SUPERCONDUCTIVITY

&

NEW SUPERCONDUCTORS

PRESENTED BY

SUPRAVAT PRATIHAR

M.Sc. [Final Year]

2015-2016

DEPARTMENT OF CHEMISTRY

C.M.D. P.G. COLLEGE

BILASPUR UNIVERSITY

Superconductors

An element, inter-metallic alloy, or compound that will

conduct electricity without resistance below a certain

temperature, magnetic field, and applied current.

Definition of Superconductor:

1911: discovery of superconductivity

Whilst measuring the resistivity of

“pure” Hg he noticed that the electrical

resistance dropped to zero at 4.2K

Discovered by Kamerlingh Onnes

in 1911 during first low temperature

measurements to liquefy helium

In 1912 he found that the resistive

state is restored in a magnetic field or

at high transport currents

1913

A Brief History of Superconductors In 1911 superconductivity was first observed in mercury by Dutch physicist

Heike Kamerlingh Onnes of Leiden University. When he cooled it to the temperature of liquid helium, 4 degrees Kelvin, its resistance suddenly disappeared!

In 1933 Walter Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. This phenomenon is known as perfect diamagnetism and is often refe red to as the Meissnereffect.

Since then major developments have been made in both the discovery of higher temperature superconductors as well as progress in the theory of superconductivity. In 1957 the 1st major advancement in the theory was made by American physicists John Bardeen, Leon Cooper, and John Schrieffer. Their Theories of Superconductivity became known as the BCS theory - abbreviated for the first letter of each man's last name - and won them a Nobel prize in 1972. BCS theory explained superconductivity at temperatures close to absolute zero for elements and simple alloys. However, at higher temperatures and with different superconductor systems, the BCS theory has become inadequate to fully explain how superconductivity is occurring.

INTRODUCTION

The electrical resistivity of a metallic conductor decreases

gradually as temperature is lowered due to decrease of

vibrational resistance of atoms. In ordinary conductors,

such as copper or silver, this decrease is limited by

impurities and other defects. Even near absolute zero, a

real sample of a normal conductor shows some resistance.

In a superconductor, the resistance drops abruptly to zero

when the material is cooled below its critical temperature.

An electric current flowing through a loop

of superconducting wire can persist indefinitely with no

power source.

In a normal conductor, an electric current may be visualized

as a fluid of electrons moving across a heavy ionic lattice. The

electrons are constantly colliding with the ions in the lattice,

and during each collision some of the energy carried by the

current is absorbed by the lattice and converted into heat,

which is essentially the vibrational kinetic energy of the lattice

ions. As a result, the energy carried by the current is constantly

being dissipated. This is the phenomenon of electrical

resistance.

The situation is different in a superconductor. In a

conventional superconductor, the electronic fluid cannot be

resolved into individual electrons. Instead, it consists of

bound pairs of electrons known as Cooper pairs. This pairing

is caused by an attractive force between electrons from the

exchange of phonons.

The mechanism of superconduction is well-understood for low-temperature materials

but there is as yet no settled explanation of high-temperature superconductivity.The

central concept of low-temperature superconduction is the existence of a Cooper pair,

a pair of electrons that exists on account of the indirect electron–electron interactions

fostered by the nuclei of the atoms in the lattice. Thus, if one electron is in a particular

region of a solid, the nuclei there move toward it to give a distorted local structure (Fig.

20.68). Because that local distortion is rich in positive charge, it is favourable for a

second electron to join the first. Hence, there is a virtual attraction between the two

electrons, and they move together as a pair. The local distortion can be easily disrupted

by thermal motion of the ions in the solid, so the virtual attraction occurs only at very

low temperatures. A Cooper pair undergoes less scattering than an individual electron

as it travels through the solid because the distortion caused by one electron can attract

back the other electron should it be scattered out of its path in a collision. Because the

Cooper pair is stable against scattering, it can carry charge freely through the solid, and

hence give rise to superconduction. ATKINS’

PHYSICAL

CHEMISTRY.

