S perconductivity What Is a Superconductor? R Brief History A superconductor is an element, inter- a Characteristic of Superconductor metallic alloy, or compound that wi electricity without resistance below a a Important Superconductors temperature. e Once set in motion. electrical current will superconducting material- making it the closest thing to perpetual motion in nature. e Superconductivity is a"macroscopic quantum Superconductivity Superconductors Compared to Other Conductors tThe temperature dependent Fewer electrons are excited from the change between superconducting and normal conductors), into the acceptor band (in type ext dThe temperature at which valence band to the conductio this drastic decrease Metol n intrinsic semiconductors) ductors show a decrease in superconductor. Fewer vibrations result in a more ro. This is the Superconducting Critical Temperature Tc Three Temperatures the temperature at which the system(sample) L Moonset)onset transition onducting state into a superconducting stat characterized by zero de electrical resistivity lation of normal resistance R a Tdmin)-the middle transition Dormal d the oint that resistance drops to rn P 骂T。 the temperature when resistance drops to zero For YBa Cu0 42K .T=905K and △Tc1K
1 Superconductivity Brief History Characteristic of Superconductors Applications Important Superconductors What Is a Superconductor? A superconductor is an element, intermetallic alloy, or compound that will conduct electricity without resistance below a certain temperature. Once set in motion, electrical current will flow forever in a closed loop of superconducting material –making it the closest thing to perpetual motion in nature. Superconductivity is a “macroscopic quantum phenomenon”. Superconductivity Materials become superconductors below some critical temperature, TC. The temperature dependent change between superconducting and normal conduction is abrupt! The temperature at which this drastic decrease in resistance occurs is the critical temperature of a superconductor. Abrupt change! Resistance goes to zero. This is the critical temperature. Superconductors Compared to Other Conductors Semiconductors show a increase in resistance as the temperature is decreased. Fewer electrons are excited from the donor band (in n-type extrinsic semiconductors), into the acceptor band (in p-type extrinsic semiconductors), and from the valence band to the conduction band (in intrinsic semiconductors). Metal conductors show a decrease in resistance as the temperature is decreased. Fewer vibrations result in a more ‘perfect’lattice. Superconducting Critical Temperature Tc = the temperature at which the system (sample) undergoes a phase transition from a normal conducting state into a superconducting state, characterized by zero dc electrical resistivity. normal superconductor Three Temperatures Tc(onset) — onset transition temperature, when the R-T curve begin to departure from the linear relation of normal resistance Rn. Tc(min) — the middle transition temperature, which correspond the point that resistance drops to Rn/2. T¥ — the temperature when resistance drops to zero. For YBa2Cu3O7-d : •Tc(onset)=95K， •Tc(min)=91K •T¥=90.5K and △Tc=1K
Discovery of Superconductivity Mercury Superconducting Transition by H. Kamerlingh Onnes (1911) historically the first to show superconduct that its critical nagnetic 019 T. so the amount =42K carry is also limited. I How the Superconductivity Was First Discovered? Superconductive Element m2m画mPHx 图图 atmosphere and the temperature increased. It was ThEN that they activity was first discovered. (Not on cooling article, there is a description that "the tap 出出其 Li: Element With the Highest Tc Materials Transition temp. (K 270°C) superconducting Nb3sn 238(249C the lightest metal of 25(148°C 135~165K ition temperature(Te of 20 K at 48GPa. This elements with low Ra reve a very high ggests that metallie hydrogen mbers will have high transition
