov Petrovich Terletskij (1912, St. Petersburg-1993, Moscow) concerning his meeting with professor Niels Bohr in Kopenhagen from 24 september 1945 till 22 november 1945 under the task of Soviet KGB and personally Lavrentii Berija. Some additional informations concerning previous preparations of the trip, the final stage of the mission, as well as general considerations about the development of Physics, persons of physicists and nuclear technologies has been given by the author of recollections throughout the text
Realization of Localized Bohr-like Wavepackets
Mestayer, J. J.; Wyker, B.; Lancaster, J. C.; Dunning, F. B.; Reinhold, Carlos O; Yoshida, S.; Burgdorfer, J.
2008-01-01
We demonstrate a protocol to create localized wavepackets in very-high-n Rydberg states which travel in nearly circular orbits around the nucleus. Although these wavepackets slowly dephase and eventually lose their localization, their motion can be monitored over several orbital periods. These wavepackets represent the closest analog yet achieved to the original Bohr model of the hydrogen atom, i.e., an electron in circular classical orbit around the nucleus. Possible extension of the approach to create so far elusive "planetary atoms" in highly correlated stable multiply-excited states is discussed.
Bohr Sommerfeld quantisation and molecular potentials
Shayak Bhattacharjee; D. S. Ray; J. K. Bhattacharjee
2011-12-19
We use the Bohr Sommerfeld quantization rule along with a perturbative evaluation of the action intergral to find exact energy levels for the P\\"oschl-Teller potential (both hyperbolic and trigonometric forms), the Morse potential, and the Rosen Morse potential. Combining perturbation theory with the simplest asymptotic evaluation of the action integral allows us to obtain all the energy levels of the Lennard-Jones potential with an accuracy greater than 0.1 per cent and serves to confirm that the perturbation results for P\\"oschl-Teller and Morse Potentials are exact.
Bohr-Sommerfeld Quantization of Space
Eugenio Bianchi; Hal M. Haggard
2012-08-10
We introduce semiclassical methods into the study of the volume spectrum in loop gravity. The classical system behind a 4-valent spinnetwork node is a Euclidean tetrahedron. We investigate the tetrahedral volume dynamics on phase space and apply Bohr-Sommerfeld quantization to find the volume spectrum. The analysis shows a remarkable quantitative agreement with the volume spectrum computed in loop gravity. Moreover, it provides new geometrical insights into the degeneracy of this spectrum and the maximum and minimum eigenvalues of the volume on intertwiner space.
The electric field of Bohr's atom
NASA Astrophysics Data System (ADS)
Streltsov, V. N.
On the basis of the Lienard-Wiechert potential it is shown that the electric field of the simplest Bohr atom oscillates though the mean (per period) value is equal to zero. The calculation with the use of the generally accepted presentation of the moving charge field (in the form of spheroid) gives the mean value of electric potential different from zero. A detailed answer to the criticism of our approach to the known problem of the electric potential of a neutral current-carrying ring is given.
Photovoltaics: Separating Multiple Excitons
Nozik, A. J.
2012-05-01
Scientists have demonstrated an efficient process for generating multiple excitons in adjacent silicon nanocrystals from a single high-energy photon. Their findings could prove useful for a wide range of photovoltaic applications.
100th anniversary of Bohr's model of the atom.
Schwarz, W H Eugen
2013-11-18
In the fall of 1913 Niels Bohr formulated his atomic models at the age of 27. This Essay traces Bohr's fundamental reasoning regarding atomic structure and spectra, the periodic table of the elements, and chemical bonding. His enduring insights and superseded suppositions are also discussed. PMID:24123759
Davidson potential and SUSYQM in the Bohr Hamiltonian
Georgoudis, P. E.
2013-06-10
The Bohr Hamiltonian is modified through the Shape Invariance principle of SUper-SYmmetric Quantum Mechanics for the Davidson potential. The modification is equivalent to a conformal transformation of Bohr's metric, generating a different {beta}-dependence of the moments of inertia.
Bohr's Creation of his Quantum Atom
NASA Astrophysics Data System (ADS)
Heilbron, John
2013-04-01
Fresh letters throw new light on the content and state of Bohr's mind before and during his creation of the quantum atom. His mental furniture then included the atomic models of the English school, the quantum puzzles of Continental theorists, and the results of his own studies of the electron theory of metals. It also included the poetry of Goethe, plays of Ibsen and Shakespeare, novels of Dickens, and rhapsodies of Kierkegaard and Carlyle. The mind that held these diverse ingredients together oscillated between enthusiasm and dejection during the year in which Bohr took up the problem of atomic structure. He spent most of that year in England, which separated him for extended periods from his close-knit family and friends. Correspondence with his fianc'ee, Margrethe Nørlund, soon to be published, reports his ups and downs as he adjusted to J.J. Thomson, Ernest Rutherford, the English language, and the uneven course of his work. In helping to smooth out his moods, Margrethe played an important and perhaps an enabling role in his creative process.
Infantile high myopia in Bohring-Opitz syndrome.
Simpson, Andrew R H; Gibbon, Caspar E A; Quinn, Anthony G; Turnpenny, Peter D
2007-10-01
Bohring-Opitz syndrome is a rare genetic condition of uncertain inheritance. It was first delineated by Bohring and coworkers in 1999 and up to 15 possible cases have been reported. It has both ophthalmic and systemic features and represents a unique syndrome considered to be distinct from Opitz C trigonocephaly syndrome. The classic features of Bohring-Opitz syndrome include prominent metopic suture, exophthalmos, hypertelorism, cleft lip and palate, flexion deformities of the upper limbs, nevi flammei, and significant neurodevelopmental delay. We report a child with Bohring-Opitz syndrome and infantile high myopia. Bohring's original description of the phenotype did not include myopia but since then both this case and two others have reported this association. The presence of high myopia may be helpful in identifying suitable candidate genes and elucidating the genetic mechanism, as well as alerting ophthalmologists to the importance of refraction for affected children. PMID:17498985
Resisting the Bohr Atom: The Early British Opposition
NASA Astrophysics Data System (ADS)
Kragh, Helge
2011-03-01
When Niels Bohr's theory of atomic structure appeared in the summer and fall of 1913, it quickly attracted attention among British physicists. While some of the attention was supportive, others was critical. I consider the opposition to Bohr's theory from 1913 to about 1915, including attempts to construct atomic theories on a classical basis as alternatives to Bohr's. I give particular attention to the astrophysicist John W. Nicholson, who was Bohr's most formidable and persistent opponent in the early years. Although in the long run Nicholson's objections were inconsequential, for a short period of time his atomic theory was considered to be a serious rival to Bohr's. Moreover, Nicholson's theory is of interest in its own right.
Bohr effect of hemoglobins: Accounting for differences in magnitude.
Okonjo, Kehinde O
2015-09-01
The basis of the difference in the Bohr effect of various hemoglobins has remained enigmatic for decades. Fourteen amino acid residues, identical in pairs and located at specific 'Bohr group positions' in human hemoglobin, are implicated in the Bohr effect. All 14 are present in mouse, 11 in dog, eight in pigeon and 13 in guinea pig hemoglobin. The Bohr data for human and mouse hemoglobin are identical: the 14 Bohr groups appear at identical positions in both molecules. The dog data are different from the human because three Bohr group positions are occupied by non-ionizable groups in dog hemoglobin; the pigeon data are vastly different from the human because six Bohr group positions are occupied by non-ionizable groups in pigeon hemoglobin. The guinea pig data are quite complex. Quantitative analyses showed that only the pigeon data could be fitted with the Wyman equation for the Bohr effect. We demonstrate that, apart from guinea pig hemoglobin, the difference between the Bohr effect of each of the other hemoglobins and of pigeon hemoglobin can be accounted for quantitatively on the basis of the occupation of some of their Bohr group positions by non-ionizable groups in pigeon hemoglobin. We attribute the anomalous guinea pig result to a new salt-bridge formed in its R2 quaternary structure between the terminal NH3(+) group of one ?-chain and the COO(-) terminal group of the partner ?-chain in the same molecule. The pKas of this NH3(+) group are 6.33 in the R2 and 4.59 in the T state. PMID:26102019
NASA Technical Reports Server (NTRS)
Harris, Michael R.
1987-01-01
Resonator configurations permitting operation with large mode radius while maintaining good transverse mode discrimination are considered. Stable resonators incorporating an intracavity telescope and unstable resonator geometries utilizing an output coupler with a Gaussian reflectivity profile are shown to enable large radius single mode laser operation. Results of heterodyne studies of pulsed CO2 lasers with large (11mm e sup-2 radius) fundamental mode sizes are presented demonstrating minimal frequency sweeping in accordance with the theory of laser-induced medium perturbations.
Triplet exciton dissociation in singlet exciton fission photovoltaics.
Jadhav, Priya J; Brown, Patrick R; Thompson, Nicholas; Wunsch, Benjamin; Mohanty, Aseema; Yost, Shane R; Hontz, Eric; Van Voorhis, Troy; Bawendi, Moungi G; Bulovi?, Vladimir; Baldo, Marc A
2012-12-01
Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption. PMID:22968762
Raji Heyrovska
2008-01-22
An earlier finding that the van der waals radii are related to their de broglie wavelengths for some non-metallic elements has been extended here to show that in fact, they vary linearly with the ground state bohr radii for all the elements of groups 1a to 8 a. Similarly, the valence shell radii and the covalent radii are shown to be linearly dependent on the bohr radii. One table of data and 5 figures have been provided here showing that all the above radii are sums of two lengths, one of which is a multiple of the bohr radius and the other, a positive or negative constant for each group of elements.
Wiseman, Howard M., E-mail: H.Wiseman@Griffith.edu.au
2013-11-15
By rigorously formalizing the Einstein–Podolsky–Rosen (EPR) argument, and Bohr’s reply, one can appreciate that both arguments were technically correct. Their opposed conclusions about the completeness of quantum mechanics hinged upon an explicit difference in their criteria for when a measurement on Alice’s system can be regarded as not disturbing Bob’s system. The EPR criteria allow their conclusion–incompleteness–to be reached by establishing the physical reality of just a single observable q (not of both q and its conjugate observable p), but I show that Bohr’s definition of disturbance prevents the EPR chain of reasoning from establishing even this. Moreover, I show that Bohr’s definition is intimately related to the asymmetric concept of quantum discord from quantum information theory: if and only if the joint state has no Alice-discord, she can measure any observable without disturbing (in Bohr’s sense) Bob’s system. Discord can be present even when systems are unentangled, and this has implications for our understanding of the historical development of notions of quantum nonlocality. -- Highlights: •Both the EPR argument, and Bohr’s reply, were technically correct. •Their opposed conclusions came from different criteria for disturbance. •Bohr’s criterion works against even the simplified (one-variable) EPR argument. •Bohr’s criterion for disturbance is intimately related to quantum discord. •This illuminates the historical development of notions of quantum nonlocality.
Multiscale photosynthetic exciton transfer
A. K. Ringsmuth; G. J. Milburn; T. M. Stace
2012-06-14
Photosynthetic light harvesting provides a natural blueprint for bioengineered and biomimetic solar energy and light detection technologies. Recent evidence suggests some individual light harvesting protein complexes (LHCs) and LHC subunits efficiently transfer excitons towards chemical reaction centers (RCs) via an interplay between excitonic quantum coherence, resonant protein vibrations, and thermal decoherence. The role of coherence in vivo is unclear however, where excitons are transferred through multi-LHC/RC aggregates over distances typically large compared with intra-LHC scales. Here we assess the possibility of long-range coherent transfer in a simple chromophore network with disordered site and transfer coupling energies. Through renormalization we find that, surprisingly, decoherence is diminished at larger scales, and long-range coherence is facilitated by chromophoric clustering. Conversely, static disorder in the site energies grows with length scale, forcing localization. Our results suggest sustained coherent exciton transfer may be possible over distances large compared with nearest-neighbour (n-n) chromophore separations, at physiological temperatures, in a clustered network with small static disorder. This may support findings suggesting long-range coherence in algal chloroplasts, and provides a framework for engineering large chromophore or quantum dot high-temperature exciton transfer networks.
NASA Astrophysics Data System (ADS)
Meyer, B. K.
In the preceding chapter, we concentrated on the properties of free excitons. These free excitons may move through the sample and hit a trap, a nonradiative or a radiative recombination center. At low temperatures, the latter case gives rise to either deep center luminescence, mentioned in Sect. 7.1 and discussed in detail in Chap. 9, or to the luminescence of bound exciton complexes (BE or BEC). The chapter continues with the most prominent of these BECs, namely A-excitons bound to neutral donors. The next aspects are the more weakly BEs at ionized donors. The Sect. 7.4 treats the binding or localization energies of BEC from a theoretical point of view, while Sect. 7.5 is dedicated to excited states of BECs, which contain either holes from deeper valence bands or an envelope function with higher quantum numbers. The last section is devoted to donor-acceptor pair transitions. There is no section devoted specifically to excitons bound to neutral acceptors, because this topic is still partly controversially discussed. Instead, information on these A0X complexes is scattered over the whole chapter, however, with some special emphasis seen in Sects. 7.1, 7.4, and 7.5.
Volume Spectrum from Bohr-Sommerfeld Quantization
NASA Astrophysics Data System (ADS)
Haggard, Hal; Bianchi, Eugenio
2011-04-01
As first observed by Roger Penrose, angular momentum vectors can be used to describe geometrical objects, such as convex polyhedra. A remarkable outgrowth of this idea is that spaces of geometrical shapes can be endowed with a phase space structure. This allows all the tools of dynamical systems and semiclassical mechanics to be explored in the context of geometrical shapes. From the perspective of discrete approaches to gravity, such as the Regge Calculus where space is chopped into tetrahedral pieces, this opens fascinating new prospects. Here we present a discrete spectrum for the volume of a tetrahedron as obtained from Bohr-Sommerfeld quantization. We discuss connections with Loop Quantum Gravity and the implications for approximate treatments of more complex geometries.
Bohr's correspondence principle for atomic transport calculations
Viviana P. Ramunni; Alejandro M. F. Rivas
2015-03-26
In this work we perform a comparison between Classical Molecular Static (CMS) and quantum Density Functional Theory (DFT) calculations in order to obtain the diffusion coefficients for diluted \\emph{Fe-Cr} alloys. We show that, in accordance with Bohr's correspondence principle, as the size of the atomic cell (total number of atoms) is increased, quantum results with DFT approach to the classical ones obtained with CMS. Quantum coherence effects play a crucial role in the difference arising between CMS and DFT calculations. Also, thermal contact with the environment destroys quantum coherent effects making the classical behavior to emerge. Indeed, CMS calculations are in good agreement with available experimental data. We claim that, the atomic diffusion process in metals is a classical phenomena. Then, if reliable semi empirical potentials are available, a classical treatment of the atomic transport in metals is much convenient than DFT.
Helical topological exciton condensates
NASA Astrophysics Data System (ADS)
Michetti, Paolo; Budich, Jan C.; Trauzettel, Björn
2014-03-01
We investigate a bilayer system of critical HgTe quantum wells each featuring a spin-degenerate pair of massless Dirac fermions. In the presence of an electrostatic inter-layer Coulomb coupling, we determine the exciton condensate order parameter of the system self-consistently. Calculating the bulk topological Z2 invariant of the resulting mean field Hamiltonian, we discover a novel time reversal symmetric topological exciton condensate state coined the helical topological exciton condensate. We argue that this phase can exist for experimentally relevant parameters. Interestingly, due to its multi-band nature, the present bilayer model exhibits a nontrivial interplay between spontaneous symmetry breaking and topology: Depending on which symmetry the condensate order parameter spontaneously picks in combined orbital and spin space, stable minima in the free energy corresponding to both trivial and nontrivial gapped states can be found.
Exciton-exciton interaction under elliptically polarized light excitation
NASA Astrophysics Data System (ADS)
Robart, D.; Amand, T.; Marie, X.; Brousseau, M.; Barrau, J.; Bacquet, G.
1996-05-01
We illustrate how interesting it is to use an elliptically polarized laser beam for the investigation of the polarization properties of dense excitonic systems in semiconductor quantum wells. We investigate the spectral splitting of the exciton luminescence, observed in GaAs multiple-quantum-well structures at high exciton density, when the polarization of the resonant laser beam is progressively varied from circular determination of the strengths of both repulsive and attractive parts of the interaction between the excitons. We investigate the stability of the polarized excitonic phase as a function of both the ellipticity and the intensity of the photogenerating picosecond laser beam and measure the longitudinal and the transverse spin observations illustrate the driving role of the exciton-exciton exchange interaction in the spin relaxation mechanism at high density.
Bohr Compacti cations of Non-Abelian Groups Joan E. Hart y and Kenneth Kunen zx
Kunen, Ken
Bohr Compacti#12;cations of Non-Abelian Groups #3; Joan E. Hart y and Kenneth Kunen zx May 23, 2002 Abstract We investigate properties of the Bohr compacti#12;cation, bG, and the Bohr topology, G group G, its Bohr compacti#12;cation bG is its maximal com- pacti#12;cation, and G # denotes G given
NIL-BOHR SETS OF INTEGERS BERNARD HOST AND BRYNA KRA
Kra, Bryna
NIL-BOHR SETS OF INTEGERS BERNARD HOST AND BRYNA KRA Abstract. We study relations between subsets density or a set with bounded gaps) or in terms of additive structure (such as a Bohr set). Bohr sets theory. Here we introduce a higher order version of Bohr sets and give various properties
Exciton multiplication from first principles.
Jaeger, Heather M; Hyeon-Deuk, Kim; Prezhdo, Oleg V
2013-06-18
Third-generation photovolatics require demanding cost and power conversion efficiency standards, which may be achieved through efficient exciton multiplication. Therefore, generating more than one electron-hole pair from the absorption of a single photon has vast ramifications on solar power conversion technology. Unlike their bulk counterparts, irradiated semiconductor quantum dots exhibit efficient exciton multiplication, due to confinement-enhanced Coulomb interactions and slower nonradiative losses. The exact characterization of the complicated photoexcited processes within quantum-dot photovoltaics is a work in progress. In this Account, we focus on the photophysics of nanocrystals and investigate three constituent processes of exciton multiplication, including photoexcitation, phonon-induced dephasing, and impact ionization. We quantify the role of each process in exciton multiplication through ab initio computation and analysis of many-electron wave functions. The probability of observing a multiple exciton in a photoexcited state is proportional to the magnitude of electron correlation, where correlated electrons can be simultaneously promoted across the band gap. Energies of multiple excitons are determined directly from the excited state wave functions, defining the threshold for multiple exciton generation. This threshold is strongly perturbed in the presence of surface defects, dopants, and ionization. Within a few femtoseconds following photoexcitation, the quantum state loses coherence through interactions with the vibrating atomic lattice. The phase relationship between single excitons and multiple excitons dissipates first, followed by multiple exciton fission. Single excitons are coupled to multiple excitons through Coulomb and electron-phonon interactions, and as a consequence, single excitons convert to multiple excitons and vice versa. Here, exciton multiplication depends on the initial energy and coupling magnitude and competes with electron-phonon energy relaxation. Multiple excitons are generated through impact ionization within picoseconds. The basis of exciton multiplication in quantum dots is the collective result of photoexcitation, dephasing, and nonadiabatic evolution. Each process is characterized by a distinct time-scale, and the overall multiple exciton generation dynamics is complete by about 10 ps. Without relying on semiempirical parameters, we computed quantum mechanical probabilities of multiple excitons for small model systems. Because exciton correlations and coherences are microscopic, quantum properties, results for small model systems can be extrapolated to larger, realistic quantum dots. PMID:23459543
Effective Cleaning Radius Studies
Churnetski, B.V.
2001-10-15
This report discusses results of testing done in the Savannah River Laboratory half tank and full tank mockup facilities using kaolin clay slurries and the relationship between cleaning radius and pump and slurry characteristics.
Relativistic Corrections to the Bohr Model of the Atom
ERIC Educational Resources Information Center
Kraft, David W.
1974-01-01
Presents a simple means for extending the Bohr model to include relativistic corrections using a derivation similar to that for the non-relativistic case, except that the relativistic expressions for mass and kinetic energy are employed. (Author/GS)
Gregory D. Scholes; Garry Rumbles
2006-01-01
Nanoscale systems are forecast to be a means of integrating desirable attributes of molecular and bulk regimes into easily processed materials. Notable examples include plastic light-emitting devices and organic solar cells, the operation of which hinge on the formation of electronic excited states, excitons, in complex nanostructured materials. The spectroscopy of nanoscale materials reveals details of their collective excited states,
Triplet exciton caging in two dimensions
S. Arnold; R. R. Alfano; M. Pope; W. Yu; P. Ho; R. Selsby; J. Tharrats; C. E. Swenberg
1976-01-01
It is proposed that the bimolecular process of triplet exciton fusion to form singlet excitons can be enhanced by reducing the size of the domain in which the triplet exciton pair is free to move. These small domains, or exciton cages, are much more effective when the host material is highly anisotropic, and the triplet excitons are constrained to move
When champions meet: Rethinking the Bohr--Einstein debate
N. P. Landsman
2005-11-01
Einstein's philosophy of physics (as clarified by Fine, Howard, and Held) was predicated on his Trennungsprinzip, a combination of separability and locality, without which he believed objectification, and thereby "physical thought" and "physical laws", to be impossible. Bohr's philosophy (as elucidated by Hooker, Scheibe, Folse, Howard, Held, and others), on the other hand, was grounded in a seemingly different doctrine about the possibility of objective knowledge, namely the necessity of classical concepts. In fact, it follows from Raggio's Theorem in algebraic quantum theory that - within an appropriate class of physical theories - suitable mathematical translations of the doctrines of Bohr and Einstein are equivalent. Thus - upon our specific formalization - quantum mechanics accommodates Einstein's Trennungsprinzip if and only if it is interpreted a la Bohr through classical physics. Unfortunately, the protagonists themselves failed to discuss their differences in this constructive way, since their debate was dominated by Einstein's ingenious but ultimately flawed attempts to establish the "incompleteness" of quantum mechanics. This aspect of their debate may still be understood and appreciated, however, as reflecting a much deeper and insurmountable disagreement between Bohr and Einstein on the knowability of Nature. Using the theological controversy on the knowability of God as a analogy, Einstein was a Spinozist, whereas Bohr could be said to be on the side of Maimonides. Thus Einstein's off-the-cuff characterization of Bohr as a 'Talmudic philosopher' was spot-on.
Effect of dephasing on exciton superradiance and exciton cavity polaritons
NASA Astrophysics Data System (ADS)
Björk, Gunnar; Pau, Stanley; Jacobson, Joseph M.; Cao, Hui; Yamamoto, Yoshihisa
1996-05-01
Quantum-well exciton superradiance and exciton cavity polarization formation both require a substantial spatial coherence area in order to become the dominant exciton field interaction. In both interaction processes the quantum-well (in-plane) momentum is conserved. Momentum scattering, which is due, e.g., to interaction with a phonon reservoir, quickly localizes an initially delocalized exciton and randomizes the excitation momentum. We take a close look at how momentum scattering influences measurements of excitonic superradiance and of exciton cavity polariton splitting. An important conclusion is that, in general, measurements of the emitted light do not correspond to the evolution of the system as a whole. Therefore, e.g., the measured decay rates do not correspond to the true decay rate of the system.
Howard, Don
Revisiting the Einstein-Bohr Dialogue Don Howard Einstein and Bohr No names loom larger in the history of twentieth-century physics, and rightly so, Albert Einstein and Niels Bohr being the figures identified complementarity as the chief novelty in the quantum description of nature, Einstein for having
Shamirzaev, T. S., E-mail: timur@thermo.isp.nsc.ru; Toropov, A. I.; Bakarov, A. K.; Zhuravlev, K. S. [Institute of Semiconductor Physics (Russian Federation); Kobitski, A. Yu.; Wagner, H. P.; Zahn, D. R. T. [Institut fuer Physik, TU Chemnitz (Germany)
2006-05-15
The stationary and time-resolved polariton radiation in ultrahigh quality AIGaAs layers have been studied. It has been found that elastic exciton-exciton collisions lead to the appearance of a low-energy line of polariton radiation. We show that the rate of exciton-to-polariton transitions caused by elastic exciton-exciton collisions is determined not only by the density of the excitonic gas, but also by its temperature; this is in accordance with existing theoretical predictions.
2D materials: Ultrafast exciton dynamics
NASA Astrophysics Data System (ADS)
Marie, Xavier; Urbaszek, Bernhard
2015-09-01
Time-resolved measurements of the exciton dynamics in tungsten diselenide monolayers reveal ultrafast radiative recombination of the exciton ground state (~150 fs) and the interplay between optically bright and dark excitons.
NASA Astrophysics Data System (ADS)
Carlson, Carl E.
2015-05-01
The proton size, specifically its charge radius, was thought known to about 1% accuracy. Now a new method probing the proton with muons instead of electrons finds a radius about 4% smaller, and to boot gives an uncertainty limit of about 0.1%. We review the different measurements, some of the calculations that underlie them, some of the suggestions that have been made to resolve the conflict, and give a brief overview new related experimental initiatives. At present, however, the resolution to the problem remains unknown.
Lifetimes of excitons in cuprous oxide
Joon Ik Jang
2005-01-01
A direct gap semiconductor Cu2O provides a model system for studying relaxation kinetics and thermodynamics of excitons due to exciton-phonon and exciton-exciton interactions. As a bound state of electron and hole, an exciton makes itself visible by radiative recombination either direct or phonon-assisted process. If excitons can be raised to sufficient densities by pulsed laser excitation, they may undergo Bose-Einstein
Ma, Xuedan; Roslyak, Oleskiy; Duque, Juan G; Pang, Xiaoying; Doorn, Stephen K; Piryatinski, Andrei; Dunlap, David H; Htoon, Han
2015-07-01
Pump-dependent photoluminescence imaging and second-order photon correlation studies have been performed on individual single-walled carbon nanotubes (SWCNTs) at room temperature. These studies enable the extraction of both the exciton diffusion constant and the Auger recombination coefficient. A linear correlation between these parameters is attributed to the effect of environmental disorder in setting the exciton mean free path and capture-limited Auger recombination at this length scale. A suppression of photon antibunching is attributed to the creation of multiple spatially nonoverlapping excitons in SWCNTs, whose diffusion length is shorter than the laser spot size. We conclude that complete antibunching at room temperature requires an enhancement of the exciton-exciton annihilation rate that may become realizable in SWCNTs allowing for strong exciton localization. PMID:26182119
NASA Astrophysics Data System (ADS)
Ma, Xuedan; Roslyak, Oleskiy; Duque, Juan G.; Pang, Xiaoying; Doorn, Stephen K.; Piryatinski, Andrei; Dunlap, David H.; Htoon, Han
2015-07-01
Pump-dependent photoluminescence imaging and second-order photon correlation studies have been performed on individual single-walled carbon nanotubes (SWCNTs) at room temperature. These studies enable the extraction of both the exciton diffusion constant and the Auger recombination coefficient. A linear correlation between these parameters is attributed to the effect of environmental disorder in setting the exciton mean free path and capture-limited Auger recombination at this length scale. A suppression of photon antibunching is attributed to the creation of multiple spatially nonoverlapping excitons in SWCNTs, whose diffusion length is shorter than the laser spot size. We conclude that complete antibunching at room temperature requires an enhancement of the exciton-exciton annihilation rate that may become realizable in SWCNTs allowing for strong exciton localization.
Excited States of the A and B Free Excitons in CuInSe2
NASA Astrophysics Data System (ADS)
Yakushev, Michael V.; Luckert, Franziska; Faugeras, Clement; Karotki, Anatoli V.; Mudryi, Alexander V.; Martin, Robert W.
2011-05-01
CuInSe2 single crystals, grown by the vertical Bridgman technique were studied using polarisation resolved photoluminescence (PL) at cryogenic temperatures. The emission lines related to the first (n = 2) excited states for the A and B free excitons were observed in the PL spectra at 1.0481 and 1.0516 eV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (EgA = 1.050 eV and EgB = 1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.
Excited states of the free excitons in CuInSe2 single crystals
NASA Astrophysics Data System (ADS)
Yakushev, M. V.; Luckert, F.; Faugeras, C.; Karotki, A. V.; Mudryi, A. V.; Martin, R. W.
2010-10-01
High-quality CuInSe2 single crystals were studied using polarization resolved photoluminescence (PL) and magnetophotoluminescence (MPL). The emission lines related to the first (n=2) excited states for the A and B free excitons were observed in the PL and MPL spectra at 1.0481 meV and 1.0516 meV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 meV and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (EgA=1.050 eV and EgB=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.
Reconstructing Bohr's Reply to EPR in Algebraic Quantum Theory
Masanao Ozawa; Yuichiro Kitajima
2011-11-26
Halvorson and Clifton have given a mathematical reconstruction of Bohr's reply to Einstein, Podolsky and Rosen (EPR), and argued that this reply is dictated by the two requirements of classicality and objectivity for the description of experimental data, by proving consistency between their objectivity requirement and a contextualized version of the EPR reality criterion which had been introduced by Howard in his earlier analysis of Bohr's reply. In the present paper, we generalize the above consistency theorem, with a rather elementary proof, to a general formulation of EPR states applicable to both non-relativistic quantum mechanics and algebraic quantum field theory; and we clarify the elements of reality in EPR states in terms of Bohr's requirements of classicality and objectivity, in a general formulation of algebraic quantum theory.
Bohr model and dimensional scaling analysis of atoms and molecules
NASA Astrophysics Data System (ADS)
Svidzinsky, Anatoly; Chen, Goong; Chin, Siu; Kim, Moochan; Ma, Dongxia; Murawski, Robert; Sergeev, Alexei; Scully, Marlan; Herschbach, Dudley
It is generally believed that the old quantum theory, as presented by Niels Bohr in 1913, fails when applied to few electron systems, such as the H2 molecule. Here we review recent developments of the Bohr model that connect it with dimensional scaling procedures adapted from quantum chromodynamics. This approach treats electrons as point particles whose positions are determined by optimizing an algebraic energy function derived from the large-dimension limit of the Schrödinger equation. The calculations required are simple yet yield useful accuracy for molecular potential curves and bring out appealing heuristic aspects. We first examine the ground electronic states of H2, HeH, He2, LiH, BeH and Li2. Even a rudimentary Bohr model, employing interpolation between large and small internuclear distances, gives good agreement with potential curves obtained from conventional quantum mechanics. An amended Bohr version, augmented by constraints derived from Heitler-London or Hund-Mulliken results, dispenses with interpolation and gives substantial improvement for H2 and H3. The relation to D-scaling is emphasized. A key factor is the angular dependence of the Jacobian volume element, which competes with interelectron repulsion. Another version, incorporating principal quantum numbers in the D-scaling transformation, extends the Bohr model to excited S states of multielectron atoms. We also discuss kindred Bohr-style applications of D-scaling to the H atom subjected to superstrong magnetic fields or to atomic anions subjected to high frequency, superintense laser fields. In conclusion, we note correspondences to the prequantum bonding models of Lewis and Langmuir and to the later resonance theory of Pauling, and discuss prospects for joining D-scaling with other methods to extend its utility and scope.
The Bohr Model of the EarthSun System* Frank Rioux
Rioux, Frank
The Bohr Model of the EarthSun System* Frank Rioux Assuming the earth executes a circular orbit with the Bohr model for the earthsun system. Is this a legitimate example of the correspondence principle? E G
Exciton-photon correlations in bosonic condensates of exciton-polaritons
NASA Astrophysics Data System (ADS)
Kavokin, Alexey V.; Sheremet, Alexandra S.; Shelykh, Ivan A.; Lagoudakis, Pavlos G.; Rubo, Yuri G.
2015-07-01
Exciton-polaritons are mixed light-matter quasiparticles. We have developed a statistical model describing stochastic exciton-photon transitions within a condensate of exciton polaritons. We show that the exciton-photon correlator depends on the rate of incoherent exciton-photon transformations in the condensate. We discuss implications of this effect for the quantum statistics of photons emitted by polariton lasers.
Solution of the Bohr hamiltonian for soft triaxial nuclei
L. Fortunato; S. De Baerdemacker; K. Heyde
2006-07-24
The Bohr-Mottelson model is solved for a generic soft triaxial nucleus, separating the Bohr hamiltonian exactly and using a number of different model-potentials: a displaced harmonic oscillator in $\\gamma$, which is solved with an approximated algebraic technique, and Coulomb/Kratzer, harmonic/Davidson and infinite square well potentials in $\\beta$, which are solved exactly. In each case we derive analytic expressions for the eigenenergies which are then used to calculate energy spectra. Here we study the chain of osmium isotopes and we compare our results with experimental information and previous calculations.
Donor Bound Excitons Confined in Wurtzite InGaN/GaN Quantum Dot Nanowire Heterostructures
NASA Astrophysics Data System (ADS)
Zhang, Min; Shi, Jun-Jie
2013-09-01
Within the framework of the effective-mass approximation, the donor bound exciton states and interband optical transitions in InGaN/GaN strained quantum dot (QD) nanowire heterostructures (NWHETs) are investigated using a variational method, in which the built-in electric field (BEF) effect due to the spontaneous and piezoelectric polarizations and the three-dimensional (3D) confinement of the electron and hole in the QD are considered. Our results show that the position of the ionized donor, the strong BEF, the In-composition and the QD structural parameters have a significant influence on the donor bound exciton binding energy, the electron interband optical transitions and the exciton oscillator strength. The donor bound exciton binding energy increases obviously if the donor position changes from the left-interface to the right-interface. The BEF reduces the bound exciton binding energy and the exciton oscillator strength. The donor bound exciton binding energy increases, if the In-fraction increases. The emission wavelength monotonically increases if the QD height and radius increase.
Chem. Educator 2007, 12, 243245 243 Bohr Model Calculations for Atoms and Ions
Rioux, Frank
Chem. Educator 2007, 12, 243245 243 Bohr Model Calculations for Atoms and Ions Frank Rioux@csbsju.edu Received March 1, 2007. Accepted June 30, 2007. Abstract: A deBroglieBohr model is described that can publications in the pedagogical literature [1, 2] that showed how extending the Bohr model to two- and three
Lacunarity and the Bohr Topology Kenneth Kunen \\Lambda and Walter Rudin
Kunen, Ken
Lacunarity and the Bohr Topology Kenneth Kunen \\Lambda and Walter Rudin Department of Mathematics continuous. This is the Bohr topology of G. If G = Z, the additive group of the integers, and A is a Hadamard or cubic polynomial with integer coefficients, then the closure of f(Z) in the Bohr compactification of Zis
Mathematical Analysis of a Bohr Atom Model Goong Chen1,2
Hsu, Sze-Bi
Mathematical Analysis of a Bohr Atom Model Goong Chen1,2 , Zhonghai Ding3 , Sze-Bi Hsu1,4 , Moochan Kim2 , and Jianxin Zhou1 Abstract N. Bohr proposed in 1913 a model for atoms and molecules objective of this paper is to provide a rigorous mathematical analysis for the Bohr atom model. We have
A Simple Proof of Bohr's Vern I. Paulsen and Dinesh Singh
Paulsen, Vern
A Simple Proof of Bohr's Inequality Vern I. Paulsen and Dinesh Singh ABSTRACT. The classical inequality of Bohr concerning Taylor coeficients of bounded holomorphic functions on the unit disk, has a rather short and easy proof of the inequality. 1 Introduction Harald Bohr in 1914 obtained the following
On the Cauchy problem for scalar conservation laws on the Bohr compactification of Rn
On the Cauchy problem for scalar conservation laws on the Bohr compactification of Rn E.Yu. Panov Abstract We study the Cauchy problem for a multidimensional scalar conserva- tion law on the Bohr of entropy solutions as time t +. 1 Introduction. Let AP(Rn ) be the algebra of Bohr almost periodic
Chromatic Numbers and Bohr Topologies Berit Nilsen Givens y and Kenneth Kunen zx
Kunen, Ken
Chromatic Numbers and Bohr Topologies #3; Berit Nilsen Givens y and Kenneth Kunen zx October 16, 2002 Abstract We use chromatic numbers of hypergraphs to study the Bohr topol- ogy G # on discrete # . 1 Introduction If G is a (discrete) abelian group, then G # denotes G with its Bohr topol- ogy
A de Broglie-Bohr Model for the Hydrogen Atom Frank Rioux
Rioux, Frank
A de Broglie-Bohr Model for the Hydrogen Atom Frank Rioux Chemistry Department CSB|SJU The 1913 Bohr model of the hydrogen atom was replaced by Schrodinger's wave mechanical model in 1926. However, Bohr's model is still profitably taught today because of its conceptual and mathematical simplicity
Bohr Topologies and Compact Function Joan E. Hart y and Kenneth Kunen zx
Kunen, Ken
Bohr Topologies and Compact Function Spaces #3; Joan E. Hart y and Kenneth Kunen zx August 15, 2001 Abstract We consider (discrete) structures, A, for a countable language. A # denotes A with its Bohr spaces to char- acterize the possible compact subspaces of topological structures endowed with the Bohr
Exciton energy Kataura plot and excitonic effect of single wall carbon nanotubes
Maruyama, Shigeo
Exciton energy Kataura plot and excitonic effect of single wall carbon nanotubes Kentaro Sato1 in the different environment. From our calculation we show the exciton energy Kataura plot for different samples
Quantum Explorers: Bohr, Jordan, and Delbrück Venturing into Biology
NASA Astrophysics Data System (ADS)
Joaquim, Leyla; Freire, Olival; El-Hani, Charbel N.
2015-08-01
This paper disentangles selected intertwined aspects of two great scientific developments: quantum mechanics and molecular biology. We look at the contributions of three physicists who in the 1930s were protagonists of the quantum revolution and explorers of the field of biology: Niels Bohr, Pascual Jordan, and Max Delbrück. Their common platform was the defense of the Copenhagen interpretation in physics and the adoption of the principle of complementarity as a way of looking at biology. Bohr addressed the problem of how far the results reached in physics might influence our views about life. Jordan and Delbrück were followers of Bohr's ideas in the context of quantum mechanics and also of his tendency to expand the implications of the Copenhagen interpretation to biology. We propose that Bohr's perspective on biology was related to his epistemological views, as Jordan's was to his political positions. Delbrück's propensity to migrate was related to his transformation into a key figure in the history of twentieth-century molecular biology.
Revisiting Bohr's quantization hypothesis for the atomic orbitals
Sales, J H O; Suzuki, A T
2006-01-01
We deduce the quantization of the atomic orbit for the hydrogen's atom model proposed by Bohr without using his hypothesis of angular momentum quantization. We show that his hypothesis can be deduced from and is a consequence of the Planck's energy quantization.
Creation of non-dispersive Bohr-like wavepackets
NASA Astrophysics Data System (ADS)
Mestayer, J. J.; Wyker, B.; Dunning, F. B.; Yoshida, S.; Reinhold, C. O.; Burgdörfer, J.
2009-11-01
The use of a periodic train of half-cycle pulses to maintain strongly-localized wavepackets in high-n (n ~ 306) atoms that travel in near-circular orbits about the nucleus is demonstrated. The wavepacket is non-dispersive for hundreds of orbits and mimics the original Bohr model of the hydrogen atom.
A Bohr's Semiclassical Model of the Black Hole Thermodynamics
V. Pankovic; M. Predojevic; P. Grujic
2007-09-12
We propose a simple procedure for evaluating the main thermodynamical attributes of a Schwarzschild's black hole: Bekenstein-Hawking entropy, Hawking's temperature and Bekenstein's quantization of the surface area. We make use of the condition that the circumference of a great circle on the black hole horizon contains finite number of the corresponding reduced Compton's wavelength. It is essentially analogous to Bohr's quantization postulate in Bohr's atomic model interpreted by de Broglie's relation. We present black hole radiation in the form conceptually analogous to Bohr's postulate on the photon emission by discrete quantum jump of the electron within the Old quantum theory. It enables us, in accordance with Heisenberg's uncertainty relation and Bohr's correspondence principle, to make a rough estimate of the time interval for black hole evaporation, which turns out very close to time interval predicted by the standard Hawking's theory. Our calculations confirm Bekenstein's semiclassical result for the energy quantization, in variance with Frasca's (2005) calculations. Finally we speculate about the possible source-energy distribution within the black hole horizon.
