What Is Bose-Einstein Condensation? De Broglie (1929 Nobel Prize winner) proposed that all matter is composed of waves.Their wavelengths are given by h mv PDF created with pdfFactory trial version www.pdffactory.com
What Is Bose-Einstein Condensation? De Broglie (1929 Nobel Prize winner) proposed that all matter is composed of waves. Their wavelengths are given by mv h l = PDF created with pdfFactory trial version www.pdffactory.com
What is Bose-Einstein condensation(BEC)? High Temperature T: thermal velocity v density d-3 "Billiard balls" Low AdBy Temperature T: De Broglie wavelength 入dB=h/mv T-1/2 "Wave packets" T-Tcrit Bose-Einstein Condensation 入dBed "Matter wave overlap" T=0: Pure Bose condensate "Giant matter wave" PDF created with pdfFactory trial version www.pdffactory.com
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Against Our Intuition?! vi *In most everyday matter,the de Broglie wavelength is much shorter than the distance separating the atoms.In this case,the wave nature of atoms cannot be noticed,and they behave as particles. The wave nature of atoms become noticeable when the de Broglie wavelength is roughly the same as the atomic distance. *This happens when the temperature is low enough,so that they have low velocities. PDF created with pdfFactory trial version www.pdffactory.com
Against Our Intuition?! ÙIn most everyday matter, the de Broglie wavelength is much shorter than the distance separating the atoms. In this case, the wave nature of atoms cannot be noticed, and they behave as particles. ÙThe wave nature of atoms become noticeable when the de Broglie wavelength is roughly the same as the atomic distance. ÙThis happens when the temperature is low enough, so that they have low velocities. PDF created with pdfFactory trial version www.pdffactory.com
oNot all particles can have BEC.This is related to the spin of the particles. The spin quantum number of a particle can be an integer or a half-integer. o Single protons,neutrons and electrons have a spin of They are called fermions.They cannot appear in the same quantum state.BEC cannot take place. o Some atoms contain an even number of fermions. They have a total spin of whole number.They are called bosons. o Bosons show strong "social"behaviour,and can have BEC. oExample:A 23Na atom has 11 protons,12 neutrons and 11 electrons. PDF created with pdfFactory trial version www.pdffactory.com
lNot all particles can have BEC. This is related to the spin of the particles. lThe spin quantum number of a particle can be an integer or a half-integer. lSingle protons, neutrons and electrons have a spin of ½. They are called fermions. They cannot appear in the same quantum state. BEC cannot take place. lSome atoms contain an even number of fermions. They have a total spin of whole number. They are called bosons. lBosons show strong “social” behaviour, and can have BEC. lExample: A 23Na atom has 11 protons, 12 neutrons and 11 electrons. PDF created with pdfFactory trial version www.pdffactory.com
Weakly interacting Weakly interacting Bose gas Fermi gas Mean-field theory BCS theory PDF created with pdfFactory trial version www.pdffactory.com
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