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 △Tc1K1 Superconductivity Brief History Characteristic of Superconductors Applications Important Superconductors What Is a Superconductor? A superconductor is an element, inter￾metallic 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 semi￾conductors), 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