Bohr Hamiltonian with deformation-dependent mass term
Dennis Bonatsos; P. Georgoudis; D. Lenis; N. Minkov; C. Quesne
2009-12-18
The Bohr Hamiltonian describing the collective motion of atomic nuclei is modified by allowing the mass to depend on the nuclear deformation. Exact analytical expressions are derived for spectra and wave functions in the case of a gamma-unstable Davidson potential, using techniques of supersymmetric quantum mechanics. Numerical results in the Xe-Ba region are discussed.
Would Bohr be born if Bohm were born before Born?
H. Nikolic
2007-09-10
I discuss a hypothetical historical context in which a Bohm-like deterministic interpretation of the Schrodinger equation could have been proposed before the Born probabilistic interpretation and argue that in such a context the Copenhagen (Bohr) interpretation would probably have never achieved great popularity among physicists.
Equivariant asymptotics for Bohr-Sommerfeld Lagrangian submanifolds
Marco Debernardi; Roberto Paoletti
2006-01-31
Suppose given a complex projective manifold $M$ with a fixed Hodge form $\\Omega$. The Bohr-Sommerfeld Lagrangian submanifolds of $(M,\\Omega)$ are the geometric counterpart to semi-classical physical states, and their geometric quantization has been extensively studied. Here we revisit this theory in the equivariant context, in the presence of a compatible (Hamiltonian) action of a connected compact Lie group.
"Bohr and Einstein": A Course for Nonscience Students
ERIC Educational Resources Information Center
Schlegel, Richard
1976-01-01
A study of the concepts of relativity and quantum physics through the work of Bohr and Einstein is the basis for this upper level course for nonscience students. Along with their scientific philosophies, the political and moral theories of the scientists are studied. (CP)
Quantum Explorers: Bohr, Jordan, and Delbrück Venturing into Biology
NASA Astrophysics Data System (ADS)
Joaquim, Leyla; Freire, Olival; El-Hani, Charbel N.
2015-09-01
This paper disentangles selected intertwined aspects of two great scientific developments: quantum mechanics and molecular biology. We look at the contributions of three physicists who in the 1930s were protagonists of the quantum revolution and explorers of the field of biology: Niels Bohr, Pascual Jordan, and Max Delbrück. Their common platform was the defense of the Copenhagen interpretation in physics and the adoption of the principle of complementarity as a way of looking at biology. Bohr addressed the problem of how far the results reached in physics might influence our views about life. Jordan and Delbrück were followers of Bohr's ideas in the context of quantum mechanics and also of his tendency to expand the implications of the Copenhagen interpretation to biology. We propose that Bohr's perspective on biology was related to his epistemological views, as Jordan's was to his political positions. Delbrück's propensity to migrate was related to his transformation into a key figure in the history of twentieth-century molecular biology.
Proton Radius Puzzle 1 Muonic hydrogen and the proton radius
Pachucki, Krzysztof
Proton Radius Puzzle 1 Muonic hydrogen and the proton radius puzzle Randolf Pohl Max-681 Warsaw, Poland Key Words Laser Spectroscopy, Atomic Physics, Proton Structure, Exotic Atoms, Nuclear extraction of the proton radius by Pohl et al. from the mea- #12;Annu. Rev. Nucl. Part. Sci. 2013, Vol. 63
NSDL National Science Digital Library
2012-07-20
ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Atomic Radius page includes resources for teaching students about trends in atomic radius.
Distal Radius Fracture (Broken Wrist)
... Academy of Orthopaedic Surgeons. Distal Radius Fracture (Broken Wrist) The radius is the larger of the two bones of the forearm. The end toward the wrist is called the distal end. A fracture of ...
What is complementarity?: Niels Bohr and the architecture of quantum theory
NASA Astrophysics Data System (ADS)
Plotnitsky, Arkady
2014-12-01
This article explores Bohr’s argument, advanced under the heading of ‘complementarity,’ concerning quantum phenomena and quantum mechanics, and its physical and philosophical implications. In Bohr, the term complementarity designates both a particular concept and an overall interpretation of quantum phenomena and quantum mechanics, in part grounded in this concept. While the argument of this article is primarily philosophical, it will also address, historically, the development and transformations of Bohr’s thinking, under the impact of the development of quantum theory and Bohr’s confrontation with Einstein, especially their exchange concerning the EPR experiment, proposed by Einstein, Podolsky and Rosen in 1935. Bohr’s interpretation was progressively characterized by a more radical epistemology, in its ultimate form, which was developed in the 1930s and with which I shall be especially concerned here, defined by his new concepts of phenomenon and atomicity. According to this epistemology, quantum objects are seen as indescribable and possibly even as inconceivable, and as manifesting their existence only in the effects of their interactions with measuring instruments upon those instruments, effects that define phenomena in Bohr’s sense. The absence of causality is an automatic consequence of this epistemology. I shall also consider how probability and statistics work under these epistemological conditions.
Two-dimensional exciton revisited
NASA Astrophysics Data System (ADS)
Parfitt, D. G. W.; Portnoi, M. E.
2003-04-01
We present some interesting mathematical results arising from a consideration of two-dimensional excitons, screened and unscreened. These include bound-state wave functions in the momentum representation and a new integral relation in terms of special functions.
Cavity enhanced transport of excitons
Johannes Schachenmayer; Claudiu Genes; Edoardo Tignone; Guido Pupillo
2015-05-20
We show that exciton-type transport in certain materials can be dramatically modified by their inclusion in an optical cavity: the modification of the electromagnetic vacuum mode structure introduced by the cavity leads to transport via delocalized polariton modes rather than through tunneling processes in the material itself. This can help overcome exponential suppression of transmission properties as a function of the system size in the case of disorder and other imperfections. We exemplify massive improvement of transmission for excitonic wave-packets through a cavity, as well as enhancement of steady-state exciton currents under incoherent pumping. These results may have implications for experiments of exciton transport in disordered organic materials. We propose that the basic phenomena can be observed in quantum simulators made of Rydberg atoms, cold molecules in optical lattices, as well as in experiments with trapped ions.
Singlet exciton fission in solution
Walker, Brian J.; Musser, Andrew J.; Beljonne, David; Friend, Richard H.
2013-11-17
Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley–Queisser limit in single-junction solar cells. Although the process through...
How fast is excitonic electroabsorption?
Schmitt-Rink, S; Chemla, D S; Knox, W H; Miller, D A
1990-01-01
Many semiconductor light modulators rely on changes in excitonic absorption induced by electric fields. We study their temporal response in the framework of a one-dimensional model, for which we solve exactly the timedependent Schrödinger equation. For a homogeneously broadened system, the electroabsorption response time is found to be simply the inverse of the (field-induced) exciton linewidth, which can be as short as 50 fsec. PMID:19759711
Bohr model and dimensional scaling analysis of atoms and molecules
NASA Astrophysics Data System (ADS)
Urtekin, Kerim
It is generally believed that the old quantum theory, as presented by Niels Bohr in 1913, fails when applied to many-electron systems, such as molecules, and nonhydrogenic atoms. It is the central theme of this dissertation to display with examples and applications the implementation of a simple and successful extension of Bohr's planetary model of the hydrogenic atom, which has recently been developed by an atomic and molecular theory group from Texas A&M University. This "extended" Bohr model, which can be derived from quantum mechanics using the well-known dimentional scaling technique is used to yield potential energy curves of H2 and several more complicated molecules, such as LiH, Li2, BeH, He2 and H3, with accuracies strikingly comparable to those obtained from the more lengthy and rigorous "ab initio" computations, and the added advantage that it provides a rather insightful and pictorial description of how electrons behave to form chemical bonds, a theme not central to "ab initio" quantum chemistry. Further investigation directed to CH, and the four-atom system H4 (with both linear and square configurations), via the interpolated Bohr model, and the constrained Bohr model (with an effective potential), respectively, is reported. The extended model is also used to calculate correlation energies. The model is readily applicable to the study of molecular species in the presence of strong magnetic fields, as is the case in the vicinities of white dwarfs and neutron stars. We find that magnetic field increases the binding energy and decreases the bond length. Finally, an elaborative review of doubly coupled quantum dots for a derivation of the electron exchange energy, a straightforward application of Heitler-London method of quantum molecular chemistry, concludes the dissertation. The highlights of the research are (1) a bridging together of the pre- and post quantum mechanical descriptions of the chemical bond (Bohr-Sommerfeld vs. Heisenberg-Schrodinger), and (2) the reporting of the appearance of new bound states of H2 in the presence of very strong magnetic fields. The new states emerge above the critical value of 5 x 107 G, and hence cannot be obtained perturbatively.
Creation of non-dispersive Bohr-like wave packets
NASA Astrophysics Data System (ADS)
Mestayer, Jeff; Wyker, B.; Dunning, F. B.; Reinhold, C. O.; Yoshida, S.; Burgdörfer, J.
2009-05-01
We demonstrate the use of a periodic train of half-cycle pulses to create strongly-localized non-dispersive wave packets in very-high-n (n ˜ 300) Rydberg atoms that travel in near-circular orbits about the nucleus. This motion can be maintained for hundreds of orbital periods mimicking the original Bohr model of the hydrogen atom which envisioned an electron in circular classical orbit about the nucleus. The conditions for formation of non-dispersive Bohr-like wave packets are discussed with the aid of Classical Trajectory Monte Carlo (CTMC) simulations and demonstrated through experiment. Research supported by the NSF, the Robert A. Welch Foundation, the OBES, U.S. DoE to ORNL, and by the FWF (Austria).
Analytical solutions of the Bohr Hamiltonian with the Morse potential
I. Boztosun; D. Bonatsos; I. Inci
2008-04-10
Analytical solutions of the Bohr Hamiltonian are obtained in the $\\gamma$-unstable case, as well as in an exactly separable rotational case with $\\gamma\\approx 0$, called the exactly separable Morse (ES-M) solution. Closed expressions for the energy eigenvalues are obtained through the Asymptotic Iteration Method (AIM), the effectiveness of which is demonstrated by solving the relevant Bohr equations for the Davidson and Kratzer potentials. All medium mass and heavy nuclei with known $\\beta_1$ and $\\gamma_1$ bandheads have been fitted by using the two-parameter $\\gamma$-unstable solution for transitional nuclei and the three-parameter ES-M for rotational ones. It is shown that bandheads and energy spacings within the bands are well reproduced for more than 50 nuclei in each case.
Analytical solutions of the Bohr Hamiltonian with the Morse potential
Boztosun, I.; Inci, I.; Bonatsos, D.
2008-04-15
Analytical solutions of the Bohr Hamiltonian are obtained in the {gamma}-unstable case, as well as in an exactly separable rotational case with {gamma}{approx_equal}0, called the exactly separable Morse (ES-M) solution. Closed expressions for the energy eigenvalues are obtained through the asymptotic iteration method (AIM), the effectiveness of which is demonstrated by solving the relevant Bohr equations for the Davidson and Kratzer potentials. All medium mass and heavy nuclei with known {beta}{sub 1} and {gamma}{sub 1} bandheads have been fitted by using the two-parameter {gamma}-unstable solution for transitional nuclei and the three-parameter ES-M for rotational ones. It is shown that bandheads and energy spacings within the bands are well reproduced for more than 50 nuclei in each case.
Singular Bohr-Sommerfeld Rules for 2D Integrable Systems
Yves Colin de Verdiere; San Vu Ngoc
2000-05-26
In this paper, we describe Bohr-Sommerfeld rules for semi-classical completely integrable systems with 2 degrees of freedom with non degenerate singularities (Morse-Bott singularities) under the assumption that the energy level of the first Hamiltonian is non singular. The more singular case of {\\it focus-focus} singularities is studied in [Vu Ngoc San, CPAM 2000] and [Vu Ngoc San, PhD 1998] The case of 1 degree of freedom has been studied in [Colin de Verdiere-Parisse, CMP 1999] Our theory is applied to some famous examples: the geodesics of the ellipsoid, the $1:2$-resonance, and Schroedinger operators on the sphere $S^2$. A numerical test shows that the semiclassical Bohr-Sommerfeld rules match very accurately the ``purely quantum'' computations.
Steering Quantum States Towards Classical Bohr-Like Orbits
Dunning, F. B.; Reinhold, Carlos O; Yoshida, S.; Burgdorfer, J.
2010-01-01
This article furnishes an introduction to the properties of time-dependent electronic wavefunctions in atoms and to physics at the interface between the quantum and classical worlds. We describe how, almost 100 years after the introduction of the Bohr model of the atom, it is now possible using pulsed electric fields to create in the laboratory localized wavepackets in high-n (n ~ 300) Rydberg atoms that travel in near-circular Bohr-like orbits mimicking the behavior of a classical electron. The control protocols employed are explained with the aid of quantum and classical dynamics. Remarkably, while many aspects of the underlying behavior can be described using classical arguments, even at n ~ 300 purely quantum effects such as revivals can be seen.
The Gravity and The Quantum: A Bohr-inspired Synthesis
Wagh, S M; Wagh, Abhijit H; Wagh, Sanjay M.
2006-01-01
An effective angular momentum quantization condition of the form $mvr=n\\hbar(m/m_F)$ is used to obtain a Bohr-like model of Hydrogen-type atoms and a modified Schr\\"{o}dinger equation. Newton's constant, $G$, of Gravitation gets explicitly involved through the fundamental mass $m_F$ as defined in the sequel. This non-relativistic formalism may be looked upon as a ``testing ground'' for the more general synthesis of the gravity and the quantum.
Creation of nondispersive Bohr-like wave packets
NASA Astrophysics Data System (ADS)
Mestayer, J. J.; Wyker, B.; Dunning, F. B.; Yoshida, S.; Reinhold, C. O.; Burgdörfer, J.
2009-03-01
We demonstrate the use of a periodic train of half-cycle pulses to maintain strongly-localized wave packets in very-high- n (ñ300) Rydberg atoms that travel in near-circular orbits about the nucleus. This motion can be followed for hundreds of orbital periods and mimics the original Bohr model of the hydrogen atom which envisioned an electron in circular classical orbit about the nucleus.
Microscopic Uni-axial Bohr-Mottelson Rotational Model
Gulshani, P. [NUTECH Services, 3313 Fenwick Cres., Mississauga, Ontario, L5L 5N1 (Canada)
2010-08-04
A microscopic version of the phenomenological Bohr-Mottelson unified adiabatic rotational model is derived using only space-fixed particle coordinates, and without imposing any constraints on the particle coordinates or the intrinsic wavefunction. It is shown that this can done only for rigid flow. A collective-rotation velocity field is defined and is used to show that, although their Hamiltonians are closely related, the flows in a multi-fermion and single-particle system are inherently different.
Creation of Non-dispersive Bohr-like Wavepackets
Mestayer, J. J.; Wyker, B.; Dunning, F. B.; Yoshida, S.; Reinhold, Carlos O; Burgdorfer, J.
2009-01-01
We demonstrate the use of a periodic train of half-cycle pulses to maintain strongly-localized wavepackets in very-high-n (n~300) Rydberg atoms that travel in near circular orbits about the nucleus. This motion can be followed for hundreds of orbital periods and mimics the original Bohr model of the hydrogen atom which envisioned an electron in circular classical orbit about the nucleus.
Bohr-Sommerfeld Lagrangians of moduli spaces of Higgs bundles
NASA Astrophysics Data System (ADS)
Biswas, Indranil; Gammelgaard, Niels Leth; Logares, Marina
2015-08-01
Let X be a compact connected Riemann surface of genus at least two. Let MH(r , d) denote the moduli space of semistable Higgs bundles on X of rank r and degree d. We prove that the compact complex Bohr-Sommerfeld Lagrangians of MH(r , d) are precisely the irreducible components of the nilpotent cone in MH(r , d) . This generalizes to Higgs G-bundles and also to the parabolic Higgs bundles.
The Gravity and The Quantum: A Bohr-inspired Synthesis
Sanjay M. Wagh; Abhijit H Wagh
2006-08-03
An effective angular momentum quantization condition of the form $mvr=n\\hbar(m/m_F)$ is used to obtain a Bohr-like model of Hydrogen-type atoms and a modified Schr\\"{o}dinger equation. Newton's constant, $G$, of Gravitation gets explicitly involved through the fundamental mass $m_F$ as defined in the sequel. This non-relativistic formalism may be looked upon as a ``testing ground'' for the more general synthesis of the gravity and the quantum.
Bohr--Sommerfeld Lagrangians of moduli spaces of Higgs bundles
Indranil Biswas; Niels Leth Gammelgaard; Marina Logares
2015-04-03
Let $X$ be a compact connected Riemann surface of genus at least two. Let $M_H(r,d)$ denote the moduli space of semistable Higgs bundles on $X$ of rank $r$ and degree $d$. We prove that the compact complex Bohr-Sommerfeld Lagrangians of $M_H(r,d)$ are precisely the irreducible components of the nilpotent cone in $M_H(r,d)$. This generalizes to Higgs $G$-bundles and also to the parabolic Higgs bundles.
Turnaround radius in modified gravity
Faraoni, Valerio
2015-01-01
In an accelerating universe in General Relativity there is a maximum radius above which a shell of test particles cannot collapse, but is dispersed by the cosmic expansion. This radius could be used in conjunction with observations of large structures to constrain the equation of state of the universe. We extend the concept of turnaround radius to modified theories of gravity for which the gravitational slip is non-vanishing.
Exciton dynamicsstudied via internal THz transitions
Kaindl, R.A.; Hagele, D.; Carnahan, M.A.; Lovenich, R.; Chemla,D.S.
2003-02-26
We employ a novel, ultrafast terahertz probe to investigatethe dynamical interplay of optically-induced excitons and unboundelectron-hole pairs in GaAs quantum wells. Resonant creation ofheavy-hole excitons induces a new low-energy oscillator linked totransitions between the internal exciton degrees of freedom. The timeresolved terahertz optical conductivity is found to be a probe wellsuited for studies of fundamental processes such as formation, relaxationand ionization of excitons.
Stimulated light backscattering from exciton Bose condensate
Yu. E. Lozovik; I. V. Ovchinnikov
2001-01-01
A new effect—light backscattering from exciton Bose-condensate—is considered. This effect is connected with the photoinduced\\u000a coherent recombination of two excitons in the condensate with the production of two photons with opposite momenta. The effect\\u000a of two-exciton coherent recombination leads also to the appearance of the second-order coherence in exciton luminescence connected\\u000a with squeezing between photon states with opposite momenta. The
Exciton-photon correlations in bosonic condensates of exciton-polaritons
Kavokin, Alexey V.; Sheremet, Alexandra S.; Shelykh, Ivan A.; Lagoudakis, Pavlos G.; Rubo, Yuri G.
2015-01-01
Exciton-polaritons are mixed light-matter quasiparticles. We have developed a statistical model describing stochastic exciton-photon transitions within a condensate of exciton polaritons. We show that the exciton-photon correlator depends on the rate of incoherent exciton-photon transformations in the condensate. We discuss implications of this effect for the quantum statistics of photons emitted by polariton lasers. PMID:26153979
Exciton-photon correlations in bosonic condensates of exciton-polaritons.
Kavokin, Alexey V; Sheremet, Alexandra S; Shelykh, Ivan A; Lagoudakis, Pavlos G; Rubo, Yuri G
2015-01-01
Exciton-polaritons are mixed light-matter quasiparticles. We have developed a statistical model describing stochastic exciton-photon transitions within a condensate of exciton polaritons. We show that the exciton-photon correlator depends on the rate of incoherent exciton-photon transformations in the condensate. We discuss implications of this effect for the quantum statistics of photons emitted by polariton lasers. PMID:26153979
De novo nonsense mutations in ASXL1 cause Bohring-Opitz syndrome.
Hoischen, Alexander; van Bon, Bregje W M; Rodríguez-Santiago, Benjamín; Gilissen, Christian; Vissers, Lisenka E L M; de Vries, Petra; Janssen, Irene; van Lier, Bart; Hastings, Rob; Smithson, Sarah F; Newbury-Ecob, Ruth; Kjaergaard, Susanne; Goodship, Judith; McGowan, Ruth; Bartholdi, Deborah; Rauch, Anita; Peippo, Maarit; Cobben, Jan M; Wieczorek, Dagmar; Gillessen-Kaesbach, Gabriele; Veltman, Joris A; Brunner, Han G; de Vries, Bert B B A
2011-08-01
Bohring-Opitz syndrome is characterized by severe intellectual disability, distinctive facial features and multiple congenital malformations. We sequenced the exomes of three individuals with Bohring-Opitz syndrome and in each identified heterozygous de novo nonsense mutations in ASXL1, which is required for maintenance of both activation and silencing of Hox genes. In total, 7 out of 13 subjects with a Bohring-Opitz phenotype had de novo ASXL1 mutations, suggesting that the syndrome is genetically heterogeneous. PMID:21706002
Reflections Concerning Niels Bohr's Refutation of the Einstein-Podolsky-Rosen-Paradox
NASA Astrophysics Data System (ADS)
Fuchs, Klaus
The controverse discussion between Bohr and Einstein concerning the interpretation of quantum theory is resumed by a reappraisal of some arguments in the view of epistemological problems, which have come to the fore in recent times.Translated AbstractReflektionen über Niels Bohrs Widerlegung des Einstein-Podolsky-Rosen-ParadoxonDie Kontroverse zwischen Bohr und Einstein über die Interpretation der Quantentheorie wird mit einer Neubewertung einiger Argumente im Lichte der erkenntnistheoretischen Probleme, die in neuerer Zeit in den Vordergrund gerückt sind, wiederaufgenommen.
Exciton coupling in molecular crystals
NASA Technical Reports Server (NTRS)
Ake, R. L.
1976-01-01
The implications of perfect exciton coupling and molecular vibrations were investigated, as well as the effect they have on the lifetime of singlet and triplet excitons coupled in a limiting geometry. Crystalline bibenzyl, Cl4Hl4, provided a situation in which these mechanisms involving exciton coupling can be studied in the limit of perfect coupling between units due to the crystal's geometry. This geometry leads to a coupling between the two halves of the molecule resulting in a splitting of the molecular excited states. The study reported involves an experimental spectroscopic approach and begins with the purification of the bibenzyl. The principal experimental apparatus was an emission spectrometer. A closed cycle cryogenic system was used to vary the temperature of the sample between 20 K and 300 K. The desired results are the temperature-dependent emission spectra of the bibenzyl; in addition, the lifetimes and quantum yields measured at each temperature reveal the effect of competing radiationless processes.
Excitonic polaritons in Fibonacci quasicrystals.
Hendrickson, J; Richards, B C; Sweet, J; Khitrova, G; Poddubny, A N; Ivchenko, E L; Wegener, M; Gibbs, H M
2008-09-29
The fabrication and characterization of light-emitting one-dimensional photonic quasicrystals based on excitonic resonances is reported. The structures consist of high-quality GaAs/AlGaAs quantum wells grown by molecular-beam epitaxy with wavelength-scale spacings satisfying a Fibonacci sequence. The polaritonic (resonant light-matter coupling) effects and light emission originate from the quantum well excitonic resonances. Measured reflectivity spectra as a function of detuning between emission and Bragg wavelength are in good agreement with excitonic polariton theory. Photoluminescence experiments show that active photonic quasicrystals, unlike photonic crystals, can be good light emitters: While their long-range order results in a stopband similar to that of photonic crystals, the lack of periodicity results in strong emission. PMID:18825174
Is the bag radius unobservable?
NASA Astrophysics Data System (ADS)
Je?abek, M.; Heller, K. J.; Nowak, M. A.
1986-01-01
The mean isoscalar charge radius of the chiral bag is calculated. The Cheshire Cat model (CCM), which assumes invariance of physical quantities under changes in the bag radius R, is adopted and tested. The CCM works for 0 ? R ? .2 fm within an accuracy of 30%. However, we suggest that other observables may exhibit a stronger dependence on the chiral angle.
Intramolecular radiationless transitions dominate exciton relaxation dynamics
NASA Astrophysics Data System (ADS)
Jumper, Chanelle C.; Anna, Jessica M.; Stradomska, Anna; Schins, Juleon; Myahkostupov, Mykhaylo; Prusakova, Valentina; Oblinsky, Daniel G.; Castellano, Felix N.; Knoester, Jasper; Scholes, Gregory D.
2014-04-01
Reports of long-lived exciton coherences have lead researchers to expect that model dimer systems inevitably generate exciton superposition states observable by two-dimensional electronic spectroscopy. Here we report a careful photophysical characterization of a model dimer system, a diacetylene-linked perylenediimide dimer to examine that issue. The absorption spectrum of the dimer shows molecular exciton splitting, indicating that excitation is delocalized. The assignment of exciton states was supported by other photophysical measurements as well as theoretical calculations. Ultrafast two-dimensional electronic spectroscopy was employed to identify and characterize excitonic and vibrational features, as they evolve over time. Population transfer between the two exciton states is found to happen in <50 fs, thus preventing the sustainment of exciton coherences. We show that such fast radiationless relaxation cannot be explained by coupling to a solvent spectral density and is therefore missed by standard approaches such as Redfield theory and the hierarchical equations of motion.
An Increased Bohr Effect in Sickle Cell Anemia
Yoshihiro Ueda; Ronald L. Nagel; Robert M. Bookchin
1979-01-01
Recent findings that hemoglobin S gelation was greatly increased only between blood and sickling are pH-dependent and also pH 7.4 and 7.2 (cell pH 7.2 and 7.0. a shift influence oxygen affinity suggested that that strongly affects gelation). with Llog the red cells containing this hemoglobin p50\\/ LpH -0.92 to -0.99 (normal variant might show an abnormal Bohr 0.42 to
Realization of localized Bohr-like wave packets.
Mestayer, J J; Wyker, B; Lancaster, J C; Dunning, F B; Reinhold, C O; Yoshida, S; Burgdörfer, J
2008-06-20
We demonstrate a protocol to create localized wave packets in very-high-n Rydberg states which travel in nearly circular orbits around the nucleus. Although these wave packets slowly dephase and eventually lose their localization, their motion can be monitored over several orbital periods. These wave packets represent the closest analog yet achieved to the original Bohr model of the hydrogen atom, i.e., an electron in a circular classical orbit around the nucleus. The possible extension of the approach to create "planetary atoms" in highly correlated stable multiply excited states is discussed. PMID:18643582
Realization of Localized Bohr-Like Wave Packets
NASA Astrophysics Data System (ADS)
Mestayer, J. J.; Wyker, B.; Lancaster, J. C.; Dunning, F. B.; Reinhold, C. O.; Yoshida, S.; Burgdörfer, J.
2008-06-01
We demonstrate a protocol to create localized wave packets in very-high-n Rydberg states which travel in nearly circular orbits around the nucleus. Although these wave packets slowly dephase and eventually lose their localization, their motion can be monitored over several orbital periods. These wave packets represent the closest analog yet achieved to the original Bohr model of the hydrogen atom, i.e., an electron in a circular classical orbit around the nucleus. The possible extension of the approach to create “planetary atoms” in highly correlated stable multiply excited states is discussed.
Bohr Hamiltonian with Davidson potential for triaxial nuclei
Yigitoglu, I.; Bonatsos, Dennis
2011-01-15
A solution of the Bohr Hamiltonian appropriate for triaxial shapes, involving a Davidson potential in {beta} and a steep harmonic oscillator in {gamma}, centered around {gamma}={pi}/6, is developed. Analytical expressions for spectra andB(E2) transition rates ranging from a triaxial vibrator to the rigid triaxial rotator are obtained and compared to experimental results. Using a variational procedure, we point out that the Z(5) solution, in which an infinite square well potential in {beta} is used, corresponds to the critical point of the shape phase transition from a triaxial vibrator to the rigid triaxial rotator.
Collective quadrupole excitations in the 50Bohr Hamiltonian
L. Prochniak; K. Zajac; K. Pomorski; S. G. Rohozinski; J. Srebrny
1998-05-23
The generalized Bohr Hamiltonian is applied to a description of low-lying collective excitations in even-even isotopes of Te, Xe, Ba, Ce, Nd and Sm. The collective potential and inertial functions are determined by means of the Strutinsky method and the cranking model, respectively. A shell-dependent parametrization of the Nilsson potential is used. An approximate particle-number projection is performed in treatment of pairing correlations. The effect of coupling with the pairing vibrations is taken into account approximately when determining the inertial functions. The calculation does not contain any free parameter.
Bohr Hamiltonian with Davidson potential for triaxial nuclei
I. Yigitoglu; Dennis Bonatsos
2010-12-16
A solution of the Bohr Hamiltonian appropriate for triaxial shapes, involving a Davidson potential in beta and a steep harmonic oscillator in gamma, centered around gamma=30 degrees, is developed. Analytical expressions for spectra and B(E2) transition rates ranging from a triaxial vibrator to the rigid triaxial rotator are obtained and compared to experiment. Using a variational procedure it is pointed out that the Z(5) solution, in which an infinite square well potential in beta is used, corresponds to the critical point of the shape phase transition from a triaxial vibrator to the rigid triaxial rotator.
Challenges to Bohr's Wave-Particle Complementarity Principle
NASA Astrophysics Data System (ADS)
Rabinowitz, Mario
2013-02-01
Contrary to Bohr's complementarity principle, in 1995 Rabinowitz proposed that by using entangled particles from the source it would be possible to determine which slit a particle goes through while still preserving the interference pattern in the Young's two slit experiment. In 2000, Kim et al. used spontaneous parametric down conversion to prepare entangled photons as their source, and almost achieved this. In 2012, Menzel et al. experimentally succeeded in doing this. When the source emits entangled particle pairs, the traversed slit is inferred from measurement of the entangled particle's location by using triangulation. The violation of complementarity breaches the prevailing probabilistic interpretation of quantum mechanics, and benefits Bohm's pilot-wave theory.
Bohr and Besicovitch almost periodic discrete sets and quasicrystals
Favorov, Sergey
2010-01-01
A discrete set $A$ in the Euclidian space is almost periodic if the measure with the unite masses at points of the set is almost periodic in the weak sense. We investigate properties of such sets in the case when $A-A$ is discrete. In particular, if $A$ is a Bohr almost periodic set, we prove that $A$ is a union of a finite number of translates of a certain full--rank lattice. If $A$ is a Besicovitch almost periodic set, then there exists a full-rank lattice such that in most cases a nonempty intersection of its translate with $A$ is large.
All conjugated copolymer excitonic multiferroics.
Lohrman, Jessica; Liu, Yueying; Duan, Shaofeng; Zhao, Xiaoyong; Wuttig, Manfred; Ren, Shenqiang
2013-02-01
A substantial magnetoelectric coupling effect of an excitonic all-conjugated block copolymer multiferroics consisting of electronically distinct polythiophene derivatives is reported. The observations open new avenues for the multifunctional all-conjugated block copolymer synthesis and electric field tunable multiferroic devices. PMID:23172730
Unusual Raman scattering by Bose-condensed excitons
Yu. E Lozovik; A. V Poushnov
1998-01-01
Teh unusual Raman scattering by Bose-condensed excitons caused by simultaneous recombination (or creation) of two excitons is investigated. It is shown that this scattering takes place only in the Bose-condensed interacting exciton system and is accompanied by the simultaneous recombination (or creation) of two excitons with equal and opposite momenta leaving the occupation numbers of excitonic states with p ?
Hwang, Gyuweon
2015-01-01
Quantum dots (QDs) are semiconductor nanocrystals having a size comparable to or smaller than its exciton Bohr radius. The small size of QDs leads to the quantum confinement effects in their electronic structures. Their ...
NASA Astrophysics Data System (ADS)
Simhony, M.
1997-04-01
The 'freeing' of a conduction electron and hole within a solid requires absorption of their binding energy E_g. Excitons are formed with the absorption of certain allowed energies Ea smaller than E_g, or when the 'free' electron and hole emit the energy E_n=E_g-E_a, which is their binding energy in the exciton. The exciton disappears on absorption of the En energy, freeing the electron and hole, or on emission of the Ea energy, with the recombination of the pair. In the electron-positron lattice (epola) space, (M.Simhony,Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994 (292pp).) neutrinos of energy En may form when a pair of host particles, bound in the lattice by the energy _bE=1.02 MeV, absorbs an energy E_a=_bE-E_n, or when a free electron and positron emit the energy En and fall into the neutrino bonds. The neutrino disappears on absorption of the En energy, freeing the two particles, or on emission of the Ea energy, when they fall into the lattice bonds. For the creation and anihilation of excitons in solids and of neutrinos in the epola, the lattices must contain irregularities able to provide En (or E_a) energy levels. Such irregularities are abundant in solids, with their close-packed, overlapping, thermally vibrating host and impurity atoms and ions, thus excitons are quite common. In our epola, the temperature is 3K only, and the hosts are 50 particle radii away from one another. Epola excitation, able to create or annihilate neutrinos, are scarce. Hence the few neutrinos, created here in (or near to) nuclear reactions, as well as solar neutrinos, have a long lifetime in our epola.
Extracting Atomic and Molecular Parameters From the de BroglieBohr Model of the Atom
Rioux, Frank
the classical definition of kinetic energy to the quantum mechanical version expressed finally in atomic unitsExtracting Atomic and Molecular Parameters From the de BroglieBohr Model of the Atom Frank Rioux The 1913 Bohr model of the hydrogen atom was replaced by Schrödingers wave mechanical model in 1926
Molecular Basis of the Bohr Effect in Arthropod Hemocyanin
Hirota, S.; Kawahara, T; Beltramini, M; Di Muro, P; Magliozzo, R; Peisach, J; Powers, L; Tanaka, N; Nagao, S; Bubacco, L
2008-01-01
Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, kon, rather than changes in koff. In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS. It was found that the geometry of copper in the oxygenated protein is unchanged at all pH values investigated, while significant changes were observed for the deoxygenated protein as a function of pH. The interpretation of these changes was based on previously described correlations between spectral lineshape and coordination geometry obtained for model compounds of known structure A pH-dependent change in the geometry of cuprous copper in the active site of deoxyHc, from pseudotetrahedral toward trigonal was assigned from the observed intensity dependence of the 1s ? 4pz transition in x-ray absorption near edge structure (XANES) spectra. The structural alteration correlated well with increase in oxygen affinity at alkaline pH determined in flash photolysis experiments. These results suggest that the oxygen binding rate in deoxyHc depends on the coordination geometry of Cu(I) and suggest a structural origin for the Bohr effect in arthropod Hcs.
EPR-Bohr and Quantum Trajectories: Entaglement and Nonlocality
Edward R. Floyd
2010-01-26
Quantum trajectories are used to investigate the EPR-Bohr debate in a modern sense by examining entanglement and nonlocality. We synthesize a single "entanglement molecule" from the two scattered particles of the EPR experiment. We explicitly investigate the behavior of the entanglement molecule rather than the behaviors of the two scattered particles to gain insight into the EPR-Bohr debate. We develop the entanglement molecule's wave function in polar form and its reduced action, both of which manifest entanglement. We next apply Jacobi's theorem to the reduced action to generate the equation of quantum motion for the entanglement molecule to produce its quantum trajectory. The resultant quantum trajectory manifests entanglement and has retrograde segments interspersed between segments of forward motion. This alternating of forward and retrograde segments generates nonlocality and, within the entanglement molecule, action at a distance. Dissection of the equation of quantum motion for the entanglement molecule, while rendering the classical behavior of the two scattered particles, also reveals an emergent "entanglon" that maintains the entanglement between the scattered particles. The characteristics of the entanglon and its relationship to nonlocality are examined.
Experimental Observation of Bohr's Nonlinear Fluidic Surface Oscillation
Songky Moon; Younghoon Shin; Hojeong Kwak; Juhee Yang; Sang-Bum Lee; Soyun Kim; Kyungwon An
2015-04-20
Niels Bohr in the early stage of his career developed a nonlinear theory of fluidic surface oscillation in order to study surface tension of liquids. His theory includes the nonlinear interaction between multipolar surface oscillation modes, surpassing the linear theory of Rayleigh and Lamb. It predicts a specific normalized magnitude of $0.41\\dot{6}\\eta^2$ for an octapolar component, nonlinearly induced by a quadrupolar one with a magnitude of $\\eta$ much less than unity. No experimental confirmation on this prediction has been reported. Nonetheless, accurate determination of multipolar components is important as in optical fiber spinning, film blowing and recently in optofluidic microcavities for ray and wave chaos studies and photonics applications. Here, we report experimental verification of his theory. By using optical forward diffraction, we measured the cross-sectional boundary profiles at extreme positions of a surface-oscillating liquid column ejected from a deformed microscopic orifice. We obtained a coefficient of $0.42\\pm0.08$ consistently under various experimental conditions. We also measured the resonance mode spectrum of a two-dimensional cavity formed by the cross-sectional segment of the liquid jet. The observed spectra agree well with wave calculations assuming a coefficient of $0.415\\pm0.010$. Our measurements establish the first experimental observation of Bohr's hydrodynamic theory.
Loss, Daniel
and November 1913, Niels Bohr published a seminal trilogy of papers1 in the Philosophical Magazine. In them, he and its cavalier disregard of classical electromagnetic theory". To mark the centenary of the `Bohr atom theory of atomic structure (see, for example, refs 3,4). Furthermore, the strong influence of Bohr
Fission of singlet excitons into triplet-exciton pairs in molecular crystals
M. Chabr; D. F. Williams
1977-01-01
A kinetic model of singlet-exciton fission into pairs of triplet excitons in aromatic hydrocarbon crystals is presented. The model is based on Suna's hopping model for triplet-exciton fusion. The assumptions made in this description of fission and the relationship between fusion and fission are analyzed in detail. According to this theoretical model, the magnetic field modulation of anthracene hot singlet
Exciton Binding Energy of Monolayer WS2
Zhu, Bairen; Chen, Xi; Cui, Xiaodong
2015-01-01
The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach to measuring the exciton binding energy of monolayer WS2 with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71 ± 0.01?eV around K valley in the Brillouin zone. PMID:25783023
Exciton Binding Energy of Monolayer WS2
NASA Astrophysics Data System (ADS)
Zhu, Bairen; Chen, Xi; Cui, Xiaodong
2015-03-01
The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach to measuring the exciton binding energy of monolayer WS2 with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71 +/- 0.01 eV around K valley in the Brillouin zone.
Exciton binding energy of monolayer WS?.
Zhu, Bairen; Chen, Xi; Cui, Xiaodong
2015-01-01
The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach to measuring the exciton binding energy of monolayer WS? with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71 ± 0.01?eV around K valley in the Brillouin zone. PMID:25783023
Extraordinary Exciton Conductance Induced by Strong Coupling
NASA Astrophysics Data System (ADS)
Feist, Johannes; Garcia-Vidal, Francisco J.
2015-05-01
We demonstrate that exciton conductance in organic materials can be enhanced by several orders of magnitude when the molecules are strongly coupled to an electromagnetic mode. Using a 1D model system, we show how the formation of a collective polaritonic mode allows excitons to bypass the disordered array of molecules and jump directly from one end of the structure to the other. This finding could have important implications in the fields of exciton transistors, heat transport, photosynthesis, and biological systems in which exciton transport plays a key role.
Extraordinary exciton conductance induced by strong coupling
Johannes Feist; Francisco J. Garcia-Vidal
2015-01-07
We demonstrate that exciton conductance in organic materials can be enhanced by several orders of magnitude when the molecules are strongly coupled to an electromagnetic mode. Using a 1D model system, we show how the formation of a collective polaritonic mode allows excitons to bypass the disordered array of molecules and jump directly from one end of the structure to the other. This finding could have important implications in the fields of exciton transistors, heat transport, photosynthesis, and biological systems in which exciton transport plays a key role.
NASA Astrophysics Data System (ADS)
Tang, Yanhao; Xie, Wei; Mandal, Krishna C.; McGuire, John A.; Lai, Chih Wei
2015-09-01
We analyze exciton spin dynamics in GaSe under nonresonant circularly polarized optical pumping with an exciton spin-flip rate-equation model. The model reproduces polarized time-dependent photoluminescence measurements in which the initial circular polarization approaches unity even when pumping with 0.15 eV excess energy. At T = 10 K, the exciton spin relaxation exhibits a biexponential decay with sub-20 ps and >500 ps time constants, which are also reproduced by the rate-equation model assuming distinct spin-relaxation rates for hot (nonequilibrium) and cold band-edge excitons.
Extraordinary exciton conductance induced by strong coupling.
Feist, Johannes; Garcia-Vidal, Francisco J
2015-05-15
We demonstrate that exciton conductance in organic materials can be enhanced by several orders of magnitude when the molecules are strongly coupled to an electromagnetic mode. Using a 1D model system, we show how the formation of a collective polaritonic mode allows excitons to bypass the disordered array of molecules and jump directly from one end of the structure to the other. This finding could have important implications in the fields of exciton transistors, heat transport, photosynthesis, and biological systems in which exciton transport plays a key role. PMID:26024185
Ground state energy of N Frenkel excitons
NASA Astrophysics Data System (ADS)
Pogosov, W.; Combescot, M.