Page-737

• In 1957, Bardeen, Cooper, and Schrieffer (BCS) theorized that

superconductivity was the result of electrons binding to form particles

called Cooper pairs

• The electrons exchange vibrational lattice energy called phonons which can

result in the electrons becoming attracted to one another

• Recently, antiferromagnetism has been linked to the explanation of high

temperature ceramic superconductivity

• By changing the chemical composition, BaFe2(As1-xPx)2 has been observed

to have an internal magnetic critical point

• As the composition is changed, antiferromagnetism decreases until it

disappears, resulting in superconductivity

(Top) Lattice of an antiferromagnet. The electron spins are

antiparallel, leading to cancellation of the magnetic field.

(Bottom) Cooper pair formation. Electrons bind during

superconductivity and create boson particles called Cooper pairs.

Basic Principles

• Below a critical temperature (Tc), the

resistance of a superconducting material

becomes almost zero causing current to

flow indefinitely and with no power loss

• No voltage difference is needed to

maintain a current.

• Above a current density,

superconductivity is lost in the material.

• A supercurrent can flow across an

insulating junction in what is called the

Josephson Effect. Cooper pairs can do

this due to quantum tunneling Critical temperature, current density, and magnetic field boundary

separating superconducting and normal conducting states.

Superconductivity can only occur within the teardrop figure.

Schematic of the

Josephson Effect; this

effect allows

electrons to jump

through insulators

In superconducting materials, the characteristics of superconductivity

appear when the temperature T is lowered below a critical

temperature Tc. The value of this critical temperature varies from

material to material. Conventional superconductors usually have

critical temperatures ranging from around 20 K to less than 1 K.

Solid mercury, for example, has a critical temperature of 4.2 K. As of

2009, the highest critical temperature found for a conventional

superconductor is 39 K for magnesium diboride (MgB2), although this

material displays enough exotic properties that there is some doubt

about classifying it as a "conventional" superconductor.

Cuprate superconductors can have much higher critical

temperatures: YBa2Cu3O7, one of the first cuprate superconductors to

be discovered, has a critical temperature of 92 K, and mercury-based

cuprates have been found with critical temperatures in excess of

130 K. The explanation for these high critical temperatures remains

unknown. Electron pairing due to phonon exchanges explains

superconductivity in conventional superconductors, but it does not

explain superconductivity in the newer superconductors that have a

very high critical temperature.

Similarly, at a fixed temperature below the critical

temperature, superconducting materials cease to

superconduct when an external magnetic field is applied

which is greater than the critical magnetic field. This is

because the Gibbs free energy of the superconducting

phase increases quadratically with the magnetic field while

the free energy of the normal phase is roughly independent

of the magnetic field. If the material superconducts in the

absence of a field, then the superconducting phase free

energy is lower than that of the normal phase and so for

some finite value of the magnetic field (proportional to the

square root of the difference of the free energies at zero

magnetic field) the two free energies will be equal and a

phase transition to the normal phase will occur.

Comparison of superconductor

and standard conductor in a

magnetic field. The

superconductor excludes itself

from the field while the field

passes through the conductor.

Superconductor Conductor

• The phenomena of expelling magnetic flux

experienced by superconductors is called

the Meissner Effect.

• The Meissner Effect can be understood as

perfect diamagnetism, where the magnetic

moment of the material cancels the external

field or M = - H.

• The critical field and temperature are

interdependent through:

Bc= B0[1-(T/Tc)2 ]

1933: Meissner-Ochsenfeld effect

Ideal conductor! Ideal diamagnetic!

Meissner effect

When a superconductor is placed in a weak

external magnetic field H, and cooled below its

transition temperature, the magnetic field is ejected. The

Meissner effect does not cause the field to be

completely ejected but instead the field penetrates the

superconductor but only to a very small distance,

characterized by a parameter λ, called the London

penetration depth, decaying exponentially to zero within

the bulk of the material. The Meissner effect is a

defining characteristic of superconductivity. For most

superconductors, the London penetration depth is on the

order of 100 nm.

