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| In [[condensed matter physics]], '''biexcitons''' are created from two free [[excitons]].
| | The main advantage of using the blog is that anyone can use the Word - Press blog and customize the elements in the theme regardless to limited knowledge about internet and website development. It is used by around 25% of all new websites, and there are more than 27 thousand plugins currently available. This is a service where people write articles using a specific keyword you have given them. Donor oocytes and menopausal pregnancy: Oocyte donation to women of advanced reproductive age: pregnancy results and obstetrical outcomes in patients 45 years and older. If you are happy with your new look then click "Activate 'New Theme'" in the top right corner. <br><br>These websites can be easily customized and can appear in the top rankings of the major search engines. If you have any issues with regards to in which and how to use [http://9ja.in/wordpress_dropbox_backup_738220 wordpress backup plugin], you can speak to us at our website. While direct advertising is limited to few spots in your site and tied to fixed monthly payment by the advertisers, affiliate marketing can give you unlimited income as long as you can convert your traffic to sales. This plugin is a must have for anyone who is serious about using Word - Press. You can up your site's rank with the search engines by simply taking a bit of time with your site. Now a days it has since evolved into a fully capable CMS platform which make it, the best platform in the world for performing online business. <br><br>This gives a clearer picture that online shoppers are familiar with the WP ecommerce system. By using Word - Press MLM websites or blogs, you and your companies presence on the internet can be created swiftly and simply. We can active Akismet from wp-admin > Plugins > Installed Plugins. Provide the best and updated information to the web searchers and make use of these wonderful free themes and create beautiful websites. If you have any questions on starting a Word - Press food blog or any blog for that matter, please post them below and I will try to answer them. <br><br>It has become a more prevalent cause of infertility and the fertility clinic are having more and more couples with infertility problems. php file in the Word - Press root folder and look for this line (line 73 in our example):. Normally, the Word - Press developers make a thorough research on your website goals and then ingrain the most suitable graphical design elements to your website. So, we have to add our social media sharing buttons in website. The popularity of Word - Press has increased the demand for Word - Press themes and these themes sells like hot cake on the internet. <br><br>He loves sharing information regarding wordpress, Majento, Drupal and Joomla development tips & tricks. I'm a large fan of using Word - Press to create pretty much any sort of web page. In simple words, this step can be interpreted as the planning phase of entire PSD to wordpress conversion process. This is because of the customization that works as a keystone for a SEO friendly blogging portal website. As with a terminology, there are many methods to understand how to use the terminology. |
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| == Formation of biexcitons ==
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| In quantum information and computation, it is essential to construct coherent combinations of quantum states.
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| The basic quantum operations can be performed on a sequence of pairs of physically distinguishable quantum bits and, therefore, can be illustrated by a simple four-level system.
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| In an optically driven system where the <math>| 0 1 \rangle</math> and <math>| 1 0 \rangle</math> states can be directly excited, direct excitation of the upper <math>| 1 1 \rangle</math> level from the ground state <math>| 0 0 \rangle</math> is usually forbidden and the most efficient alternative is coherent nondegenerate two-photon excitation, using <math>| 0 1 \rangle</math> or <math>| 1 0 \rangle</math> as an intermediate state.
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| <ref>G. Chen et al, "Biexciton Quantum Coherence in a Single Quantum Dot", ''Phys. Rev. Lett.'', '''88''' (11), 117901 (2002)</ref>
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| <ref>Xiaoqin Li et al, "An All-Optical Quantum Gate in a Semiconductor Quantum Dot", ''Science'', '''301''', 809 (2003)</ref>
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| [[Image:Biexciton levels.gif|thumb|Model for a single [[quantum dots]]. <math>E_b</math> is the biexciton binding energy]]
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| == Observation of biexcitons ==
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| Three possibilities of observing biexcitons exist:
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| <ref>G. Vektrais, "A new approach to the molecular biexciton theory", ''J. Chem. Phys.'', '''101''' (4), 3031 (1994)</ref>
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| (a) excitation from the one-[[exciton]] band to the biexciton band (pump-probe experiments);
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| (b) two-photon absorption of light from the ground state to the biexciton state;
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| (c) [[luminescence]] from a biexciton state made up from two free [[excitons]] in a dense [[exciton]] system.
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| == Binding energy of biexcitons ==
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| The biexciton is a [[quasi-particle]] formed from two [[excitons]], and its energy is expressed as
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| :<math>E_{b} = 2 E_{X} - E_{XX}</math> | |
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| where <math>E_{XX}</math> is the biexciton energy, <math>E_{X}</math> is the [[exciton]] energy, and
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| :<math>E_{b}</math> is the biexciton binding energy.