2 Mercury Superconducting Transition Mercury was historically the first to show superconductivity. Its practical usefulness is limited by the fact that its critical magnetic field is only 0.019 T, so the amount of electric current it can carry is also limited. Discovery of Superconductivity by H. Kamerlingh Onnes (1911) How the Superconductivity Was First Discovered? (This story was told by Prof. P. Kes of Leiden in 1993 at a NATO summer school in Erice, Italy.) There were two assistants working for Onnes, Horst and Dorshman (these names need to be confirmed). The son of Dorshman told Prof. Kes in 1992 the story of the discovery of superconductivity his father used to tell to his son. They were studying the resistance of mercury with a resistance bridge. One day, by pumping on liquid He in the cryostat, they realized that for some reason the resistance bridge did not seem to be working properly because it was not giving any signal. After they stopped the pump, by mistake, they forgot to re-open the valve to release the evaporated He gas from the cryostat. The pressure increased beyond atmosphere and the temperature increased. It was THEN that they noticed that the resistance of mercury recovered! This is how the superconductivity was first discovered. (Not on cooling, but on warming mercury!) In the Leiden Communication article, there is a description that “the tap (valve) Eak2”was used to increase the temperature. Superconductive Elements Table from Burns A15 compounds alloy Materials Transition temp.(K) Al 1.2 (-272°C) Sn 3.4 (-270°C) Pb 7.2 (-266°C) Nb3Sn 23.8 (-249°C) LaSrCuO 40 (-233°C) YBaCuO 90 (-178°C) BiSrCaCuO 107 (-166°C) TlBaCaCuO 125 (-148°C) HgBaCaCuO 135 ~ 165K Li: Element With the Highest TC K. Shimizu et al., Nature 2002, 419, 587. Superconductivity at high temperatures is expected in elements with low atomic numbers. For example, it has been predicted that when hydrogen is compressed to its dense metallic phase (at pressures exceeding 400 GPa), it will become superconducting with a transition temperature above room temperature. Such pressures are difficult to produce in a laboratory setting, so the predictions are not easily confirmed. Under normal conditions lithium is the lightest metal of all the elements, and may become superconducting at lower pressures. In this work, Li shows superconducting at pressures greater than 30 GPa, with a pressure dependent transition temperature (Tc) of 20 K at 48GPa. This is the highest observed Tc of any element; it confirms the expectation that elements with low atomic numbers will have high transition temperatures, and suggests that metallic hydrogen will have a very high Tc
Superconductivity of Iron Fe) re dependence of the Superconductivity 908, Kammerlingh-Onnes experiments on liquid He(a GPa. A 10% drop in resistivity perconductivity at around 1.5 K. Hg resistance: 0.08 ohm 5K to 0.000003 ohm @ 4.2K Shimizuet al Nature 2001. 112316 The temperature dependence of the magnetization 986, G. Bednorz, K. H Muller (BM,. La-Ba-Cu-O Oxide: Te=35K expanded in the upr K. The lower inset shows the disappearance of the Meissner signal in iron when the pressure is decreased to 3.5 GPain the b c.c. phase. in La.0(1986tp Discovery of Superconduct Brief History of Superconductivity b1911 Kamerlingh Onnes discovered superconductivity in Hg b1913 Kamerlingh Onnes won the Nobel Prize in Physics 21953 Superconductivity was reported in V Si at Tc=175K 21972 Bardee, Cooper& Schrieffer won the Nobel Prize 86 Muller and Bednorz (IBM-Zzurich) 21987 Muller and Bednorz won the Nobe forefront of research 1988 Te was pushed to 120K in a ceramic containing Ca and a1993 Hg Ca Cu, Og was found to superconduct at Te=133K 39K Superconductivity in MgB2 Characteristics of Superconductors In MgB, hexa Ing or uI until a force is appley rs., ring continues in centered on the hexagons duced magnetic field ure2001,410,63 exactly opposes the applied field. The material is strongly MgB, like graphite, has strong o bonds in the carbon atoms, not all the a the boron planes has a much stronger effec ate a magnet above the of strong electro surface of the superconductor
