Tunnel Diode - Quantum Device Lab

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The Nobel Prize in Physics 1913 "for his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium" Leiden University, Leiden, the Netherlands Heike Kamerlingh Onnes b. 1853, d. 1926 The Nobel Prize in Physics 1987 "for their important break-through in the discovery of superconductivity in ceramic materials" IBM Zurich Research <strong>Lab</strong>oratory Rüschlikon, Switzerland J. Georg Bednorz Germany b. 1950 K. Alexander Müller Switzerland b. 1927 phys4.19 Page 7 Magnetic Effects - the critical temperature T c of a superconductor depends on the magnetic field (see figure) - in a type I superconductor the zero resistance state disappears altogether at a threshold critical field B c that depends on the material and the temperature - the maximum critical field occurs at zero temperature Superconductor T c and B c - because of the limited critical fields of type I superconductors they are of limited use in applications for field generation with coils material T c [K] B c [T] Al 1.18 0.015 Hg 4.15 0.041 In 3.41 0.028 Pb 7.19 0.080 Sn 3.72 0.031 Zn 0.85 0.005 phys4.19 Page 8
Meissner Effect - superconductors are perfectly diamagnetic - in a type I superconductor field below the critical field is expelled completely from the material when cooled through T c , see figure - in this Meissner effect screening currents are induced in the superconductor to cancel the externally applied field - this effect distinguishes a superconductor from an ideal conductor - type II superconductors below a first critical field Bc1 behave like type I superconductors, above B c1 and below a second critical field B c2 magnetic flux can penetrate into the material bringing it to a mixed superconducting/normal state - B c2 critical fields can be high so that these materials are interesting for generating magnetic fields material T c [K] B c2 [T] Nb 3 Sn 18.0 24.5 phys4.19 Page 9 Cooper Pairs and Bardeen-Cooper-Schrieffer (BCS) theory - in conventional superconductors electrons attract each other through deformations induced in the crystal lattice - materials with strong lattice vibrations are usually poor conductors at room temperature but maybe superconductors at low temperatures - a hint of this fact was first found when it was noted that the T c of different superconductors depends on the isotope used, e.g. T c ( 199 Hg) = 4.161 and T c ( 204 Hg) = 4.126 - two electrons (Fermions) form a single Cooper pair (Boson) with the electrons being in a singlet state with zero angular momentum - the binding energy E g , also called the gap energy, is typically on the order of 1 meV and can be measured using microwave absorption - at temperatures above 0 K some Cooper pairs are broken up by thermal fluctuations, the remaining electrons interact with the Cooper pairs effectively reducing the gap energy (see figure) phys4.19 Page 10
Page 1 and 2: Tunnel Diode - in a heavily doped p
Page 3: Field Effect Transistor (FET) - an

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