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| When a biexciton is annihilated, it disintegrates into a free [[exciton]] and a photon. The energy of the photon is smaller than that of the biexciton by the biexciton binding energy,
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| so the biexciton [[luminescence]] peak appears on the low-energy side of the [[exciton]] peak.
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| The biexciton binding energy in semiconductor [[quantum dots]] has been the subject of extensive theoretical study. Because a biexciton is a composite of two electrons and two holes, we must solve a four-body problem under spatially restricted conditions. The biexciton binding energies for CuCl [[quantum dots]], as measured by the site selective [[luminescence]] method, increased with decreasing [[quantum dot]] size. The data were well fitted by the function
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| :<math>B_{XX} = \frac{c_1}{a^2} + \frac{c_2}{a} + B_{bulk}</math>
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| where <math>B_{XX}</math> is biexciton binding energy, <math>a</math> is the radius of the [[quantum dots]], <math>B_{bulk}</math> is the binding energy of bulk crystal, and <math>c_1</math> and <math>c_2</math> are fitting parameters.
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| <ref>S. Park et al, "Fabrication of CuCl Quantum Dots and the Size Dependence of the Biexciton Binding Energy", ''Journal of the Korean Physical Society'', '''37''' (3), 309-312 (2000)</ref>
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| === A simple model for describing binding energy of biexcitons ===
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| In the effective-mass approximation, the [[Hamiltonian (quantum mechanics)|Hamiltonian]] of the system consisting of two electrons (1, 2) and two holes (a, b) is given by
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| :<math>H_{XX} = - \frac{\hbar^2}{2 m_e^*} ({\nabla_1}^2 + {\nabla_2}^2) - \frac{\hbar^2}{2 m_h^*} ({\nabla_a}^2 + {\nabla_b}^2) + V</math>
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| where <math>m_e^*</math> and <math>m_h^*</math> are the effective masses of electrons and holes, respectively, and
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| :<math>V = V_{12} - V_{1a} - V_{1b} - V_{2a} - V_{2b} + V_{ab}</math>
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| where <math>V_{ij}</math> denotes the [[Coulomb interaction]] between the charged particles <math>i</math> and <math>j</math> (<math>i, j = 1, 2, a, b</math> denote the two electrons and two holes in the biexciton) given by
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| :<math>V_{ij} = \frac{e^2}{\epsilon |\mathbf{r}_i - \mathbf{r}_j|}</math>
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| where <math>\epsilon</math> is the dielectric constant of the material.
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| Denoting <math>\mathbf{R}</math> and <math>\mathbf{r}</math> are the c.m. coordinate and the relative coordinate of the biexciton, respectively, and <math>M = m_e^* + m_h^*</math> is the [[Effective mass (solid-state physics)|effective mass]] of the [[exciton]], the Hamiltonian becomes
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| :<math>H_{XX} = - \frac{\hbar^2}{4 M} {\nabla_R}^2 - \frac{\hbar^2}{M} {\nabla_r}^2 - \frac{\hbar^2}{2 \mu} ({\nabla_{1a}}^2 + {\nabla_{2b}}^2) + V</math>
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| where <math>1/\mu = 1/{m_e^*} + 1/{m_h^*}</math>; <math>{\nabla_{1a}}^2</math> and <math>{\nabla_{2b}}^2</math> are the Laplacians with respect to relative coordinates between electron and hole, respectively.
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| And <math>{\nabla_r}^2</math> is that with respect to relative coordinate between the c. m. of [[excitons]], and <math>{\nabla_R}^2</math> is that with respect to the c. m. coordinate <math>\mathbf{R}</math> of the system.
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| In the units of the [[exciton]] Rydberg and [[Bohr radius]], the Hamiltonian can be written in dimensionless form
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| :<math>H_{XX} = - ({\nabla_{1a}}^2 + {\nabla_{2b}}^2) - {2 \sigma}{(1 + \sigma)^2} {\nabla_r}^2 + V </math> | |
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| where <math>\sigma = {m_e^*}/{m_h^*}</math> with neglecting kinetic energy operator of c. m. motion. And <math>V</math> can be written as
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| :<math>V = 2 (\frac{1}{r_{12}} - \frac{1}{r_{1a}} - \frac{1}{r_{1b}} - \frac{1}{r_{2a}} - \frac{1}{r_{2b}} + \frac{1}{r_{ab}})</math>
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| To solve the problem of the bound states of the biexciton complex, it is required to find the wave functions <math>\psi</math> satisfying the wave equation
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| :<math>H_{XX} \psi = E_{XX} \psi</math>
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| If the eigenvalue <math>E_{XX}</math> can be obtained, the binding energy of the biexciton can be also acquired
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| :<math>E_{b} = 2 E_{X} - E_{XX}</math>
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| where <math>E_{b}</math> is the binding energy of the biexciton and <math>E_{X}</math> is the energy of [[exciton]].