2009-03-01
By using the composite many-body theory for Frenkel excitons we have recently developed, we here derive the ground state energy of N Frenkel excitons in the Born approximation through the Hamiltonian mean value in a state made of N identical Q = 0 excitons. While this quantity reads as a density expansion in the case of Wannier excitons, due to many-body effects induced by fermion exchanges between N composite particles, we show that the Hamiltonian mean value for N Frenkel excitons only contains a first order term in density, just as for elementary bosons. Such a simple result comes from a subtle balance, difficult to guess a priori, between fermion exchanges for two or more Frenkel excitons appearing in Coulomb term and the ones appearing in the N exciton normalization factor - the cancellation being exact within terms in 1/Ns where Ns is the number of atomic sites in the sample. This result could make us naively believe that, due to the tight binding approximation on which Frenkel excitons are based, these excitons are just bare elementary bosons while their composite nature definitely appears at various stages in the precise calculation of the Hamiltonian mean value.
Excitonic dephasing in semimagnetic semiconductors
NASA Astrophysics Data System (ADS)
Cundiff, S. T.; Hellmann, R.; Koch, M.; Mackh, G.; Waag, A.; Landwehr, G.; Knox, W. H.; Göbel, E. O.
1996-06-01
The presence of magnetic ions in a dilute semiconductor quantum well is shown to decrease dramatically the low-temperature excitonic dephasing time measured by transient four-wave mixing. The decrease is associated with the magnetic nature of the material. Surprisingly, the application of a magnetic field does not significantly change the dephasing time, which indicates that there must exist a fast dephasing mechanism in addition to the spin-spin interactions responsible for magnetic polaron formation.
Localized Excitons in Carbon Nanotubes.
NASA Astrophysics Data System (ADS)
Adamska, Lyudmyla; Doorn, Stephen K.; Tretiak, Sergei
2015-03-01
It has been historically known that unintentional defects in carbon nanotubes (CNTs) may fully quench the fluorescence. However, some dopants may enhance the fluorescence by one order of magnitude thus turning the CNTs, which are excellent light absorbers, in good emitters. We have correlated the experimentally observed photoluminescence spectra to the electronic structure simulations. Our experiment reveals multiple sharp asymmetric emission peaks at energies 50-300 meV red-shifted from that of the lowest bright exciton peak. Our simulations suggest an association of these peaks with deep trap states tied to different specific chemical adducts. While the wave functions of excitons in undoped CNTs are delocalized, those of the deep-trap states are strongly localized and pinned to the dopants. These findings are consistent with the experimental observation of asymmetric broadening of the deep trap emission peaks, which can result from scattering of acoustic phonons on localized excitons. Our work lays the foundation to utilize doping as a generalized route for wave function engineering and direct control of carrier dynamics in SWCNTs toward enhanced light emission properties for photonic applications.
Semiclassical quantization of Bohr orbits in the helium atom
NASA Astrophysics Data System (ADS)
Belov, V. V.; Maksimov, V. A.
2007-05-01
We use the complex WKB-Maslov method to construct the semiclassical spectral series corresponding to the resonance Bohr orbits in the helium atom. The semiclassical energy levels represented as the Rydberg tetra series correspond to the doubly symmetrically excited states of helium-like atoms. This level series contains the Rydberg triple series reported by Richter and Wintgen in 1991, which corresponds to the Z2+e-e- configuration of electrons observed by Eichmann and his collaborators in experiments on the laser excitation of the barium atom in 1992. The lower-level extrapolation of the formula obtained for the semiclassical spectrum gives the value of the ground state energy, which differs by 6% from the experimental value obtained by Bergeson and his collaborators in 1998. We also calculate the fine structure of the semiclassical spectrum due to the spin-orbit and spin-spin interactions of electrons.
Experimental Observation of Bohr's Nonlinear Fluidic Surface Oscillation
Moon, Songky; Kwak, Hojeong; Yang, Juhee; Lee, Sang-Bum; Kim, Soyun; An, Kyungwon
2015-01-01
Niels Bohr in the early stage of his career developed a nonlinear theory of fluidic surface oscillation in order to study surface tension of liquids. His theory includes the nonlinear interaction between multipolar surface oscillation modes, surpassing the linear theory of Rayleigh and Lamb. It predicts a specific normalized magnitude of $0.41\\dot{6}\\eta^2$ for an octapolar component, nonlinearly induced by a quadrupolar one with a magnitude of $\\eta$ much less than unity. No experimental confirmation on this prediction has been reported. Nonetheless, accurate determination of multipolar components is important as in optical fiber spinning, film blowing and recently in optofluidic microcavities for ray and wave chaos studies and photonics applications. Here, we report experimental verification of his theory. By using optical forward diffraction, we measured the cross-sectional boundary profiles at extreme positions of a surface-oscillating liquid column ejected from a deformed microscopic orifice. We obtained...
Nekrasov Functions and Exact Bohr-Sommerfeld Integrals
A. Mironov; A. Morozov
2009-11-04
In the case of SU(2), associated by the AGT relation to the 2d Liouville theory, the Seiberg-Witten prepotential is constructed from the Bohr-Sommerfeld periods of 1d sine-Gordon model. If the same construction is literally applied to monodromies of exact wave functions, the prepotential turns into the one-parametric Nekrasov prepotential F(a,\\epsilon_1) with the other epsilon parameter vanishing, \\epsilon_2=0, and \\epsilon_1 playing the role of the Planck constant in the sine-Gordon Shroedinger equation, \\hbar=\\epsilon_1. This seems to be in accordance with the recent claim in arXiv:0908.4052 and poses a problem of describing the full Nekrasov function as a seemingly straightforward double-parametric quantization of sine-Gordon model. This also provides a new link between the Liouville and sine-Gordon theories.
Challenges to the Bohr Wave Particle Complementarity Principle
Mario Rabinowitz
2012-10-30
Contrary to the Bohr complementarity principle, in 1995 Rabinowitz proposed that by using entangled particles from the source it would be possible to determine which slit a particle goes through while still preserving the interference pattern in the Young two slit experiment. In 2000, Kim et al used spontaneous parametric down conversion to prepare entangled photons as their source, and almost achieved this. In 2012, Menzel et al. experimentally succeeded in doing this. When the source emits entangled particle pairs, the traversed slit is inferred from measurement of the entangled particle location by using triangulation. The violation of complementarity breaches the prevailing probabilistic interpretation of quantum mechanics, and benefits the Bohm pilot wave theory.
Einstein-Bohr controversy and theory of hidden variables
Milos V. Lokajicek
2010-12-16
It has been shown by us recently that Einstein was right in his controversy with Bohr or that the so called hidden-variable theory should be preferred to the Copenhagen quantum mechanics. In the following paper the corresponding arguments will be shortly repeated. The main attention will be then devoted to explaining main differences between these two quantum alternatives, differing in the access to the problem of chance, causality and locality of microscopic objects. The actual meaning of the mentioned hidden variables will be discussed, too, the essence of which remained practically unclear during all past discussions. It will be shown that the theory of hidden variables (or Schroedinger equation alone) is able to represent the properties of the whole known physical reality.
Revisiting Bohr's principle of complementarity using a quantum device
Jian-Shun Tang; Yu-Long Li; Chuan-Feng Li; Guang-Can Guo
2012-04-24
Bohr's principle of complementarity lies at the central place of quantum mechanics, according to which the light is chosen to behave as a wave or particles, depending on some exclusive detecting devices. Later, intermediate cases are found, but the total information of the wave-like and particle-like behaviors are limited by some inequalities. One of them is Englert-Greenberger (EG) duality relation. This relation has been demonstrated by many experiments with the classical detecting devices. Here by introducing a quantum detecting device into the experiment, we find the limit of the duality relation is exceeded due to the interference between the photon's wave and particle properties. However, our further results show that this experiment still obey a generalized EG duality relation. The introducing of the quantum device causes the new phenomenon, provides an generalization of the complementarity principle, and opens new insights into our understanding of quantum mechanics.
Bohr-Sommerfeld conditions for several commuting Hamiltonians
C. Anne; A-M. Charbonnel
2002-10-11
The goal of this paper is to find the quantization conditions of Bohr-Sommerfeld of k quantum Hamiltonians acting on the euclidian space of dimension n, depending on a small parameter h, and which commute to each other. That is we determine, around a regular energy level E of the euclidian space of dimension k the principal term of the asymptotics in h of the eigenvalues of the operators that are associated to a common eigenfunction. Thus we localize the so-called joint spectrum of the operators. Under the assumption that the classical Hamiltonian flow of the joint principal symbol is periodic with constant periods on the energy level of E(a submanifold of codimension k) we prove that the part of the joint spectrum lying in a small neighbourhood of E is localized near a lattice of size h determined in terms of actions and Maslov indices. The multiplicity of the spectrum is also determined.
Violation of Bohr's Complementarity: One Slit or Both?
Shahriar S. Afshar
2007-01-09
We have implemented a novel double-slit "which-way" experiment which raises interesting questions of interpretation. Coherent laser light is passed through a converging lens and then through a dual pinhole producing two beams crossing over at the focal point of the lens, and fully separating further downstream providing which-way information. A thin wire is then placed at a minimum of the interference pattern formed at the cross-over region. No significant reduction in the total flux or resolution of the separated beams is found, providing evidence for coexistence of perfect interference and which-way information in the same experiment, contrary to the common readings of Bohr's principle of complementarity. This result further supports the conclusions of the original experiment by the author in which an imaging lens was employed to obtain which-way information. Finally, a short discussion of the novel non-perturbative measurement technique for ensemble properties is offered.
Bohr's correspondence principle: The cases for which it is exact
Makowski, Adam J.; Gorska, Katarzyna J. [Institute of Physics, Nicholas Copernicus University, ul.Grudziadzka 5/7, 87-100 Torun (Poland)
2002-12-01
Two-dimensional central potentials leading to the identical classical and quantum motions are derived and their properties are discussed. Some of zero-energy states in the potentials are shown to cancel the quantum correction Q=(-({Dirac_h}/2{pi}){sup 2}/2m){delta}R/R to the classical Hamilton-Jacobi equation. The Bohr's correspondence principle is thus fulfilled exactly without taking the limits of high quantum numbers, of ({Dirac_h}/2{pi}){yields}0, or of the like. In this exact limit of Q=0, classical trajectories are found and classified. Interestingly, many of them are represented by closed curves. Applications of the found potentials in many areas of physics are briefly commented.
Exciton circular dichroism in channelrhodopsin.
Pescitelli, Gennaro; Kato, Hideaki E; Oishi, Satomi; Ito, Jumpei; Maturana, Andrés Daniel; Nureki, Osamu; Woody, Robert W
2014-10-16
Channelrhodopsins (ChRs) are of great interest currently because of their important applications in optogenetics, the photostimulation of neurons. The absorption and circular dichroism (CD) spectra of C1C2, a chimera of ChR1 and ChR2 of Chlamydomonas reinhardtii, have been studied experimentally and theoretically. The visible absorption spectrum of C1C2 shows vibronic fine structure in the 470 nm band, consistent with the relatively nonpolar binding site. The CD spectrum has a negative band at 492 nm (??(max) = -6.17 M(-1) cm(-1)) and a positive band at 434 nm (??(max) = +6.65 M(-1) cm(-1)), indicating exciton coupling within the C1C2 dimer. Time-dependent density functional theory (TDDFT) calculations are reported for three models of the C1C2 chromophore: (1) the isolated protonated retinal Schiff base (retPSB); (2) an ion pair, including the retPSB chromophore, two carboxylate side chains (Asp 292, Glu 162), modeled by acetate, and a water molecule; and (3) a hybrid quantum mechanical/molecular mechanical (QM/MM) model depicting the binding pocket, in which the QM part consists of the same ion pair as that in (2) and the MM part consists of the protein residues surrounding the ion pair within 10 Å. For each of these models, the CD of both the monomer and the dimer was calculated with TDDFT. For the dimer, DeVoe polarizability theory and exciton calculations were also performed. The exciton calculations were supplemented by calculations of the coupling of the retinal transition with aromatic and peptide group transitions. For the dimer, all three methods and three models give a long-wavelength C2-axis-polarized band, negative in CD, and a short-wavelength band polarized perpendicular to the C2 axis with positive CD, differing in wavelength by 1-5 nm. Only the retPSB model gives an exciton couplet that agrees qualitatively with experiment. The other two models give a predominantly or solely positive band. We further analyze an N-terminal truncated mutant because it was assumed that the N-terminal domain has a crucial role in the dimerization of ChRs. However, the CD spectrum of this mutant has an exciton couplet comparable to that of the wild-type, demonstrating that it is dimeric. Patch-clamp experiments suggest that the N-terminal domain is involved in protein stabilization and channel kinetics rather than dimerization or channel activity. PMID:25247388
Molecular basis of the Bohr effect in arthropod hemocyanin.
Hirota, Shun; Kawahara, Takumi; Beltramini, Mariano; Di Muro, Paolo; Magliozzo, Richard S; Peisach, Jack; Powers, Linda S; Tanaka, Naoki; Nagao, Satoshi; Bubacco, Luigi
2008-11-14
Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, k(on), rather than changes in k(off). In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS. It was found that the geometry of copper in the oxygenated protein is unchanged at all pH values investigated, while significant changes were observed for the deoxygenated protein as a function of pH. The interpretation of these changes was based on previously described correlations between spectral lineshape and coordination geometry obtained for model compounds of known structure (Blackburn, N. J., Strange, R. W., Reedijk, J., Volbeda, A., Farooq, A., Karlin, K. D., and Zubieta, J. (1989) Inorg. Chem., 28, 1349-1357). A pH-dependent change in the geometry of cuprous copper in the active site of deoxyHc, from pseudotetrahedral toward trigonal was assigned from the observed intensity dependence of the 1s --> 4p(z) transition in x-ray absorption near edge structure (XANES) spectra. The structural alteration correlated well with increase in oxygen affinity at alkaline pH determined in flash photolysis experiments. These results suggest that the oxygen binding rate in deoxyHc depends on the coordination geometry of Cu(I) and suggest a structural origin for the Bohr effect in arthropod Hcs. PMID:18725416
New cases of Bohring-Opitz syndrome, update, and critical review of the literature.
Bohring, Axel; Oudesluijs, Grétel G; Grange, Dorothy K; Zampino, Giuseppe; Thierry, Patrick
2006-06-15
We report on four additional unrelated cases of Bohring-Opitz syndrome with the highly characteristic phenotype of facial anomalies including bulging forehead over the metopic suture, frontal nevus flammeus, exophthalmos, hypertelorism, upslanting palpebral fissures, and cleft lip and/or palate, as well as flexion deformities of the upper limbs, multiple other anomalies, and severe failure to thrive. We also update the clinical outcome of the patients reported in the original article by Bohring et al. [Am J Med Genet 85:438-446] and critically review the subsequently published cases considered to have Bohring-Opitz syndrome. PMID:16691589
Josephson effects in condensates of excitons and exciton polaritons
Shelykh, I. A.; Solnyshkov, D. D.; Pavlovic, G.; Malpuech, G.
2008-07-15
We analyze theoretically the phenomena related to the Josephson effect for exciton and polariton condensates, taking into account their specific spin degrees of freedom. We distinguish between two types of Josephson effects: the extrinsic effect, related to the coherent tunneling of particles with the same spin between two spatially separated potential traps, and the intrinsic effect, related to the 'tunneling' between different spinor components of the condensate within the same trap. We show that the Josephson effect in the nonlinear regime can lead to nontrivial polarization dynamics and produce spontaneous separation of the condensates with opposite polarization in real space.
COVER IMAGE Exciton-polariton fluids --which
Loss, Daniel
COVER IMAGE Exciton-polariton fluids -- which are composed of composite lightmatter bosons. These authors demonstrate the nucleation and dynamics of vortexanti-vortex pairs in the flow of exciton-polaritons vortex pairs in a polariton quantum fluid Gaël Nardin, Gabriele Grosso, Yoan Léger, Barbara Pie
Excitons in AlN under pressure.
NASA Astrophysics Data System (ADS)
Christensen, Niels E.; Laskowski, Robert
2008-03-01
First-principles calculations based on solution of the Bethe-Salpeter equation of excitons in the high-pressure AlN phase show that a delocalization-localization transition occurs as additional pressure is applied. The transition, which is associated with a sudden increase in exciton binding energy, is related to a pressure-induced rearrangement of the energy bands.
Diffusion of Singlet Excitons in Tetracene Crystals
G. Vaubel; H. Baessler
1970-01-01
The diffusion length ls of singlet excitons in crystalline tetracene was measured in the temperature range 293 to 160 °K utilizing the quenching effect exerted on the crystal fluorescence by exciton traps located at the crystal surface. It is found that ls = 120 ± 10 Å at room temperature. It increases exponentially with decreasing temperature until it approaches a
arXiv:cond-mat/0211340v115Nov2002 APS/123-QED Stark effect upon the effective mass and radius
Elkhoury, Jean
arXiv:cond-mat/0211340v115Nov2002 APS/123-QED Stark effect upon the effective mass and radius mass of the exciton by the application of the Mattis-Gallinar effective mass formula [D. C. Mattis and J.-P. Gallinar, Phys. Rev. Lett. 53, 1391 (1984)]. We obtain positive and negative effective masses
Thermodynamic efficiency limit of excitonic solar cells
Giebink, Noel C.; Wiederrecht, Gary P.; Wasielewski, Michael R.; Forrest, Stephen R.
2011-01-01
Excitonic solar cells, comprised of materials such as organic semiconductors, inorganic colloidal quantum dots, and carbon nanotubes, are fundamentally different than crystalline, inorganic solar cells in that photogeneration of free charge occurs through intermediate, bound exciton states. Here, we show that the Second Law of Thermodynamics limits the maximum efficiency of excitonic solar cells below the maximum of 31% established by Shockley and Queisser [J. Appl. Phys. 32, 510 (1961)] for inorganic solar cells (whose exciton-binding energy is small). In the case of ideal heterojunction excitonic cells, the free energy for charge transfer at the interface, ?G, places an additional constraint on the limiting efficiency due to a fundamental increase in the recombination rate, with typical -?G in the range 0.3 to 0.5 eV decreasing the maximum efficiency to 27% and 22%, respectively.
The structure and dynamics of molecular excitons.
Bardeen, Christopher J
2014-01-01
The photophysical behavior of organic semiconductors is governed by their excitonic states. In this review, I classify the three different exciton types (Frenkel singlet, Frenkel triplet, and charge transfer) typically encountered in organic semiconductors. Experimental challenges that arise in the study of solid-state organic systems are discussed. The steady-state spectroscopy of intermolecular delocalized Frenkel excitons is described, using crystalline tetracene as an example. I consider the problem of a localized exciton diffusing in a disordered matrix in detail, and experimental results on conjugated polymers and model systems suggest that energetic disorder leads to subdiffusive motion. Multiexciton processes such as singlet fission and triplet fusion are described, emphasizing the role of spin state coherence and magnetic fields in studying singlet ? triplet pair interconversion. Singlet fission provides an example of how all three types of excitons (triplet, singlet, and charge transfer) may interact to produce useful phenomena for applications such as solar energy conversion. PMID:24313684
The Structure and Dynamics of Molecular Excitons
NASA Astrophysics Data System (ADS)
Bardeen, Christopher J.
2014-04-01
The photophysical behavior of organic semiconductors is governed by their excitonic states. In this review, I classify the three different exciton types (Frenkel singlet, Frenkel triplet, and charge transfer) typically encountered in organic semiconductors. Experimental challenges that arise in the study of solid-state organic systems are discussed. The steady-state spectroscopy of intermolecular delocalized Frenkel excitons is described, using crystalline tetracene as an example. I consider the problem of a localized exciton diffusing in a disordered matrix in detail, and experimental results on conjugated polymers and model systems suggest that energetic disorder leads to subdiffusive motion. Multiexciton processes such as singlet fission and triplet fusion are described, emphasizing the role of spin state coherence and magnetic fields in studying singlet -- triplet pair interconversion. Singlet fission provides an example of how all three types of excitons (triplet, singlet, and charge transfer) may interact to produce useful phenomena for applications such as solar energy conversion.
Electric arc radius and characteristics
Fang, T.M.
1980-09-30
The heat transfer equation of an arc discharge has been solved. The arc is assumed to be a cylinder with negligible axial variation and the dominant heat transfer process is conduction radially inside the column and radiation/convection at the outside edge. The symmetric consideration allows a simple one-dimensional formulation. By taking into account proper variation of the electrical conductivity as function of temperature, the heat balance equation has been solved analytically. The radius of the arc and its current-field characteristics have also been obtained. The conventional results that E approx. I/sup 0/ /sup 5385/ and R approx. I/sup 0/ /sup 7693/ with E being the applied field, I the current, and R the radius of the cylindrical arc, have been proved to be simply limiting cases of our more general characteristics. The results can be applied quite widely including, among others, the neutral beam injection project in nuclear fusion and MHD energy conversion.
High efficiency organic multilayer photodetectors based on singlet exciton fission
J. Lee; P. Jadhav; M. A. Baldo
2009-01-01
We employ an exciton fission process that converts one singlet exciton into two triplet excitons to increase the quantum efficiency of an organic multilayer photodetector beyond 100%. The photodetector incorporates ultrathin alternating donor-acceptor layers of pentacene and C60, respectively. By comparing the quantum efficiency after separate pentacene and C60 photoexcitation we find that singlet exciton fission in pentacene enhances the
Exciton Scattering via Algebraic Topology
Michael J. Catanzaro; Vladimir Y. Chernyak; John R. Klein
2015-05-10
This mathematics paper uses algebraic and differential topology to study a significant problem in chemistry. The problem is to compute the number of electronic excitations (excitons) associated to a molecule equipped with scattering data. We will exhibit a lower bound to this number using intersection theory in the unitary group. When the segment lengths of our molecule are sufficiently large, our bound is sharp. The tools used to attack the problem are an index theorem and an explicit cell structure on the unitary group.
Excitonic superconductivity in copper oxides
Tesanovic, Z.; Bishop, A.R.; Martin, R.L.; Harris, C.
1988-01-01
We discuss the possibility of excitonic superconductivity in high T/sub c/ copper oxides. The Hamiltonians describing CuO/sub 2/ planes supports both antiferromagnetism and low-lying Cu /longleftrightarrow/ O intra- and interband charge fluctuations. One crosses from one regime to another as the number of holes per unit cell increases. The high T/sub c/ superconductivity takes place at hole concentrations most favorable for intraband charge transfer excitations. The dynamic polarizability of the environment surrounding CuO/sub 2/ planes plays an important role in enhancing T/sub c/. 15 refs., 4 figs.
NASA Astrophysics Data System (ADS)
Tseng, Frank; Simsek, Ergun; Gunlycke, Daniel
2015-03-01
Monolayer transition-metal dichalcogenides form a direct bandgap predicted in the visible regime making them attractive host materials for various electronic and optoelectronic applications. Due to a weak dielectric screening in these materials, strongly bound electron-hole pairs or excitons have binding energies up to at least several hundred meV's. While the conventional wisdom is to think of excitons as hydrogen-like quasi-particles, we show that the hydrogen model breaks down for these experimentally observed strongly bound, room-temperature excitons. To capture these non-hydrogen-like photo-excitations, we introduce an atomistic model for excitons that predicts both bright excitons and dark excitons, and their broken degeneracy in these two-dimensional materials. For strongly bound exciton states, the lattice potential significantly distorts the envelope wave functions, which affects predicted exciton peak energies. The combination of large binding energies and non-degeneracy of exciton states in monolayer transition metal dichalogendies may furthermore be exploited in room temperature applications where prolonged exciton lifetimes are necessary. This work has been funded by the Office of Naval Research (ONR), directly and through the Naval Research Laboratory (NRL). F.T and E.S acknowledge support from NRL through the NRC Research Associateship Program and ONR Summer Faculty Program, respectively.
An Infrared-Finite Algorithm for Rayleigh Scattering Amplitudes, and Bohr's Frequency Condition
Volker Bach; Jürg Fröhlich; Alessandro Pizzo
2007-01-01
In this paper, we rigorously justify Bohr’s frequency condition in atomic spectroscopy. Moreover, we construct an algorithm\\u000a enabling us to calculate the transition amplitudes for Rayleigh scattering of light at an atom, up to a remainder term of\\u000a arbitrarily high order in the finestructure constant. Our algorithm is constructive and circumvents the infrared divergences\\u000a that invalidate standard perturbation theory.
Lightcurve Analysis of 3948 Bohr and 4874 Burke: An International Collaboration
NASA Astrophysics Data System (ADS)
Klinglesmith, Daniel A., III; Risley, Ethan; Turk, Janek; Vargas, Angelica; Warren, Curtis; Ferrero, Andrea
2013-01-01
An international collaboration provided complete coverage of the 24.884 Â± 0.002 h period for 3948 Bohr and a confirmation of a 3.657 Â± 0.001 h period for 4874 Burke. The amplitudes were A = 0.89 Â± 0.10 mag for 3948 Bohr and A = 0.22 Â± 0.07 mag for 4874 Burke.
Optical properties of an exciton bound to an ionized impurity in ZnO/SiO2 quantum dots
NASA Astrophysics Data System (ADS)
Dallali, Lobna; Jaziri, Sihem; Martínez-Pastor, Juan
2015-05-01
The energy of the ground and the excited states for the exciton and the binding energy of the acceptor-donor exciton complexes (A- , X) and (D+ , X) as a function of the radius for an impurity position located in the center in the spherical ZnO quantum dots (QDs) embedded in a SiO2 matrix are calculated using the effective mass approximation under the diagonalzation matrix technique, including a three-dimensional confinement of carrier in the QD and assuming a finite depth. Numerical results show that the binding energy of the acceptor-donor exciton complexes is very sensitive to the quantum dot size. These results could be particularly helpful since they are closely related to experiments performed on such nanoparticles. This may allow us to improve the stability and efficiency of the semiconductor quantum dot luminescence which is, in fact, considered critical.
The effect of the initial exciton numbers on {sup 54,56}Fe(p, xp) Pre-Equilibrium Reactions
Boeluekdemir, M. H., E-mail: bolukdemir@gmail.com [Gazi University, Faculty of Arts and Sciences, Department of Physics (Turkey); Tel, E. [Osmaniye Korkut Ata University, Faculty of Arts and Sciences, Department of Physics (Turkey); Ayd Latin-Small-Letter-Dotless-I n, A. [Kirikkale University, Faculty of Arts and Sciences, Department of Physics (Turkey); Okuducu, S. [Gazi University, Faculty of Arts and Sciences, Department of Physics (Turkey); Kaplan, A. [Sueleyman Demirel University, Faculty of Arts and Sciences, Department of Physics (Turkey)
2011-02-15
In pre-equilibrium nuclear reactions, the geometry-dependent hybrid model is applied with the use of the neutron and proton densities to investigate the effect of initial exciton numbers on the nucleon emission spectra. The initial exciton numbers calculated with the theoretical neutron and proton densities have been obtained within the Skryme-Hartree-Fock method with SKM* and SLy4 forces on target nuclei in the {sup 54,56}Fe(p, xp) reaction at 61.5-MeV incident proton energy by using a new calculationmethod of Tel et al. Also, the differences between the initial exciton numbers for protons and neutrons as a function of nuclear radius, focusing on systematic discrepancies correlated to differences in the proton and neutron densities have been investigated.
Smit, J D; Sick, H; Peterhans, A; Gersonde, K
1986-03-01
The dioxygen affinity of Dicrocoelium dendriticum haemoglobin was determined as a function of pH with a thin-layer diffusion technique. From the oxygen dissociation and association curves Hill coefficients h equal 1 were obtained throughout. Ultracentrifugation studies prove this haemoglobin to be monomeric irrespective of pH and ligation state. Thus, Dicrocoelium haemoglobin is a non-cooperative monomer. It has the highest O2 affinity so far known for any monomeric haemoglobin: its half-saturation pressure, p50 value, ranges at 25 degrees C from 0.016 mm Hg to 0.15 mm Hg (2.13-20.0 Pa) dependent on pH. Dicrocoelium haemoglobin shows an acid Bohr effect only and as such it constitutes a new class of haemoglobins. Its log p50 versus pH plot (Bohr effect curve) is characterized by a large amplitude, delta log p50 = 0.96, and an inflection point (Bohr effect pK) at pH 5.0. A model for the acid Bohr effect of D. dendriticum haemoglobin is proposed. By generalization, both the alkaline and the acid Bohr effect in various monomeric haemoglobins may arise from a single Bohr group complex (salt bridge). PMID:3956482
Maximilian Schlosshauer; Kristian Camilleri
2008-04-10
It is now widely accepted that environmental entanglement and the resulting decoherence processes play a crucial role in the quantum-to-classical transition and the emergence of "classicality" from quantum mechanics. To this extent, decoherence is often understood as signifying a break with the Copenhagen interpretation, and in particular with Bohr's view of the indispensability of classical concepts. This paper analyzes the relationship between Bohr's understanding of the quantum-classical divide and his doctrine of classical concepts and the decoherence-based program of emergent classicality. By drawing on Howard's reconstruction of Bohr's doctrine of classical concepts, and by paying careful attention to a hitherto overlooked disagreement between Heisenberg and Bohr in the 1930s about the placement of the quantum-classical "cut," we show that Bohr's view of the quantum-classical divide can be physically justified by appealing to decoherence. We also discuss early anticipations of the role of the environment in the quantum-classical problem in Heisenberg's writings. Finally, we distinguish four different formulations of the doctrine of classical concepts in an effort to present a more nuanced assessment of the relationship between Bohr's views and decoherence that challenges oversimplified statements frequently found in the literature.
Exciton localization and drift in tailored-potential quantum nanowires
Szeszko, J. Rudra, A.; Kapon, E.; Belykh, V. V.; Sibeldin, N. N.
2014-06-30
Exciton recombination dynamics in tailored-potential, site-controlled AlGaAs quantum wires (QWRs) are studied. Time-resolved photoluminescence spectra evidence exciton localization in weakly disordered “uniform” QWRs, whereas deterministic bandgap grading is shown to suppress localization and promote exciton drift along the potential gradient. Measured exciton transit times between two quantum dot probes placed at opposite ends of the potential gradient yield the effective 1D exciton mobility as >1300 cm{sup 2}/(eVs).
Optical nutation in the exciton range of spectrum
Khadzhi, P. I. [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of)] [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of); Vasiliev, V. V., E-mail: vasscorp@mail.ru [Taras Shevchenko Transnistria State University (Moldova, Republic of)
2013-08-15
Optical nutation in the exciton range of spectrum is studied in the mean field approximation taking into account exciton-photon and elastic exciton-exciton interactions. It is shown that the features of nutation development are determined by the initial exciton and photon densities, the resonance detuning, the nonlinearity parameter, and the initial phase difference. For nonzero initial exciton and photon concentrations, three regimes of temporal evolution of excitons and photons exist: periodic conversion of excitons to photons and vice versa, aperiodic conversion of photons to excitons, and the rest regime. In the rest regime, the initial exciton and photon densities are nonzero and do not change with time. The oscillation amplitudes and periods of particle densities determined by the system parameters are found. The exciton self-trapping and photon trapping appearing in the system at threshold values of the nonlinearity parameter were predicted. As this parameter increases, the oscillation amplitudes of the exciton and photon densities sharply change at the critical value of the nonlinearity parameter. These two phenomena are shown to be caused by the elastic exciton-exciton interaction, resulting in the dynamic concentration shift of the exciton level.
Evolution of a patient with Bohring-Opitz syndrome.
Pierron, Sophie; Richelme, Christian; Triolo, Valérie; Mas, Jean Christophe; Griffet, Jacques; Karmous-Benailly, Houda; Quere, M; Kaname, Tadashi; Lambert, Jean-Claude; Giuliano, Fabienne
2009-08-01
We detailed the story from birth to the age of 5 years 9 months, of the oldest patient reported with a Bohring-Opitz syndrome with the three main diagnostic criteria: characteristic facial appearance, fixed contractures of the upper limbs and severe feeding difficulties. The facial anomalies described in our patient were microcephaly, bitemporal narrowing, "puffy" cheeks, forehead naevus flammeus, hypoplastic orbital ridges, prominent eyes, broad nasal bridge, high arched palate, buccal-alveola frenula and retrognathism. The magnetic resonance imaging (MRI) of the brain showed a hypoplastic corpus callosum and a narrowed upper cervical canal; and the cervical MRI showed a malformation of the atlas consisting in an agenesis of the anterior arch and an anterior slip of the posterior arch. We focused on her neurological and nutritional evolution. Despite the gastrostomy and a Nissen fundoplication at age 7 months, she still had developmental growth delays overall (<3rd centile). At 3 years 9 months of age, she began to put on weight quickly, which seemed to be atypical. Meanwhile she developed epilepsy, which was controlled with specific drugs. Currently, she is 5 years 9 months old and has significant psychomotor retardation, although this disease is often fatal in early childhood, due to obstructive apnea and unexplained bradycardia. PMID:19606480
Complementarity in the Bohr-Einstein Photon Box
Dennis Dieks; Sander Lam
2007-05-18
The photon box thought experiment can be considered a forerunner of the EPR-experiment: by performing suitable measurements on the box it is possible to ``prepare'' the photon, long after it has escaped, in either of two complementary states. Consistency requires that the corresponding box measurements be complementary as well. At first sight it seems, however, that these measurements can be jointly performed with arbitrary precision: they pertain to different systems (the center of mass of the box and an internal clock, respectively). But this is deceptive. As we show by explicit calculation, although the relevant quantities are simultaneously measurable, they develop non-vanishing commutators when calculated back to the time of escape of the photon. This justifies Bohr's qualitative arguments in a precise way; and it illustrates how the details of the dynamics conspire to guarantee the requirements of complementarity. In addition, our calculations exhibit a ``fine structure'' in the distribution of the uncertainties over the complementary quantities: depending on \\textit{when} the box measurement is performed, the resulting quantum description of the photon differs. This brings us close to the argumentation of the later EPR thought experiment.
Complementarity in the Einstein-Bohr Photon Box
Dennis Dieks; Sander Lam
2007-05-18
The photon box thought experiment can be considered a forerunner of the EPR-experiment: by performing suitable measurements on the box it is possible to ``prepare'' the photon, long after it has escaped, in either of two complementary states. Consistency requires that the corresponding box measurements be complementary as well. At first sight it seems, however, that these measurements can be jointly performed with arbitrary precision: they pertain to different systems (the center of mass of the box and an internal clock, respectively). But this is deceptive. As we show by explicit calculation, although the relevant quantities are simultaneously measurable, they develop non-vanishing commutators when calculated back to the time of escape of the photon. This justifies Bohr's qualitative arguments in a precise way; and it illustrates how the details of the dynamics conspire to guarantee the requirements of complementarity. In addition, our calculations exhibit a ``fine structure'' in the distribution of the uncertainties over the complementary quantities: depending on when the box measurement is performed, the resulting quantum description of the photon differs. This brings us close to the argumentation of the later EPR thought experiment.
Memories of Crisis: Bohr, Kuhn, and the Quantum Mechanical ``Revolution''
NASA Astrophysics Data System (ADS)
Seth, Suman
2013-04-01
``The history of science, to my knowledge,'' wrote Thomas Kuhn, describing the years just prior to the development of matrix and wave mechanics, ``offers no equally clear, detailed, and cogent example of the creative functions of normal science and crisis.'' By 1924, most quantum theorists shared a sense that there was much wrong with all extant atomic models. Yet not all shared equally in the sense that the failure was either terribly surprising or particularly demoralizing. Not all agreed, that is, that a crisis for Bohr-like models was a crisis for quantum theory. This paper attempts to answer four questions: two about history, two about memory. First, which sub-groups of the quantum theoretical community saw themselves and their field in a state of crisis in the early 1920s? Second, why did they do so, and how was a sense of crisis related to their theoretical practices in physics? Third, do we regard the years before 1925 as a crisis because they were followed by the quantum mechanical revolution? And fourth, to reverse the last question, were we to call into the question the existence of a crisis (for some at least) does that make a subsequent revolution less revolutionary?
Thrombocytopenia-absent radius syndrome.
Toriello, Helga V
2011-09-01
Thrombocytopenia-absent radius (TAR) syndrome is a relatively uncommon condition characterized by absent radii with the presence of thumbs and congenital or early-onset thrombocytopenia that tends to resolve in childhood. The precise cause of this condition is unknown, although recently a microdeletion of chromosome 1q21.1 has been found in all investigated individuals. However, this microdeletion alone is not sufficient to cause TAR syndrome, and another, uncharacterized genetic alteration is thought to be involved in the pathogenesis. PMID:22102274
Hu, Miao; Bi, Cheng; Yuan, Yongbo; Xiao, Zhengguo; Dong, Qingfeng; Shao, Yuchuan; Huang, Jinsong
2015-05-13
The nonexcitonic character for organometal trihalide perovskites is demonstrated by examining the field-dependent exciton dissociation behavior. It is found that photogenerated excitons can be effectively dissociated into free charges inside perovskite without the assistance of charge extraction layer or external field, which is a stark contrast to the charge-separation behavior in excitonic materials in the same photovoltaic operation system. PMID:25641931
Photoluminescence due to inelastic exciton-exciton scattering in ZnMgO-alloy thin film
Chia, C. H.; Chen, J. N.; Hu, Y. M.
2011-09-26
We studied the photoluminescence of ZnMgO thin film, grown by the radiofrequency sputtering method, as a function of excitation intensity and temperature. As the excitation intensity increases, a nonlinear emission band caused by the radiative recombination of the inelastic exciton-exciton scattering was detected at low temperature. We found that the inelastic exciton-exciton scattering process can only persist up to T {approx} 260 K. The nonlinear emission band observed at room temperature is due to the radiative recombination of the electron-hole plasma.
Triplet excitons: Bringing dark states to light
NASA Astrophysics Data System (ADS)
Bardeen, Christopher J.
2014-11-01
Semiconducting quantum dots have been used to harvest triplet excitons produced through singlet fission in organic semiconductors. These hybrid organic-inorganic materials may boost the efficiency of solar cells.
Topologically protected excitons in porphyrin thin films
Joel Yuen-Zhou; Semion S. Saikin; Norman Y. Yao; Alán Aspuru-Guzik
2014-06-05
The control of exciton transport in organic materials is of fundamental importance for the development of efficient light-harvesting systems. This transport is easily deteriorated by traps in the disordered energy landscape. Here, we propose and analyze a system that supports topological Frenkel exciton edge states. Backscattering of these chiral Frenkel excitons is prohibited by symmetry, ensuring that the transport properties of such a system are robust against disorder. To implement our idea, we propose a two-dimensional periodic array of tilted porphyrins interacting with a homogenous magnetic field. This field serves to break time-reversal symmetry and results in lattice fluxes that that mimic the Aharonov-Bohm phase acquired by electrons. Our proposal is the first blueprint for realizing topological phases of matter in molecular aggregates and suggests a paradigm for engineering novel excitonic materials.
Correlated exciton dynamics in semiconductor nanostructures
Wen, Patrick, Ph. D. Massachusetts Institute of Technology
2013-01-01
The absorption and dissipation of energy in semiconductor nanostructures are often determined by excited electron dynamics. In semiconductors, one fundamentally important electronic state is an exciton, an excited electron ...
Cavity-enhanced transport of excitons.
Schachenmayer, Johannes; Genes, Claudiu; Tignone, Edoardo; Pupillo, Guido
2015-05-15
We show that exciton-type transport in certain materials can be dramatically modified by their inclusion in an optical cavity: the modification of the electromagnetic vacuum mode structure introduced by the cavity leads to transport via delocalized polariton modes rather than through tunneling processes in the material itself. This can help overcome exponential suppression of transmission properties as a function of the system size in the case of disorder and other imperfections. We exemplify massive improvement of transmission for excitonic wave packets through a cavity, as well as enhancement of steady-state exciton currents under incoherent pumping. These results may have implications for experiments of exciton transport in disordered organic materials. We propose that the basic phenomena can be observed in quantum simulators made of Rydberg atoms, cold molecules in optical lattices, as well as in experiments with trapped ions. PMID:26024186
Can disorder enhance incoherent exciton diffusion?