• The strange magnetic

properties created by

superconductors can cause the

material to levitate in place

over a magnet

• The superconductor will

remain a certain distance from

the magnet but will not flip

over or reorient

• This video demonstrates this

phenomena and potential for

levitation applications

http://www.youtube.com/watch?v=6lmtbLu5nxw

Critical Temperatures of Conducting Materials• In most metals such as titanium,

copper, or lead, resistivity decreases

as temperature decreases

• However, the resistivity suddenly

drops to near zero at a critical

temperature (Tc)

• Metals and metal alloys have a

critical temperature of less than

about 20 K, which is extremely low

and difficult to achieve.

• Yttrium Barium Copper Oxide

(YBCO) has a critical temperature

of 92 K and others are even higher.

These temperatures can be achieved

by utilizing liquid nitrogen, a

relatively cheap coolant.

• Some metals become superconductors at extremely

low temperatures

• Some of these include mercury, lead, tin, aluminum,

lead, niobium, cadmium, gallium, zinc, and

zirconium

• Unfortunately, the critical temperatures are too low

for practical application

• For example, Aluminum has a Tc of only 1.20K,

nearly impossible to reach by conventional methods

Aluminum tubing can become

superconductive at very low

temperatures.http://www.globalmetals.com/aluminum-

tubestubing.html

Fig. 12.2: Lead can also become superconductive at low

temperatures.http://39clues.wikia.com/wiki/Lead

High-temperature superconductors (abbreviated high-Tc or HTS) are

materials that behave as superconductors at unusually high temperatures.

The first high-Tc superconductor was discovered in 1986 by IBM

researchers Georg Bednorz and K. Alex Müller,who were awarded the

1987 Nobel Prize in Physics "for their important break-through in the

discovery of superconductivity in ceramic materials".

Whereas "ordinary" or metallic superconductors usually have transition

temperatures (temperatures below which they superconduct) below 30 K

(−243.2 °C), HTS have been observed with transition temperatures as high

as 138 K (−135 °C). Until 2008, only certain compounds of copper and

oxygen (so-called "cuprates") were believed to have HTS properties, and

the term high-temperature superconductor was used interchangeably with

cuprate superconductor for compounds such as bismuth strontium

calcium copper oxide (BSCCO) and yttrium barium copper oxide

(YBCO). However, several iron-based compounds (the iron pnictides) are

now known to be superconducting at high temperatures.

High-temperature

superconductivity

YBa2Cu307

Discovered: 1987 by Paul Chu

Tc: 90-95K

Bc2: 100 Tesla at 77 K

Jc: 1.0x109 A/m2 at 77 K

Referred to as “1-2-3” superconductor

because of the ratio of the three metallic

elements

Type: Type II Ceramic

YBaCuO superconductors

• Yttrium Barium Copper Oxide was the first

superconductor developed with a Tc above the

boiling point of Nitrogen (Tc=90 K).

• Thallium Barium Calcium Copper Oxide has

the highest Tc out of all superconductors

(Tc=125 K)

• Copper Oxides are believed to be good

superconductors partly due to the Jahn-Teller

effect, which causes the 2 oxygens on opposite

sites of the octahedron to be farther from the

copper than the other 4 oxygens of the

octahedron.

• This suggests that the electrons interact

strongly with the positions of copper and

oxygen in the lattice (Cooper pair).

• Antiferromagnetism must be eliminated for

superconductivity to appear.

CopperIron

Cava, J.R. Sci. Amer. 1990.

(top): Illustration of a ceramic lattice. The Jahn-Teller

effect causes the superconductivity here.

(bottom): Levitation caused by the interactions of

electrons and oxygen, and therefore superconductivity.

Fig : Other copper oxides that are also superconducting. These ceramics show potential for applications.

For industrial setting, the toxicity of the materials should be considered. Cava, J.R. Sci. Amer. 1990.

