Have a Problem You Can Solve That’s Not a Problem, It’s an Opportunity Have a Problem You Can’t Solve That is an Even Greater Opportunity ========= The Duckman
Prof. D.G. Kuberkar Department of Physics Saurashtra University RAJKOT - 360 005, INDIA E-mail: email@example.com
Historical Landmarks in Superconductivity • 1911 Kamerlingh Onnes discovered superconductivity in Hg at Tc=4 K • 1913 Kamerlingh Onnes won the Nobel Prize in Physics • 1933 Meissner and Ochsenfeld discovered the Meissner Effect • 1941 Superconductivity in Nb nitride at Tc=16 K • 1953 Superconductivity reported in V 3 Si at Tc=17.5K • 1957 Microscopic BCS theory of superconductivity • 1962 The Josephson effect is predicted based on the BCS theory • 1962 Development of first superconducting wire (Westinghouse) • 1972 Bardeen, Cooper & Schrieffer win the Nobel Prize in Physics • 1973 Josephson wins the Nobel Prize in Physics • 1986 Müller and Bednorz (IBM-Zurich) discovered High Temperature Superconductivity in La-Ba-Cu-O at Tc=35K • 1987 Müller and Bednorz win the Nobel Prize in Physics • 1987 Superconductivity found in YBCO copper oxide at Tc=92K !!! • 1988 Tc is pushed to 120K in a ceramic containing Ca and Tl • 1993 Superconductivity in HgBa 2 Ca 2 Cu 3 O 8 at Tc=133K
<ul><li>Physical Properties </li></ul><ul><li>Critical Temperature </li></ul><ul><li>Critical Magnetic field </li></ul><ul><li>Meissner Effect </li></ul><ul><li>Isotope effect </li></ul>
What is superconductor? <ul><li>Superconductors have two outstanding features: </li></ul><ul><li>1) Zero electrical resistivity . </li></ul><ul><li>This means that an electrical current in a superconducting ring continues indefinitely until a force is applied to oppose the current. </li></ul><ul><li>2) The magnetic field inside a bulk sample is zero (the Meissner effect) . </li></ul><ul><li>When a magnetic field is applied current flows in the outer skin of the material leading to an induced magnetic field that exactly opposes the applied field. </li></ul><ul><li>The material is strongly diamagnetic as a result. </li></ul><ul><li>In the Meissner effect experiment, a magnet floats above the surface of the superconductor </li></ul>
WHAT IS SUPERCONDUCTIVITY ? For some materials, the resistivity vanishes at some low temperature: they become superconducting . Superconductivity is the ability of certain materials to conduct electrical current with no resistance. Thus, superconductors can carry large amounts of current with little or no loss of energy. Type I superconductors: pure metals, have low critical field Type II superconductors: primarily of alloys or inter-metallic compounds.
The Critical Field <ul><li>An important characteristic of all superconductors is that the superconductivity is "quenched" when the material is exposed to a sufficiently high magnetic field. </li></ul><ul><li>This magnetic field, H c , is called the critical field. </li></ul><ul><li>Type II superconductors have two critical fields. </li></ul><ul><li>The first is a low-intensity field, H c1 , which partially suppresses the superconductivity. </li></ul><ul><li>The second is a much higher critical field, H c2 , which totally quenches the superconductivity. </li></ul>
The Critical Field <ul><li>The critical field, H C , that destroys the superconducting effect obeys a parabolic law of the form: </li></ul><ul><li>where H o = constant, T = temperature, T c = critical temperature. </li></ul><ul><li>In general, the higher T c , the higher H c . </li></ul>
MEISSNER EFFECT B T > T C T < T C B When you place a superconductor in a magnetic field, the field is expelled below T C . Magnet Superconductor Currents i appear, to cancel B. i x B on the superconductor produces repulsion.
Types I Superconductors <ul><li>There are 30 pure metals which exhibit zero resistivity at low temperature. </li></ul><ul><li>They are called Type I superconductors ( Soft Superconductors ). </li></ul><ul><li>The superconductivity exists only below their critical temperature and below a critical magnetic field strength. </li></ul>
Type I Superconductors Mat. T c (K) Be 0 Rh 0 W 0.015 Ir 0.1 Lu 0.1 Hf 0.1 Ru 0.5 Os 0.7 Mo 0.92 Zr 0.546 Cd 0.56 U 0.2 Ti 0.39 Zn 0.85 Ga 1.083 Mat. T c (K) Gd* 1.1 Al 1.2 Pa 1.4 Th 1.4 Re 1.4 Tl 2.39 In 3.408 Sn 3.722 Hg 4.153 Ta 4.47 V 5.38 La 6.00 Pb 7.193 Tc 7.77 Nb 9.46
Type II Superconductors <ul><li>Starting in 1930 with lead-bismuth alloys, were found which exhibited superconductivity; they are called Type II superconductors ( Hard Superconductors ). </li></ul><ul><li>They were found to have much higher critical fields and therefore could carry much higher current densities while remaining in the superconducting state. </li></ul>
Compound T C (K) PbMo 6 S 8 12.6 SnSe 2 (Co(C 5 H 5 ) 2 ) 0.33 6.1 K 3 C 60 19.3 Cs 3 C 60 40 (15 kbar applied pressure) Ba 0.6 K 0.4 BiO 3 30 La l.85 Sr 0.l5 CuO 4 40 Nd l.85 Ce 0.l5 CuO 4 22 YBa 2 Cu 3 O 7 90 Tl 2 Ba 2 Ca 2 Cu 3 O 10 125 HgBa 2 Ca 2 Cu 3 O 8+d 133
 Critical temp of mercury with isotopic man 199.5 is 4.1850K. Calculate its critical temperature when its isotopic mass changes to 203.4
 Calculate J C for 1 mm dia wire of bad at (a) 4.2 K and (b) 7K A parabolic dependence of H C upon T may be assumed. Given T C for lead is 7.18 K and H C for lead is 6.5 × 10 4 amp/meter.
<ul><li>Magnetic Sensors </li></ul><ul><li>Gradiometers </li></ul><ul><li>Oscilloscopes </li></ul><ul><li>Decoders </li></ul><ul><li>Analogue to Digital Converters </li></ul><ul><li>Samplers </li></ul><ul><li>Oscillators </li></ul><ul><li>Microwave Amplifiers </li></ul><ul><li>Sensors for Biomedical Scientific and Defense Purposes </li></ul><ul><li>Digital Circuit Development for Integrated Circuits </li></ul><ul><li>Microprocessors </li></ul><ul><li>Random Access Memories </li></ul>
APPLICATIONS: Medical The superconducting magnet coils produce a large and uniform magnetic field inside the patient's body. MRI (Magnetic Resonance Imaging) scans produce detailed images of soft tissues.
APPLICATIONS: Power Superconducting Transmission Cable From American Superconductor The cable configuration features a conductor made from HTS wires wound around a flexible hollow core. Liquid nitrogen flows through the core, cooling the HTS wire to the zero resistance state. The conductor is surrounded by conventional dielectric insulation. The efficiency of this design reduces losses.
Cooper Pairs Breaking of Cooper Pairs Due to Magnetic Fields
APPLICATIONS: Superconducting Magnetic Levitation The Yamanashi MLX01MagLev Train The track are walls with a continuous series of vertical coils of wire mounted inside. The wire in these coils is not a superconductor. As the train passes each coil, the motion of the superconducting magnet on the train induces a current in these coils, making them electromagnets. The electromagnets on the train and outside produce forces that levitate the train and keep it centered above the track. In addition, a wave of electric current sweeps down these outside coils and propels the train forward.