3 Superconductivity of Iron (Fe) Shimizu et al., Nature 2001, 412, 316 •Temperature dependence of the electrical resistivity of iron at 25 GPa. A 10% drop in resistivity indicates the onset of superconductivity at around 1.5 K. The temperature dependence of the magnetization of iron under pressure obtained by cooling the sample at a magnetic field of 130 G. The signal at 21 GPa (the area enclosed by the dotted line is expanded in the upper inset) shows the appearance of diamagnetism at temperatures below 1.7 K, which is confirmed by the signal given by tin at 2.7 K. The lower inset shows the disappearance of the Meissner signal in iron when the pressure is decreased to 3.5 GPa in the b.c.c. phase. 1908, Kammerlingh-Onnes experiments on liquid He ( a few ml) Hg resistance: 0.08 ohm @ 5K to 0.000003 ohm @ 4.2 K 1986, J. G. Bednorz , K. H. Muller (IBM) La-Ba-Cu-O Oxide: Tc = 35 K Superconductivity Discovery of Superconductivity in La-Ba-Cu-O (1986) “At the extreme forefront of research in superconductivity is the empirical search for new materials.”(1983) Brief History of Superconductivity 1911 Kamerlingh Onnes discovered superconductivity in Hg at Tc=4K 1913 Kamerlingh Onnes won the Nobel Prize in Physics 1933 Meissner and Ochsenfeld discovered the Meissner Effect 1941 Superconductivity was reported in Nb nitride at Tc=16K 1953 Superconductivity was reported in V3Si at Tc=17.5K 1962 Development of first superconducting wire 1972 Bardee, Cooper & Schrieffer won 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 won the Nobel Prize in Physics 1987 Superconductivity was found in YBCO copper oxide at Tc=92K !!! 1988 Tcwas pushed to 120K in a ceramic containing Ca and Tl 1993 HgBa2Ca2Cu3O8 was found to superconduct at Tc=133K 39K Superconductivity in MgB2 In MgB2 , hexagonal honeycomb layers of boron atoms alternate with layers of magnesium atoms, centered on the hexagons. MgB2 , like graphite, has strong s bonds in the planes and weak p bonds between them, but since boron atoms have fewer electrons than carbon atoms, not all the s bonds in the boron planes are occupied. And because not all the s bonds are filled, lattice vibration in the boron planes has a much stronger effect, resulting in the formation of strong electron pairs confined to the planes. Nagamatsu et al. Nature 2001, 410, 63 Characteristics of Superconductors Loss of Resistance! ¾¾ Zero electrical resistivity. This means that an electrical current in a superconducting ring continues indefinitely (at least for a very long time ~ years … ), without dissipation through the ring or until a force is applied to oppose the current. MeissnerEffect! ¾¾ Superconductors expel all magnetic flux in a process called the Meissner effect. The magnetic field inside a bulk sample is zero. 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. The material is strongly diamagnetic as a result. A superconductor excludes magnetic flux. In this experiment, this is used to levitate a magnet above the surface of the superconductor
Meissner Effect Two Easy Experiments Showing Meissner Effect CWhen a superconducting sample is cooled below the magnetic field (ie. lines of the induction b)are quid nitrogen is added to a reservoir beneath the superconductor. (The ushed out peroonductor is actually just out of of the cup )A maller magnet levitates about a A superconductor is a perfect diamagnet! centimeter above it B Three Barriers of Superconducting Materials Critical Magnetic Field wA sufficiently strong external magnetic field can destroy the superconducting state 素 Jc High Tc(critical temperature) ohase diagram of I experimental High Je (critical current density) Application Uses of Superconductors [Levitation wire MagLev trains have been under development in Japan for the past two decades rgy loss by ahe train floats above the track using superconducting High voltage needed Wire with superconduct magnet dThere's no friction between the train and the"rail so les E Wire with superconductor energy is lost and the train can reach much higher speeds No energy loss No high voltage needed. 戀 Storage of electricity. Cut end of superconductor