Lee, Elizabeth M Y; Willard, Adam P
2015-01-01
Recent experiments aimed at probing the dynamics of excitons have revealed that semiconducting films composed of disordered molecular subunits, unlike expectations for their perfectly ordered counterparts, can exhibit a time-dependent diffusivity in which the effective early time diffusion constant is larger than that of the steady state. This observation has led to speculation about what role, if any, microscopic disorder may play in enhancing exciton transport properties. In this article, we present the results of a model study aimed at addressing this point. Specifically, we present a general model, based upon F\\"orster theory, for incoherent exciton diffusion in a material composed of independent molecular subunits with static energetic disorder. Energetic disorder leads to heterogeneity in molecule-to-molecule transition rates which we demonstrate has two important consequences related to exciton transport. First, the distribution of local site-specific diffusivity is broadened in a manner that results i...
Singlet exciton fission in solution.
Walker, Brian J; Musser, Andrew J; Beljonne, David; Friend, Richard H
2013-12-01
Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley-Queisser limit in single-junction solar cells. Although the process through which singlet fission occurs is not well characterized, some local order is thought to be necessary for intermolecular coupling. Here, we report a triplet yield of 200% and triplet formation rates approaching the diffusion limit in solutions of bis(triisopropylsilylethynyl (TIPS)) pentacene. We observe a transient bound excimer intermediate, formed by the collision of one photoexcited and one ground-state TIPS-pentacene molecule. The intermediate breaks up when the two triplets separate to each TIPS-pentacene molecule. This efficient system is a model for future singlet-fission materials and for disordered device components that produce cascades of excited states from sunlight. PMID:24256865
Singlet exciton fission in solution
NASA Astrophysics Data System (ADS)
Walker, Brian J.; Musser, Andrew J.; Beljonne, David; Friend, Richard H.
2013-12-01
Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley-Queisser limit in single-junction solar cells. Although the process through which singlet fission occurs is not well characterized, some local order is thought to be necessary for intermolecular coupling. Here, we report a triplet yield of 200% and triplet formation rates approaching the diffusion limit in solutions of bis(triisopropylsilylethynyl (TIPS)) pentacene. We observe a transient bound excimer intermediate, formed by the collision of one photoexcited and one ground-state TIPS-pentacene molecule. The intermediate breaks up when the two triplets separate to each TIPS-pentacene molecule. This efficient system is a model for future singlet-fission materials and for disordered device components that produce cascades of excited states from sunlight.
Multiple Exciton Generation Solar Cells
Luther, J. M.; Semonin, O. E.; Beard, M. C.; Gao, J.; Nozik, A. J.
2012-01-01
Heat loss is the major factor limiting traditional single junction solar cells to a theoretical efficiency of 32%. Multiple Exciton Generation (MEG) enables efficient use of the solar spectrum yielding a theoretical power conversion efficiency of 44% in solar cells under 1-sun conditions. Quantum-confined semiconductors have demonstrated the ability to generate multiple carriers but present-day materials deliver efficiencies far below the SQ limit of 32%. Semiconductor quantum dots of PbSe and PbS provide an active testbed for developing high-efficiency, inexpensive solar cells benefitting from quantum confinement effects. Here, we will present recent work of solar cells employing MEG to yield external quantum efficiencies exceeding 100%.
Exciton-polariton wakefields in semiconductor microcavities
H. Terças. J. T. Mendonça
2014-02-06
We consider the excitation of polariton wakefields due to a propagating source in a semiconductor micro cavity. We show that two kinds of wakes are possible, depending on the constituents fraction (either exciton or photon) of the polariton wavefunction. The nature of the wakefields (pure excitonic or polaritonic) can be controled by changing the speed of propagation of the external pump. This process could be used as a diagnostic for the internal parameters of the microcavity.
Excitonic states in polar molecular crystals
NASA Astrophysics Data System (ADS)
Gruodis, Alytis; Alisauskaite, Vidita; Jursenas, Saulius; Valkunas, Leonas; Muzikante, Inta
2003-08-01
Fluorescence and reflectance spectra of dipolar N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) molecular crystals of ? and ? crystallographic modifications have been studied over a wide temperature range. The luminescence spectral properties have been discussed by means of the self-trapped exciton model. The crystal phase transition in both ? and ? modifications resulting in the deeply-trapped excitonic state formation has been observed at low temperatures, below 60 K.
Treatment of distal radius fractures.
Lichtman, David M; Bindra, Randipsingh R; Boyer, Martin I; Putnam, Matthew D; Ring, David; Slutsky, David J; Taras, John S; Watters, William C; Goldberg, Michael J; Keith, Michael; Turkelson, Charles M; Wies, Janet L; Haralson, Robert H; Boyer, Kevin M; Hitchcock, Kristin; Raymond, Laura
2010-03-01
The clinical practice guideline is based on a systematic review of published studies on the treatment of distal radius fractures in adults. None of the 29 recommendations made by the work group was graded as strong; most are graded as inconclusive or consensus; seven are graded as weak. The remaining five moderate-strength recommendations include surgical fixation, rather than cast fixation, for fractures with postreduction radial shortening >3 mm, dorsal tilt >10 degrees , or intra-articular displacement or step-off >2 mm; use of rigid immobilization rather than removable splints for nonsurgical treatment; making a postreduction true lateral radiograph of the carpus to assess dorsal radial ulnar joint alignment; beginning early wrist motion following stable fixation; and recommending adjuvant treatment with vitamin C to prevent disproportionate pain. PMID:20190108
Proton radius from Bayesian inference
NASA Astrophysics Data System (ADS)
Graczyk, Krzysztof M.; Juszczak, Cezary
2014-11-01
The methods of Bayesian statistics are used to extract the value of the proton radius from the elastic e p scattering data in a model-independent way. To achieve that goal a large number of parametrizations (equivalent to neural network schemes) are considered and ranked by their conditional probability P (parametrization |data ) instead of using the minimal error criterion. As a result the most probable proton radii values (rEp=0.899 ±0.003 fm, rMp=0.879 ±0.007 fm) are obtained and systematic error due to freedom in the choice of parametrization is estimated. Correcting the data for the two-photon-exchange effect leads to smaller differences between the extracted values of rEp and rMp. The results disagree with recent muonic atom measurements.
Physical theory of excitons in conducting polymers.
Brazovskii, Serguei; Kirova, Natasha
2010-07-01
In this tutorial review, we cover the solid state physics approach to electronic and optical properties of conducting polymers. We attempt to bring together languages and advantages of the solid state theory for polymers and of the quantum chemistry for monomers. We consider polymers as generic one-dimensional semiconductors with features of strongly correlated electronic systems. Our model combines the long range electron-hole Coulomb attraction with a specific effect of strong intra-monomer electronic correlations, which results in effective intra-monomer electron-hole repulsion. Our approach allows to go beyond the single-chain picture and to compare excitons for polymers in solutions and in films. The approach helps connecting such different questions as shallow singlet and deep triplet excitons, stronger binding of interchain excitons in films, crossings of excitons' branches, 1/N energies shifts in oligomers. We describe a strong suppression of the luminescence from free charge carriers by long-range Coulomb interactions. Main attention is devoted to the most requested in applications phenyl based polymers. The specifics of the benzene ring monomer give rise to existence of three possible types of excitons: Wannier-Mott, Frenkel and intermediate ones. We discuss experimental manifestations of various excitons and of their transformations. We touch effects of the time-resolved self-trapping by libron modes leading to formation of torsion polarons. PMID:20517580
Exciton quasicondensation in one-dimensional systems
NASA Astrophysics Data System (ADS)
Werman, Yochai; Berg, Erez
2015-06-01
Two Luttinger liquids, with an equal density and opposite sign of charge carriers, may exhibit enhanced excitonic correlations. We term such a system an exciton quasicondensate, with a possible realization being two parallel oppositely doped quantum wires, coupled by repulsive Coulomb interactions. We show that this quasiexciton condensate can be stabilized in an extended range of parameters, in both spinless and spinful systems. We calculate the interwire tunneling current-voltage characteristic, and find that a negative differential conductance is a signature of excitonic correlations. For spinful electrons, the excitonic regime is shown to be distinct from the usual quasi-long-range ordered Wigner crystal phase characterized by power-law density wave correlations. The two phases can be clearly distinguished through their interwire tunneling current-voltage characteristics. In the quasiexciton condensate regime the tunneling conductivity diverges at low temperatures and voltages, whereas in the Wigner crystal it is strongly suppressed. Both the Wigner crystal and the excitonic regime are characterized by a divergent Coulomb drag at low temperature. Finally, metallic carbon nanotubes are considered as a special case of such a one-dimensional setup, and it is shown that exciton condensation is favorable due to the additional valley degree of freedom.
Exciton Resonances in Novel Silicon Carbide Polymers
NASA Astrophysics Data System (ADS)
Burggraf, Larry; Duan, Xiaofeng
2015-05-01
A revolutionary technology transformation from electronics to excitionics for faster signal processing and computing will be advantaged by coherent exciton transfer at room temperature. The key feature required of exciton components for this technology is efficient and coherent transfer of long-lived excitons. We report theoretical investigations of optical properties of SiC materials having potential for high-temperature excitonics. Using Car-Parinello simulated annealing and DFT we identified low-energy SiC molecular structures. The closo-Si12C12 isomer, the most stable 12-12 isomer below 1100 C, has potential to make self-assembled chains and 2-D nanostructures to construct exciton components. Using TDDFT, we calculated the optical properties of the isomer as well as oligomers and 2-D crystal formed from the isomer as the monomer unit. This molecule has large optical oscillator strength in the visible. Its high-energy and low-energy transitions (1.15 eV and 2.56 eV) are nearly pure one-electron silicon-to-carbon transitions, while an intermediate energy transition (1.28 eV) is a nearly pure carbon-to-silicon one-electron charge transfer. These results are useful to describe resonant, coherent transfer of dark excitons in the nanostructures. Research supported by the Air Force Office of Scientific Research.
The Laplacian spectral radius of some graphs
Jianxi Li; Wai Chee Shiu; Wai Hong Chan
2009-01-01
The Laplacian spectral radius of a graph is the largest eigenvalue of the associated Laplacian matrix. In this paper, we determine those graphs which maximize the Laplacian spectral radius among all bipartite graphs with (edge-)connectivity at most k. We also characterize graphs of order n with k cut-edges, having Laplacian spectral radius equal to n.
Bohr's Electron was Problematic for Einstein: String Theory Solved the Problem
NASA Astrophysics Data System (ADS)
Webb, William
2013-04-01
Neils Bohr's 1913 model of the hydrogen electron was problematic for Albert Einstein. Bohr's electron rotates with positive kinetic energies +K but has addition negative potential energies - 2K. The total net energy is thus always negative with value - K. Einstein's special relativity requires energies to be positive. There's a Bohr negative energy conflict with Einstein's positive energy requirement. The two men debated the problem. Both would have preferred a different electron model having only positive energies. Bohr and Einstein couldn't find such a model. But Murray Gell-Mann did! In the 1960's, Gell-Mann introduced his loop-shaped string-like electron. Now, analysis with string theory shows that the hydrogen electron is a loop of string-like material with a length equal to the circumference of the circular orbit it occupies. It rotates like a lariat around its centered proton. This loop-shape has no negative potential energies: only positive +K relativistic kinetic energies. Waves induced on loop-shaped electrons propagate their energy at a speed matching the tangential speed of rotation. With matching wave speed and only positive kinetic energies, this loop-shaped electron model is uniquely suited to be governed by the Einstein relativistic equation for total mass-energy. Its calculated photon emissions are all in excellent agreement with experimental data and, of course, in agreement with those -K calculations by Neils Bohr 100 years ago. Problem solved!
Interaction of Dirac Fermion excitons and biexciton-exciton cascade in graphene quantum dots
NASA Astrophysics Data System (ADS)
Ozfidan, Isil; Korkusinski, Marek; Hawrylak, Pawel
2015-03-01
We present a microscopic theory of interacting Dirac quasi-electrons and quasi-holes confined in graphene quantum dots. The single particle states of quantum dots are described using a tight binding model and screened direct, exchange, and scattering Coulomb matrix elements are computed using Slater pz orbitals. The many-body ground and excited states are expanded in a finite number of electron-hole pair excitations from the Hartree-Fock ground state and computed using exact diagonalization techniques. The resulting exciton and bi-exciton spectrum reflects the degeneracy of the top of the valence and bottom of the conduction band characteristic of graphene quantum dots with C3 symmetry. We study the interaction of multi-electron and hole complexes as a function of quantum dot size, shape and strength of Coulomb interactions. We identify two degenerate bright exciton (X) states and a corresponding biexciton (XX) state as XX-X cascade candidates, a source of entangled photon pairs. We next calculate the exciton to bi-exciton transitions detected in transient absorption experiments to extract the strength of exciton-exciton interactions and biexciton binding energies. We further explore the possibility of excitonic instability.
Exciton correlations and input-output relations in non-equilibrium exciton superfluids
Ye, Jinwu, E-mail: jy306@ccs.msstate.edu [Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048 (China) [Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048 (China); Department of Physics and Astronomy, Mississippi State University, MS 39762 (United States); Sun, Fadi; Yu, Yi-Xiang [Department of Physics and Astronomy, Mississippi State University, MS 39762 (United States) [Department of Physics and Astronomy, Mississippi State University, MS 39762 (United States); Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China); Liu, Wuming [Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China)] [Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China)
2013-02-15
The photoluminescence (PL) measurements on photons and the transport measurements on excitons are the two types of independent and complementary detection tools to search for possible exciton superfluids in electron-hole semi-conductor bilayer systems. In fact, it was believed that the transport measurements can provide more direct evidences on superfluids than the spectroscopic measurements. It is important to establish the relations between the two kinds of measurements. In this paper, using quantum Heisenberg-Langevin equations, we establish such a connection by calculating various exciton correlation functions in the putative exciton superfluids. These correlation functions include both normal and anomalous greater, lesser, advanced, retarded, and time-ordered exciton Green functions and also various two exciton correlation functions. We also evaluate the corresponding normal and anomalous spectral weights and the Keldysh distribution functions. We stress the violations of the fluctuation and dissipation theorem among these various exciton correlation functions in the non-equilibrium exciton superfluids. We also explore the input-output relations between various exciton correlation functions and those of emitted photons such as the angle resolved photon power spectrum, phase sensitive two mode squeezing spectrum and two photon correlations. Applications to possible superfluids in the exciton-polariton systems are also mentioned. For a comparison, using conventional imaginary time formalism, we also calculate all the exciton correlation functions in an equilibrium dissipative exciton superfluid in the electron-electron coupled semi-conductor bilayers at the quantum Hall regime at the total filling factor {nu}{sub T}=1. We stress the analogies and also important differences between the correlations functions in the two exciton superfluid systems. - Highlights: Black-Right-Pointing-Pointer Establish the relations between photoluminescence and transport measurements. Black-Right-Pointing-Pointer Stress the violations of the fluctuation-dissipation theorem in non-equilibrium systems. Black-Right-Pointing-Pointer Explore the input-output relations between excitons and photons. Black-Right-Pointing-Pointer Discuss differences between non-equilibrium systems and dissipative ones.
Microscopic theories of excitons and their dynamics
NASA Astrophysics Data System (ADS)
Berkelbach, Timothy C.
This thesis describes the development and application of microscopically-defined theories of excitons in a wide range of semiconducting materials. In Part I, I consider the topic of singlet exciton fission, an organic photophysical process which generates two spin-triplet excitons from one photoexcited spin-singlet exciton. I construct a theoretical framework that couples a realistic treatment of the static electronic structure with finite-temperature quantum relaxation techniques. This framework is applied separately, but consistently, to the problems of singlet fission in pentacene dimers, crystalline pentacene, and crystalline hexacene. Through this program, I am able to rationalize observed behaviors and make non-trivial predictions, some of which have been confirmed by experiment. In Part II, I present theoretical developments on the properties of neutral excitons and charged excitons (trions) in atomically thin transition metal dichalcogenides. This work includes an examination of material trends in exciton binding energies via an effective mass approach. I also present an experimental and theoretical collaboration, which links the unconventional disposition of excitons in the Rydberg series to the peculiar screening properties of atomically thin materials. The light-matter coupling in these materials is examined within low-energy models and is shown to give rise to bright and dark exciton states, which can be qualitatively labeled in analogy with the hydrogen series. In Part III, I explore theories of relaxation dynamics in condensed phase environments, with a focus on methodology development. This work is aimed towards biological processes, including resonant energy transfer in chromophore complexes and electron transfer in donor-bridge-acceptor systems. Specifically, I present a collaborative development of a numerically efficient but highly accurate hybrid approach to reduced dynamics, which exploits a partitioning of environmental degrees of freedom into those that evolve "fast" and "slow," as compared to the internal system dynamics. This method is tested and applied to the spin-boson model, a two-site Frenkel exciton model, and the seven-site Fenna-Matthews-Olson complex. I conclude with a collaborative analysis of a recently developed polaron-transformed quantum master equation, which is shown to accurately interpolate between the well-known Redfield and Forster theories, even in challenging donor-bridge-acceptor arrangements.
Excitons in the optical properties of nanotubes
NASA Astrophysics Data System (ADS)
Spataru, Catalin
2006-03-01
We present ab initio calculation of self-energy and electron-hole interaction (excitonic) effects on the optical spectra of single-walled carbon and BN nanotubes. We employed a many-electron Green's function approach that determines both the quasiparticle and optical excitations from first principles. We found important many-electron effects that explain many of the puzzling experimental findings in the optical spectrum of these quasi-one dimensional systems, and the calculated spectra are in excellent quantitative agreement with measurements. In carbon nanotubes, excitons can bind by as much as one eV in semiconducting nanotubes^a). We discovered that bound excitons also exist in metallic carbon nanotubes with binding energy of many tens of meVs^a). Excitonic effects are shown to be even more inportant in BN nanotubes than in carbon nanotubes. Unlike the carbon nanotubes, theory predicts that excitons in some BN nanotubes are comprised of coherent superposition of transitions from several different subband pairs^b). We have also calculated the radiative lifetime of excitons in semiconducting carbon nanotubes. Assuming a thermal occupation of bright and dark exciton bands, we find an effective radiative lifetime of the order of 10 ns at room temperature, in good accord with recent experiments^c). a) C.D. Spataru, S. Ismail-Beigi, L.X. Benedict and S.G. Louie, Phys. Rev. Lett. 92, 077402 (2004). b) C.-H. Park, C.D. Spataru and S.G. Louie, to be published. c) C.D. Spataru, S. Ismail-Beigi, R.B. Capaz and S.G. Louie, in press Phys. Rev. Lett.
Heterogeneous exciton dynamics revealed by two-dimensional optical spectroscopy.
Stiopkin, Igor; Brixner, Tobias; Yang, Mino; Fleming, Graham R
2006-10-12
We show that optical two-dimensional (2D) spectroscopy can recover ultrafast heterogeneous dynamics of closely spaced delocalized exciton states from a molecular exciton manifold characterized by a single absorption band. The complete experimental third-order nonlinear optical response from room-temperature J-aggregates in liquid phase is reproduced for the first time with self-consistent Frenkel exciton theory combined with modified Redfield theory. We show that exciton relaxation between the exciton states and nuclear-motion-induced exchange-narrowed energy fluctuations of individual delocalized exciton states can be distinguished because these two processes lead to a distinctively different evolution of the absolute 2D spectrum. Our technique also allows recovery of the variation of the exciton relaxation rates as well as the degree of exciton delocalization across the absorption band. PMID:17020391
Intrinsic Exciton Linewidth in Monolayer Transition Metal Dichalcogenides
NASA Astrophysics Data System (ADS)
Hao, Kai; Moody, Galan; Dass, Chandriker; Chen, Chang-Hsiao; Li, Lain-Jong; Singh, Akshay; Tran, Kha; Clark, Genevieve; Xu, Xiaodong; Bergäuser, Gunnar; Malic, Ermin; Knorr, Andreas; Li, Xiaoqin
2015-03-01
Excitons in monolayer transition metal dichalcogenides (TMDCs) exhibit exceptionally large binding energy, strong optical absorption, and spin valley coupling. These characteristics make TMDCs a promising system for optoelectronics and valleytronics. An important yet unknown property of excitons in TMDCs is the intrinsic homogeneous linewidth, which reflect radiative recombination and irreversible dissipative decay. Here, we use optical coherent two-dimensional spectroscopy to reveal the exciton homogeneous linewidth in monolayer CVD grown Tungsten Diselenide (WSe2). With excitation density and temperature dependent measurements, exciton-exciton interaction and exciton-phonon interactions are quantitatively evaluated. Extrapolating to zero density and temperature, we obtain a residual homogeneous linewidth of ~ 1.5 meV, which places a lower bound of 0.2 ps on the exciton radiative lifetime. This result is consistent with microscopic calculations, which suggest that fast radiative decay of delocalized excitons arises from their large oscillator strength. We acknowledge AFOSR and NSF for funding.
Investigating exciton correlations using coherent multidimensional optical spectroscopy
Turner, Daniel Burton
2010-01-01
The optical measurements described in this thesis reveal interactions among bound electron-hole pairs known as excitons in a semiconductor nanostructure. Excitons are quasiparticles that can form when light is absorbed by ...
Generation of Quasiclassical Bohr-Like Wave Packets Using Half-Cycle Pulses
Mestayer, J. J.; Wyker, B.; Dunning, F. B.; Reinhold, Carlos O; Yoshida, S.; Burgdorfer, J.
2008-08-01
We demonstrate the experimental realization of Bohr-like atoms by applying a pulsed unidirectional field, termed a half-cycle pulse (HCP), to atoms in quasi-two-dimensional near-circular states. This leads to creation of localized wave packets that travel in near-circular orbits and mimic the dynamics of an electron in the original Bohr model of the hydrogen atom. This motion can be followed for several orbital periods before the localization of the wave packet is lost due to dephasing. We show, however, that localization can be recovered by application of further HCPs.
Calculation of Helium Ground State Energy by Bohr's Theory-Based Methods
Tsubono, Youhei
2009-01-01
Bohr's model agreed with the hydrogen spectrum results, but did not agree with the spectrum of Helium. Here we show that Bohr's model-based methods can calculate the experimental value (-79.005 eV) of Helium ground state energy correctly. we suppose the orbital planes of the two electrons are perpendicular to each other. By a computational method, we calculate the Coulomb force among the particles, and the number of de Broglie's waves contained in the short segment at short time intervals. Our results demonstrate that two electrons of Helium are actually moving around, not as electron clouds.
Generation of quasiclassical Bohr-like wave packets using half-cycle pulses
NASA Astrophysics Data System (ADS)
Mestayer, J. J.; Wyker, B.; Dunning, F. B.; Reinhold, C. O.; Yoshida, S.; Burgdörfer, J.
2008-10-01
We demonstrate the experimental realization of Bohr-like atoms by applying a pulsed unidirectional field, termed a half-cycle pulse (HCP), to atoms in quasi-two-dimensional near-circular states. This leads to creation of localized wave packets that travel in near-circular orbits and mimic the dynamics of an electron in the original Bohr model of the hydrogen atom. This motion can be followed for several orbital periods before the localization of the wave packet is lost due to dephasing. We show, however, that localization can be recovered by application of further HCPs.
EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited
H. Nikolic
2012-05-28
In 1930 Einstein argued against consistency of the time-energy uncertainty relation by discussing a thought experiment involving a measurement of mass of the box which emitted a photon. Bohr seemingly triumphed over Einstein by arguing that the Einstein's own general theory of relativity saves the consistency of quantum mechanics. We revisit this thought experiment from a modern point of view at a level suitable for undergraduate readership and find that neither Einstein nor Bohr was right. Instead, this thought experiment should be thought of as an early example of a system demonstrating nonlocal "EPR" quantum correlations, five years before the famous Einstein-Podolsky-Rosen paper.
Bohr quantum theory of the magnetic monopoles and classical electron electromagnetic mass problem
Vladan Pankovic
2015-08-28
In the first part of this work we apply Bohr (old or naive quantum atomic) theory for analysis of the remarkable electro-dynamical problem of magnetic monopoles. We reproduce formally exactly some basic elements of the Dirac magnetic monopoles theory, especially Dirac electric/magnetic charge quantization condition. It follows after application of Bohr theory at the system, simply called magnetic monopole "atom", consisting of the practically standing, massive magnetic monopole as the "nucleus" and electron rotating stable around magnetic monopole under magnetic and electrostatic interactions. Also, in the second part of this work we suggest a simple solution of the classical electron electromagnetic mass problem.
Bohr's Correspondence Principle and The Area Spectrum of Quantum Black Holes
Shahar Hod
1998-12-15
During the last twenty-five years evidence has been mounting that a black-hole surface area has a {\\it discrete} spectrum. Moreover, it is widely believed that area eigenvalues are {\\it uniformally} spaced. There is, however, no general agreement on the {\\it spacing} of the levels. In this letter we use Bohr's correspondence principle to provide this missing link. We conclude that the area spacing of a black-hole is $4\\hbar \\ln 3$. This is the unique spacing consistent both with the area-entropy {\\it thermodynamic} relation for black holes, with Boltzmann-Einstein formula in {\\it statistical physics} and with {\\it Bohr's correspondence principle}.
EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited
Nikolic, H
2012-01-01
In 1930 Einstein argued against consistency of the time-energy uncertainty relation by discussing a thought experiment involving a measurement of mass of the box which emitted a photon. Bohr seemingly triumphed over Einstein by arguing that the Einstein's own general theory of relativity saves the consistency of quantum mechanics. We revisit this thought experiment from a modern point of view and find that neither Einstein nor Bohr was right. Instead, this thought experiment should be thought of as an early example of a system demonstrating nonlocal "EPR" quantum correlations, five years before the famous Einstein-Podolsky-Rosen paper.
Spectral dimension and Bohr's formula for Schrödinger operators on unbounded fractal spaces
NASA Astrophysics Data System (ADS)
Chen, Joe P.; Molchanov, Stanislav; Teplyaev, Alexander
2015-09-01
We establish an asymptotic formula for the eigenvalue counting function of the Schrödinger operator -{{? }}+V for some unbounded potentials V on several types of unbounded fractal spaces. We give sufficient conditions for Bohr’s formula to hold on metric measure spaces which admit a cellular decomposition, and then verify these conditions for fractafolds and fractal fields based on nested fractals. In particular, we partially answer a question of Fan, Khandker, and Strichartz regarding the spectral asymptotics of the harmonic oscillator potential on the infinite blow-up of a Sierpinski gasket.
Disorder-enhanced exciton delocalization in an extended dendrimer
NASA Astrophysics Data System (ADS)
Pouthier, Vincent
2014-08-01
The exciton dynamics in a disordered extended dendrimer is investigated numerically. Because a homogeneous dendrimer exhibits few highly degenerate energy levels, a dynamical localization arises when the exciton is initially located on the periphery. However, it is shown that the disorder lifts the degeneracy and favors a delocalization-relocalization transition. Weak disorder enhances the delocalized nature of the exciton and improves any quantum communication, whereas strong disorder prevents the exciton from propagating in accordance with the well-known Anderson theory.
Excitons in Time-Dependent Density-Functional Theory.
Ullrich, Carsten A; Yang, Zeng-Hui
2016-01-01
This chapter gives an overview of the description of the optical and dielectric properties of bulk insulators and semiconductors in time-dependent density-functional theory (TDDFT), with an emphasis on excitons. We review the linear-response formalism for periodic solids, discuss excitonic exchange-correlation kernels, calculate exciton binding energies for various materials, and compare the treatment of excitons with TDDFT and with the Bethe-Salpeter equation. PMID:25805143
BOSE-EINSTEIN CONDENSATION OF EXCITONS: PROMISE AND DISAPPOINTMENT
Zimmermann, Roland
with exciton physics was not reading one of the famous text- books like the `Knox' (Knox, 1963), but trying important, however, are two other facts. In the exciton case, anomalous propagators have a simple physical to the original idea of the excitonic insulator (Bucher et al., 1991; Wachter, 2005). When driving the band gap
Observation of Bogoliubov excitations in exciton-polariton condensates
Loss, Daniel
LETTERS Observation of Bogoliubov excitations in exciton-polariton condensates S. UTSUNOMIYA1 on the quantitative level was carried out for atomic BEC3 using the two-photon Bragg scattering technique4 . Exciton-polaritons experiments with exciton-polaritons have demonstrated several interesting signatures from the viewpoint
Singlet exciton fission in pure and doped anthracene
K. von Burg; I. Zschokke-Gränacher
1979-01-01
On the basis of the kinetic model by Merrifield for triplet exciton fusion in molecular crystals, we have derived an expression which describes the reciprocal process, i.e., the anisotropy of the prompt fluorescence in the presence of singlet exciton fission in a magnetic field. For the first time a thorough comparison of Merrifield's theory with singlet exciton fission experiments is
Singlet exciton fission in pure and doped anthracene
K. von Burg
1979-01-01
On the basis of the kinetic model by Merrifield for triplet exciton fusion in molecular crystals, we have derived an expression which describes the reciprocal process, i.e., the anisotropy of the prompt fluorescence in the presence of singlet exciton fission in a magnetic field. For the first time a thorough comparison of Merrifield’s theory with singlet exciton fission experiments is
BoseEinstein condensation of excitons in bilayer electron systems
Eisenstein, Jim
BoseEinstein condensation of excitons in bilayer electron systems J. P. Eisenstein1 * & A. H. Mac'. An ordered electronic state in which excitons condense into a single quantum state was proposed clear evidence for this phenomenon and explain why exciton condensation in the quantum Hall regime
Emission Spectrum from the Bose-Condensed Excitonic Molecules
Masahiro Inoue; Eiichi Hanamura
1976-01-01
The emission spectrum is given for radiative decay of the excitonic molecules in the Bose-condensed state at finite temperature which is described in the framework of the Bogoliubov approximation. We take into account the final state interaction of an exciton created in the radiative process with the environment of the Bose-condensed excitonic molecules. The emission spectrum is characterized by a
Polynomial fits and the proton radius puzzle
NASA Astrophysics Data System (ADS)
Kraus, E.; Mesick, K. E.; White, A.; Gilman, R.; Strauch, S.
2014-10-01
The proton radius puzzle refers to the ?7? discrepancy that exists between the proton charge radius determined from muonic hydrogen and that determined from electronic hydrogen spectroscopy and electron-proton scattering. One possible partial resolution to the puzzle includes errors in the extraction of the proton radius from ep elastic scattering data. This possibility is made plausible by certain fits that extract a smaller proton radius from the scattering data consistent with that determined from muonic hydrogen. The reliability of some of these fits that yield a smaller proton radius was studied. We found that fits of form factor data with a truncated polynomial fit are unreliable and systematically give values for the proton radius that are too small. Additionally, a polynomial fit with a ?reduced2?1 is not a sufficient indication for a reliable result.
Puzzling out the proton radius puzzle
NASA Astrophysics Data System (ADS)
Mihovilovi?, Miha; Merkel, Harald; Weber, Adrian
2014-11-01
The discrepancy between the proton charge radius extracted from the muonic hydrogen Lamb shift measurement and the best present value obtained from the elastic scattering experiments, remains unexplained and represents a burning problem of today's nuclear physics: after more than 50 years of research the radius of a basic constituent of matter is still not understood. This paper presents a summary of the best existing proton radius measurements, followed by an overview of the possible explanations for the observed inconsistency between the hydrogen and the muonic-hydrogen data. In the last part the upcoming experiments, dedicated to remeasuring the proton radius, are described.
Förster Coupling in Nanoparticle Excitonic Circuits
Rebentrost, P.; Stopa, M.; Aspuru-Guzik, Alan
2010-08-11
Exciton transport in semiconductor nanoparticles underlies recent experiments on electrically controlled nanostructures and proposals for new artificial light-harvesting systems. In this work, we develop a novel method for the numerical evaluation of the Förster matrix element, based on a three-dimensional real space grid and the self-consistent solution of the mesoscopic exciton in a macroscopic dielectric environment. This method enables the study of the role of the nanoparticle shape, spatially varying dielectric environments, and externally applied electric fields. Depending on the orientation of the transition dipole, the Förster coupling is shown to be either increased or decreased as a function of the nanoparticle shape and of the properties of the dielectric environment. In the presence of an electric field, we investigate the relation between excitonic binding and confinement effects. We also study a type II core-shell quantum dot where electron and hole are spatially separated due to a particular configuration of the band structure.
Harvesting excitons through plasmonic strong coupling
NASA Astrophysics Data System (ADS)
Gonzalez-Ballestero, Carlos; Feist, Johannes; Moreno, Esteban; Garcia-Vidal, Francisco J.
2015-09-01
Exciton harvesting is demonstrated in an ensemble of quantum emitters coupled to localized surface plasmons. When the interaction between emitters and the dipole mode of a metallic nanosphere reaches the strong-coupling regime, the exciton conductance is greatly increased. The spatial map of the conductance matches the plasmon field intensity profile, which indicates that transport properties can be tuned by adequately tailoring the field of the plasmonic resonance. Under strong coupling, we find that pure dephasing can have detrimental or beneficial effects on the conductance, depending on the effective number of participating emitters. Finally, we show that the exciton transport in the strong-coupling regime occurs on an ultrafast time scale given by the inverse Rabi splitting (˜10 fs), which is orders of magnitude faster than transport through direct hopping between the emitters.
Floquet exciton condensation in graphene bilayers
NASA Astrophysics Data System (ADS)
Zhang, Chuanyi; Zhang, Weifeng; Jin, Guojun
2015-08-01
We theoretically study the Floquet exciton condensation, which denotes the exciton condensation under an off-resonant circularly polarized light, in graphene bilayers. The polarized light greatly affects the gap function of the condensate as well as the related physical quantities, e.g., the condensate fraction and superfluid density both having maximal values as the photoillumination parameter varies. We find that the critical temperature rises fast and then slowly approaches a constant upon increasing the photoillumination parameter. The variation of the drag conductivity is obvious in a small range just below the critical temperature; furthermore, there exists competition between the photoillumination parameter and temperature in the gap function and drag conductivity. It is believed that these results can facilitate the experimental investigations of the Floquet exciton condensation in graphene bilayers.
Nanocrystal skins with exciton funneling for photosensing.
Akhavan, Shahab; Cihan, Ahmet Fatih; Bozok, Berkay; Demir, Hilmi Volkan
2014-06-25
Highly photosensitive nanocrystal (NC) skins based on exciton funneling are proposed and demonstrated using a graded bandgap profile across which no external bias is applied in operation for light-sensing. Four types of gradient NC skin devices (GNS) made of NC monolayers of distinct sizes with photovoltage readout are fabricated and comparatively studied. In all structures, polyelectrolyte polymers separating CdTe NC monolayers set the interparticle distances between the monolayers of ligand-free NCs to <1 nm. In this photosensitive GNS platform, excitons funnel along the gradually decreasing bandgap gradient of cascaded NC monolayers, and are finally captured by the NC monolayer with the smallest bandgap interfacing the metal electrode. Time-resolved measurements of the cascaded NC skins are conducted at the donor and acceptor wavelengths, and the exciton transfer process is confirmed in these active structures. These findings are expected to enable large-area GNS-based photosensing with highly efficient full-spectrum conversion. PMID:24599603
Bright and dark excitons in semiconductor carbon nanotubes
Tretiak, Sergei [Los Alamos National Laboratory
2008-01-01
We report electronic structure calculations of finite-length semiconducting carbon nanotubes using the time dependent density functional theory (TD-DFT) and the time dependent Hartree Fock (TD-HF) approach coupled with semiempirical AM1 and ZINDO Hamiltonians. We specifically focus on the energy splitting, relative ordering, and localization properties of the optically active (bright) and optically forbidden (dark) states from the lowest excitonic band of the nanotubes. These excitonic states are very important in competing radiative and non-radiative processes in these systems. Our analysis of excitonic transition density matrices demonstrates that pure DFT functionals overdelocalize excitons making an electron-hole pair unbound; consequently, excitonic features are not presented in this method. In contrast, the pure HF and A111 calculations overbind excitons inaccurately predicting the lowest energy state as a bright exciton. Changing AM1 with ZINDO Hamiltonian in TD-HF calculations, predicts the bright exciton as the second state after the dark one. However, in contrast to AM1 calculations, the diameter dependence of the excitation energies obtained by ZINDO does not follow the experimental trends. Finally, the TD-DFT approach incorporating hybrid functions with a moderate portion of the long-range HF exchange, such as B3LYP, has the most generality and predictive capacity providing a sufficiently accurate description of excitonic structure in finite-size nanotubes. These methods characterize four important lower exciton bands. The lowest state is dark, the upper band is bright, and the two other dark and nearly degenerate excitons lie in-between. Although the calculated energy splittings between the lowest dark and the bright excitons are relatively large ({approx}0.1 eV), the dense excitonic manifold below the bright exciton allows for fast non-radiative relaxation leasing to the fast population of the lowest dark exciton. This rationalizes the low luminescence efficiency in nanotubes.
Triplet exciton dynamics in rubrene single crystals
NASA Astrophysics Data System (ADS)
Ryasnyanskiy, Aleksandr; Biaggio, Ivan
2011-11-01
The decay of the photoluminescence excited in rubrene single crystals by picosecond pulses is measured over 7 orders of magnitude and more than 4 time decades. We identify the typical decay dynamics due to triplet-triplet interaction. We show that singlet exciton fission and triplet fusion quantum yields in rubrene are both very large, and we directly determine a triplet exciton lifetime of 100±20 ?s, which explains the delayed buildup of a large photocurrent that has been reported earlier for low excitation densities.
Heat pumping with optically driven excitons
Erik M. Gauger; Joachim Wabnig
2010-06-07
We present a theoretical study showing that an optically driven excitonic two-level system in a solid state environment acts as a heat pump by means of repeated phonon emission or absorption events. We derive a master equation for the combined phonon bath and two-level system dynamics and analyze the direction and rate of energy transfer as a function of the externally accessible driving parameters. We discover that if the driving laser is detuned from the exciton transition, cooling the phonon environment becomes possible.
Autolocalization of a dipolar exciton gas
NASA Astrophysics Data System (ADS)
Andreev, S. V.
2015-07-01
We present a theory of autolocalization as a mechanism of formation of the macroscopically ordered exciton state (MOES) in semiconductor quantum wells. We show that the onset of a crystalline order having a macroscopic spatial period is possible in the systems where, in addition to long-range dipolar repulsion, the excitons exhibit resonant pairing at short distances. Our theory suggests that the central part of each condensate in the MOES may represent the long-sought bosonic analog of the Bardeen-Cooper-Schrieffer (BCS) superconductor.
Special Solutions of the Bohr Hamiltonian Related to Shape Phase Transitions in Nuclei
Dennis Bonatsos; D. Lenis; D. Petrellis
2007-01-19
Nuclei exhibit quantum phase transitions (earlier called ground state phase transitions) between different shapes as the number of nucleons is modified, resulting in changes in the ground and low lying nuclear states. Special solutions of the Bohr Hamiltonian appropriate for the critical point of such shape phase transitions, as well as other special solutions applicable to relevant nuclear regions are described.
EPR before EPR: A 1930 Einstein-Bohr thought Experiment Revisited
ERIC Educational Resources Information Center
Nikolic, Hrvoje
2012-01-01
In 1930, Einstein argued against the consistency of the time-energy uncertainty relation by discussing a thought experiment involving a measurement of the mass of the box which emitted a photon. Bohr seemingly prevailed over Einstein by arguing that Einstein's own general theory of relativity saves the consistency of quantum mechanics. We revisit…
Bohr's complementarity relation and the violation of CP symmetry in the neutral kaon system
NASA Astrophysics Data System (ADS)
Hiesmayr, Beatrix C.; Huber, Marcus
2008-05-01
We test Bohr's complementary relation, for single and bipartite neutral kaons. They present a system that is oscillating, decaying and breaks the CP symmetry. We discuss the effect of the CP violation and moreover show that the quantity that complements the single partite information for bipartite kaons is an entanglement measure. Which is independent of CP violation, while nonlocality is sensitive to CP violation.
The Hydrogen Atom of Bohr; 2, Mean Lifetime of an Ensemble of Excited Hydrogen atoms
Kamenov, P S
1999-01-01
"Does God play dice with the Universe?" The natural width of excited hydrogen atoms are found using the Bohr's model of this atom and de Broglie's ideas. The mean life time of the excited states is a characteristic only of a statistical ensemble of many atoms.