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| <ref>J. Liu et al, "Binding Energy of biexcitons in Two-Dimensional Semiconductors", ''Chin. Phys. Lett.'', '''15''' (8), 588 (1998)</ref>
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| === Binding energy in nanotubes ===
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| Biexcitons with bound complexes formed by two [[excitons]] are predicted to be surprisingly stable for [[carbon nanotube]] in a wide diameter range.
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| Thus, a biexciton binding energy exceeding the inhomogeneous [[exciton]] line width is predicted for a wide range of nanotubes.
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| The biexciton binding energy in carbon nanotube is quite accurately approximated by an inverse dependence on <math>r</math>, except perhaps for the smallest values of <math>r</math>.
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| :<math>E_{XX} \approx \frac{0.195 eV}{r}</math>
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| The actual biexciton binding energy is inversely proportional to the physical nanotube radius.
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| <ref>T. G. Perdersen et al, "Stability and Signatures of biexcitons in Carbon nanotubes", ''Nanolett.'', '''5''' (2), 291 (2005)</ref>
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| Experimental evidence of biexcitons has yet to be found.
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| === Binding energy in CuCl QDs ===
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| The binding energy of biexcitons increase with the decrease in their size and its size dependence and bulk value are well represented by the expression
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| :<math>\frac{78}{{a^*}^2} + \frac{52}{{a^*}} + 33</math> (meV)
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| where <math>a^*</math> is the effective radius of microcrystallites in a unit of nm. The enhanced [[Coulomb interaction]] in microcrystallites still increase the biexciton binding energy in the large-size regime, where the quantum confinement energy of [[excitons]] is not considerable.
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| <ref>Y. Masumoto et al, "Biexciton binding energy in CuCl quantum dots", ''Phys. Rev. B'', '''50''' (24), 18658 (1994)</ref>
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| == References ==
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| {{reflist|2}}
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| [[Category:Condensed matter physics]]
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| [[Category:Spintronics]]
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| [[Category:Quasiparticles]]
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The main advantage of using the blog is that anyone can use the Word - Press blog and customize the elements in the theme regardless to limited knowledge about internet and website development. It is used by around 25% of all new websites, and there are more than 27 thousand plugins currently available. This is a service where people write articles using a specific keyword you have given them. Donor oocytes and menopausal pregnancy: Oocyte donation to women of advanced reproductive age: pregnancy results and obstetrical outcomes in patients 45 years and older. If you are happy with your new look then click "Activate 'New Theme'" in the top right corner.
These websites can be easily customized and can appear in the top rankings of the major search engines. If you have any issues with regards to in which and how to use wordpress backup plugin, you can speak to us at our website. While direct advertising is limited to few spots in your site and tied to fixed monthly payment by the advertisers, affiliate marketing can give you unlimited income as long as you can convert your traffic to sales. This plugin is a must have for anyone who is serious about using Word - Press. You can up your site's rank with the search engines by simply taking a bit of time with your site. Now a days it has since evolved into a fully capable CMS platform which make it, the best platform in the world for performing online business.
This gives a clearer picture that online shoppers are familiar with the WP ecommerce system. By using Word - Press MLM websites or blogs, you and your companies presence on the internet can be created swiftly and simply. We can active Akismet from wp-admin > Plugins > Installed Plugins. Provide the best and updated information to the web searchers and make use of these wonderful free themes and create beautiful websites. If you have any questions on starting a Word - Press food blog or any blog for that matter, please post them below and I will try to answer them.
It has become a more prevalent cause of infertility and the fertility clinic are having more and more couples with infertility problems. php file in the Word - Press root folder and look for this line (line 73 in our example):. Normally, the Word - Press developers make a thorough research on your website goals and then ingrain the most suitable graphical design elements to your website. So, we have to add our social media sharing buttons in website. The popularity of Word - Press has increased the demand for Word - Press themes and these themes sells like hot cake on the internet.
He loves sharing information regarding wordpress, Majento, Drupal and Joomla development tips & tricks. I'm a large fan of using Word - Press to create pretty much any sort of web page. In simple words, this step can be interpreted as the planning phase of entire PSD to wordpress conversion process. This is because of the customization that works as a keystone for a SEO friendly blogging portal website. As with a terminology, there are many methods to understand how to use the terminology.