4 Meissner Effect When a superconducting sample is cooled below Tc in the presence of an external magnetic field, the magnetic field (i.e., lines of the induction B) are pushed out. A superconductor is a perfect diamagnet ! Two Easy Experiments Showing Meissner Effect Liquid nitrogen is added to a reservoir beneath the superconductor. (The superconductor is actually just out of sight beneath the rim of the cup.) A smaller magnet levitates about a centimeter above it. Three Barriers of Superconducting Materials High Tc (critical temperature) High Hc (critical magnetic field) High Jc (critical current density) Critical Magnetic Field A sufficiently strong external magnetic field can destroy the superconducting state critical magnetic field phase diagram of Itype superconductor experimental data Application wire Existing wire - Energy loss by resistance - High voltage needed Wire with superconductor - No energy loss - No high voltage needed. - Storage of electricity. Cut end of superconductor wire Wire with superconductor Uses of Superconductors [Levitation] “MagLev”trains have been under development in Japan for the past two decades The train floats above the track using superconducting magnets. There’s no friction between the train and the “rail”so less energy is lost and the train can reach much higher speeds
Application Magnetic levitating Vehicle Josephson devic principle SQUID Superconducting QUantum Interference Device train conducting loop interrupted in 2 places by sephson junctions When sufficient electrical current is conducte proportional to the strength of any nearby magnetic field. car with superconductor? Uses of Superconductors Application IMagnetic Resor per computer doctors to see what is happening inside the body without Without superconductor I directly performing surgery large heat, large electric power eld of mRI as the superconducting magnet can be smaller and more efficient than an equivalent conventional magnet. no heat, small electric power use Application-Particle Colliders Hi gh Temperature Superconductors Particle colliders are v running tracks that are cUprate superconductors have been the focus of researcher because they conduct at relatively high temperature e ight before they are collided with one angotherspeed of The collision usually nough energy to split Particle colliders were used to discover many sub They do this by cycling the particle using magnetic fields, continually inereasing the speed of the particle tn the Y, B, Cu, O compounds: Y, Ba, and O have xidation states of +3, +2, and-2, respectively. tThis results in copper having mixed oxidation states +2 a similar result is obtained for the other materials tTheir structures are related to that of perovskite(CaTiO
5 Application Magnetic levitating Vehicle •principle •car with superconductor? •train Application Josephson device SQUID (Superconducting QUantum Interference Device ) A superconducting loop interrupted in 2 places by Josephson junctions. When sufficient electrical current is conducted across the squid body, a voltage is generated proportional to the strength of any nearby magnetic field. Uses of Superconductors [Magnetic Resonance Imaging] MRI is a technique developed in the 1940s that allows doctors to see what is happening inside the body without directly performing surgery. The development of superconductors has improved the field of MRI as the superconducting magnet can be smaller and more efficient than an equivalent conventional magnet. Application Super computer - Without superconductor : large heat, large electric power use - with superconductor : no heat, small electric power use ß Particle colliders are very large running tracks that are used to accelerate particles (i.e. electrons, positrons, hadrons and more) to speeds approaching the speed of light before they are collided with one another. –The collision usually possess enough energy to split the particles into smaller particles. –Particle colliders were used to discover many sub - nuclear particles such as taus and neutrinos. ß They do this by cycling the particle using magnetic fields, continually increasing the speed of the particle. Application ¾ Particle Colliders High Temperature Superconductors Cuprate superconductors have been the focus of researchers because they conduct at relatively high temperature (Tc > 77K). In the Y, Ba, Cu, O compounds: Y, Ba, and O have oxidation states of +3, +2, and -2, respectively. This results in copper having mixed oxidation states +2 and +3. A similar result is obtained for the other materials. Their structures are related to that of perovskite (CaTiO3 ). Compound Tc/K Compound Tc/K YBa2Cu 3O7 93 Tl 2CaBa2Cu 2O8 119 YBa2Cu 4O8 80 Tl 2Ca2 Ba2Cu 2O7 128 Y2 Ba4Cu 7O15 93 TlCaBa2 Cu2 O7 103 Bi2 CaSr2 Cu2O6 92 TlCa2B a2Cu 3O8 110 Bi2 Ca2S r2Cu3 O10 110 Tl 0.5Pb0.5Ca2S r2Cu 3O9 120