Forlani, L; Marini, M A
1993-02-01
A cooperative model applied to hydrogen ligand binding curves of normal human hemoglobin indicates that the Bohr effect is a cooperative (n) change rather than a pK shift. The analysis suggests a molecular mechanism whose energetic justification acquires a specific physiological significance. PMID:8385518
The thermal Casimir effect for conducting plates and the Bohr-van Leeuwen theorem
Giuseppe Bimonte
2009-11-12
We examine recent prescriptions for estimating the thermal Casimir force between two metallic plates from the point of view of their consistency with the Bohr-van Leeuwen theorem of classical statistical physics. We find that prescriptions including the effect of ohmic dissipation satisfy the theorem, while prescriptions that neglect ohmic dissipation do not.
Bohr Hamiltonian, mass coefficients, and the structure of well deformed axially symmetric nuclei
Jolos, R. V.; Brentano, P. von
2008-12-15
It is shown that in the Bohr Hamiltonian the use of three different mass coefficients for the two vibrational and the rotational modes is very important for the correct description of the properties of the well deformed axially symmetric nuclei. Four parameters per nucleus are needed to describe the relative values of energies and B(E2)'s.
M. A. Caprio
2011-05-21
Detailed quantitative predictions are obtained for phonon and multiphonon excitations in well-deformed rotor nuclei within the geometric framework, by exact numerical diagonalization of the Bohr Hamiltonian in an SO(5) basis. Dynamical gamma deformation is found to significantly influence the predictions through its coupling to the rotational motion. Basic signatures for the onset of rigid triaxial deformation are also obtained.
Bell's theorem and Bohr's principle that the measurement must be classical
Antoine Suarez
2002-02-23
In a recent paper Karl Hess and Walter Philipp claim that hidden local variables cannot be ruled out. We argue that their claim is only valid if one gives up Bohr's principle that the measuring instruments must be classical, and this principle belongs to the foundations of scientific knowledge: Therefore, nonlocal influences can be considered demonstrated.
Caprio, M. A.
2011-06-15
Detailed quantitative predictions are obtained for phonon and multiphonon excitations in well-deformed rotor nuclei within the geometric framework, by exact numerical diagonalization of the Bohr Hamiltonian in an SO(5) basis. Dynamical {gamma} deformation is found to significantly influence the predictions through its coupling to the rotational motion. Basic signatures for the onset of rigid triaxial deformation are also obtained.
Fluctuation and commensurability effect of exciton density wave
NASA Astrophysics Data System (ADS)
Yang, Sen; Butov, L. V.; Simons, B. D.; Campman, K. L.; Gossard, A. C.
2015-06-01
At low temperatures, indirect excitons formed at the in-plane electron-hole interface in a coupled-quantum-well structure undergo a spontaneous transition into a spatially modulated state. We report on the control of the instability wavelength, measurement of the dynamics of the exciton emission pattern, and observation of the fluctuation and commensurability effect of the exciton density wave. We found that fluctuations are suppressed when the instability wavelength is commensurate with defect separation along the exciton density wave. The commensurability effect is also found in numerical simulations within the model describing the exciton density wave in terms of an instability due to stimulated processes.
Radar determination of the radius of venus.
Melbourne, W G; Muhleman, D O; O'handley, D A
1968-05-31
The radius of Venus has been determined from radar-range data taken at the Jet Propulsion Laboratory's Goldstone facility. A simultaneous intergration of the equations of motion of the solar-system fit to this time-delay data gave a value of 6053.7 +/- 2.2 kilometers. A discussion of other Venusian radius determinations is made. PMID:17768890
Excitons in Cuprous Oxide: Photoionization and Other Multiphoton Processes
NASA Astrophysics Data System (ADS)
Frazer, Nicholas Laszlo
In cuprous oxide (Cu2O), momentum from the absorption of two infrared photons to make an orthoexciton is conserved and detected through the photon component of a resulting mixed exciton/photon (quadrupole exciton polariton) state. I demonstrated that this process, which actually makes the photon momentum more precisely defined, is disrupted by photoionization of excitons. Some processes are known to affect exciton propagation in both the pump and exciton stages, such as phonon emission, exciton-exciton (Auger) scattering, and third harmonic generation. These processes alone were not able to explain all observed losses of excitons or all detected scattering products, which lead me to design an optical pump-probe experiment to measure the exciton photoionization cross section, which is (3.9+/-0.2) x 10-22 m2. This dissertation describes the synthesis of cuprous oxide crystals using oxidation of copper, crystallization from melt with the optical floating zone method, and annealing. The cuprous oxide crystals were characterized using time and space resolved luminescence, leading to the discovery of new defect properties. Selection rules and overall efficiency of third harmonic generation in these crystals were characterized. Exciton photoionization was demonstrated through the depletion of polariton luminescence by an optical probe, the production of phonon linked luminescence as a scattering product, temporal delay of the probe, and time resolved luminescence. The results are integrated with the traditional dynamical model of exciton densities. An additional investigation of copper/cuprous oxide/gold photovoltaic devices is appended.
Intracavity optical pumping of J-aggregate microcavity exciton polaritons
Bradley, M. Scott; Bulovic, Vladimir
2010-07-29
We demonstrate intracavity optical pumping of J-aggregate microcavity exciton polaritons. The use of ultrathin layer-by-layer J-aggregate thin films as the strongly coupled exciton medium allows for inclusion of a thermally evaporated luminescent cavity spacer layer, through which the lower-branch exciton-polariton states are resonantly pumped. We present a measurement of the lower-branch exciton-polariton occupation in room-temperature microcavity devices containing J-aggregated molecular thin films under low-density steady-state excitation. The observed exciton-polariton occupation shows a Maxwell-Boltzmann distribution at T=300?K , indicating thermalization of exciton polaritons in the lower energy branch. This device design enables us to propose a new type of “polariton laser” architecture for microcavity exciton polaritons.
Dynamics of the Excitonic Coupling in Organic Crystals
NASA Astrophysics Data System (ADS)
Aragó, Juan; Troisi, Alessandro
2015-01-01
We show that the excitonic coupling in molecular crystals undergoes a very large fluctuation at room temperature as a result of the combined thermal motions of the nuclei. This observation dramatically affects the description of exciton transport in organic crystals and any other phenomenon (like singlet fission or exciton dissociation) that originates from an exciton in a molecular crystal or thin film. This unexpected result is due to the predominance of the short-range excitonic coupling mechanisms (exchange, overlap, and charge-transfer mediated) over the Coulombic excitonic coupling for molecules in van der Waals contact. To quantify this effect we develop a procedure to evaluate accurately the short-range excitonic coupling (via a diabatization scheme) along a molecular dynamics trajectory of the representative molecular crystals of anthracene and tetracene.
Dynamics of the excitonic coupling in organic crystals.
Aragó, Juan; Troisi, Alessandro
2015-01-16
We show that the excitonic coupling in molecular crystals undergoes a very large fluctuation at room temperature as a result of the combined thermal motions of the nuclei. This observation dramatically affects the description of exciton transport in organic crystals and any other phenomenon (like singlet fission or exciton dissociation) that originates from an exciton in a molecular crystal or thin film. This unexpected result is due to the predominance of the short-range excitonic coupling mechanisms (exchange, overlap, and charge-transfer mediated) over the Coulombic excitonic coupling for molecules in van der Waals contact. To quantify this effect we develop a procedure to evaluate accurately the short-range excitonic coupling (via a diabatization scheme) along a molecular dynamics trajectory of the representative molecular crystals of anthracene and tetracene. PMID:25635554
Red cell organic phosphates and Bohr effects in house sparrow blood.
Maginniss, L A
1985-01-01
CO2 and fixed acid Bohr effects (d log PO2/d pH) were determined for fresh whole blood of adult house sparrow (Passer domesticus) at 35, 41 and 45 degrees C. At each temperature, the effects of titrating blood with CO2 at constant base excess (CO2 Bohr effect) were similar at P50 (35 degrees, -0.48; 41 degrees, -0.49; 45 degrees, -0.49). The CO2 Bohr slopes were also reasonably saturation independent between 10 and 90% S. Fixed acid Bohr values, determined by titrating sparrow blood with HCl and NaHCO3 at 4% CO2, were significantly less than the corresponding CO2 coefficients at half saturation (35 degrees, -0.43; 41 degrees, -0.39; 45 degrees, -0.41). The difference between CO2 and H+ Bohr effects, assumed here to represent carbamino CO2 binding to hemoglobin, decreased in magnitude with increasing saturation at each temperature. Inositol pentaphosphate (IPP, 3.1 mumol/ml RBC) and ATP (7.7 mumol/ml RBC) were the major organic phosphates present in Passer erythrocytes. CO2 and organic phosphates are known to complete for common binding sites on the Hb molecule. Because of IPP's strong binding affinity and high concentration in most avian red cells, carbamate formation is generally suppressed in bird blood. The presence of a small but significant specific CO2 effect in Passer blood may indicate that one or both sparrow isohemoglobins has reduced affinity for IPP and/or ATP, permitting CO2 to compete more effectively in Hb-carbamate formation. PMID:3919436
Good Vibrations: Plasmon-Exciton Coupling
facilities renovated under NSF ARI-R2 DMR-0963361. References Maier, Stefan A. Plasmonics: Fundamentals binding energy (0.5 eV) Au nanoparticles (40 nm width x 20 nm height x variable length) HSQ spacer layer Energy Shift Conclusions Wavelength Extinction Excitation PLintensity Two exciton peak resonances of MoS2
(Gene sequencing by scanning molecular exciton microscopy)
Not Available
1991-01-01
This report details progress made in setting up a laboratory for optical microscopy of genes. The apparatus including a fluorescence microscope, a scanning optical microscope, various spectrometers, and supporting computers is described. Results in developing photon and exciton tips, and in preparing samples are presented. (GHH)
Singlet exciton fission in a hexacene derivative.
Lee, Jiye; Bruzek, Matthew J; Thompson, Nicholas J; Sfeir, Matthew Y; Anthony, John E; Baldo, Marc A
2013-03-13
Hexacene, an acene with six benzene rings, is notable for its exceptionally small triplet energy, around one third of the singlet energy. Herein, singlet fission, i.e., conversion of a singlet exciton into two triplets, is demonstrated in a thin film of hexacene derivative, employing both transient absorption spectroscopy and magnetic field effects on photocurrent. PMID:23293054
Excitons in T-shaped quantum wires
NASA Astrophysics Data System (ADS)
Szymanska, M. H.; Littlewood, P. B.; Needs, R. J.
2001-05-01
We calculate energies, oscillator strengths for radiative recombination, and two-particle wave functions for the ground-state exciton and around 100 excited states in a T-shaped quantum wire. We include the single-particle potential and the Coulomb interaction between the electron and hole on an equal footing, and perform exact diagonalization of the two-particle problem within a finite-basis set. We calculate spectra for all of the experimentally studied cases of T-shaped wires including symmetric and asymmetric GaAs/AlxGa1-xAs and InyGa1-yAs/AlxGa1-xAs structures. We study in detail the shape of the wave functions to gain insight into the nature of the various states for selected symmetric and asymmetric wires in which laser emission has been experimentally observed. We also calculate the binding energy of the ground-state exciton and the confinement energy of the one-dimensional (1D) quantum-wire-exciton state with respect to the 2D quantum-well exciton for a wide range of structures, varying the well width and the Al molar fraction x. We find that the largest binding energy of any wire constructed to date is 16.5 meV. We also notice that in asymmetric structures, the confinement energy is enhanced with respect to the symmetric forms with comparable parameters but the binding energy of the exciton is then lower than in the symmetric structures. For GaAs/AlxGa1-xAs wires we obtain an upper limit for the binding energy of around 25 meV in a 10-Å -wide GaAs/AlAs structure that suggests that other materials must be explored in order to achieve room-temperature applications. There are some indications that InyGa1-yAs/AlxGa1-xAs might be a good candidate.
Relaxation of excitons in semimagnetic asymmetric double quantum wells
Zaitsev, S. V., E-mail: szaitsev@issp.ac.ru; Brichkin, A. S.; Dorozhkin, P. S. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation); Bacher, G. [Universitaet Duisburg-Essen, Lehrstuhl Werkstoffe der Electrotechnik (Germany)
2008-07-15
The steady-state circular-polarized photoluminescence in semimagnetic asymmetric double quantum wells based on Cd(Mn,Mg)Te is studied thoroughly in relation to the polarization of intrawell nonresonance photoexcitation in magnetic fields Bup to 9 T. In low fields B, in which the exciton in the magnetic well is higher in energy than the exciton in the nonmagnetic well, the complete interwell relaxation of excitons is observed. In fields higher than B{sub c} = 3-6 T, at which the exciton level in the magnetic well crosses the field-independent exciton level in the nonmagnetic well, the magnetic-field-induced red shift of the exciton in the magnetic well is accompanied by the establishment of a nonequilibrium distribution of excitons. This suggests that spin relaxation plays an important part in the interwell separation of excitons in the spin-dependent potential of the heterostructure. The efficiency of spin relaxation is controlled by mixing of valence band states in the nonmagnetic well and by splitting of heavy and light holes {delta}{sub hh-lh}. Different modes of interwell tunneling are observed in different field regions separated by the field B{sub c}* > B{sub c} corresponding to the crossing of the localized excitons in the nonmagnetic well and free excitons in the magnetic well. Possible mechanisms of interwell tunnel relaxation are discussed.
Excitonic polarons in low-dimensional transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Thilagam, A.
2015-05-01
We examine the excitonic polaron properties of common monolayer transition metal dichalcogenides (MoS2, MoSe2, WS2 and WSe2). The excitonic polaron is formed when excitons interact with acoustic or optical phonons via coupling to the deformation potentials associated with the conduction and valence bands. A unitary transformation which performs an approximate diagonalization of the exciton-phonon operator is used to evaluate the ground state energy of the excitonic polaron. We derive analytical expressions of the changes in the excitonic polaron energy and mass at small exciton wavevectors involving the deformation potential due to optical phonons. The polaronic effect of the monolayer transition metal dichalcogenides is examined by comparing changes in the energy gap shift and effective masses based on known deformation potential constants for carrier-phonon interactions. Our results indicate the occurrence of comparable energy shifts when the ground state exciton interacts with optical or acoustic phonons. We extend our calculations to explore the influence of exciton-lattice interactions on the binding energies and the self-trapping of excitons in two-dimensional layers of transition metal dichalcogenides.
Multivariate Refinable Hermite Interpolants Spectral Radius Optimization
Multivariate Refinable Hermite Interpolants and Spectral Radius Optimization Thomas P.ÂY. Yu and analyze a class of multivariate subdivision schemes with a special Hermite interpolatory property; as well
Remarks on the proton charge radius
Hirohisa Ishikawa; Keiji Watanabe
2011-07-08
Proton charge radius is calculated from the electromagnetic form factor of proton parameterized by the dispersion relation. The calculated charge radius is a little larger than that obtained by the Lamb shift of the $\\mu$ mesic atom. As the result is sensitive to the experimental data of proton electric form factor at small momentum transfer, more accurate data are required to draw conclusion if the result of the nucleon form factor is different or not from that obtained Pohl et al.
Accurate Determination of the Solar Photospheric Radius
Brown, T M
1998-01-01
The Solar Diameter Monitor measured the duration of solar meridian transits during the 6 years 1981 to 1987, spanning the declining half of solar cycle 21. We have combined these photoelectric measurements with models of the solar limb-darkening function, deriving a mean value for the solar near-equatorial radius of 695.508 +- .026 Mm. Annual averages of the radius are identical within the measurement error of +- .037 Mm.
Bohr effect induced by CO2 and fixed acid at various levels of O2 saturation in duck blood.
Meyer, M; Holle, J P; Scheid, P
1978-09-29
The Bohr factor, phi = delta log Po2/deltapH, was determined at various levels of hemoglobin O2 saturation (SO2) in fresh whole blood of the duck. Plasma pH was varied by either changing PCO2 of the blood at constant base excess (CO2 Bohr factor, phiCO2) or by addition of NaHCO3 and HCl at constant PCO2 (fixed acid BOHR factor, phiAH). No differences were found between phiCO2 and phiAH at SO2 levels between 20 and 85%, and there was no saturation dependence of the Bohr factor, its average value being -0.44. It is concluded that in whole blood of this bird species CO2 exerts no direct effect on the O2 affinity of hemoglobin. PMID:30069
Intrachain exciton dynamics in conjugated polymer chains in solution
NASA Astrophysics Data System (ADS)
Tozer, Oliver Robert; Barford, William
2015-08-01
We investigate exciton dynamics on a polymer chain in solution induced by the Brownian rotational motion of the monomers. Poly(para-phenylene) is chosen as the model system and excitons are modeled via the Frenkel exciton Hamiltonian. The Brownian fluctuations of the torsional modes were modeled via the Langevin equation. The rotation of monomers in polymer chains in solution has a number of important consequences for the excited state properties. First, the dihedral angles assume a thermal equilibrium which causes off-diagonal disorder in the Frenkel Hamiltonian. This disorder Anderson localizes the Frenkel exciton center-of-mass wavefunctions into super-localized local exciton ground states (LEGSs) and higher-energy more delocalized quasi-extended exciton states (QEESs). LEGSs correspond to chromophores on polymer chains. The second consequence of rotations—that are low-frequency—is that their coupling to the exciton wavefunction causes local planarization and the formation of an exciton-polaron. This torsional relaxation causes additional self-localization. Finally, and crucially, the torsional dynamics cause the Frenkel Hamiltonian to be time-dependent, leading to exciton dynamics. We identify two distinct types of dynamics. At low temperatures, the torsional fluctuations act as a perturbation on the polaronic nature of the exciton state. Thus, the exciton dynamics at low temperatures is a small-displacement diffusive adiabatic motion of the exciton-polaron as a whole. The temperature dependence of the diffusion constant has a linear dependence, indicating an activationless process. As the temperature increases, however, the diffusion constant increases at a faster than linear rate, indicating a second non-adiabatic dynamics mechanism begins to dominate. Excitons are thermally activated into higher energy more delocalized exciton states (i.e., LEGSs and QEESs). These states are not self-localized by local torsional planarization. During the exciton's temporary occupation of a LEGS—and particularly a quasi-band QEES—its motion is semi-ballistic with a large group velocity. After a short period of rapid transport, the exciton wavefunction collapses again into an exciton-polaron state. We present a simple model for the activated dynamics which is in agreement with the data.
Intrachain exciton dynamics in conjugated polymer chains in solution.
Tozer, Oliver Robert; Barford, William
2015-08-28
We investigate exciton dynamics on a polymer chain in solution induced by the Brownian rotational motion of the monomers. Poly(para-phenylene) is chosen as the model system and excitons are modeled via the Frenkel exciton Hamiltonian. The Brownian fluctuations of the torsional modes were modeled via the Langevin equation. The rotation of monomers in polymer chains in solution has a number of important consequences for the excited state properties. First, the dihedral angles assume a thermal equilibrium which causes off-diagonal disorder in the Frenkel Hamiltonian. This disorder Anderson localizes the Frenkel exciton center-of-mass wavefunctions into super-localized local exciton ground states (LEGSs) and higher-energy more delocalized quasi-extended exciton states (QEESs). LEGSs correspond to chromophores on polymer chains. The second consequence of rotations-that are low-frequency-is that their coupling to the exciton wavefunction causes local planarization and the formation of an exciton-polaron. This torsional relaxation causes additional self-localization. Finally, and crucially, the torsional dynamics cause the Frenkel Hamiltonian to be time-dependent, leading to exciton dynamics. We identify two distinct types of dynamics. At low temperatures, the torsional fluctuations act as a perturbation on the polaronic nature of the exciton state. Thus, the exciton dynamics at low temperatures is a small-displacement diffusive adiabatic motion of the exciton-polaron as a whole. The temperature dependence of the diffusion constant has a linear dependence, indicating an activationless process. As the temperature increases, however, the diffusion constant increases at a faster than linear rate, indicating a second non-adiabatic dynamics mechanism begins to dominate. Excitons are thermally activated into higher energy more delocalized exciton states (i.e., LEGSs and QEESs). These states are not self-localized by local torsional planarization. During the exciton's temporary occupation of a LEGS-and particularly a quasi-band QEES-its motion is semi-ballistic with a large group velocity. After a short period of rapid transport, the exciton wavefunction collapses again into an exciton-polaron state. We present a simple model for the activated dynamics which is in agreement with the data. PMID:26328813
On Quasi-Normal Modes, Area Quantization and Bohr Correspondence Principle
NASA Astrophysics Data System (ADS)
Corda, Christian
2015-10-01
In (Int. Journ. Mod. Phys. D 14, 181 2005), the author Khriplovich verbatim claims that "the correspondence principle does not dictate any relation between the asymptotics of quasinormal modes and the spectrum of quantized black holes" and that "this belief is in conflict with simple physical arguments". In this paper we analyze Khriplovich's criticisms and realize that they work only for the original proposal by Hod, while they do not work for the improvements suggested by Maggiore and recently finalized by the author and collaborators through a connection between Hawking radiation and black hole (BH) quasi-normal modes (QNMs). This is a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. Thus, QNMs can be really interpreted as BH quantum levels (the "electrons" of the "Bohr-like BH model").Our results have also important implications on the BH information puzzle.
Does God Play Dice with Universe The Hydrogen Atomic Model of Bohr and de Broglie
Kamenov, P S
1999-01-01
In this paper it is shown that if one accept assumption of de Broglie that "unitary wave-particle" exists simultaneously and this coexistence is real, then one can find the mean life time of the hydrogen atom of Bohr (intensities). Something more, the acceptance of de Broglie's ideas show that a single excited hydrogen atom decays at exactly predictable moment (after excitation). The natural width of excited hydrogen atoms are found using the Bohr's model of this atom and de Broglie's ideas. The mean life time of the excited states is a characteristic only of a statistical ensemble of many atoms and coincide exactly with experimental data and can be used for analytical applications. It is shown also that resonant Mossbauer absorption in time domain provides a qualitative evidence of the existence of "own lifetime" for first excited states of the nuclei.
On quasi-normal modes, area quantization and Bohr correspondence principle
Corda, Christian
2015-01-01
In Int. Journ. Mod. Phys. D 14, 181 (2005) Khriplovich verbatim claims that "the correspondence principle does not dictate any relation between the asymptotics of quasinormal modes and the spectrum of quantized black holes" and that "this belief is in conflict with simple physical arguments". In this paper we analyze Khriplovich's criticisms and realize that they work only for the original proposal by Hod, while they do not work for the improvements suggested by Maggiore and recently finalized by the author and collaborators through a connection between Hawking radiation and black hole (BH) quasi-normal modes (QNMs). This is a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. Thus, QNMs can be really interpreted as BH quantum levels (the "electrons" of the "Bohr-like BH model"). Our results have also important implications on the BH information puzzle.
On quasi-normal modes, area quantization and Bohr correspondence principle
Christian Corda
2015-03-30
In Int. Journ. Mod. Phys. D 14, 181 (2005), the author Khriplovich verbatim claims that "the correspondence principle does not dictate any relation between the asymptotics of quasinormal modes and the spectrum of quantized black holes" and that "this belief is in conflict with simple physical arguments". In this paper we analyze Khriplovich's criticisms and realize that they work only for the original proposal by Hod, while they do not work for the improvements suggested by Maggiore and recently finalized by the author and collaborators through a connection between Hawking radiation and black hole (BH) quasi-normal modes (QNMs). This is a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. Thus, QNMs can be really interpreted as BH quantum levels (the "electrons" of the "Bohr-like BH model"). Our results have also important implications on the BH information puzzle.
Bohr's complementarity relation and the violation of the CP symmetry in high energy physics
Beatrix C. Hiesmayr; Marcus Huber
2007-11-08
We test Bohr's complementary relation, which captures the most counterintuitive difference of a classical and a quantum world, for single and bipartite neutral kaons. They present a system that is naturally interfering, oscillating and decaying. Moreover, kaons break the CP symmetry (C...charge conjugation, P...parity). In detail we discuss the effect of the CP violation on Bohr's relation, i.e. the effect on the "particle-like" information and the "wave-like" information. Further we show that the quantity that complements the single partite information for bipartite kaons is indeed concurrence, a measure of entanglement, strengthening our concept of entanglement. We find that the defined entanglement measure is independent of CP violation while it has been shown that nonlocality is sensitive to CP violation.
On Quasi-Normal Modes, Area Quantization and Bohr Correspondence Principle
NASA Astrophysics Data System (ADS)
Corda, Christian
2015-04-01
In (Int. Journ. Mod. Phys. D 14, 181 2005), the author Khriplovich verbatim claims that "the correspondence principle does not dictate any relation between the asymptotics of quasinormal modes and the spectrum of quantized black holes" and that "this belief is in conflict with simple physical arguments". In this paper we analyze Khriplovich's criticisms and realize that they work only for the original proposal by Hod, while they do not work for the improvements suggested by Maggiore and recently finalized by the author and collaborators through a connection between Hawking radiation and black hole (BH) quasi-normal modes (QNMs). This is a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. Thus, QNMs can be really interpreted as BH quantum levels (the "electrons" of the "Bohr-like BH model").Our results have also important implications on the BH information puzzle.
A Bohr-type model with gravity as the attractive force
C. G. Vayenas; S. Souentie; A. Fokas
2014-12-23
We formulate a Bohr-type rotating particle model for three light particles of the same rest mass, forming a bound rotational state under the influence of their gravitational attraction, in the same way that electrostatic attraction leads to the formation of a bound proton-electron state in the classical Bohr model of the H atom. By using special relativity, the equivalence principle and the de Broglie wavelength equation, we find that when the three rotating particles have the rest masses of neutrinos or antineutrinos then surprisingly the rest mass of the rotating state has the rest mass of the stable baryons, i.e. of the proton and the neutron. This rest mass is due almost exclusively to the kinetic energy of the rotating neutrinos. The results are found to be consistent with the theory of general relativity. Predictions for the properties of these bound rotational states are compared with experimental values.
Ultrafast dynamics of excitons in tetracene single crystals
Birech, Zephania; Schwoerer, Heinrich, E-mail: heso@sun.ac.za [Laser Research Institute, Stellenbosch University, Stellenbosch 7600 (South Africa)] [Laser Research Institute, Stellenbosch University, Stellenbosch 7600 (South Africa); Schwoerer, Markus [Department of Physics, University of Bayreuth, Bayreuth (Germany)] [Department of Physics, University of Bayreuth, Bayreuth (Germany); Schmeiler, Teresa; Pflaum, Jens [Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg (Germany)] [Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg (Germany)
2014-03-21
Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S{sub n} on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S{sub 1} on a 40 ps timescale. The high energy Davydov component of the S{sub 1} exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.
Ultrafast dynamics of excitons in tetracene single crystals.
Birech, Zephania; Schwoerer, Markus; Schmeiler, Teresa; Pflaum, Jens; Schwoerer, Heinrich
2014-03-21
Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S(n) on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale. PMID:24655187
Ultrafast dynamics of excitons in tetracene single crystals
NASA Astrophysics Data System (ADS)
Birech, Zephania; Schwoerer, Markus; Schmeiler, Teresa; Pflaum, Jens; Schwoerer, Heinrich
2014-03-01
Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states Sn on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.
Singlet Exciton Fission in Nanostructured Organic Solar Cells
Jadhav, P. J.; Mohanty, A.; Sussman, J.; Baldo, Marc
2011-01-01
Singlet exciton fission is an efficient multiexciton generation process in organic molecules. But two concerns must be satisfied before it can be exploited in low-cost solution-processed organic solar cells. Fission must be combined with longer wavelength absorption in a structure that can potentially surpass the single junction limit, and its efficiency must be demonstrated in nanoscale domains within blended devices. Here, we report organic solar cells comprised of tetracene, copper phthalocyanine, and the buckyball C{sub 6}0. Short wavelength light generates singlet excitons in tetracene. These are subsequently split into two triplet excitons and transported through the phthalocyanine. In addition, the phthalocyanine absorbs photons below the singlet exciton energy of tetracene. To test tetracene in nanostructured blends, we fabricate coevaporated bulk heterojunctions and multilayer heterojunctions of tetracene and C{sub 60}. We measure a singlet fission efficiency of (71 ± 18)%, demonstrating that exciton fission can efficiently compete with exciton dissociation on the nanoscale.
Observation of High Angular Momentum Excitons in Cuprous Oxide
NASA Astrophysics Data System (ADS)
Thewes, J.; Heckötter, J.; Kazimierczuk, T.; Aßmann, M.; Fröhlich, D.; Bayer, M.; Semina, M. A.; Glazov, M. M.
2015-07-01
The recent observation of dipole-allowed P excitons up to principal quantum numbers of n =25 in cuprous oxide has given insight into exciton states with unprecedented spectral resolution. While so far the exciton description as a hydrogenlike complex has been fully adequate for cubic crystals, we demonstrate here distinct deviations: The breaking of rotational symmetry leads to mixing of high angular momentum F and H excitons with the P excitons so that they can be observed in absorption. The F excitons show a threefold splitting that depends systematically on n , in agreement with theoretical considerations. From detailed comparison of experiment and theory we determine the cubic anisotropy parameter of the Cu2O valence band.
Fluorescence spectroscopy, exciton dynamics, and photochemistry of single allophycocyanin trimers
Ying, L.; Sie, X.S. [Pacific Northwest National Lab., Richland, WA (United States). William R. Wiley Environmental Molecular Sciences Lab.] [Pacific Northwest National Lab., Richland, WA (United States). William R. Wiley Environmental Molecular Sciences Lab.
1998-12-10
The authors report a study of the allophycocyanin trimer (APC), a light-harvesting protein complex from cyanobacteria, by room-temperature single-molecule measurements of fluorescence spectra, lifetimes, intensity trajectories, and polarization modulation. Emission spectra of individual APC trimers are found to be homogeneous on the time scale of seconds. In contrast, their emission lifetimes are found to be widely distributed because of generation of long-lived exciton traps during the course of measurements. The intensity trajectories and polarization modulation experiments indicate reversible exciton trap formation within the three quasi-independent pairs of strong interacting {alpha}84 and {beta}84 chromophores in APC, as well as photobleaching of individual chromophores. Comparison experiments under continuous-wave and pulsed excitation reveal a two-photon mechanism for generating exciton traps and/or photobleaching, which involves exciton-exciton annihilation. These single-molecule experiments provide new insights into the spectroscopy, exciton dynamics, and photochemistry of light-harvesting complexes.
Evidence for a Bose-Einstein condensate of excitons
NASA Astrophysics Data System (ADS)
Alloing, Mathieu; Beian, Mussie; Lewenstein, Maciej; Fuster, David; González, Yolanda; González, Luisa; Combescot, Roland; Combescot, Monique; Dubin, François
2014-07-01
We report compelling evidence for a “gray” condensate of dipolar excitons, electrically polarised in a 25 nm wide GaAs quantum well. The condensate is composed by a macroscopic population of dark excitons coherently coupled to a lower population of bright excitons. To create the exciton condensate we use an all-optical approach in order to produce microscopic traps which confine a dense exciton gas (\\sim 10^{10}\\ \\text{cm}^{-2}) that yet exhibits an anomalously weak photoemission at sub-kelvin temperatures. This is the first fingerprint for the “gray” condensate. It is then confirmed by the macroscopic spatial coherence and the linear polarization of the weak excitonic photoluminescence emitted from the trap, as theoretically predicted.
Nanotransformation and current fluctuations in exciton condensate junctions.
Soller, H; Dolcini, F; Komnik, A
2012-04-13
We analyze the nonlinear transport properties of a bilayer exciton condensate that is contacted by four metallic leads by calculating the full counting statistics of electron transport for arbitrary system parameters. Despite its formal similarity to a superconductor the transport properties of the exciton condensate turn out to be completely different. We recover the generic features of exciton condensates such as counterpropagating currents driven by excitonic Andreev reflections and make predictions for nonlinear transconductance between the layers as well as for the current (cross)correlations and generalized Johnson-Nyquist relationships. Finally, we explore the possibility of connecting another mesoscopic system (in our case a quantum point contact) to the bottom layer of the exciton condensate and show how the excitonic Andreev reflections can be used for transforming voltage at the nanoscale. PMID:22587267
Observation of High Angular Momentum Excitons in Cuprous Oxide.
Thewes, J; Heckötter, J; Kazimierczuk, T; Aßmann, M; Fröhlich, D; Bayer, M; Semina, M A; Glazov, M M
2015-07-10
The recent observation of dipole-allowed P excitons up to principal quantum numbers of n=25 in cuprous oxide has given insight into exciton states with unprecedented spectral resolution. While so far the exciton description as a hydrogenlike complex has been fully adequate for cubic crystals, we demonstrate here distinct deviations: The breaking of rotational symmetry leads to mixing of high angular momentum F and H excitons with the P excitons so that they can be observed in absorption. The F excitons show a threefold splitting that depends systematically on n, in agreement with theoretical considerations. From detailed comparison of experiment and theory we determine the cubic anisotropy parameter of the Cu(2)O valence band. PMID:26207502
Optical properties of MgZnO alloys: Excitons and exciton-phonon complexes
Neumann, M. D.; Cobet, C.; Esser, N. [Leibniz-Institut fuer Analytische Wissenschaften - ISAS - e.V., Albert-Einstein-Str. 9, 12489 Berlin (Germany); Laumer, B. [I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 16, 35392 Giessen (Germany); Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Wassner, T. A. [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Eickhoff, M. [I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 16, 35392 Giessen (Germany); Feneberg, M.; Goldhahn, R. [Institut fuer Experimentelle Physik, Otto-von-Guericke-Universitaet Magdeburg, 39106 Magdeburg (Germany)
2011-07-01
The characteristics of the excitonic absorption and emission around the fundamental bandgap of wurtzite Mg{sub x}Zn{sub 1-x}O grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy with Mg contents between x = 0 and x = 0.23 are studied using spectroscopic ellipsometry and photoluminescence (PL) measurements. The ellipsometric data were analyzed using a multilayer model yielding the dielectric function (DF). The imaginary part of the DF for the alloys exhibits a pronounced feature which is attributed to exciton-phonon coupling (EPC) similar to the previously reported results for ZnO. Thus, in order to determine reliable transition energies, the spectral dependence is analyzed by a model which includes free excitonic lines, the exciton continuum, and the enhanced absorption due to EPC. A line shape analysis of the temperature-dependent PL spectra yielded in particular the emission-related free excitonic transition energies, which are compared to the results from the DF line-shape analysis. The PL linewidth is discussed within the framework of an alloy disorder model.
Electric quadrupole transitions of the Bohr Hamiltonian with the Morse potential
Inci, I. [I.N.F.N. and Dipartimento di Fisica ''Galileo Galilei,'' Universita di Padova, I-35131 Padova (Italy); Department of Physics, Akdeniz University, TR-07058 Antalya (Turkey); Bonatsos, D. [Institute of Nuclear Physics, National Centre for Scientific Research ''Demokritos,'' GR-153 10 Aghia Paraskevi, Attiki (Greece); Boztosun, I. [Department of Physics, Akdeniz University, TR-07058 Antalya (Turkey)
2011-08-15
Eigenfunctions of the collective Bohr Hamiltonian with the Morse potential have been obtained by using the asymptotic iteration method (AIM) for both {gamma}-unstable and rotational structures. B(E2) transition rates have been calculated and compared to experimental data. Overall good agreement is obtained for transitions within the ground-state band, while some interband transitions appear to be systematically underpredicted in {gamma}-unstable nuclei and overpredicted in rotational nuclei.
How Sommerfeld extended Bohr's model of the atom (1913-1916)
NASA Astrophysics Data System (ADS)
Eckert, Michael
2014-04-01
Sommerfeld's extension of Bohr's atomic model was motivated by the quest for a theory of the Zeeman and Stark effects. The crucial idea was that a spectral line is made up of coinciding frequencies which are decomposed in an applied field. In October 1914 Johannes Stark had published the results of his experimental investigation on the splitting of spectral lines in hydrogen (Balmer lines) in electric fields, which showed that the frequency of each Balmer line becomes decomposed into a multiplet of frequencies. The number of lines in such a decomposition grows with the index of the line in the Balmer series. Sommerfeld concluded from this observation that the quantization in Bohr's model had to be altered in order to allow for such decompositions. He outlined this idea in a lecture in winter 1914/15, but did not publish it. The First World War further delayed its elaboration. When Bohr published new results in autumn 1915, Sommerfeld finally developed his theory in a provisional form in two memoirs which he presented in December 1915 and January 1916 to the Bavarian Academy of Science. In July 1916 he published the refined version in the Annalen der Physik. The focus here is on the preliminary Academy memoirs whose rudimentary form is better suited for a historical approach to Sommerfeld's atomic theory than the finished Annalen-paper. This introductory essay reconstructs the historical context (mainly based on Sommerfeld's correspondence). It will become clear that the extension of Bohr's model did not emerge in a singular stroke of genius but resulted from an evolving process.
Model of molecular bonding based on the Bohr Sommerfeld picture of atoms
NASA Astrophysics Data System (ADS)
Svidzinsky, Anatoly A.; Chin, Siu A.; Scully, Marlan O.
2006-07-01
We develop a model of molecular binding based on the Bohr Sommerfeld description of atoms together with a constraint taken from conventional quantum mechanics. The model can describe the binding energy curves of H2, H3 and other molecules with striking accuracy. Our approach treats electrons as point particles with positions determined by extrema of an algebraic energy function. Our constrained model provides a physically appealing, accurate description of multi-electron chemical bonds.
Electric quadrupole transitions of the Bohr Hamiltonian with the Morse potential
I. Inci; D. Bonatsos; I. Boztosun
2011-08-04
Eigenfunctions of the collective Bohr Hamiltonian with the Morse potential have been obtained by using the Asymptotic Iteration Method (AIM) for both gamma-unstable and rotational structures. B(E2) transition rates have been calculated and compared to experimental data. Overall good agreement is obtained for transitions within the ground state band, while some interband transitions appear to be systematically underpredicted in gamma-unstable nuclei and overpredicted in rotational nuclei.
Discreteness of the volume of space from Bohr-Sommerfeld quantization
Eugenio Bianchi; Hal M. Haggard
2011-06-06
A major challenge for any theory of quantum gravity is to quantize general relativity while retaining some part of its geometrical character. We present new evidence for the idea that this can be achieved by directly quantizing space itself. We compute the Bohr-Sommerfeld volume spectrum of a tetrahedron and show that it reproduces the quantization of a grain of space found in loop gravity.
Statistical complexity, Fisher-Shannon information, and Bohr orbits in the H-atom
Jaime Sanudo; Ricardo Lopez-Ruiz
2008-03-19
The Fisher-Shannon information and a statistical measure of complexity are calculated in the position and momentum spaces for the wave functions of the H-atom. For each level of energy, it is found that these two indicators take their minimum values on the orbitals that correspond to the classical (circular) orbits in the Bohr atomic model, just those with the highest orbital angular momentum.
Holographic principle versus Bohr's principle: eternal Schwarzschild-anti-de Sitter geometry
Slava Emelyanov
2015-07-14
It is shown that Bohr's correspondence principle and the holographic principle are incompatible in the background of an eternal Schwarzschild-anti-de Sitter geometry. The argument is based on the observation that algebraic structures of local quantum field and CFT operators are not equivalent. A CFT Hilbert space representation is elaborated which may correspond to the AdS black hole in the dual theory.
M. A. Caprio
2009-01-30
Exact numerical diagonalization of the Bohr Hamiltonian by SU(1,1)xSO(5) methods is used to obtain detailed quantitative predictions for single-phonon and multi-phonon excitations in well-deformed rotor nuclei. Dynamical gamma deformation is found to significantly influence the predictions through its coupling to the rotational motion. Basic signatures for the onset of rigid triaxial deformation are obtained.
Singular Bohr-Sommerfeld conditions for 1D Toeplitz operators: hyperbolic case
Yohann Le Floch
2013-09-20
In this article, we state the Bohr-Sommerfeld conditions around a singular value of hyperbolic type of the principal symbol of a self-adjoint semiclassical Toeplitz operator on a compact connected K\\"{a}hler surface. These conditions allow the description of the spectrum of the operator in a fixed size neighbourhood of the singularity. We provide numerical computations for three examples, each associated to a different topology.
Bohr-Sommerfeld quantization condition for non-selfadjoint operators in dimension 2
A. Melin; J. Sjoestrand
2001-11-28
For a class of non-selfadjoint h-pseudodifferential operators in dimension 2, we determine all eigenvalues in an h-independent domain in the complex plane and show that they are given by a Bohr-Sommerfeld quantization condition. No complete integrability is assumed, and as a geometrical step in our proof, we get a KAM-type theorem (without small divisors) in the complex domain.