Atypical Superconductors

and the Future

As if ceramic superconductors were not strange enough, even more

mysterious superconducting systems have been discovered. One is based on

compounds centered around the "Fullerene". The fullerene name comes from

the late designer-author Buckminster Fuller. Fuller was the inventor of the

geodesic dome, a structure with a soccer ball shape. The fullerene - also called

a buckminsterfullerene or "buckyball" - exists on a molecular level when 60

carbon atoms join in a closed sphere. When doped with one or more alkali

metals the fullerene becomes a "fulleride" and has produced Tc's ranging

from 8 K for Na2Rb0.5Cs0.5C60 up to 40 K for Cs3C60. In 1993 researchers at the

State University of New York at Buffalo reported Tc's between 60 K and 70 K

forC-60 doped with the interhalogen compound ICl.

Fullerenes, like ceramic superconductors, are a fairly recent discovery. In

1985, professors Robert F. Curl, Jr. and Richard E. Smalley of Rice University

in Houston and Professor Sir Harold W. Kroto of the University of Sussex in

Brighton, England, accidentally stumbled upon them. The discovery of

superconducting alkali metal fullerides came in 1991 when Robert Haddon

and Bell Labs announced that K3C60 had been found to superconduct at 18 K.

ORGANIC SUPERCONDUCTORS

"Organic" superconductors are part of the organic conductor family which includes:

molecular salts, polymers and pure carbon systems (including carbon nanotubes and

C60 compounds). The molecular salts within this family are large organic molecules that

exhibit superconductive properties at very low temperatures. For this reason they are often

referred to as "molecular" superconductors. Their existence was theorized in 1964 by Bill

Little of Stanford University. But the first organic superconductor (TMTSF)2PF6 was not

actually synthesized until 1980 by Danish researcher Klaus Bechgaard of the University of

Copenhagen and French team members D. Jerome, A. Mazaud, and M. Ribault. About 50

organic superconductors have since been found with Tc's extending from 0.4 K to near 12 K

(at ambient pressure). Since these Tc's are in the range of Type 1 superconductors, engineers

have yet to find a practical application for them. However, their rather unusual properties

have made them the focus of intense research. These properties include giant

magnetoresistance, rapid oscillations, quantum hall effect, and more (similar to the behavior

of InAs and InSb). In early 1997, it was, in fact (TMTSF)2PF6 that a research team at SUNY

discovered could resist "quenching" up to a magnetic field strength of 6 tesla. Ordinarily,

magnetic fields a fraction as strong will completely kill superconductivity in a material.

Organic superconductors are composed of an electron donor (the planar organic molecule)

and an electron acceptor (a non-organic anion).

Superconducting Properties of Ag and Sb Substitution

on Low-Density YBa2Cu3Oδ

• Different concentrations of Silver (Ag) and Lead (Sb)

were introduced as impurities into a YBCO ceramic

compound

• It was found that the addition of Ag at an optimum

concentration enhanced both the critical temperature

and current density of YBCO. Above and below this

concentration the properties diminished

• Sb impurities did not affect the superconducting

properties of the YBCO ceramic.

• As impurities of Ag and Pb were added to YBCO, the

transition temperature range, delta Tc was affected

• The correlation between concentration of Ag or Pb

versus transition temperature difference appeared to be

random

Azhan, F.; et al. J. Supercond. Nov. Magn. 2013, 26, 921-935.

http://www.kreynet.de/asc/ybco.html

Silver (Ag)

Lead (Pb)

Figure : Adding Ag and Pb impurities to the

lattice structure of YBCO can alter its

superconductive properties slightly.

• Superconductors have potential to create a new

variety of electrical and magnetic technologies

• Superconductors will need to be improved by

researching and synthesizing a ceramic

superconductor with a high critical temperature value

• By doing this, either minimum cooling, or no

cooling at all would be needed to create

superconductive properties in the material

• For example, YBCO only requires liquid

nitrogen for cooling. Conventional freezers could

be used if the Tc could be increased to around

190 K

• Since superconductors can be applied without

solid understanding of the theory behind it, they

are an attractive materialHgBa2Ca2Cu3Ox

Figure : Applied Magnetic

Field vs Critical Temperature.

As the critical temperature

increases, the applied magnetic

field decreases.

Flukiger, R. Rev. Accel. Sci. Tech. 2012, 5, 1-23.

Patel, M.J. et. al. Nat. Confer. Rec. Trend. Engr. Tech. 2011.