Bohr-Sommerfeld quantization condition for Dirac states derived from an Ermakov-type invariant
Thylwe, Karl-Erik; McCabe, Patrick
2013-05-15
It is shown that solutions of the second-order decoupled radial Dirac equations satisfy Ermakov-type invariants. These invariants lead to amplitude-phase-type representations of the radial spinor solutions, with exact relations between their amplitudes and phases. Implications leading to a Bohr-Sommerfeld quantization condition for bound states, and a few particular atomic/ionic and nuclear/hadronic bound-state situations are discussed.
Discreteness of the volume of space from Bohr-Sommerfeld quantization.
Bianchi, Eugenio; Haggard, Hal M
2011-07-01
A major challenge for any theory of quantum gravity is to quantize general relativity while retaining some part of its geometrical character. We present new evidence for the idea that this can be achieved by directly quantizing space itself. We compute the Bohr-Sommerfeld volume spectrum of a tetrahedron and show that it reproduces the quantization of a grain of space found in loop gravity. PMID:21797533
New method for detection of exciton Bose condensation using stimulated two-photon emission
Yu. E. Lozovik; A. V. Pushnov
1999-01-01
An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton\\u000a recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation\\u000a numbers of exciton states with momenta p?0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also\\u000a analyzed. The processes under consideration
Effects of Dynamic Screening on Excitons in Metallic Carbon Nanotubes
NASA Astrophysics Data System (ADS)
Tomio, Yuh; Suzuura, Hidekatsu
Excitonic effects and the absorption spectra of metallic carbon nanotubes are studied in an effective-mass scheme by taking dynamic screening into consideration. The result shows that the dynamic screening makes the excitons in metallic carbon nanotubes more stable than the static screening neglecting the retardation in the screening of Coulomb interaction. The dynamic screening effect appears only in the exciton states and it is hardly seen in continuum states.
Bohr Hamiltonian with a deformation-dependent mass term: physical meaning of the free parameter
Dennis Bonatsos; N. Minkov; D. Petrellis
2015-06-24
Embedding of the 5-dimensional (5D) space of the Bohr Hamiltonian with a deformation-dependent mass (DDM) into a 6-dimensional (6D) space shows that the free parameter in the dependence of the mass on the deformation is connected to the curvature of the 5D space, with the special case of constant mass corresponding to a flat 5D space. Comparison of the DDM Bohr Hamiltonian to the 5D classical limit of Hamiltonians of the 6D interacting boson model (IBM), shows that the DDM parameter is proportional to the strength of the pairing interaction in the U(5) (vibrational) symmetry limit, while it is proportional to the quadrupole-quadrupole interaction in the SU(3) (rotational) symmetry limit, and to the difference of the pairing interactions among s, d bosons and d bosons alone in the O(6) (gamma-soft) limit. The presence of these interactions leads to a curved 5D space in the classical limit of IBM, in contrast to the flat 5D space of the original Bohr Hamiltonian, which is made curved by the introduction of the deformation-dependent mass.
Bohr Hamiltonian with a deformation-dependent mass term: physical meaning of the free parameter
NASA Astrophysics Data System (ADS)
Bonatsos, Dennis; Minkov, N.; Petrellis, D.
2015-09-01
Embedding the five-dimensional (5D) space of the Bohr Hamiltonian with a deformation-dependent mass (DDM) into a six-dimensional (6D) space shows that the free parameter in the dependence of the mass on the deformation is connected to the curvature of the 5D space, with the special case of constant mass corresponding to a flat 5D space. Comparison of the DDM Bohr Hamiltonian to the 5D classical limit of Hamiltonians of the 6D interacting boson model (IBM), shows that the DDM parameter is proportional to the strength of the pairing interaction in the U(5) (vibrational) symmetry limit, while it is proportional to the quadrupole–quadrupole interaction in the SU(3) (rotational) symmetry limit, and to the difference of the pairing interactions among s, d bosons and d bosons alone in the O(6) (?-soft) limit. The presence of these interactions leads to a curved 5D space in the classical limit of IBM, in contrast to the flat 5D space of the original Bohr Hamiltonian, which is made curved by the introduction of the DDM.
Excitonic gap formation in neutral bilayer structures
NASA Astrophysics Data System (ADS)
Apinyan, V.; Kope?, T. K.
2015-08-01
We consider the pairing between conduction band electrons, and the valence band holes in the neutral bilayer-type structures. By employing the bilayer Hubbard model, we show the possibility of the inter-plane exciton formation in the system without applied external field. The in-plane and inter-plane Coulomb interaction effects on the pairing mechanism are considered, and the role of the in-plane particle hopping asymmetry on the gap behavior is analyzed in the paper. We show that both Frenkel-type pairing channel and Wannier–Mott-type excitonic pairings are present in the considered system. We analyze also the structure of the chemical potential in the bilayer system. The temperature effects, and the tunable inter-plane electron hopping effects are discussed. For the Frenkel channel, we have shown a particular behavior of the chemical potential at very low temperatures, which is related to the degenerated Frenkel-gap.
Multiple exciton generation and recombination in carbon nanotubes and nanocrystals.
Kanemitsu, Yoshihiko
2013-06-18
Semiconducting nanomaterials such as single-walled carbon nanotubes (SWCNTs) and nanocrystals (NCs) exhibit unique size-dependent quantum properties. They have therefore attracted considerable attention from the viewpoints of fundamental physics and functional device applications. SWCNTs and NCs also provide an excellent new stage for experimental studies of many-body effects of electrons and excitons on optical processes in nanomaterials. In this Account, we discuss multiple exciton generation and recombination in SWCNTs and NCs for next-generation photovoltaics. Strongly correlated ensembles of conduction-band electrons and valence-band holes in semiconductors are complex quantum systems that exhibit unique optical phenomena. In bulk crystals, the carrier recombination dynamics can be described by a simple model, which includes the nonradiative single-carrier trapping rate, the radiative two-carrier recombination rate, and the nonradiative three-carrier Auger recombination rate. The nonradiative Auger recombination rate determines the carrier recombination dynamics at high carrier density and depends on the spatial localization of carriers in two-dimensional quantum wells. The Auger recombination and multiple exciton generation rates can be advantageously manipulated by nanomaterials with designated energy structures. In addition, SWCNTs and NCs show quantized recombination dynamics of multiple excitons and carriers. In one-dimensional SWCNTs, excitons have large binding energies and are very stable at room temperature. The extremely rapid Auger recombination between excitons determines the photoluminescence (PL) intensity, the PL linewidth, and the PL lifetime. SWCNTs can undergo multiple exciton generation, while strong exciton-exciton interactions and complicated exciton structures affect the quantized Auger rate and the multiple exciton generation efficiency. Interestingly, in zero-dimensional NC quantum dots, quantized Auger recombination causes unique optical phenomena. The breakdown of the k-conversion rule and strong Coulomb interactions between carriers in NCs enhance Auger recombination rate and decrease the energy threshold for multiple exciton generation. We discuss this impact of the k-conservation rule on two-carrier radiative recombination and the three-carrier Auger recombination processes in indirect-gap semiconductor Si NCs. In NCs and SWCNTs, multiple exciton generation competes with Auger recombination, surface trapping of excitons, and cooling of hot electrons or excitons. In addition, we explore heterostructured NCs and impurity-doped NCs in the context of the optimization of charge carrier extraction from excitons in NCs. PMID:23421584
Polarization-dependent exciton dynamics in tetracene single crystals.
Zhang, Bo; Zhang, Chunfeng; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min
2014-12-28
We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors. PMID:25554147
Exciton dynamics in organic molecular crystals and nanostructures
NASA Astrophysics Data System (ADS)
Bardeen, Chris
2014-03-01
The photophysical behavior of organic semiconductors is governed by their excitonic states. In this talk, we classify the three different exciton types (Frenkel singlet, Frenkel triplet, and charge-transfer) typically encountered in organic semiconductors. The availability of several different exciton bands provides the possibility of interband processes. One such process is singlet fission, where an initially excited singlet exciton can spontaneously split into a pair of spin-entangled triplet excitons. We analyze this phenomenon in detail, emphasizing the role of spin state coherence and magnetic fields in studying singlet <-- --> triplet pair interconversion. Singlet fission provides an example of how all three types of excitons (triplet, singlet, and charge-transfer) interact to generate unique nonlinear excitonic processes in molecular systems. These processes may be useful for applications like solar energy conversion, where the generation of two excitons per absorbed photon could lead to significant enhancements in the efficiency of single junction photovoltaic cells. Finally, we will briefly describe how excitons can also be used to initiate photochemical reactions in molecular crystal nanostructures, resulting in large shape changes and deformations.
Polarization-dependent exciton dynamics in tetracene single crystals
NASA Astrophysics Data System (ADS)
Zhang, Bo; Zhang, Chunfeng; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min
2014-12-01
We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors.
Triplet diffusion in singlet exciton fission sensitized pentacene solar cells
NASA Astrophysics Data System (ADS)
Tabachnyk, Maxim; Ehrler, Bruno; Bayliss, Sam; Friend, Richard H.; Greenham, Neil C.
2013-10-01
Singlet fission sensitized photovoltaics have the potential to surpass the Shockley-Queisser limit for a single-junction structure. We investigate the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction. We model the generation and diffusion of excitons to predict the spectral response. We find the triplet diffusion length in polycrystalline pentacene to be 40 nm. Poly(3-hexylthiophene) between the electrode and pentacene works both to confine triplet excitons and also to transfer photogenerated singlet excitons into pentacene with 30% efficiency. The lower bound for the singlet fission quantum efficiency in pentacene is 180 ± 15%.
Polarization-dependent exciton dynamics in tetracene single crystals
Zhang, Bo; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min
2014-01-01
We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors.
Exciton migration and quenching in poly(propylene imine) dendrimers
NASA Astrophysics Data System (ADS)
Minevi?i?t?, I.; Gulbinas, V.; Franckevi?ius, M.; Vaišnoras, R.; Marcos, M.; Serrano, J. L.
2009-05-01
Exciton migration between chromophore groups of the poly(propylene imine) dendrimer in chloroform solution and in solid state has been investigated by means of the time-resolved fluorescence measurements. Fluorescence decay kinetics, dynamic band shift and the depolarization rate have been analyzed. Exciton migration in a single dendrimer was found to be slow in comparison with temperature-dependent chromophore reorientation time of 150-600 ps. In a solid state chromophore groups form collective excitonic states responsible for the dendrimer film fluorescence. Exciton migration and localization to the lowest energy sites within the distributed density of states take place on a subnanosecond-nanosecond time scale.
Surface photovoltage in exciton absorption range in CdS
NASA Technical Reports Server (NTRS)
Morawski, A.; Banisch, R.; Lagowski, J.
1977-01-01
The high resolution, intrinsic spectra of surface photovoltage are reported for semiconducting n-type CdS single crystals. At reduced temperatures (120-160 K) the spectra exhibit three sharp maxima due to A, B and C free exciton transitions. Energy positions of these lines and valence band parameters (spin-orbit and crystal field splittings) estimated from surface photovoltage are in good agreement with values obtained by other methods. The excitonic transitions are very sensitive to surface treatment, i.e. polishing, etching, background illumination and surface doping. The mechanism of direct interaction of free excitons with surface states is proposed to explain exciton lines in surface photovoltage.
NASA Astrophysics Data System (ADS)
Furukawa, Yoshiaki; Takeuchi, Hideo; Nakayama, Masaaki
2014-05-01
We have investigated the photoluminescence (PL) dynamics of exciton–exciton scattering, the so-called P emission, at 10 K in GaAs (d nm)/AlAs (d nm) multiple quantum wells (MQWs) with d = 10 and 20. It was found that the decay rate of the P emission systematically increases with a decrease in detection energy. In contrast, the decay rate hardly depends on an excitation power, which suggests that exciton–exciton collisions do not affect the decay rate. We demonstrate that the energy dependence of the decay rate, ? text{p} - 1(E), in each MQW is consistently scaled by that of the group velocity, vtext{g}(E), of a photon-like polariton in the lower polariton branch that is the final state for the P emission: ? text{p} - 1(E) = Avtext{g}(E). This fact provides us clear evidence for the polariton characteristics of the PL dynamics of exciton–exciton scattering.
NASA Astrophysics Data System (ADS)
Yonehara, Toshiya; Goushi, Kenichi; Sawabe, Tomoaki; Takasu, Isao; Adachi, Chihaya
2015-07-01
We investigated differences between the transient state and steady state exciton–exciton annihilation rates based on Förster-type energy transfer. The exciton–exciton annihilation rate of an organic semiconductor is usually determined by transient state photoluminescence measurements using a pulsed laser or steady state photoluminescence measurements using a continuous wave laser. However, it is unclear that the respective annihilation rates determined by their rate equations are the same. In calculations with platinum-octaethylporphyrin (PtOEP) parameters, Monte Carlo simulations gave two different annihilation rates for the transient state and the steady state. The analytical models based on Förster-type energy transfer also showed the same result. These results indicate that the exciton–exciton annihilation rates in transient state and steady state are distinguished.
The optimization topography of exciton transport
Torsten Scholak; Thomas Wellens; Andreas Buchleitner
2011-08-26
Stunningly large exciton transfer rates in the light harvesting complex of photosynthesis, together with recent experimental 2D spectroscopic data, have spurred a vivid debate on the possible quantum origin of such efficiency. Here we show that configurations of a random molecular network that optimize constructive quantum interference from input to output site yield systematically shorter transfer times than classical transport induced by ambient dephasing noise.
Excition states in semiconductor quantum dots in the modified effective mass approximation
Pokutnyi, S. I. [National Academy of Sciences of Ukraine, Kurdyumov Institute of the Physics of Metals (Ukraine)], E-mail: Pokutnyi_Sergey@inbox.ru
2007-11-15
A new modified effective mass approximation is suggested to describe the excitonic energy spectrum of quantum dots of radii a comparable to the exciton Bohr radius a{sub ex}{sup 0}. It is shown that, for quantum dots simulated by infinitely deep potential wells, the effective mass approximation is appropriate for describing excitons in quantum dots of radii a {approx} a{sub ex}{sup 0}, if the reduced effective mass of the excitons, {mu}, is considered as a function of the radius of the quantum dot a, {mu} = {mu}(a)
Microcavity controlled coupling of excitonic qubits.
Albert, F; Sivalertporn, K; Kasprzak, J; Strauß, M; Schneider, C; Höfling, S; Kamp, M; Forchel, A; Reitzenstein, S; Muljarov, E A; Langbein, W
2013-01-01
Controlled non-local energy and coherence transfer enables light harvesting in photosynthesis and non-local logical operations in quantum computing. This process is intuitively pictured by a pair of mechanical oscillators, coupled by a spring, allowing for a reversible exchange of excitation. On a microscopic level, the most relevant mechanism of coherent coupling of distant quantum bits--like trapped ions, superconducting qubits or excitons confined in semiconductor quantum dots--is coupling via the electromagnetic field. Here we demonstrate the controlled coherent coupling of spatially separated quantum dots via the photon mode of a solid state microresonator using the strong exciton-photon coupling regime. This is enabled by two-dimensional spectroscopy of the sample's coherent response, a sensitive probe of the coherent coupling. The results are quantitatively understood in a rigorous description of the cavity-mediated coupling of the quantum dot excitons. This mechanism can be used, for instance in photonic crystal cavity networks, to enable a long-range, non-local coherent coupling. PMID:23612288
Excitonic coherent states: symmetries and thermalization
Diego Julio Cirilo-Lombardo
2014-08-28
In previous work [1] new bounded coherent states construction, based on a Keldysh conjecture, was introduced. As was shown in [1] the particular group structure arising from the model leads to new symmetry transformations for the coherent states system. As was shown, the emergent new symmetry transformation is reminiscent of the Bogoliubov ones and was successfully applied to describe an excitonic system showing that is intrinsically related to the stability and its general physical behavior. The group theoretical structure of the model permits to analyze its thermal properties in theoretical frameworks that arise as a consequence of the definition of the squeezed-coherent states as transformed vacua under the automorphism group of the commutation relations, as the thermofield dynamics case given by Umezawa and other similar developments [5]. On the other hand, the idea of a possible Bose--Einstein condensation (BEC) of excitons in semiconductors has attracted the attention of both experimentalists and theoreticians for more than three decades being one of the main questions what happens with the influence of non zero temperature in the case that such condensation really exists [2]. In this paper we considered the theoretical treatment of the excitonic behaviour by mean a new coherent state construction of bounded states in a quantum field theoretical context.
Excitonic effects in oxyhalide scintillating host compounds
Shwetha, G.; Kanchana, V.; Valsakumar, M. C.
2014-10-07
Ab-initio calculations based on density functional theory have been performed to study the electronic, optical, mechanical, and vibrational properties of scintillator host compounds YOX (X = F, Cl, Br, and I). Semiempirical dispersion correction schemes are used to find the effect of van der Waals forces on these layered compounds and we found this effect to be negligible except for YOBr. Calculations of phonons and elastic constants showed that all the compounds studied here are both dynamically and mechanically stable. YOF and YOI are found to be indirect band gap insulators while YOCl and YOBr are direct band gap insulators. The band gap is found to decrease as we move from fluorine to iodine, while the calculated refractive index shows the opposite trend. As the band gap decreases on going down the periodic table from YOF to YOI, the luminescence increases. The excitonic binding energy calculated, within the effective mass approximation, is found to be more for YOF than the remaining compounds, suggesting that the excitonic effect to be more in YOF than the other compounds. The optical properties are calculated within the Time-Dependent Density Functional Theory (TDDFT) and compared with results obtained within the random phase approximation. The TDDFT calculations, using the newly developed bootstrap exchange-correlation kernel, showed significant excitonic effects in all the compounds studied here.
Excitonic effects in oxyhalide scintillating host compounds
NASA Astrophysics Data System (ADS)
Shwetha, G.; Kanchana, V.; Valsakumar, M. C.
2014-10-01
Ab-initio calculations based on density functional theory have been performed to study the electronic, optical, mechanical, and vibrational properties of scintillator host compounds YOX (X = F, Cl, Br, and I). Semiempirical dispersion correction schemes are used to find the effect of van der Waals forces on these layered compounds and we found this effect to be negligible except for YOBr. Calculations of phonons and elastic constants showed that all the compounds studied here are both dynamically and mechanically stable. YOF and YOI are found to be indirect band gap insulators while YOCl and YOBr are direct band gap insulators. The band gap is found to decrease as we move from fluorine to iodine, while the calculated refractive index shows the opposite trend. As the band gap decreases on going down the periodic table from YOF to YOI, the luminescence increases. The excitonic binding energy calculated, within the effective mass approximation, is found to be more for YOF than the remaining compounds, suggesting that the excitonic effect to be more in YOF than the other compounds. The optical properties are calculated within the Time-Dependent Density Functional Theory (TDDFT) and compared with results obtained within the random phase approximation. The TDDFT calculations, using the newly developed bootstrap exchange-correlation kernel, showed significant excitonic effects in all the compounds studied here.
Excess equimolar radius of liquid drops.
Horsch, Martin; Hasse, Hans; Shchekin, Alexander K; Agarwal, Animesh; Eckelsbach, Stefan; Vrabec, Jadran; Müller, Erich A; Jackson, George
2012-03-01
The curvature dependence of the surface tension is related to the excess equimolar radius of liquid drops, i.e., the deviation of the equimolar radius from the radius defined by the macroscopic capillarity approximation. Based on the Tolman [J. Chem. Phys. 17, 333 (1949)] approach and its interpretation by Nijmeijer et al. [J. Chem. Phys. 96, 565 (1991)], the surface tension of spherical interfaces is analyzed in terms of the pressure difference due to curvature. In the present study, the excess equimolar radius, which can be obtained directly from the density profile, is used instead of the Tolman length. Liquid drops of the truncated and shifted Lennard-Jones fluid are investigated by molecular dynamics simulation in the canonical ensemble, with equimolar radii ranging from 4 to 33 times the Lennard-Jones size parameter ?. In these simulations, the magnitude of the excess equimolar radius is shown to be smaller than ?/2. This suggests that the surface tension of liquid drops at the nanometer length scale is much closer to that of the planar vapor-liquid interface than reported in studies based on the mechanical route. PMID:22587106
NASA Astrophysics Data System (ADS)
Tanona, Scott Daniel
I develop a new analysis of Niels Bohr's Copenhagen interpretation of quantum mechanics by examining the development of his views from his earlier use of the correspondence principle in the so-called 'old quantum theory' to his articulation of the idea of complementarity in the context of the novel mathematical formalism of quantum mechanics. I argue that Bohr was motivated not by controversial and perhaps dispensable epistemological ideas---positivism or neo-Kantianism, for example---but by his own unique perspective on the difficulties of creating a new working physics of the internal structure of the atom. Bohr's use of the correspondence principle in the old quantum theory was associated with an empirical methodology that used this principle as an epistemological bridge to connect empirical phenomena with quantum models. The application of the correspondence principle required that one determine the validity of the idealizations and approximations necessary for the judicious use of classical physics within quantum theory. Bohr's interpretation of the new quantum mechanics then focused on the largely unexamined ways in which the developing abstract mathematical formalism is given empirical content by precisely this process of approximation. Significant consistency between his later interpretive framework and his forms of argument with the correspondence principle indicate that complementarity is best understood as a relationship among the various approximations and idealizations that must be made when one connects otherwise meaningless quantum mechanical symbols to empirical situations or 'experimental arrangements' described using concepts from classical physics. We discover that this relationship is unavoidable not through any sort of a priori analysis of the priority of classical concepts, but because quantum mechanics incorporates the correspondence approach in the way in which it represents quantum properties with matrices of transition probabilities, the empirical meaning of which depend on the situation but in general are tied to the correspondence connection to the spectra. For Bohr, it is then the commutation relations, which arise from the formalism, which inform us of the complementary nature of this approximate representation of quantum properties via the classical equations through which we connect them to experiments.
Nuclear Charge Radius of {sup 8}He
Mueller, P.; Bailey, K.; Holt, R. J.; Janssens, R. V. F.; O'Connor, T. P. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Sulai, I. A.; Lu, Z.-T. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Physics and Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States); Villari, A. C. C.; Alcantara-Nunez, J. A.; Alves-Conde, R.; Dubois, M.; Eleon, C.; Gaubert, G.; Lecesne, N.; Saint-Laurent, M.-G.; Thomas, J.-C. [GANIL (IN2P3/CNRS-DSM/CEA), B.P. 55027 F-14076 Caen Cedex 5 (France); Drake, G. W. F. [Physics Department, University of Windsor, Windsor, Ontario, N9B 3P4 (Canada); Wang, L.-B. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2007-12-21
The root-mean-square (rms) nuclear charge radius of {sup 8}He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of {sup 6}He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from {sup 6}He to {sup 8}He is an indication of the change in the correlations of the excess neutrons and is consistent with the {sup 8}He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.
Nuclear charge radius of $^8$He
P. Mueller; I. A. Sulai; A. C. C. Villari; J. A. Alcantara-Nunez; R. Alves-Conde; K. Bailey; G. W. F. Drake; M. Dubois; C. Eleon; G. Gaubert; R. J. Holt; R. V. F. Janssens; N. Lecesne; Z. -T. Lu; T. P. O'Connor; M. -G. Saint-Laurent; J. -C. Thomas; L. -B. Wang
2008-01-03
The root-mean-square (rms) nuclear charge radius of ^8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of ^6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from ^6He to ^8He is an indication of the change in the correlations of the excess neutrons and is consistent with the ^8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.
A Maximum Radius for Habitable Planets.
Alibert, Yann
2015-09-01
We compute the maximum radius a planet can have in order to fulfill two constraints that are likely necessary conditions for habitability: 1- surface temperature and pressure compatible with the existence of liquid water, and 2- no ice layer at the bottom of a putative global ocean, that would prevent the operation of the geologic carbon cycle to operate. We demonstrate that, above a given radius, these two constraints cannot be met: in the Super-Earth mass range (1-12 Mearth), the overall maximum that a planet can have varies between 1.8 and 2.3 Rearth. This radius is reduced when considering planets with higher Fe/Si ratios, and taking into account irradiation effects on the structure of the gas envelope. PMID:26159097
Mueller, P; Sulai, I A; Villari, A C C; Alcántara-Núñez, J A; Alves-Condé, R; Bailey, K; Drake, G W F; Dubois, M; Eléon, C; Gaubert, G; Holt, R J; Janssens, R V F; Lecesne, N; Lu, Z-T; O'Connor, T P; Saint-Laurent, M-G; Thomas, J-C; Wang, L-B
2007-12-21
The root-mean-square (rms) nuclear charge radius of 8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from 6He to 8He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations. PMID:18233516
NASA Astrophysics Data System (ADS)
Mueller, P.; Sulai, I. A.; Villari, A. C. C.; Alcántara-Núñez, J. A.; Alves-Condé, R.; Bailey, K.; Drake, G. W. F.; Dubois, M.; Eléon, C.; Gaubert, G.; Holt, R. J.; Janssens, R. V. F.; Lecesne, N.; Lu, Z.-T.; O'Connor, T. P.; Saint-Laurent, M.-G.; Thomas, J.-C.; Wang, L.-B.
2007-12-01
The root-mean-square (rms) nuclear charge radius of He8, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of He6 was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from He6 to He8 is an indication of the change in the correlations of the excess neutrons and is consistent with the He8 neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.
A Maximum Radius for Habitable Planets
NASA Astrophysics Data System (ADS)
Alibert, Yann
2015-09-01
We compute the maximum radius a planet can have in order to fulfill two constraints that are likely necessary conditions for habitability: 1- surface temperature and pressure compatible with the existence of liquid water, and 2- no ice layer at the bottom of a putative global ocean, that would prevent the operation of the geologic carbon cycle to operate. We demonstrate that, above a given radius, these two constraints cannot be met: in the Super-Earth mass range (1-12 Mearth), the overall maximum that a planet can have varies between 1.8 and 2.3 Rearth. This radius is reduced when considering planets with higher Fe/Si ratios, and taking into account irradiation effects on the structure of the gas envelope.
Mass-Radius Relationships for Solid Exoplanets
S. Seager; M. Kuchner; C. Hier-Majumder; B. Militzer
2007-07-19
We use new interior models of cold planets to investigate the mass-radius relationships of solid exoplanets, considering planets made primarily of iron, silicates, water, and carbon compounds. We find that the mass-radius relationships for cold terrestrial-mass planets of all compositions we considered follow a generic functional form that is not a simple power law: $\\log_{10} R_s = k_1 + 1/3 \\log_{10}(M_s) - k_2 M_s^{k_3}$ for up to $M_p \\approx 20 M_{\\oplus}$, where $M_s$ and $R_s$ are scaled mass and radius values. This functional form arises because the common building blocks of solid planets all have equations of state that are well approximated by a modified polytrope of the form $\\rho = \\rho_0 + c P^n$. We find that highly detailed planet interior models, including temperature structure and phase changes, are not necessary to derive solid exoplanet bulk composition from mass and radius measurements. For solid exoplanets with no substantial atmosphere we have also found that: with 5% fractional uncertainty in planet mass and radius it is possible to distinguish among planets composed predominantly of iron or silicates or water ice but not more detailed compositions; with $\\sim$~5% uncertainty water ice planets with $\\gtrsim 25%$ water by mass may be identified; the minimum plausible planet size for a given mass is that of a pure iron planet; and carbon planet mass-radius relationships overlap with those of silicate and water planets due to similar zero-pressure densities and equations of state. We propose a definition of "super Earths'' based on the clear distinction in radii between planets with significant gas envelopes and those without.
Management of Severely Comminuted Distal Radius Fractures.
Brogan, David M; Richard, Marc J; Ruch, David; Kakar, Sanjeev
2015-09-01
Distal radius fractures are among the most common fractures of the upper extremity. Indications for operative and nonsurgical management have evolved over time, as have fixation techniques. Volar locking plates are commonly used in the treatment of selected distal radius fractures such as low-energy or relatively uncomplicated fractures. They have limitations, however, in the management of highly comminuted fracture patterns and in polytrauma patients. In these patients, other methods ranging from spanning fixation to fragment-specific fixation have emerged as useful alternatives in the surgeon's armamentarium for treatment of these challenging fractures. PMID:26243322
Directing energy transport in organic photovoltaic cells using interfacial exciton gates.
Menke, S Matthew; Mullenbach, Tyler K; Holmes, Russell J
2015-04-28
Exciton transport in organic semiconductors is a critical, mediating process in many optoelectronic devices. Often, the diffusive and subdiffusive nature of excitons in these systems can limit device performance, motivating the development of strategies to direct exciton transport. In this work, directed exciton transport is achieved with the incorporation of exciton permeable interfaces. These interfaces introduce a symmetry-breaking imbalance in exciton energy transfer, leading to directed motion. Despite their obvious utility for enhanced exciton harvesting in organic photovoltaic cells (OPVs), the emergent properties of these interfaces are as yet uncharacterized. Here, directed exciton transport is conclusively demonstrated in both dilute donor and energy-cascade OPVs where judicious optimization of the interface allows exciton transport to the donor-acceptor heterojunction to occur considerably faster than when relying on simple diffusion. Generalized systems incorporating multiple exciton permeable interfaces are also explored, demonstrating the ability to further harness this phenomenon and expeditiously direct exciton motion, overcoming the diffusive limit. PMID:25798712
Budker, Dmitry
Physics 250 Spring 2000 Solutions to Homework 2 Budker/Kimball Above the front door of Niels Bohr Bohr, "I certainly do not believe in this superstition. But you know," he added with a smile, "they say) where m = ±1/2 is the spin projection along the z-axis and µB is the Bohr magneton: µB = e 2mec . (9
21 CFR 886.1450 - Corneal radius measuring device.
Code of Federal Regulations, 2010 CFR
2010-04-01
...2010-04-01 false Corneal radius measuring device. 886.1450 Section 886...Devices § 886.1450 Corneal radius measuring device. (a) Identification. A corneal radius measuring device is an AC-powered...
21 CFR 886.1450 - Corneal radius measuring device.
Code of Federal Regulations, 2011 CFR
2011-04-01
...2011-04-01 false Corneal radius measuring device. 886.1450 Section 886...Devices § 886.1450 Corneal radius measuring device. (a) Identification. A corneal radius measuring device is an AC-powered...
21 CFR 886.1450 - Corneal radius measuring device.
Code of Federal Regulations, 2012 CFR
2012-04-01
...2012-04-01 false Corneal radius measuring device. 886.1450 Section 886...Devices § 886.1450 Corneal radius measuring device. (a) Identification. A corneal radius measuring device is an AC-powered...
21 CFR 886.1450 - Corneal radius measuring device.
Code of Federal Regulations, 2013 CFR
2013-04-01
...2013-04-01 false Corneal radius measuring device. 886.1450 Section 886...Devices § 886.1450 Corneal radius measuring device. (a) Identification. A corneal radius measuring device is an AC-powered...
21 CFR 886.1450 - Corneal radius measuring device.
Code of Federal Regulations, 2014 CFR
2014-04-01
...2014-04-01 false Corneal radius measuring device. 886.1450 Section 886...Devices § 886.1450 Corneal radius measuring device. (a) Identification. A corneal radius measuring device is an AC-powered...
Electroacoustic Glossary of Symbols a Radius (m), Equivalent piston radius of diaphragm (m)
Leach Jr.,W. Marshall
Appendix B Electroacoustic Glossary of Symbols a Radius (m), Equivalent piston radius of diaphragm) CAP Acoustic compliance of passive radiator suspension (m5 /N) CAS Acoustic compliance of diaphragm suspension (m5 /N) CAT Total acoustic compliance of diaphragm suspension and enclosure (m5 /N) CA1 Acoustic
The Effective Radius in Ice Clouds
Klaus Wyser
1998-01-01
The effective radius (re) is a measure of the particle size used to calculate the optical properties of clouds. The objective of this study is to derive re from the microphysical composition of ice clouds. All ice crystals are assumed to be hexagonal columns with an aspect ratio depending on their size. Several existing particle size distributions are evaluated. The
The Tidal Radius of the Arches Cluster
NASA Astrophysics Data System (ADS)
Hosek, Matthew; Lu, Jessica R.; Anderson, Jay; Ghez, Andrea; Morris, Mark; Clarkson, William
2015-08-01
At a projected distance of just ˜26 pc from the center of the Milky Way, the Arches cluster allows us to examine the structure of a young massive cluster in the strong tidal environment of the Galactic center (GC). We use the HST WFC3IR camera to conduct an astrometric and photometric study of the outer region of the Arches cluster (R > 6.25”) in order to measure its radial profile. Using proper motions we separate cluster members from field stars down to F153M = 20 mag (˜2.5 M_sun) over a 120” x 120” field of view, covering an area 144 times larger than previous proper motion studies. This is a significant improvement over photometrically-determined cluster membership, which is complicated by the high degree of differential reddening across the field. Using cluster membership probabilities, a derived extinction map, and extensive completeness simulations, we construct the radial profile of the Arches cluster to a radius of ˜80” (˜3.1 pc assuming a distance of 8 kpc). Evidence of mass segregation out to this radius is observed, and no significant tidal tail structure is apparent. We find that the projected radial extent of the Arches cluster is significantly larger than its expected tidal radius. This result suggests either that the cluster is not as close to the GC as previously thought or that it is inflated beyond its nominal tidal radius.
Effect of exciton dragging by a surface acoustic wave
NASA Astrophysics Data System (ADS)
Kovalev, V. M.; Chaplik, A. V.
2015-02-01
We present the theory of the effect of exciton dragging by a Rayleigh surface acoustic wave at temperatures above the condensation temperature of the exciton gas and at zero temperature, where the effects of the Bose-Einstein condensation of the exciton gas are most pronounced. The magnitude of the acoustic drag flux in the exciton gas at high temperatures has been calculated taking into account the exciton-exciton interaction. It has been shown that the drag flux at typical experimental parameters (at a given intensity of the surface acoustic wave (SAW)) is independent of the frequency of the acoustic wave, whereas the interaction between excitons leads to screening of the SAW-induced perturbation, which results in an exponentially fast decrease in the drag flux with an increase in the exciton density. At low temperatures, in the presence of a condensate, the drag flux of condensate particles exhibits a resonance character when the velocity of Bogoliubov excitations approaches the velocity of the acoustic wave and the magnitude of the flux is linear in the SAW frequency. The drag flux of the above-condensate particles has a threshold character: the above-condensate particles are dragged by the wave at a velocity of the acoustic wave higher than the bogolon velocity. The magnitude of the above-condensate flux is inversely proportional to the SAW frequency.
Mapping the exciton diffusion in semiconductor nanocrystal solids.
Kholmicheva, Natalia; Moroz, Pavel; Bastola, Ebin; Razgoniaeva, Natalia; Bocanegra, Jesus; Shaughnessy, Martin; Porach, Zack; Khon, Dmitriy; Zamkov, Mikhail
2015-03-24
Colloidal nanocrystal solids represent an emerging class of functional materials that hold strong promise for device applications. The macroscopic properties of these disordered assemblies are determined by complex trajectories of exciton diffusion processes, which are still poorly understood. Owing to the lack of theoretical insight, experimental strategies for probing the exciton dynamics in quantum dot solids are in great demand. Here, we develop an experimental technique for mapping the motion of excitons in semiconductor nanocrystal films with a subdiffraction spatial sensitivity and a picosecond temporal resolution. This was accomplished by doping PbS nanocrystal solids with metal nanoparticles that force the exciton dissociation at known distances from their birth. The optical signature of the exciton motion was then inferred from the changes in the emission lifetime, which was mapped to the location of exciton quenching sites. By correlating the metal-metal interparticle distance in the film with corresponding changes in the emission lifetime, we could obtain important transport characteristics, including the exciton diffusion length, the number of predissociation hops, the rate of interparticle energy transfer, and the exciton diffusivity. The benefits of this approach to device applications were demonstrated through the use of two representative film morphologies featuring weak and strong interparticle coupling. PMID:25682881
Phonons in quantum dots and their role in exciton dephasing
Zimmermann, Roland
between excitons and acoustic phonons in semicon- ductor nanostructures. The localization (confinement) in promising applications like QD lasers, single photon sources, and quantum information devices), in particular with the acoustic phonons [1, 2]. The exciton-acoustic phonon coupling is usually described
NASA Astrophysics Data System (ADS)
Zhang, Li; Shi, J. J.
2013-03-01
Based on the surface optical phonon states and their electron-phonon coupling functions obtained recently, the surface polaronic exciton states in a quasi-one-dimensional (Q1D) wurtzite nanowire (NW) are investigated by using the variational method and Lee-Low-Pines transform. In order to reflect the different confined features of Q1D wurtzite NWs in axial and radial directions and anisotropy of wurtzite nitride crystals, a two-parameter variational approach is proposed and applied to describe the polaronic exciton states in the NWs. Numerical calculations are performed for GaN NWs. The quantum size effects on the binding energies of polaronic exciton and the contributions of surface phonon modes are analyzed in detail. Our results show that the binding energy of polaronic exciton and surface phonon contribution in the wurtzite GaN NWs reaches 190 and 95 meV, respectively, which are one or two orders of magnitude larger than those in cubic GaAs-based quantum wells and NWs with the same radius. This is mainly ascribed to the strong electron-phonon interaction, the large effective masses of carriers and relatively small dielectric constants in GaN material. The numerical results also show that the two-parameter variational approach is reasonable and necessary for the description of polaronic exciton states in Q1D wurtzite GaN NWs. Moreover, the behaviors of the two variational parameters for the polaronic exciton states are quite different from those for the bound polaron states in Q1D wurtzite NWs.
Excitons bound to stacking fault planes in GaAs: a novel 2D excitonic system
NASA Astrophysics Data System (ADS)
Karin, Todd; Linpeng, Xiayu; Harvey, Sarah; Ludwig, Arne; Wieck, Andreas; Fu, Kai-Mei
2015-03-01
This work takes a first step in characterizing the unique optical properties of stacking fault defects in GaAs grown by molecular beam epitaxy. We observe narrow-band bright luminescence from carriers bound to the attractive strain potential formed by a stacking fault. The strong radiative emission is concentrated in two narrow bands (~ 90 ? eV width) at either 828.65 or 830.40 nm depending on the stacking fault orientation. Stacking fault defects can be imaged using far-field confocal microscopy by collecting the the narrow band photoluminescence. Polarization-resolved photoluminescence and magnetic field measurements are consistent with a theory of light-hole excitons bound to the stacking fault plane with a quantization axis normal to the plane. Moreover, the wavelength shift of the excitonic emission provides a direct measure of the strain potential due to this fundamental growth defect. The narrow linewidth and high homogeneity across many defects suggests excitons are bound to a single atomically-thin stacking fault plane. This work opens the door to a novel, highly homogeneous, 2D light-hole excitonic system in the well-characterized material GaAs. NSF Grant No. 1150647, DGE-1256082.
Singlet Exciton Fission and Tri plet-Tri plet Exciton Fusion in Crystalline Tet racene
Martin Pope; Nicholas E. Geacintov; Frank Vogel
1969-01-01
The dominant radiationles decay channel in crystalline tetracene at 300 °K is a fission of an excited singlet into two triplet excitons with a rate constant ?S = 1.5 × 10 ± 5% cm -sec. The efficiency of this process at room temperature is estimated as 95%and constitutesan efficient intersystem crossing mechanism. At light intensities I ? 10 quanta-cm sec
On solar radius measurements with PICARD
NASA Astrophysics Data System (ADS)
Meftah, M.; Irbah, A.; Hauchecorne, A.; Corbard, T.; Hochedez, J. F.
2014-12-01
Solar diameter measurements performed from the ground for several decades seem to indicate a relation between the solar diameter and the solar activity. If this relationship is confirmed, it would be possible to use measurements of solar diameter as a proxy of solar activity in the past since the 1715 solar eclipses, and to use this input for the reconstruction of solar irradiance in climate models. However the interpretation of ground observations is controversial, ground-based measurements being affected by refraction, by atmospheric turbulence, and perhaps by atmospheric aerosols scattering. The only way to be free from atmospheric effects is to measure from space. This is the reason why, since the beginning, the PICARD program included a space and a ground component set up at the Calern site of the Observatoire de la Côte dAzur. During the last 4 years, the PICARD space mission has been used for observing the apparent solar diameter. First results of the astrometry program include a study of the June 2012 Venus transit for solar diameter determination. From this, the value of the solar radius from one astronomical unit was found to be equal to 959.86 arc-seconds at 607.1 nm. However, concerning observed variations in time of the solar radius, instrumental effects affect the results. Space is known to represent a harsh environment for optical instruments. Nevertheless, we can use the PICARD data to monitor the solar radius variation. PICARD aims to perpetuate historical series of the solar radius measurements, in particular during the solar cycle 24. This paper presents solar radius measurements obtained with PICARD.
NASA Astrophysics Data System (ADS)
Schröter, M.; Ivanov, S. D.; Schulze, J.; Polyutov, S. P.; Yan, Y.; Pullerits, T.; Kühn, O.
2015-03-01
The influence of exciton-vibrational coupling on the optical and transport properties of molecular aggregates is an old problem that gained renewed interest in recent years. On the experimental side, various nonlinear spectroscopic techniques gave insight into the dynamics of systems as complex as photosynthetic antennae. Striking evidence was gathered that in these protein-pigment complexes quantum coherence is operative even at room temperature conditions. Investigations were triggered to understand the role of vibrational degrees of freedom, beyond that of a heat bath characterized by thermal fluctuations. This development was paralleled by theory, where efficient methods emerged, which could provide the proper frame to perform non-Markovian and non-perturbative simulations of exciton-vibrational dynamics and spectroscopy. This review summarizes the state of affairs of the theory of exciton-vibrational interaction in molecular aggregates and photosynthetic antenna complexes. The focus is put on the discussion of basic effects of exciton-vibrational interaction from the stationary and dynamics points of view. Here, the molecular dimer plays a prominent role as it permits a systematic investigation of absorption and emission spectra by numerical diagonalization of the exciton-vibrational Hamiltonian in a truncated Hilbert space. An extension to larger aggregates, having many coupled nuclear degrees of freedom, becomes possible with the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method for wave packet propagation. In fact it will be shown that this method allows one to approach the limit of almost continuous spectral densities, which is usually the realm of density matrix theory. Real system-bath situations are introduced for two models, which differ in the way strongly coupled nuclear coordinates are treated, as a part of the relevant system or the bath. A rather detailed exposition of the Hierarchy Equations Of Motion (HEOM) method will be given in terms of a stochastic decoupling ansatz. This method has become the standard in exciton-vibrational theory and illustrative examples will be presented as well as a comparison with ML-MCTDH. Applications will be shown for generic model systems as well as for small aggregates mimicking those formed by perylene bisimide dyes. Further, photosynthetic antenna complexes will be discussed, including spectral densities and the role of exciton-vibrational coupling in two-dimensional electronic spectroscopy.
A solvable model for excitonic complexes in one dimension
NASA Astrophysics Data System (ADS)
Markvardsen, Anders J.; Johnson, Neil F.
1997-08-01
It is known experimentally that stable few-body clusters containing negatively-charged electrons (e) and positively-charged holes (h) can exist in low-dimensional semiconductor nanostructures. In addition to the familiar exciton (e+h), three-body "charged excitons" (2e+h and 2h+e) have also been observed. Much less is known about the properties of such charged excitons since three-body problems are generally very difficult to solve, even numerically. Here we introduce a simple model, which can be considered as an extended Calogero model, to calculate analytically the energy spectra for both a charged exciton and a neutral exciton in a one-dimensional nanostructure, such as a finite-length quantum wire. Apart from its physical motivation, the model is of mathematical interest in that it can be related to the Heun (or Heine) equation and, as shown explicitly, highly accurate, closed form solutions can be obtained.
Exciton-mediated quantum search on a star graph
NASA Astrophysics Data System (ADS)
Pouthier, Vincent
2015-09-01
A fast and efficient quantum search algorithm is established by using the ability of an exciton to propagate along a star graph that exhibits two identical energetic defects. The first defect lies on the well-defined input site where the exciton is initially created, whereas the second defect occupies the target site whose unknown position must be determined. It is shown that when the energetic defects are judiciously chosen, specific quantum interferences arise so that the probability to observe the exciton on the target site becomes close to unity at a very short time . Consequently, a measurement of the exciton quantum state at time will reveal the identity of the position of the target site. The key point is that is the shortest time independent on the size of the graph that is physically accessible to the exciton to tunnel.
Exactly-Solvable Problems for Two-Dimensional Excitons
NASA Astrophysics Data System (ADS)
Parfitt, D. G. W.; Portnoi, M. E.
2005-04-01
Several problems in mathematical physics relating to excitons in two dimensions are considered. First, a fascinating numerical result from a theoretical treatment of screened excitons stimulates a re-evaluation of the two-dimensional hydrogen atom. This yields a new integral relation in terms of special functions, and fresh insights into the dynamical symmetry of the system are also obtained. The second problem relates to excitons in a quantizing magnetic field in the fractional quantum Hall regime. An exciton against the background of an incompressible quantum liquid is modeled as a few-particle neutral composite. A complete set of exciton basis functions is derived and classified, and some exact results are obtained for this complex few-particle problem.
Ab initio calculation of excitons in ZnO
NASA Astrophysics Data System (ADS)
Laskowski, Robert; Christensen, Niels Egede
2006-01-01
The optical absorption and excitonic properties of wurtzite ZnO are investigated by means of an ab initio approach taking into account electron-hole correlations. This is done by solving the Bethe-Salpeter equation, using the results of density functional theory calculations as a starting point. Our main focus is the calculation of the band edge optical spectra. We have identified ground states for three excitons ( A , B , and C ), with binding energies around 68meV . Excitons A and B are excited mainly by light polarized perpendicular to the c crystallographic axis. The C exciton absorbs mainly light polarized parallel to the c axis. Due to spin-orbit interactions, excitons A and C show a tiny absorption for the parallel polarization and perpendicular polarizations, respectively.
Activated singlet exciton fission in a semiconducting polymer.
Musser, Andrew J; Al-Hashimi, Mohammed; Maiuri, Margherita; Brida, Daniele; Heeney, Martin; Cerullo, Giulio; Friend, Richard H; Clark, Jenny
2013-08-28
Singlet exciton fission is a spin-allowed process to generate two triplet excitons from a single absorbed photon. This phenomenon offers great potential in organic photovoltaics, but the mechanism remains poorly understood. Most reports to date have addressed intermolecular fission within small-molecular crystals. However, through appropriate chemical design chromophores capable of intramolecular fission can also be produced. Here we directly observe sub-100 fs activated singlet fission in a semiconducting poly(thienylenevinylene). We demonstrate that fission proceeds directly from the initial 1Bu exciton, contrary to current models that involve the lower-lying 2Ag exciton. In solution, the generated triplet pairs rapidly recombine and decay through the 2Ag state. In films, exciton diffusion breaks this symmetry and we observe long-lived triplets which form charge-transfer states in photovoltaic blends. PMID:23883167
"Gray" BCS condensate of excitons and internal Josephson effect.
Combescot, Roland; Combescot, Monique
2012-07-13
It has been recently suggested that the Bose-Einstein condensate formed by excitons in the dilute limit must be dark, i.e., not coupled to photons. Here, we show that, under a density increase, the dark exciton condensate must acquire a bright component due to carrier exchange in which dark excitons turn bright. This, however, requires a density larger than a threshold which seems to fall in the forbidden region of the phase separation between a dilute exciton gas and a dense electron-hole plasma. The BCS-like condensation which is likely to take place on the dense side, must then have a dark and a bright component--which makes it "gray." It should be possible to induce an internal Josephson effect between these two coherent components, with oscillations of the photoluminescence as a strong proof of the existence for this "gray" BCS-like exciton condensate. PMID:23030185
Exciton complexes in low dimensional transition metal dichalcogenides
Thilagam, A., E-mail: thilaphys@gmail.com [Information Technology, Engineering and Environment, University of South Australia, Adelaide 5095 (Australia)
2014-08-07
We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter ?, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of ? is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton.
Nonlinear photoluminescence spectroscopy of carbon nanotubes with localized exciton states.
Iwamura, Munechiyo; Akizuki, Naoto; Miyauchi, Yuhei; Mouri, Shinichiro; Shaver, Jonah; Gao, Zhenghong; Cognet, Laurent; Lounis, Brahim; Matsuda, Kazunari
2014-11-25
We report distinctive nonlinear behavior of photoluminescence (PL) intensities from localized exciton states embedded in single-walled carbon nanotubes (SWNTs) at room temperature. We found that PL from the local states exhibits strong nonlinear behavior with increasing continuous-wave excitation power density, whereas free exciton PL shows only weak sublinear behavior. The strong nonlinear behavior was observed regardless of the origin of the local states and found to be nearly independent of the local state density. These results indicate that the strong PL nonlinearity arises from a universal mechanism to SWNTs with sparse local states. The significant nonlinear PL is attributed to rapid ground-state depletion of the local states caused by an efficient accumulation of photogenerated free excitons into the sparse local states through one-dimensional diffusional migration of excitons along the nanotube axis; this mechanism is verified by Monte Carlo simulations of exciton diffusion dynamics. PMID:25331628
Radiative properties of multicarrier bound excitons in GaAs
NASA Astrophysics Data System (ADS)
Karin, Todd; Barbour, Russell J.; Santori, Charles; Yamamoto, Yoshihisa; Hirayama, Yoshiro; Fu, Kai-Mei C.
2015-04-01
Excitons in semiconductors can have multiple lifetimes due to spin-dependent oscillator strengths and interference between different recombination pathways. In addition, strain and symmetry effects can further modify lifetimes via the removal of degeneracies. We present a convenient formalism for predicting the optical properties of k =0 excitons with an arbitrary number of charge carriers in different symmetry environments. Using this formalism, we predict three distinct lifetimes for the neutral acceptor bound exciton in GaAs, and confirm this prediction through polarization dependent and time-resolved photoluminescence experiments. We find the acceptor bound-exciton lifetimes to be To×(1 ,3 ,3/4 ) , where To=(0.61 ±0.12 ) ns . Furthermore, we provide an estimate of the intralevel and interlevel exciton spin-relaxation rates.
Redox Bohr effects and the role of heme a in the proton pump of bovine heart cytochrome c oxidase.
Capitanio, Giuseppe; Martino, Pietro Luca; Capitanio, Nazzareno; Papa, Sergio
2011-10-01
Structural and functional observations are reviewed which provide evidence for a central role of redox Bohr effect linked to the low-spin heme a in the proton pump of bovine heart cytochrome c oxidase. Data on the membrane sidedness of Bohr protons linked to anaerobic oxido-reduction of the individual metal centers in the liposome reconstituted oxidase are analysed. Redox Bohr protons coupled to anaerobic oxido-reduction of heme a (and Cu(A)) and Cu(B) exhibit membrane vectoriality, i.e. protons are taken up from the inner space upon reduction of these centers and released in the outer space upon their oxidation. Redox Bohr protons coupled to anaerobic oxido-reduction of heme a(3) do not, on the contrary, exhibit vectorial nature: protons are exchanged only with the outer space. A model of the proton pump of the oxidase, in which redox Bohr protons linked to the low-spin heme a play a central role, is described. This article is part of a Special Issue entitled: Allosteric cooperativity in respiratory proteins. PMID:21320464
Frederick, Matthew T.; Weiss, Emily A.
2010-01-01
Coordination of phenyldithiocarbamate (PTC) ligands to solution-phase colloidal CdSe quantum dots (QDs) decreases the optical band gap, E_{g}, of the QDs by up to 220 meV. These values of ?E_{g} are the largest shifts achieved by chemical modification of the surfaces of solution-phase CdSe QDs and are—by more than an order of magnitude in energy—the largest bathochromic shifts achieved for QDs in either the solution or solid phases. Measured values of ?E_{g} upon coordination to PTC correspond to an apparent increase in the excitonic radius of 0.26 ± 0.03 nm; this excitonic delocalization is independent of the size of the QD for radii, R = 1.1-1.9 nm. Density functional theory calculations indicate that the highest occupied molecular orbital of PTC is near resonant with that of the QD, and that the two have correct symmetry to exchange electron density (PTC is a ?-donor, and the photoexcited QD is a ?-acceptor). We therefore propose that the relaxation of exciton confinement occurs through delocalization of the photoexcited hole of the QD into the ligand shell.
Probing excitonic dark states in single-layer tungsten disulphide
NASA Astrophysics Data System (ADS)
Ye, Ziliang; Cao, Ting; O'Brien, Kevin; Zhu, Hanyu; Yin, Xiaobo; Wang, Yuan; Louie, Steven G.; Zhang, Xiang
2014-09-01
Transition metal dichalcogenide (TMDC) monolayers have recently emerged as an important class of two-dimensional semiconductors with potential for electronic and optoelectronic devices. Unlike semi-metallic graphene, layered TMDCs have a sizeable bandgap. More interestingly, when thinned down to a monolayer, TMDCs transform from indirect-bandgap to direct-bandgap semiconductors, exhibiting a number of intriguing optical phenomena such as valley-selective circular dichroism, doping-dependent charged excitons and strong photocurrent responses. However, the fundamental mechanism underlying such a strong light-matter interaction is still under intensive investigation. First-principles calculations have predicted a quasiparticle bandgap much larger than the measured optical gap, and an optical response dominated by excitonic effects. In particular, a recent study based on a GW plus Bethe-Salpeter equation (GW-BSE) approach, which employed many-body Green's-function methodology to address electron-electron and electron-hole interactions, theoretically predicted a diversity of strongly bound excitons. Here we report experimental evidence of a series of excitonic dark states in single-layer WS2 using two-photon excitation spectroscopy. In combination with GW-BSE theory, we prove that the excitons are of Wannier type, meaning that each exciton wavefunction extends over multiple unit cells, but with extraordinarily large binding energy (~0.7 electronvolts), leading to a quasiparticle bandgap of 2.7 electronvolts. These strongly bound exciton states are observed to be stable even at room temperature. We reveal an exciton series that deviates substantially from hydrogen models, with a novel energy dependence on the orbital angular momentum. These excitonic energy levels are experimentally found to be robust against environmental perturbations. The discovery of excitonic dark states and exceptionally large binding energy not only sheds light on the importance of many-electron effects in this two-dimensional gapped system, but also holds potential for the device application of TMDC monolayers and their heterostructures in computing, communication and bio-sensing.
Probing excitonic dark states in single-layer tungsten disulphide.
Ye, Ziliang; Cao, Ting; O'Brien, Kevin; Zhu, Hanyu; Yin, Xiaobo; Wang, Yuan; Louie, Steven G; Zhang, Xiang
2014-09-11
Transition metal dichalcogenide (TMDC) monolayers have recently emerged as an important class of two-dimensional semiconductors with potential for electronic and optoelectronic devices. Unlike semi-metallic graphene, layered TMDCs have a sizeable bandgap. More interestingly, when thinned down to a monolayer, TMDCs transform from indirect-bandgap to direct-bandgap semiconductors, exhibiting a number of intriguing optical phenomena such as valley-selective circular dichroism, doping-dependent charged excitons and strong photocurrent responses. However, the fundamental mechanism underlying such a strong light-matter interaction is still under intensive investigation. First-principles calculations have predicted a quasiparticle bandgap much larger than the measured optical gap, and an optical response dominated by excitonic effects. In particular, a recent study based on a GW plus Bethe-Salpeter equation (GW-BSE) approach, which employed many-body Green's-function methodology to address electron-electron and electron-hole interactions, theoretically predicted a diversity of strongly bound excitons. Here we report experimental evidence of a series of excitonic dark states in single-layer WS2 using two-photon excitation spectroscopy. In combination with GW-BSE theory, we prove that the excitons are of Wannier type, meaning that each exciton wavefunction extends over multiple unit cells, but with extraordinarily large binding energy (?0.7 electronvolts), leading to a quasiparticle bandgap of 2.7 electronvolts. These strongly bound exciton states are observed to be stable even at room temperature. We reveal an exciton series that deviates substantially from hydrogen models, with a novel energy dependence on the orbital angular momentum. These excitonic energy levels are experimentally found to be robust against environmental perturbations. The discovery of excitonic dark states and exceptionally large binding energy not only sheds light on the importance of many-electron effects in this two-dimensional gapped system, but also holds potential for the device application of TMDC monolayers and their heterostructures in computing, communication and bio-sensing. PMID:25162523
NASA Astrophysics Data System (ADS)
Wolfe, James P.; Jang, Joon I.
2014-12-01
Excitons in high-purity crystals of Cu2O undergo a density-dependent lifetime that opposes Bose–Einstein condensation (BEC). This rapid decay rate of excitons at a density n has generally been attributed to Auger recombination having the form dn/dt=-A{{n}2}, where A is an exciton-Auger constant. Various measurements of A, however, have reported values that are orders-of-magnitude larger than the existing theory. In response to this conundrum, recent work has suggested that excitons bind into excitonic molecules, or biexcitons, which are short-lived and expected to be optically inactive. Of particular interest is the case of excitons confined to a parabolic strain well—a method that has recently achieved exciton densities approaching BEC. In this paper we report time- and space-resolved luminescence data that supports the existence of short-lived biexcitons in a strain well, implying an exciton loss rate of the form dn/dt=-2C{{n}2} with a biexciton capture coefficient C(T) proportional to 1/T, as predicted by basic thermodynamics. This alternate theory will be considered in relation to recent experiments on the subject.
Lebedev, Vladimir S; Medvedev, A S
2012-08-31
This paper examines plasmon - exciton coupling effects in light absorption and scattering by hybrid nanoparticles consisting of a metallic core and organic dye J-aggregate shell. The spectroscopic characteristics of such particles are calculated using generalised Mie theory for two concentric spheres in a wide spectral range for various geometric parameters of the system, core materials (Ag, Au, Cu and Al) and cyanine dyes (TC, OC and PIC). We determine the eigenfrequencies of hybrid modes in the system and photoabsorption peak heights as functions of the oscillator strength of the transition in the J-band of the dye, core radius and shell thickness, and demonstrate that the interactions of a Frenkel exciton with dipole and multipole plasmons have radically different effects on the optical properties of the composite nanoparticles. Varying the particle size and the optical constants of the core and shell materials influences the number of peaks in the spectra of the particles and leads to a significant redistribution of peak heights. We identify regions where the extinction spectrum of the particles is dominated by light absorption or scattering processes. (nanophotonics)
Entangled exciton states in quantum dot molecules
NASA Astrophysics Data System (ADS)
Bayer, Manfred
2002-03-01
Currently there is strong interest in quantum information processing(See, for example, The Physics of Quantum Information, eds. D. Bouwmeester, A. Ekert and A. Zeilinger (Springer, Berlin, 2000).) in a solid state environment. Many approaches mimic atomic physics concepts in which semiconductor quantum dots are implemented as artificial atoms. An essential building block of a quantum processor is a gate which entangles the states of two quantum bits. Recently a pair of vertically aligned quantum dots has been suggested as optically driven quantum gate(P. Hawrylak, S. Fafard, and Z. R. Wasilewski, Cond. Matter News 7, 16 (1999).)(M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M. Korkusinski, Z.R. Wasilewski, O. Stern, and A. Forchel, Science 291, 451 (2001).): The quantum bits are individual carriers either on dot zero or dot one. The different dot indices play the same role as a "spin", therefore we call them "isospin". Quantum mechanical tunneling between the dots rotates the isospin and leads to superposition of these states. The quantum gate is built when two different particles, an electron and a hole, are created optically. The two particles form entangled isospin states. Here we present spectrocsopic studies of single self-assembled InAs/GaAs quantum dot molecules that support the feasibility of this proposal. The evolution of the excitonic recombination spectrum with varying separation between the dots allows us to demonstrate coherent tunneling of carriers across the separating barrier and the formation of entangled exciton states: Due to the coupling between the dots the exciton states show a splitting that increases with decreasing barrier width. For barrier widths below 5 nm it exceeds the thermal energy at room temperature. For a given barrier width, we find only small variations of the tunneling induced splitting demonstrating a good homogeneity within a molecule ensemble. The entanglement may be controlled by application of electromagnetic field. For example, using an electric field along the molecule axis we can break the entanglement. Tunneling of carriers is prevented then and emission from intra-dot and inter-dot excitons in which electron and hole are located on the same and on opposite dots, respectively, is observed. The voltage required for the entanglement breaking increases with decreasing barrier width reflecting the increasing 'robustness' of the entanglement for narrow barriers.
MASS-RADIUS RELATIONSHIPS FOR EXOPLANETS
Swift, D. C.; Eggert, J. H.; Hicks, D. G.; Hamel, S.; Caspersen, K.; Schwegler, E.; Collins, G. W.; Nettelmann, N.; Ackland, G. J.
2012-01-01
For planets other than Earth, particularly exoplanets, interpretation of the composition and structure depends largely on comparing the mass and radius with the composition expected given their distance from the parent star. The composition implies a mass-radius relation which relies heavily on equations of state calculated from electronic structure theory and measured experimentally on Earth. We lay out a method for deriving and testing equations of state, and deduce mass-radius and mass-pressure relations for key, relevant materials whose equation of state (EOS) is reasonably well established, and for differentiated Fe/rock. We find that variations in the EOS, such as may arise when extrapolating from low-pressure data, can have significant effects on predicted mass-radius relations and on planetary pressure profiles. The relations are compared with the observed masses and radii of planets and exoplanets, broadly supporting recent inferences about exoplanet structures. Kepler-10b is apparently 'Earth-like', likely with a proportionately larger core than Earth's, nominally 2/3 of the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an Fe-based core which is likely to be proportionately smaller than Earth's. GJ 1214b lies between the mass-radius curves for H{sub 2}O and CH{sub 4}, suggesting an 'icy' composition with a relatively large core or a relatively large proportion of H{sub 2}O. CoRoT-2b is less dense than the hydrogen relation, which could be explained by an anomalously high degree of heating or by higher than assumed atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation for hydrogen, suggesting the presence of a significant amount of matter of higher atomic number. CoRoT-3b lies close to the hydrogen relation. The pressure at the center of Kepler-10b is 1.5{sup +1.2}{sub -1.0} TPa. The central pressure in CoRoT-7b is probably close to 0.8 TPa, though may be up to 2 TPa. These pressures are accessible by planar shock and ramp-loading experiments at large laser facilities. The center of HAT-P-2b is probably around 210 TPa, in the range of planned National Ignition Facility experiments, and that of CoRoT-3b around 1900 TPa.
Comment on: Breakdown of Bohr's Correspondence Principle by: Bo Gao Phys. Rev. Lett. 83, 4225 (1999)
C. Tannous; J. Langlois
2001-02-07
Gao applied LeRoy and Bernstein semi-classical analysis for the energy levels in a potential of the form -C/r^n to sequences of scaled energy differences progressing towards low lying states and found a better agreement with the semi-classical prediction. We checked that for the energy levels obtained by Stwalley et al. with the same potential, the agreement with the semi-classical approximation is better for higher vibrational quantum numbers in agreement with Bohr's correspondence principle.
Geometric factors in the Bohr--Rosenfeld analysis of the measurability of the electromagnetic field
V. Hnizdo
2002-10-16
The Geometric factors in the field commutators and spring constants of the measurement devices in the famous analysis of the measurability of the electromagnetic field by Bohr and Rosenfeld are calculated using a Fourier--Bessel method for the evaluation of folding integrals, which enables one to obtain the general geometric factors as a Fourier--Bessel series. When the space region over which the factors are defined are spherical, the Fourier--Bessel series terms are given by elementary functions, and using the standard Fourier-integral method of calculating folding integrals, the geometric factors can be evaluated in terms of manageable closed-form expressions.
Two novel patients with Bohring-Opitz syndrome caused by de novo ASXL1 mutations.
Magini, Pamela; Della Monica, Matteo; Uzielli, Maria Luisa Giovannucci; Mongelli, Patrizia; Scarselli, Gloria; Gambineri, Eleonora; Scarano, Gioacchino; Seri, Marco
2012-04-01
Bohring-Opitz syndrome (BOS) is a rare condition characterized by facial anomalies, multiple malformations, failure to thrive and severe intellectual disabilities. Recently, the cause was identified on the basis of de novo heterozygous mutations in the ASXL1 gene. We report on two novel cases carrying two previously undescribed mutations (c.2407_2411del5 [p.Q803TfsX17] and c.2893C>T [p.R965X]). These new data further support ASXL1 as cause of BOS and may contribute to a more precise definition of the phenotype caused by the disruption of this gene. PMID:22419483
Jeroen van Dongen
2015-05-29
The Einstein-Rupp experiments have been unduly neglected in the history of quantum mechanics. While this is to be explained by the fact that Emil Rupp was later exposed as a fraud and had fabricated the results, it is not justified, due to the importance attached to the experiments at the time. This paper discusses Rupp's fraud, the relation between Albert Einstein and Rupp, and the Einstein-Rupp experiments, and argues that these experiments were an influence on Niels Bohr's development of complementarity and Werner Heisenberg's formulation of the uncertainty relations.
Wo die Quantentheorie Wurzeln schlug: Die Schulen von Sommerfeld, Bohr und Born
NASA Astrophysics Data System (ADS)
Eckert, Michael
Die Geburtsstunde der Quantentheorie liegt hundert Jahre zurück, aber es dauerte ein Vierteljahrhundert, bis die neue Physik Wurzeln schlug und daraus die Quantenmechanik hervorging. Auf dem Weg dahin spielten die frühen Schulen der theoretischen Physik eine wichtige Rolle. Das erste dieser Zentren war die von Arnold Sommerfeld an der Münchner Universität gegründete Pflanzstätte für theoretische Physik. In Niels Bohrs 1921 eröffneten Institut für theoretische Physik gaben sich die hoffnungsvollen Nachwuchswissenschaftler die Klinke in die Hand, und in Deutschland war nach dem Ersten Weltkrieg die Universität Göttingen eine der ersten Adressen für moderne Physik. Der dortige Mentor war Max Born.
Intrinsic frame inverse mass tensor as a function of {beta} and {gamma} in the Bohr Hamiltonian
Jolos, R. V.; Brentano, P. von
2012-04-15
Analytical expressions are derived for the components of the intrinsic frame inverse mass tensor of the Bohr Hamiltonian. These expressions contain parameters which are determined by the experimental data on the B(E2)'s and the excitation energies of the low-lying collective states. It is shown that the nondiagonal component of the intrinsic frame mass tensor has a small effect on the collective motion. It is shown also that the values of the B{sub {beta}{beta}}, B{sub {gamma}{gamma}} and the rotational mass coefficientB{sub 1} differ in the well-deformed nuclei by factor 3 or more.
Parameter-Free Solution of the Bohr Hamiltonian for Actinides Critical in the Octupole Mode
D. Lenis; Dennis Bonatsos
2005-12-06
An analytic, parameter-free (up to overall scale factors) solution of the Bohr Hamiltonian involving axially symmetric quadrupole and octupole deformations, as well as an infinite well potential, is obtained, after separating variables in a way reminiscent of the Variable Moment of Inertia (VMI) concept. Normalized spectra and B(EL) ratios are found to agree with experimental data for 226-Ra and 226-Th, the nuclei known to lie closest to the border between octupole deformation and octupole vibrations in the light actinide region.
Spectral dimension and Bohr's formula for Schrodinger operators on unbounded fractal spaces
Joe P. Chen; Stanislav Molchanov; Alexander Teplyaev
2015-07-28
We establish an asymptotic formulas for the eigenvalue counting function of the Schr\\"odinger operator $-\\Delta +V$ for some unbounded potentials $V$ on several types of unbounded fractal spaces. We give sufficient conditions for Bohr's formula to hold on metric measure spaces which admit a cellular decomposition, and then verify these conditions for fractafolds and fractal fields based on nested fractals. In particular, we partially answer a question of Fan, Khandker, and Strichartz regarding the spectral asymptotics of the harmonic oscillator potential on the infinite blow-up of a Sierpinski gasket.
Richard Durran; Andrew Neate; Aubrey Truman
2008-05-09
We consider the Bohr correspondence limit of the Schrodinger wave function for an atomic elliptic state. We analyse this limit in the context of Nelson's stochastic mechanics, exposing an underlying deterministic dynamical system in which trajectories converge to Keplerian motion on an ellipse. This solves the long standing problem of obtaining Kepler's laws of planetary motion in a quantum mechanical setting. In this quantum mechanical setting, local mild instabilities occur in the Kelperian orbit for eccentricities greater than 1/\\sqrt{2} which do not occur classically.
Milos V. Lokajicek
2006-01-03
The support of Copenhagen quantum mechanics in the discussion concerning EPR experiments has been based fundamentally on two mistakes. First, quantum mechanics as well as hidden-variable theory give the same predictions; the statement of Belinfante from 1973 about the significant difference must be denoted as mistake. Secondly, the experimental violation of Bell's inequalities has been erroneously interpreted as excluding the hidden-variable alternative, while they have been based on assumption corresponding to classical physics. The EPR experiments cannot bring, therefore, any decision in the controversy between Einstein and Bohr. However, the view of Einstein is strongly supported by experimental results concerning the light transmission through three polarizers.
AGU's historical records move to the Niels Bohr Library and Archives
NASA Astrophysics Data System (ADS)
Harper, Kristine C.
2012-11-01
As scientists, AGU members understand the important role data play in finding the answers to their research questions: no data—no answers. The same holds true for the historians posing research questions concerning the development of the geophysical sciences, but their data are found in archival collections comprising the personal papers of geophysicists and scientific organizations. Now historians of geophysics—due to the efforts of the AGU History of Geophysics Committee, the American Institute of Physics (AIP), and the archivists of the Niels Bohr Library and Archives at AIP—have an extensive new data source: the AGU manuscript collection.
van Dongen, Jeroen
2015-01-01
The Einstein-Rupp experiments have been unduly neglected in the history of quantum mechanics. While this is to be explained by the fact that Emil Rupp was later exposed as a fraud and had fabricated the results, it is not justified, due to the importance attached to the experiments at the time. This paper discusses Rupp's fraud, the relation between Albert Einstein and Rupp, and the Einstein-Rupp experiments, and argues that these experiments were an influence on Niels Bohr's development of complementarity and Werner Heisenberg's formulation of the uncertainty relations.
Third-order optical response of intermediate excitons with fractional nonlinear statistics
NASA Astrophysics Data System (ADS)
Chernyak, Vladimir; Mukamel, Shaul
1996-06-01
The interplay of exciton statistics and Coulomb interactions in the optical response of semiconductors is studied by derivation of an effective Hamiltonian written in terms of exciton operators, starting with a two-band model. Statistical effects are incorporated through the nonboson commutation relations of exciton operators, which contain an exciton-size-dependent parameter q that may vary from q=0 (boson statistics) through q<<1 (Wannier excitons) to q=2 (Frenkel excitons or Pauli statistics). A unified Green's function expression for chi (3) that applies to excitons of an arbitrary nature is derived.
Exciton states and interband absorption of cylindrical quantum dot with Morse confining potential
NASA Astrophysics Data System (ADS)
Hayrapetyan, D. B.; Kazaryan, E. M.; Kotanjyan, T. V.; Tevosyan, H. Kh.
2015-02-01
In this paper the exciton and electron sates in cylindrical quantum dot with Morse potential made of GaAs are studied. For the regime of strong size quantization, energy spectrum with the parabolic approximation case are compared. For strong and weak size quantization regimes analytic expressions for the particle energy spectrum, absorption coefficient and dependencies of effective threshold frequencies of absorption on the geometrical parameters quantum dot are obtained. For the intermediate size quantization regime the problem solved in the framework of variation method. The selection rules corresponding to different transitions between quantum levels are found. The size dispersion distribution of growing quantum dots by the radius and height by two experimentally realizing distribution functions have been taken into account. Distribution functions of Gauss, Lifshits-Slezov have been considered.
Theory of exciton transfer and diffusion in conjugated polymers
NASA Astrophysics Data System (ADS)
Barford, William; Tozer, Oliver Robert
2014-10-01
We describe a theory of Förster-type exciton transfer between conjugated polymers. The theory is built on three assumptions. First, we assume that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, and described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ?? < J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. The resulting expression for the exciton transfer rate has a familiar form, being a function of the exciton transfer integral and the effective Franck-Condon factors. The effective Franck-Condon factors are functions of the effective Huang-Rhys parameters, which are inversely proportional to the chromophore size. The Born-Oppenheimer expressions were checked against DMRG calculations, and are found to be within 10% of the exact value for a tiny fraction of the computational cost. This theory of exciton transfer is then applied to model exciton migration in conformationally disordered poly(p-phenylene vinylene). Key to this modeling is the assumption that the donor and acceptor chromophores are defined by local exciton ground states (LEGSs). Since LEGSs are readily determined by the exciton center-of-mass wavefunction, this theory provides a quantitative link between polymer conformation and exciton migration. Our Monte Carlo simulations indicate that the exciton diffusion length depends weakly on the conformation of the polymer, with the diffusion length increasing slightly as the chromophores became straighter and longer. This is largely a geometrical effect: longer and straighter chromophores extend over larger distances. The calculated diffusion lengths of ˜10 nm are in good agreement with experiment. The spectral properties of the migrating excitons are also investigated. The emission intensity ratio of the 0-0 and 0-1 vibronic peaks is related to the effective Huang-Rhys parameter of the emitting state, which in turn is related to the chromophore size. The intensity ratios calculated from the effective Huang-Rhys parameters are in agreement with experimental spectra, and the time-resolved trend for the intensity ratio to decrease with time was also reproduced as the excitation migrates to shorter, lower energy chromophores as a function of time. In addition, the energy of the exciton state shows a logarithmic decrease with time, in agreement with experimental observations.
Theory of exciton transfer and diffusion in conjugated polymers
Barford, William, E-mail: william.barford@chem.ox.ac.uk [Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ (United Kingdom); Tozer, Oliver Robert [Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ (United Kingdom); University College, University of Oxford, Oxford OX1 4BH (United Kingdom)
2014-10-28
We describe a theory of Förster-type exciton transfer between conjugated polymers. The theory is built on three assumptions. First, we assume that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, and described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ?? < J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. The resulting expression for the exciton transfer rate has a familiar form, being a function of the exciton transfer integral and the effective Franck-Condon factors. The effective Franck-Condon factors are functions of the effective Huang-Rhys parameters, which are inversely proportional to the chromophore size. The Born-Oppenheimer expressions were checked against DMRG calculations, and are found to be within 10% of the exact value for a tiny fraction of the computational cost. This theory of exciton transfer is then applied to model exciton migration in conformationally disordered poly(p-phenylene vinylene). Key to this modeling is the assumption that the donor and acceptor chromophores are defined by local exciton ground states (LEGSs). Since LEGSs are readily determined by the exciton center-of-mass wavefunction, this theory provides a quantitative link between polymer conformation and exciton migration. Our Monte Carlo simulations indicate that the exciton diffusion length depends weakly on the conformation of the polymer, with the diffusion length increasing slightly as the chromophores became straighter and longer. This is largely a geometrical effect: longer and straighter chromophores extend over larger distances. The calculated diffusion lengths of ?10 nm are in good agreement with experiment. The spectral properties of the migrating excitons are also investigated. The emission intensity ratio of the 0-0 and 0-1 vibronic peaks is related to the effective Huang-Rhys parameter of the emitting state, which in turn is related to the chromophore size. The intensity ratios calculated from the effective Huang-Rhys parameters are in agreement with experimental spectra, and the time-resolved trend for the intensity ratio to decrease with time was also reproduced as the excitation migrates to shorter, lower energy chromophores as a function of time. In addition, the energy of the exciton state shows a logarithmic decrease with time, in agreement with experimental observations.
Theory of exciton transfer and diffusion in conjugated polymers.
Barford, William; Tozer, Oliver Robert
2014-10-28
We describe a theory of Förster-type exciton transfer between conjugated polymers. The theory is built on three assumptions. First, we assume that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, and described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ?? < J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. The resulting expression for the exciton transfer rate has a familiar form, being a function of the exciton transfer integral and the effective Franck-Condon factors. The effective Franck-Condon factors are functions of the effective Huang-Rhys parameters, which are inversely proportional to the chromophore size. The Born-Oppenheimer expressions were checked against DMRG calculations, and are found to be within 10% of the exact value for a tiny fraction of the computational cost. This theory of exciton transfer is then applied to model exciton migration in conformationally disordered poly(p-phenylene vinylene). Key to this modeling is the assumption that the donor and acceptor chromophores are defined by local exciton ground states (LEGSs). Since LEGSs are readily determined by the exciton center-of-mass wavefunction, this theory provides a quantitative link between polymer conformation and exciton migration. Our Monte Carlo simulations indicate that the exciton diffusion length depends weakly on the conformation of the polymer, with the diffusion length increasing slightly as the chromophores became straighter and longer. This is largely a geometrical effect: longer and straighter chromophores extend over larger distances. The calculated diffusion lengths of ~10 nm are in good agreement with experiment. The spectral properties of the migrating excitons are also investigated. The emission intensity ratio of the 0-0 and 0-1 vibronic peaks is related to the effective Huang-Rhys parameter of the emitting state, which in turn is related to the chromophore size. The intensity ratios calculated from the effective Huang-Rhys parameters are in agreement with experimental spectra, and the time-resolved trend for the intensity ratio to decrease with time was also reproduced as the excitation migrates to shorter, lower energy chromophores as a function of time. In addition, the energy of the exciton state shows a logarithmic decrease with time, in agreement with experimental observations. PMID:25362268
Proton Radius Puzzle and Large Extra Dimensions
NASA Astrophysics Data System (ADS)
Wang, Li-Bang; Ni, Wei-Tou
2013-06-01
We propose a theoretical scenario to solve the proton radius puzzle which recently arises from the muonic hydrogen experiment. In this framework, (4+n)-dimensional theory is incorporated with modified gravity. The extra gravitational interaction between the proton and muon at very short range provides an energy shift which accounts for the discrepancy between spectroscopic results from muonic and electronic hydrogen experiments. Assuming the modified gravity is a small perturbation to the existing electromagnetic interaction, we find the puzzle can be solved with stringent constraint on the range of the new force. Our result not only provides a possible solution to the proton radius puzzle but also suggests a direction to test new physics at very small length scale.
The Epidemiology of Distal Radius Fractures
Nellans, Kate W.; Kowalski, Evan; Chung, Kevin C.
2012-01-01
Distal radius fractures are one of the most common types of fractures, accounting for around 25% of fractures in the pediatric population and up to 18% of all fractures in the elderly age group. Although the pediatric and elderly populations are at the greatest risk for this injury, distal radius fractures still have a significant impact on the health and well-being of young adults. Data from the past 40 years has documented a trend towards an overall increase in the prevalence of this injury. For the pediatric population, this increase can likely be attributed to a surge in sports related activities. The growth of the elderly population and a rise in the number of active elderly are directly responsible for the increase seen in this age group. Understanding the epidemiology of this fracture is an important step towards the improvement of the treatment strategies and preventative measures which target this debilitating injury. PMID:22554654
Proton radius puzzle and large extra dimensions
Li-Bang Wang; Wei-Tou Ni
2013-05-23
We propose a theoretical scenario to solve the proton radius puzzle which recently arises from the muonic hydrogen experiment. In this framework, 4 + n dimensional theory is incorporated with modified gravity. The extra gravitational interaction between the proton and muon at very short range provides an energy shift which accounts for the discrepancy between spectroscopic results from muonic and electronic hydrogen experiments. Assuming the modified gravity is a small perturbation to the existing electromagnetic interaction, we find the puzzle can be solved with stringent constraint on the range of the new force. Our result not only provides a possible solution to the proton radius puzzle but also suggest a direction to test new physics at very small length scale.
Ulnar Shortening Osteotomy for Distal Radius Malunion
Kamal, Robin N.; Leversedge, Fraser J.
2014-01-01
Background?Malunion is a common complication of distal radius fractures. Ulnar shortening osteotomy (USO) may be an effective treatment for distal radius malunion when appropriate indications are observed. Methods?The use of USO for treatment of distal radius fracture malunion is described for older patients (typically patients >50 years) with dorsal or volar tilt less than 20 degrees and no carpal malalignment or intercarpal or distal radioulnar joint (DRUJ) arthritis. Description of Technique?Preoperative radiographs are examined to ensure there are no contraindications to ulnar shortening osteotomy. The neutral posteroanterior (PA) radiograph is used to measure ulnar variance and to estimate the amount of ulnar shortening required. An ulnar, mid-sagittal incision is used and the dorsal sensory branch of the ulnar nerve is preserved. An USO-specific plating system with cutting jig is used to create parallel oblique osteotomies to facilitate shortening. Intraoperative fluoroscopy and clinical range of motion are checked to ensure adequate shortening and congruous reduction of the ulnar head within the sigmoid notch. Results?Previous outcomes evaluation of USO has demonstrated improvement in functional activities, including average flexion-extension and pronosupination motions, and patient reported outcomes. Conclusion?The concept and technique of USO are reviewed for the treatment of distal radius malunion when specific indications are observed. Careful attention to detail related to surgical indications and to surgical technique typically will improve range of motion, pain scores, and patient-reported outcomes and will reduce the inherent risks of the procedure, such as ulnar nonunion or the symptoms related to unrecognized joint arthritis. Level of Evidence:?Level IV PMID:25097811
Optimal jet radius in kinematic dijet reconstruction
Gregory Soyez
2010-07-23
Obtaining a good momentum reconstruction of a jet is a compromise between taking it large enough to catch the perturbative final-state radiation and small enough to avoid too much contamination from the underlying event and initial-state radiation. In this paper, we compute analytically the optimal jet radius for dijet reconstructions and study its scale dependence. We also compare our results with previous Monte-Carlo studies.