• If a high critical temperature

superconductor is developed that has a

critical temperature that is higher than

HBCCO (133 K), more practical

applications will become feasible

• Electrical power transmission through

superconducting materials and wire

o Low power loss

o Low voltage required for high

current

o Utilizes less physical space

• Computer signal transmission

o Low resistivity allows for

computing speed to increase

greatly

http://gigaom.com/2010/10/06/superconducting-wire-powering-up-korean-smart-grid/

Power lines demonstrating the great reduction of

space needed by utilizing superconducting wire

rather than standard cables.

Figure : Example of a superconducting cable. The liquid nitrogen

coolant is part of the cable in order to keep the superconductor wire

below the critical temperature. These cables can greatly reduce the

physical space needed in our electrical infrastructure.

• Some applications are used today:

o Magnetic Resonance Imaging

o Nuclear Magnetic Resonance

Spectroscopy

• Future applications can benefit from

interesting magnetic properties displayed

by superconductors

• Particle Accelerators

• Magnetic Levitation

o High-Speed Magnetic Levitation

Trains for mass transport

o By utilizing levitation, friction

between the train and the track is

eliminated

o This can allow trains to increase

their speed dramatically

Figure :(top/middle): MRI

scanners currently utilize

superconductors.

Figure :(bottom): Mag-Lev train

demonstrating the potential of using

superconductors in mass-transport.

•Particle Accelerators

•Generators

•Transportation

•Power Transmission

•Electric Motors

•Military

•Computing

•Medical

•B Field Detection (SQUIDS)

The Yamanashi MLX01 MagLev train

Application of

Superconductors

MAGLEV TRAIN:Maglev (derived from magnetic levitation) is a

transport method that uses magnetic levitation to move

vehicles without touching the ground. With maglev, a

vehicle travels along a guideway using magnets to

create both lift and propulsion, thereby reducing

friction by a great extent and allowing very high

speeds.

The Shanghai Maglev Train, also known as

the Transrapid, is the fastest commercial train currently

in operation and has a top speed of 430 km/h

(270 mph). The line was designed to connect Shanghai

Pudong International Airport and the outskirts of

central Pudong, Shanghai. It covers a distance of 30.5

kilometres in 8 minutes.

The linear motor car experiment vehicles MLX01-01 of Central Japan Railway

Company. The technology has the potential to exceed 4000 mph (6437 km/h) if

deployed in an evacuated tunnel.

MAGLEV: flying train

Shanghai Maglev Train (SMT)

Superconducting RF cavities for colliders

The Large Hadron Collider | CERN

Energy transmission

Powerful superconducting magnets

Scientific and industrial NMR facilities

900 MHz superconductive

NMR installation. It is used

For pharmacological

investigations of various

bio-macromolecules.

Yokohama City University

BRUKER AEON-1GHz

NEXTGEN NMR

Medical NMR tomography equipment

G scan - an Open Standing MRI scanner

Superconducting Magnets to Protect Spacecraft

from Radiation:While on Earth, the planet protects us from space radiation

and cosmic rays with its magnetic field. NASA scientists are

now working on an analogous approach to protect spacecraft

from space radiation outside of Earth’s protective envelope.

NASA along with its partners is exploring the possibility of

using superconducting magnets to generate magnetic fields

around space probes and space habitats to protect them from

space radiation and cosmic rays.

A Superconducting E-bomb (EMP BOMB):

"The U.S. Air Force has hit Iraqi TV with an experimental

electronmagetic pulse device called the 'E-Bomb' in an attempt to knock

it off the air and shut down Saddam Hussein's propaganda machine. Iraqi

satellite TV, which broadcasts 24 hours a day outside Iraq, went off the

air around 4:30 a.m. local time."

- CBS News, 3-25-03

E-bombs can unleash in a flash as much electrical power 2 billion watts

or more as the Hoover Dam generates in 24 hours. [And], although the

Pentagon prefers not to use experimental weapons on the battlefield, "the

world intervenes from time to time," - Defense Secretary Donald

Rumsfeld.

- Time Magazine, 1-19-03

An e-bomb (electromagnetic bomb) is a weapon that uses an

intense electromagnetic field to create a brief pulse

of energy that affects electronic circuitry without harming

humans or buildings. At low levels, the pulse temporarily

disables electronics systems; mid-range levels corrupt

computer data. Very high levels completely destroy

electronic circuitry, thus disabling any type of machine that

uses electricity, including computers, radios, and ignition

systems in vehicles.

ELECTROMAGNETIC PULSE WEAPONS CAN DISABLE

ALL ELECTRONIC EQUIPMENTS INSIDE THE RANGE:

A directed-energy weapon (DEW) emits highly focused

energy or EMP, transferring that energy to a target to damage

it.

Potential applications of this technology include anti-

personnel weapon systems, potential missile defence system,

and the disabling of lightly armored vehicles such as cars,

drones, jet skis, and electronic devices such as mobile

phones.

• Superconductivity is a state of thermodynamical equilibrium where the

electrical resistance is 0 and that is achieved at near 0 K temperatures

• External magnetic flux is expelled from the superconductor in what is

called the Meissner effect. The application of an external magnetic flux

also lowers the critical temperature at which superconductivity is

achieved. After a critical flux, superconductivity can no longer be

achieved

• Using superconducting materials in circuit elements would mean zero

power loss due to resistance. Also, no voltage difference would be

needed to maintain the current.

• Adding impurities to ceramic superconductors can alter the critical

temperature and critical current density

• Superconducting ceramic materials have shown the most promise for

future technologies because of their relatively high critical temperatures

• The underlying principles of superconductivity are explained through

an interactive attraction between electrons (Cooper pair) and their

interaction with lattice vibrations (phonons).

Figure : Structural

interpretation of a

ceramic superconductor.

Notice how there are

layers of molecules

sandwiched between

others.

http://physics.aps.org/story/v9/st12

IMPORTANT SOURCES:

Research Groups and Institutions:

•Kamerlingh Onnes Laboratory | Leiden University - Netherlands

•Superconductivity and Magnetism | Argonne National Labs

•Superconducting Stripes | La Sapienza University - Italy

•Superconductivity Group | University of Rome - Italy

•Superconductivity Group at UiO | University of Oslo - Norway

•Superconductivity Group | University of Durham - UK

•Rapid Single-Flux Quantum Laboratory | State University of New York

•DHV Research Group | University of Illinois at Urbana-Champaign

•Texas Center for Superconductivity | University of Houston

•The Lemberger Superconductivity Lab | Ohio State Univ.

•Institute for Superconducting and Electronic Materials | Australia

•Quantum Chaos and Superconductivity | Northeastern University

•Bar-Ilan Institute of Superconductivity | Israel

•Weizmann Institute of Science | Superconductivity Group - Israel

•A S T R A | Applied Superconductivity & Training - Slovakia

•B. Verkin Institute for Low Temperature Physics and Engineering | Ukraine

•AIST | National Institute of Advanced Industrial Science and Technology - Japan

•Nanoscale Superconductivity and Magnetism | University of Leuven - Belgium

Manufacturers/Industry:

CAN Superconductors | HTS Bulk

Superconductors for Practical Applications

SuperPower, Inc. | Developer and Producer of 2G

HT Superconducting Wire

Star Cryoelectronics | Thin Film, Squid, and

Biomedical Products

ATKINS’ PHYSICAL CHEMISTRY, Eighth Edition. Peter Atkins, Julio

de Paula.

Physical Chemistry (Third Edition). Robert G. Mortimer.

Cava, J.R.; Superconductors and beyond 1-2-3. Scientific American 1990.

http://www.superconductors.org/

https://en.wikipedia.org/wiki/Superconductivity

Flukiger, R. Overview of Superconductivity and Challenges in

Applications. Reviews of Accelerator Science and Technology. 2012, 5, 1-

23.

Patel, M.J.; Agrawal, D.H.; Pathan, A.M. Review on Superconductivity:

The Phenomenon Occurred at Low Temperature. National Conferences on

Recent Trends in Engineering & Technology. 2011.