Recent progress on large Larmor radius theory
Coppins, M.; Arber, T. D.; Russell, P. G. F.; Scheffel, J.
1997-05-05
An overview of theoretical work on large Larmor radius stability of the z-pinch is presented, highlighting two recent innovations. Firstly, finite electron temperature has been included for the linear m=0 instability. Compared to the usual cold electron case, growth rates are increased and are closer to those of ideal MHD. Secondly, a 2-D hybrid code has been written to study the non-linear development of the m=0 instability. First results provide no evidence of instability saturation.
Essential radiographic evaluation for distal radius fractures.
Medoff, Robert J
2005-08-01
Fractures of the distal radius can be complex injuries, often generating multiple fragments with distortion of the normal anatomy in all three dimensions. Superficial assessment of the injury on the standard PA and lateral radiographs often can result in incomplete recognition of the injury pattern and a misdirected approach to treatment. In addition, failure to recognize subtle radiographic findings may result in the acceptance of a reduction that has significant residual incongruency and articular surface disruption. Standard radiographs of the distal radius can provide a wealth of information about the topography of the bone if the surgeon knows what to look for. The ability to recognize detailed landmarks and parameters on the radiographic images and convert this information into a three-dimensional visual image is a skill that requires education and training. As more aggressive treatments have emerged for anatomic restoration of the bony and articular anatomy, accurate identification of the pattern of injury has become essential. Parameters such as the tear drop angle, AP distance, and articular separation have been recognized only recently. Because these parameters reflect the congruency of the articular surface,it would be natural to assume that postreduction films in which these parameters are abnormal would compromise clinical outcome. Because nearly all historical studies do not include routine evaluation of these parameters, knowledge of radiographic correlation with clinical outcome is still incomplete. At the same time, previous studies to assess outcome of distal radius fractures may be compromised by the failure to recognize residual deformity and articular incongruency that would have been evident with measurement of these parameters. With careful understanding of the radiographic landmarks, radiographic parameters, and patterns of injury, the surgeon can visualize a more accurate picture of the fracture itself and the reduction. As a result, treatment decisions for distal radius fractures can be based on a more thorough understanding of the anatomy of the injury, and future grading of radiographic results may reflect more accurately the precision of the articular restoration. PMID:16039439
On the radius of habitable planets
Alibert, Yann
2013-01-01
The conditions that a planet must fulfill to be habitable are not precisely known. However, it is comparatively easier to define conditions under which a planet is very likely not habitable. Finding such conditions is important as it can help select, in an ensemble of potentially observable planets, which ones should be observed in greater detail for characterization studies. Assuming, as in the Earth, that the presence of a C-cycle is a necessary condition for long-term habitability, we derive, as a function of the planetary mass, a radius above which a planet is likely not habitable. We compute the maximum radius a planet can have to fulfill two constraints: surface conditions compatible with the existence of liquid water, and no ice layer at the bottom of a putative global ocean. We demonstrate that, above a given radius, these two constraints cannot be met. We compute internal structure models of planets, using a five-layer model (core, inner mantle, outer mantle, ocean, and atmosphere), for different mas...
Open universes from finite radius bubbles
Cohn, J D
1996-01-01
The interior of a vacuum bubble in de Sitter space may give an open universe with sufficient homogeneity to agree with observations. Here, previous work by Bucher, Goldhaber and Turok is extended to describe a thin bubble wall with nonzero radius and energy difference across the wall. The vacuum modes present before formation of the bubble propagate into the interior of the open universe and the power spectrum of the resulting gauge invariant gravitational potential is calculated. It appears to become scale invariant on small scales, with onset at about the same scale as that found in the zero radius case. There is sensitivity to the radius and energy difference at large scales, but it is expected that they cannot be strongly constrained because of cosmic variance. As the prediction of a scale invariant spectrum seems to be robust with respect to variation of these parameters at small scales, it apparently is a generic feature of the contribution of these modes for these thin wall models.
The Rossby radius in the Arctic Ocean
NASA Astrophysics Data System (ADS)
Nurser, A. J. G.; Bacon, S.
2014-11-01
The first (and second) baroclinic deformation (or Rossby) radii are presented north of ~60° N, focusing on deep basins and shelf seas in the high Arctic Ocean, the Nordic seas, Baffin Bay, Hudson Bay and the Canadian Arctic Archipelago, derived from climatological ocean data. In the high Arctic Ocean, the first Rossby radius increases from ~5 km in the Nansen Basin to ~15 km in the central Canadian Basin. In the shelf seas and elsewhere, values are low (1-7 km), reflecting weak density stratification, shallow water, or both. Seasonality strongly impacts the Rossby radius only in shallow seas, where winter homogenization of the water column can reduce it to below 1 km. Greater detail is seen in the output from an ice-ocean general circulation model, of higher resolution than the climatology. To assess the impact of secular variability, 10 years (2003-2012) of hydrographic stations along 150° W in the Beaufort Gyre are also analysed. The first-mode Rossby radius increases over this period by ~20%. Finally, we review the observed scales of Arctic Ocean eddies.
Mass-Radius diagram for compact stars
NASA Astrophysics Data System (ADS)
Carvalho, G. A.; Marinho, R. M., Jr.; Malheiro, M.
2015-07-01
The compact stars represent the final stage in the evolution of ordinary stars, they are formed when a star ceases its nuclear fuel, in this point the process that sustain its stability will stop. After this, the internal pressure can no longer stand the gravitational force and the star colapses [2]. In this work we investigate the structure of these stars which are described by the equations of Tolman-Openheimer-Volkof (TOV) [1]. These equations show us how the pressure varies with the mass and radius of the star. We consider the TOV equations for both relativistic and non-relativistic cases. In the case of compact stars (white dwarfs and neutron stars) the internal pressure that balances the gravitational pressure is essentialy the pressure coming from the degeneracy of fermions. To have solved the TOV equations we need a equation of state that shows how this internal pressure is related to the energy density or mass density. Instead of using politropic equations of state we have solved the equations numericaly using the exact relativistic energy equation for the model of fermion gas at zero temperature. We obtain results for the mass-radius relation for white dwarfs and we compared with the results obtained using the politropic equations of state. In addition we discussed a good fit for the mass-radius relation.
The effective pore radius of screen wicks
Imura, Hideaki; Kozai, Hiroaki; Ikeda, Yuji
1994-10-01
The effective pore radius in screen-wick heat pipes was investigated, which is very important for the prediction of maximum heat transfer rates due to capillary limitation. An equation for the effective pore radius of the screen wicks was derived based on the model of the screen geometry. The capillary height for stainless steel and phosphor bronze screens was measured using water, ethyl alcohol, and Freon 113 as the test liquids. The effect of surface treatment (acid cleaning and oxidation) on the capillary height was also examined. From the comparison of the experimental data for water and ethyl alcohol with those for Freon 113, it was indicated that the contact angle was 24.2{degree} for water and 16.9{degree} for ethyl alcohol. Consequently, it was found that the effective pore radius of the screen wicks could be predicted fairly well from the expression presented in this study, and that the contact angle should be taken into consideration to evaluate the maximum capillary pressure accurately.
Role of phonons in Josephson oscillations of excitonic and polaritonic condensates
Magnusson, E. B.; Flayac, H.; Malpuech, G.; Shelykh, I. A. [Science Institute, University of Iceland, Dunhagi-3, IS-107 Reykjavik (Iceland); LASMEA, Clermont Universite-Universite Blaise Pascal, BP 10448, 63000 Clermont-Ferrand (France) and LASMEA, UMR 6602, CNRS, 63177 Aubiere (France); Science Institute, University of Iceland, Dunhagi-3, IS-107 Reykjavik (Iceland) and International Institute for Physics, Av. Odilon Gomes de Lima, 1722, CEP 59078-400 Capim Macio Natal, RN (Brazil)
2010-11-15
We analyze theoretically the role of the exciton-phonon interactions in phenomena related to the Josephson effect between two spatially separated exciton and exciton-polariton condensates. We consider the role of the dephasing introduced by phonons in such phenomena as Josephson tunneling, self-trapping and spontaneous polarization separation. In the regime of cw pumping we find a remarkable bistability effect arising from exciton-exciton interactions as well as regimes of self-sustained regular and chaotic oscillations.
Manifestation of exciton Bose condensation in induced two-phonon emission and Raman scattering
Yu. E. Lozovik; A. V. Poushnov
1998-01-01
The unusual two-photon emission by Bose-condensed excitons caused by simultaneous recombination of two excitons with opposite momenta leaving the occupation numbers of excitonic states with momenta p!=0 unchanged (below coherent two-exciton recombination) is investigated. Raman scattering accompanied by the analogous two-exciton recombination (or creation) is also analyzed. The excess momentum equal to the change of the electromagnetic field momentum in
Exciton Dynamics in Semiconducting Carbon Nanotubes
Graham, Matt; Chmeliov, Javgenij; Ma, Yingzhong; Shinohara, Nori; Green, Alexander A.; Hersam, Mark C.; Valkunas, Leonas; Fleming, Graham
2010-01-01
We report femtosecond transient absorption spectroscopic study on the (6, 5) single-walled carbon nanotubes and the (7, 5) inner tubes of a dominant double-walled carbon nanotube species. We found that the dynamics of exciton relaxation probed at the first transition-allowed state (E11) of a given tube type exhibits a markedly slower decay when the second transition-allowed state (E22) is excited than that measured by exciting its first transition-allowed state (E11). A linear intensity dependence of the maximal amplitude of the transient absorption signal is found for the E22 excitation, whereas the corresponding amplitude scales linearly with the square root of the E11 excitation intensity. Theoretical modeling of these experimental findings was performed by developing a continuum model and a stochastic model with explicit consideration of the annihilation of coherent excitons. Our detailed numerical simulations show that both models can reproduce reasonably well the initial portion of decay kinetics measured upon the E22 and E11 excitation of the chosen tube species, but the stochastic model gives qualitatively better agreement with the intensity dependence observed experimentally than those obtained with the continuum model.
Nanoscale Charge Transport in Excitonic Solar Cells
Venkat Bommisetty, South Dakota State University
2011-06-23
Excitonic solar cells, including all-organic, hybrid organic-inorganic and dye-sensitized solar cells (DSSCs), offer strong potential for inexpensive and large-area solar energy conversion. Unlike traditional inorganic semiconductor solar cells, where all the charge generation and collection processes are well understood, these excitonic solar cells contain extremely disordered structures with complex interfaces which results in large variations in nanoscale electronic properties and has a strong influence on carrier generation, transport, dissociation and collection. Detailed understanding of these processes is important for fabrication of highly efficient solar cells. Efforts to improve efficiency are underway at a large number of research groups throughout the world focused on inorganic and organic semiconductors, photonics, photophysics, charge transport, nanoscience, ultrafast spectroscopy, photonics, semiconductor processing, device physics, device structures, interface structure etc. Rapid progress in this multidisciplinary area requires strong synergetic efforts among researchers from diverse backgrounds. Such effort can lead to novel methods for development of new materials with improved photon harvesting and interfacial treatments for improved carrier transport, process optimization to yield ordered nanoscale morphologies with well defined electronic structures.
Robust excitons inhabit soft supramolecular nanotubes.
Eisele, Dörthe M; Arias, Dylan H; Fu, Xiaofeng; Bloemsma, Erik A; Steiner, Colby P; Jensen, Russell A; Rebentrost, Patrick; Eisele, Holger; Tokmakoff, Andrei; Lloyd, Seth; Nelson, Keith A; Nicastro, Daniela; Knoester, Jasper; Bawendi, Moungi G
2014-08-19
Nature's highly efficient light-harvesting antennae, such as those found in green sulfur bacteria, consist of supramolecular building blocks that self-assemble into a hierarchy of close-packed structures. In an effort to mimic the fundamental processes that govern nature's efficient systems, it is important to elucidate the role of each level of hierarchy: from molecule, to supramolecular building block, to close-packed building blocks. Here, we study the impact of hierarchical structure. We present a model system that mirrors nature's complexity: cylinders self-assembled from cyanine-dye molecules. Our work reveals that even though close-packing may alter the cylinders' soft mesoscopic structure, robust delocalized excitons are retained: Internal order and strong excitation-transfer interactions--prerequisites for efficient energy transport--are both maintained. Our results suggest that the cylindrical geometry strongly favors robust excitons; it presents a rational design that is potentially key to nature's high efficiency, allowing construction of efficient light-harvesting devices even from soft, supramolecular materials. PMID:25092336
CCMR: Exciton Blocking Layers in Organic Photovoltaics
NSDL National Science Digital Library
Becker, Katherine
2007-08-29
Organic solar cells have been attracting increased attention recently as an alternative to more costly silicon cells. Organic photovoltaics can be lightweight, processed on flexible substrates, and use less energy to produce [1]. However, significant barriers in efficiency and longevity must be overcome before such cells are commercially viable. Current organic cells can reach only up to 6% efficiency in the lab, while commercially available silicon cells average 15% efficiency [2, 3]. Cell longevity is also severely restricted by the tendency of C60 to increase in resistance when exposed to oxygen. Exciton blocking layers (EBLs) have been exploited to increase longevity [4], mechanically protect the donor and acceptor layers [5] and increase efficiency [6]. Until recently, primarily bathocuproine (BCP) has been used, with some investigation into tris-8-hydroxyquinolinato aluminum (Alq3) [5] and bathophenanthroline (BPhen) [6]. There has also been investigation into the positive effects of annealing on efficiency [7,8,9]. This research seeks to evaluate the effects of thermal annealing on 4 different exciton blocking layer types: BCP, Alq3, BPhen, and NBPhen, a close relative of BPhen.
Photonics meets excitonics: natural and artificial molecular aggregates
NASA Astrophysics Data System (ADS)
Saikin, Semion K.; Eisfeld, Alexander; Valleau, Stéphanie; Aspuru-Guzik, Alán
2013-02-01
Organic molecules store the energy of absorbed light in the form of charge-neutral molecular excitations - Frenkel excitons. Usually, in amorphous organic materials, excitons are viewed as quasiparticles, localized on single molecules, which diffuse randomly through the structure. However, the picture of incoherent hopping is not applicable to some classes of molecular aggregates - assemblies of molecules that have strong near-field interaction between electronic excitations in the individual subunits. Molecular aggregates can be found in nature, in photosynthetic complexes of plants and bacteria, and they can also be produced artificially in various forms including quasi-one dimensional chains, two-dimensional films, tubes, etc. In these structures light is absorbed collectively by many molecules and the following dynamics of molecular excitation possesses coherent properties. This energy transfer mechanism, mediated by the coherent exciton dynamics, resembles the propagation of electromagnetic waves through a structured medium on the nanometer scale. The absorbed energy can be transferred resonantly over distances of hundreds of nanometers before exciton relaxation occurs. Furthermore, the spatial and energetic landscape of molecular aggregates can enable the funneling of the exciton energy to a small number of molecules either within or outside the aggregate. In this review we establish a bridge between the fields of photonics and excitonics by describing the present understanding of exciton dynamics in molecular aggregates.
Giant Rydberg excitons in the copper oxide Cu2O.
Kazimierczuk, T; Fröhlich, D; Scheel, S; Stolz, H; Bayer, M
2014-10-16
A highly excited atom having an electron that has moved into a level with large principal quantum number is a hydrogen-like object, termed a Rydberg atom. The giant size of Rydberg atoms leads to huge interaction effects. Monitoring these interactions has provided insights into atomic and molecular physics on the single-quantum level. Excitons--the fundamental optical excitations in semiconductors, consisting of an electron and a positively charged hole--are the condensed-matter analogues of hydrogen. Highly excited excitons with extensions similar to those of Rydberg atoms are of interest because they can be placed and moved in a crystal with high precision using microscopic energy potential landscapes. The interaction of such Rydberg excitons may allow the formation of ordered exciton phases or the sensing of elementary excitations in their surroundings on a quantum level. Here we demonstrate the existence of Rydberg excitons in the copper oxide Cu2O, with principal quantum numbers as large as n = 25. These states have giant wavefunction extensions (that is, the average distance between the electron and the hole) of more than two micrometres, compared to about a nanometre for the ground state. The strong dipole-dipole interaction between such excitons is indicated by a blockade effect in which the presence of one exciton prevents the excitation of another in its vicinity. PMID:25318523
Synthesis and Exciton Dynamics of Triplet Sensitized Conjugated Polymers.
Andernach, Rolf; Utzat, Hendrik; Dimitrov, Stoichko D; McCulloch, Iain; Heeney, Martin; Durrant, James R; Bronstein, Hugo
2015-08-19
We report the synthesis of a novel polythiophene-based host-guest copolymer incorporating a Pt-porphyrin complex (TTP-Pt) into the backbone for efficient singlet to triplet polymer exciton sensitization. We elucidated the exciton dynamics in thin films of the material by means of Transient Absorption Spectrosopcy (TAS) on multiple time scales and investigated the mechanism of triplet exciton formation. During sensitization, singlet exciton diffusion is followed by exciton transfer from the polymer backbone to the complex where it undergoes intersystem crossing to the triplet state of the complex. We directly monitored the triplet exciton back transfer from the Pt-porphyrin to the polymer and found that 60% of the complex triplet excitons were transferred with a time constant of 1087 ps. We propose an equilibrium between polymer and porphyrin triplet states as a result of the low triplet diffusion length in the polymer backbone and hence an increased local triplet population resulting in increased triplet-triplet annihilation. This novel system has significant implications for the design of novel materials for triplet sensitized solar cells and upconversion layers. PMID:26200595
Rioux, Frank
The Bohr Model of the Earth-Sun System* Data for the earth-sun system assuming a circular earth with the Bohr model for the earth-sun system. Is this a legitimate example of the correspondence principle? E G
A Bohr-type model of a composite particle using gravity as the attractive force
NASA Astrophysics Data System (ADS)
Vayenas, C. G.; Souentie, S.; Fokas, A.
2014-07-01
We formulate a Bohr-type rotating particle model for three light particles of rest mass mo each, forming a bound rotational state under the influence of their gravitational attraction, in the same way that electrostatic attraction leads to the formation of a bound proton-electron state in the classical Bohr model of the H atom. By using special relativity, the equivalence principle and the de Broglie wavelength equation, we find that when each of the three rotating particles has the same rest mass as the rest mass of a neutrino or an antineutrino (˜0.05 eV/c2) then surprisingly the composite rotating state has the rest mass of the stable baryons, i.e. of the proton and the neutron (˜1 GeV/c2). This rest mass is due almost exclusively to the kinetic energy of the rotating particles. The results are found to be consistent with the theory of general relativity. The model contains no unknown parameters, describes both asymptotic freedom and confinement and also provides good agreement with QCD regarding the QCD condensation temperature. Predictions for the thermodynamic and other physical properties of these bound rotational states are compared with experimental values.
ZM theory III: Classical oscillators and semi-classical Bohr-Sommerfeld quantization
Yaneer Bar-Yam
2006-04-30
We consider the description of classical oscillatory motion in ZM theory, and explore the relationship of ZM theory to semi-classical Bohr-Sommerfeld quantization. The treatment illustrates some features of ZM theory, especially the inadequacies of classical and semi-classical treatments due to non-analyticity of the mapping of classical trajectories onto the ZM clock field. While the more complete ZM formalism is not developed here, the non-analyticities in the classical treatment resemble issues in the comparison of classical and quantum formalisms. We also show that semi-classical quantization is valid for a periodic manifold in ZM theory, though the quantum number $n=0$ is allowed, as it would be in quantum mechanics for a periodic manifold. Still, this suggests a connection to the first-order success of Bohr theory in describing the phenomenology of atomic quantum states. The approximate nature of the semi-classical treatment of three dimensional atomic orbits is, however, also apparent in relation to ZM theory. These observations are preliminary to a discussion of ZM theory in relation to quantum mechanics and quantum field theory in subsequent papers.
Vladan Pankovic; Darko V. Kapor
2010-09-10
In this work we consider some consequences of the Bohr-Sommerfeld-Hansson (Old or quasi-classical) quantum theory of the Newtonian gravity, i.e. of the "gravitational atom". We prove that in this case (for gravitational central force and quantized angular momentum) centrifugal acceleration becomes formally-theoretically dependent (proportional to fourth degree) of the mass of "gravitational electron" rotating around "gravitational nucleus" for any quantum number (state). It seemingly leads toward a paradoxical breaking of the relativistic equivalence principle which contradicts to real experimental data. We demonstrate that this equivalence principle breaking does not really appear in the (quasi classical) quantum theory, but that it necessary appears only in a hypothetical extension of the quantum theory that needs a classical like interpretation of the Bohr-Sommerfeld angular momentum quantization postulate. It is, in some sense, similar to Bell-Aspect analysis that points out that a hypothetical deterministic extension of the quantum mechanics, in distinction to usual quantum mechanics, can reproduce experimental data if and only if it is non-local (superluminal) in contradiction with relativistic locality (luminality) principle.
Exactly separable version of the Bohr Hamiltonian with the Davidson potential
Dennis Bonatsos; E. A. McCutchan; N. Minkov; R. F. Casten; P. Yotov; D. Lenis; D. Petrellis; I. Yigitoglu
2008-07-28
An exactly separable version of the Bohr Hamiltonian is developed using a potential of the form u(beta)+u(gamma)/beta^2, with the Davidson potential u(beta)= beta^2 + beta_0^4/beta^2 (where beta_0 is the position of the minimum) and a stiff harmonic oscillator for u(gamma) centered at gamma=0. In the resulting solution, called exactly separable Davidson (ES-D), the ground state band, gamma band and 0_2^+ band are all treated on an equal footing. The bandheads, energy spacings within bands, and a number of interband and intraband B(E2) transition rates are well reproduced for almost all well-deformed rare earth and actinide nuclei using two parameters (beta_0, gamma stiffness). Insights regarding the recently found correlation between gamma stiffness and the gamma-bandhead energy, as well as the long standing problem of producing a level scheme with Interacting Boson Approximation SU(3) degeneracies from the Bohr Hamiltonian, are also obtained.
Einstein–Bohr recoiling double-slit gedanken experiment performed at the molecular level
NASA Astrophysics Data System (ADS)
Liu, Xiao-Jing; Miao, Quan; Gel'Mukhanov, Faris; Patanen, Minna; Travnikova, Oksana; Nicolas, Christophe; Ågren, Hans; Ueda, Kiyoshi; Miron, Catalin
2015-02-01
Double-slit experiments illustrate the quintessential proof for wave–particle complementarity. If information is missing about which slit the particle has traversed, the particle, behaving as a wave, passes simultaneously through both slits. This wave-like behaviour and corresponding interference is absent if ‘which-slit’ information exists. The essence of Einstein–Bohr's debate about wave–particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. To measure the recoil of a slit, the slits should move independently. We showcase a materialization of this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case owing to Doppler labelling of the counter-propagating atomic slits, in full agreement with Bohr's complementarity.
The theory of the Bohr-Weisskopf effect in the hyperfine structure
F. F. Karpeshin; M. B. Trzhaskovskaya
2015-03-21
For twenty years research into the anomalies in the HF spectra was going in a wrong direction by fighting the related Bohr-Weisskopf effect. As a way out, the model-independent way is proposed of estimating the nuclear radii from the hyper-fine splitting. The way is based on analogy of HFS to internal conversion coefficients, and the Bohr-Weisskopf effect - to the anomalies in the internal conversion coefficients. This makes transparent It is shown that the parameters which can be extracted from the data are the even nuclear moments of the magnetization distribution. The radii $R_2$ and (for the first time) $R_4$ are thus obtained by analysis of the experimental HFS for the H- and Li-like ions of $^{209}$Bi. The critical prediction of the HFS for the $2p_{1/2}$ state is discussed. The moments may be determined in this way only if the higher QED effects are properly taken into account. Therefore, this set of the parameters form a basis of a strict QED test. Experimental prospects are discussed, aimed at retrieving data on the HFS values for a set of a few-electron configurations of the atom.
Josephson oscillations between exciton condensates in electrostatic traps
Rontani, Massimo
2009-08-15
Technological advances allow for tunable lateral confinement of cold dipolar excitons in coupled quantum wells. We consider theoretically the Josephson effect between exciton condensates in two traps separated by a weak link. The flow of the exciton supercurrent is driven by the dipole-energy difference between the traps. The Josephson oscillations may be observed after ensemble average of the time correlation of photons separately emitted from the two traps. The fringe visibility is controlled by the trap coupling and is robust against quantum and thermal fluctuations.
Evidence for a Surface Exciton in KBr via Laser Desorption
Beck, Kenneth M. (BATTELLE (PACIFIC NW LAB)); Joly, Alan G. (BATTELLE (PACIFIC NW LAB)); Hess, Wayne P. (BATTELLE (PACIFIC NW LAB))
2001-01-01
We demonstrate that direct photoexcitation of the KBr surface exciton leads to desorption of hyperthermal neutral bromine atoms. We have for the first time produced separately the hyperthermal and the near-thermal components of neutral halogen emission from an alkali halide. The source of hyperthermal bromine emission is attributed to decay of a surface exciton excited at photon energies below that of the bulk exciton. We further demonstrate that the frequently observed near-thermal component is derived from excitation within the bulk crystal. Our experimental data provides strong support to a theoretical emission model previously described in the literature.
Evidence for a surface exciton in KBr via laser desorption
Beck, Kenneth M.; Joly, Alan G.; Hess, Wayne P.
2001-03-15
We demonstrate that direct photoexcitation of the single crystal KBr surface leads to desorption of hyperthermal neutral bromine atoms. We have produced separately the hyperthermal and the near-thermal components of neutral halogen emission from an alkali halide. The source of hyperthermal bromine emission is attributed to decay of a surface exciton excited at photon energies below that of the bulk exciton. We argue that the frequently observed near-thermal component is derived from excitation within the bulk crystal. Our experimental data provide strong support to a theoretical excitonic emission model previously described in the literature.
Renormalized frequency shift of superradiant excitons in thin semiconductor films
NASA Astrophysics Data System (ADS)
Lee, Yung-Chang; Chuu, Der-San; Mei, Wai-Ning
1992-08-01
The radiative frequency shift of an exciton in a thin semiconductor film, like its radiative level width, is shown to be superradiatively enhanced. Unlike the latter, however, a finite frequency shift can only be obtained after proper renormalization for the correlated system. The shift is found to be inversely proportional to the square of the factor k0d and proportional to the film thickness T, k0=Eqn/?c, Eqn being the exciton energy gap and d the lattice constant of the semiconductor. Therefore, the coherent frequency shift can be observed experimentally if one varies the thickness, or the exciton energy gap Eqn by imposing high pressure.
Excitonic AND Logic Gates on DNA Brick Nanobreadboards
2015-01-01
A promising application of DNA self-assembly is the fabrication of chromophore-based excitonic devices. DNA brick assembly is a compelling method for creating programmable nanobreadboards on which chromophores may be rapidly and easily repositioned to prototype new excitonic devices, optimize device operation, and induce reversible switching. Using DNA nanobreadboards, we have demonstrated each of these functions through the construction and operation of two different excitonic AND logic gates. The modularity and high chromophore density achievable via this brick-based approach provide a viable path toward developing information processing and storage systems. PMID:25839049
Photoluminescence of high-density exciton-polariton condensates
Natsuko Ishida; Tim Byrnes; Tomoyuki Horikiri; Franco Nori; Yoshihisa Yamamoto
2015-01-15
We examine the photoluminescence of highly-excited exciton-polariton condensates in semiconductor microcavities. Under strong pumping, exciton-polariton condensates have been observed to undergo a lasing transition where strong coupling between the excitons and photons is lost. We discuss an alternative high-density scenario, where the strong coupling is maintained. We find that the photoluminescence smoothly transitions between the lower polariton energy to the cavity photon energy. An intuitive understanding of the change in spectral characteristics is given, as well as differences to the photoluminescence characteristics of the lasing case.
NASA Astrophysics Data System (ADS)
Liu, Su; Borys, Nicholas J.; Huang, Jing; Talapin, Dmitri V.; Lupton, John M.
2012-07-01
CdSe/CdS nanocrystal tetrapods are interesting building blocks for excitonic circuits, where the flow of excitation energy is gated by an external stimulus. The physical morphology of the nanoparticle, along with the electronic structure, which favors electron delocalization between the two semiconductors, suggests that all orientations of a particle relative to an external electric field will allow for excitons to be dissociated, stored, and released at a later time. While this approach, in principle, works, and fluorescence quenching of over 95% can be achieved electrically, we find that discrete trap states within the CdS are required to dissociate and store the exciton. These states are rapidly filled up with increasing excitation density, leading to a dramatic reduction in quenching efficiency. Charge separation is not instantaneous on the CdS excitonic antennae in which light absorption occurs, but arises from the relaxed exciton following hole localization in the core. Consequently, whereas strong electromodulation of the core exciton is observed, the core multiexciton and the CdS arm exciton are not affected by an external electric field.
Colorado at Boulder, University of
Why we should teach the Bohr model and how to teach it effectively S. B. McKagan,1 K. K. Perkins,2 2008 Some education researchers have claimed that we should not teach the Bohr model of the atom designed to test this claim by developing a curriculum on models of the atom, including the Bohr
NSDL National Science Digital Library
This is a task from the Illustrative Mathematics website that is one part of a complete illustration of the standard to which it is aligned. Each task has at least one solution and some commentary that addresses important asects of the task and its potential use. Here are the first few lines of the commentary for this task: Given the height $h$ and volume $V$ of a certain cylinder, Jill uses the formula r=\\sqrt{\\frac{V}{\\pi h}} to compute its radius to be 20 meters. If a s...
Giant cell tumour of the proximal radius.
Singh, A P; Mahajan, S; Singh, A P
2009-11-01
A 52-year-old Indian woman presented with a progressively increasing swelling and pain in the right elbow for the past eight months, which was not associated with trauma or constitutional symptoms. The patient was diagnosed to have Campanacci grade III giant cell tumour of the proximal radius, and was treated with above elbow amputation. The patient has not shown any recurrence after five years of follow-up. The case was reported because of its rarity and the unusual site of occurrence of the tumour. PMID:19960152
Kirm, M.; Nagirnyi, V.; Feldbach, E.; De Grazia, M.; Carre, B.; Merdji, H.; Guizard, S.; Geoffroy, G.; Gaudin, J.; Fedorov, N.; Martin, P.; Vasil'ev, A.; Belsky, A. [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Service des Photons Atomes et Molecules, CEA/Iramis, 91191 Gif sur Yvette (France); Laboratoire des Solides Irradies, CEA/Iramis, CNRS and Ecole Polytechnique, 91128 Palaiseau (France); European XFEL, Notkestrasse 85, 22607 Hamburg (Germany); Laboratoire CELIA, CNRS, CEA et Universite de Bordeaux I, 33400 Talence (France); Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS, UMR5620, Universite Lyon 1, Villeurbanne F-69622 (France)
2009-06-15
Exciton-exciton interaction is experimentally revealed and quantitatively analyzed in a wide band-gap scintillator material CdWO{sub 4}. Under high-intensity femtosecond vacuum ultraviolet excitation, the CdWO{sub 4} luminescence is quenched, while its decay becomes essentially nonexponential. We propose an analytical model, which successfully reproduces the decay kinetics recorded in a wide range of excitation densities. The dipole-dipole interaction between excitons leading to their nonradiative decay is shown to be the main cause of a nonproportional response common for many scintillators.
as evidence for exciton condensation L. V. Butov and A. I. Filin Institute of Solid State Physics, Russian to the long lifetime of indirect interwell excitons, exciton condensation analogous to the Bose- Einstein condensation of bosons is expected to occur in coupled quantum wells CQW's . The critical con- ditions
Wan, Yan; Guo, Zhi; Zhu, Tong; Yan, Suxia; Johnson, Justin; Huang, Libai
2015-10-01
Singlet fission presents an attractive solution to overcome the Shockley-Queisser limit by generating two triplet excitons from one singlet exciton. However, although triplet excitons are long-lived, their transport occurs through a Dexter transfer, making them slower than singlet excitons, which travel by means of a Förster mechanism. A thorough understanding of the interplay between singlet fission and exciton transport is therefore necessary to assess the potential and challenges of singlet-fission utilization. Here, we report a direct visualization of exciton transport in single tetracene crystals using transient absorption microscopy with 200?fs time resolution and 50?nm spatial precision. These measurements reveal a new singlet-mediated transport mechanism for triplets, which leads to an enhancement in effective triplet exciton diffusion of more than one order of magnitude on picosecond to nanosecond timescales. These results establish that there are optimal energetics of singlet and triplet excitons that benefit both singlet fission and exciton diffusion. PMID:26391077
Phase coherence and spectral functions in the two-dimensional excitonic systems
NASA Astrophysics Data System (ADS)
Apinyan, V.; Kope?, T. K.
2015-09-01
The nonlocal correlation mechanism between excitonic pairs is considered for a two dimensional exciton system. On the base of the unitary decomposition of the usual electron operator, we include the electron phase degrees of freedom into the problem of interacting excitons. Applying the path integral formalism, we treat the excitonic insulator state (EI) and the Bose-Einstein condensation (BEC) of preformed excitonic pairs as two independent problems. For the BEC of excitons the phase field variables play a crucial role. We derive the expression of the local EI order parameter by integrating out the phase variables. Then, considering the zero temperature limit, we obtain the excitonic BEC transition probability function, by integrating out the fermions. We calculate the normal excitonic Green functions for the conduction and valence band electrons and we derive the excitonic spectral functions, both analytically and numerically. Different values of the Coulomb interaction parameter are considered.
Exciton-dominant electroluminescence from a diode of monolayer MoS{sub 2}
Ye, Yu; Ye, Ziliang; Gharghi, Majid; Zhu, Hanyu; Wang, Yuan [NSF Nanoscale Science and Engineering Center, University of California, 3112 Etcheverry Hall, Berkeley, California 94720 (United States); Zhao, Mervin; Yin, Xiaobo; Zhang, Xiang, E-mail: xiang@berkeley.edu [NSF Nanoscale Science and Engineering Center, University of California, 3112 Etcheverry Hall, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States)
2014-05-12
In two-dimensional monolayer MoS{sub 2}, excitons dominate the absorption and emission properties. However, the low electroluminescent efficiency and signal-to-noise ratio limit our understanding of the excitonic behavior of electroluminescence. Here, we study the microscopic origin of the electroluminescence from a diode of monolayer MoS{sub 2} fabricated on a heavily p-type doped silicon substrate. Direct and bound-exciton related recombination processes are identified from the electroluminescence. At a high electron-hole pair injection rate, Auger recombination of the exciton-exciton annihilation of the bound exciton emission is observed at room temperature. Moreover, the efficient electrical injection demonstrated here allows for the observation of a higher energy exciton peak of 2.255?eV in the monolayer MoS{sub 2} diode, attributed to the excited exciton state of a direct-exciton transition.
Excitonic condensation in systems of strongly correlated electrons.
Kuneš, Jan
2015-08-26
The idea of exciton condensation in solids was introduced in the 1960s with the analogy of superconductivity in mind. While exciton supercurrents have been realised only in artificial quantum-well structures so far, the application of the concept of excitonic condensation to bulk solids leads to a rich spectrum of thermodynamic phases with diverse physical properties. In this review we discuss recent developments in the theory of exciton condensation in systems described by Hubbard-type models. In particular, we focus on the connections to their various strong-coupling limits that have been studied in other contexts, e.g. cold atoms physics. One of our goals is to provide a 'dictionary' that would allow the reader to efficiently combine results obtained in these different fields. PMID:26218828
Charge Transfer Excitons at van der Waals Interfaces.
Zhu, Xiaoyang; Monahan, Nicholas R; Gong, Zizhou; Zhu, Haiming; Williams, Kristopher W; Nelson, Cory A
2015-07-01
The van der Waals interfaces of molecular donor/acceptor or graphene-like two-dimensional (2D) semiconductors are central to concepts and emerging technologies of light-electricity interconversion. Examples include, among others, solar cells, photodetectors, and light emitting diodes. A salient feature in both types of van der Waals interfaces is the poorly screened Coulomb potential that can give rise to bound electron-hole pairs across the interface, i.e., charge transfer (CT) or interlayer excitons. Here we address common features of CT excitons at both types of interfaces. We emphasize the competition between localization and delocalization in ensuring efficient charge separation. At the molecular donor/acceptor interface, electronic delocalization in real space can dictate charge carrier separation. In contrast, at the 2D semiconductor heterojunction, delocalization in momentum space due to strong exciton binding may assist in parallel momentum conservation in CT exciton formation. PMID:26001297
Effect of correlation of local fluctuations on exciton coherence
Chen, Xin; Silbey, Robert J.
2010-01-01
Recent experimental studies have shown both oscillations of exciton populations and long lasting coherence in multichromophoric systems such as photosynthetic light harvesting systems and conjugated polymers. It has been suggested that this quantum effect is due to correlations of the fluctuations of site energies among the closely packed chromophores in the protein environment. In addition to these, there is the strong possibility of correlations between site energies and transfer matrix elements. In order to understand the role of such correlations we generalize the Haken–Strobl–Reineker (HSR) model to include the energetic correlations and the site diagonal-off-diagonal correlations in a systematic way. The extended HSR model in the exciton basis is also constructed and allows us to study the dynamics of the exciton populations and coherences. With the extended model, we can provide insight into how these correlations affect the evolution of the populations and coherences of excitons by comparing to the original HSR model with uncorrelated fluctuating environments.
Discovery of bound excitons in twisted bilayer graphene
NASA Astrophysics Data System (ADS)
Patel, Hiral; Park, Jiwoong; Graham, Matt
2015-03-01
Recent first principle Bethe-Salpeter simulations of twisted bilayer graphene (tBLG), predict that the unique geometry of tBLG's overlapping interlayer 2p orbitals produce a strong destructive coherence effect that results in stable, strongly bound exciton states. We directly probe the electronic dynamics of twisted bilayer graphene for the first time by developing a unique ultrafast confocal microscopy approach that combines transient absorption, and transmission electron microscopy. We find resonantly excited twisted bilayer regions display distinct, long-lived dynamics that are not present in 0o stacked bilayers. We further map out the electronic structure using one and two-photon transient absorption microscopy to observe signatures of both unbound and strongly bound excitonic states predicted by the theory. The probable existence of the stable excitons opens up the possibility of efficient carrier extraction by exploiting the unusual hybrid metallic-excitonic nature in twisted bilayer graphene systems.
Excitons in ultrathin organic-inorganic perovskite crystals
NASA Astrophysics Data System (ADS)
Yaffe, Omer; Chernikov, Alexey; Norman, Zachariah M.; Zhong, Yu; Velauthapillai, Ajanthkrishna; van der Zande, Arend; Owen, Jonathan S.; Heinz, Tony F.
2015-07-01
We demonstrate the formation of large sheets of layered organic-inorganic perovskite (OIPC) crystals, as thin as a single unit cell, prepared by mechanical exfoliation. The resulting two-dimensional OIPC nanosheets of 2.4 nm thickness are direct semiconductors with an optical band gap of 2.4 eV. They exhibit unusually strong light-matter interaction with an optical absorption as high as 25% at the main excitonic resonance, as well as bright photoluminescence. We extract an exciton binding energy of 490 meV from measurement of the series of excited exciton states. The properties of the excitons are shown to be strongly influenced by the changes in the dielectric surroundings. The environmental sensitivity of these ultrathin OIPC sheets is further reflected in the strong suppression of a thermally driven phase transition present in the bulk crystals.
Topologically protected excitons in porphyrin thin films
Saikin, Semion K.
he control of exciton transport in organic materials is of fundamental importance for the development of efficient light-harvesting systems. This transport is easily deteriorated by traps in the disordered energy landscape. ...