Parinov I.A. Microstructure and Properties of High-Temperature Superconductors

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8 1 Superconductors and Superconductivity

1999, the solid realization of the qubit in SQUID loop was proposed [471].

This idea is based on using “exotic” superconductors with symmetry of pa-

rameter of the superconducting order, D, which is lower than symmetry of

crystalline lattice (e.g., HTSC YBa

, possessing d-wave symmetry of

D in superconducting CuO

layers). In 2000, a new computer architecture,

namely, hybrid technology multi-threaded architecture (HTMT), was started.

The schemes of rapid single ﬂux quantum (RSFQ) are the basis of the com-

puter, and it is assumed that the superconducting supercomputer will carry

out up to 10

ﬂoating-point operations per second. The RSFQ conception

is based on using shunted Josephson junctions. In 2003, a formation of the

entangled state between two solid superconducting qubits [834] has been

demonstrated. In 2004, a coherent coupling of Josephson qubit with harmonic

modes of transmitting line (for “charge” qubit [1124]) and with plasma oscil-

lations (for “ﬂux” qubit [148]) has been carried out. By disposing Josephson

qubits on one chip, it is possible in principle to organize their coupling, by

means of electromagnetic waves. In the case of actual HTSC applications, it is

necessary to reach 5% current spread per plate with 10

Josephson junctions.

The areas of application of HTSC products are divided into passive and

magnetic ones based on the state (diamagnetic or ferromagnetic) of the sample

in working regime (see Table 1.1). The capability of superconductor pushes

oﬀ external magnetic ﬁeld is used in the diamagnetic state (in this case, an

existence of origin of the external direct ﬁeld is assumed). On the other hand,

superconductor itself becomes the origin of magnetic ﬁeld in the ferromagnetic

state (state with “freezed” magnetic ﬂux).

III. Transportation. The next main directions of superconductivity appli-

cations in the aviation and astronautics have been formed, namely:

(1) Systems of electromechanical start.

In the construction of the newest single-pass motor of air- spacecraft, the

necessary air inﬂow is attained at super-sound velocities of apparatus; it only

demands initial acceleration of the craft. For this aim, it is possible to use

the take-oﬀ superconducting platform does not leaving the airport limits, but

Table 1.1. Passive and magnetic applications of HTSC

Passive applications Magnetic applications

Magnetic bearings Quasi-continuous magnets

Fly-wheels Magnetic separation

Cryogenic pumps MagLevs

Filling systems Magnetic captures

Hysteresis motors (rotor) Motors (stator)

Linear carrying capacitors Magnetic dampers

Inertial transformers Control of bundles of the charge particles

Electric drives Magnetic apparatus

Magnetic screens

1.2 Progress and Prognosis of Superconductivity Applications 9

racing aircraft up to sound velocity. The electromagnetic systems of start from

Earth to its orbit, using HTSC magnet or linear synchronous motor, present

themselves the high-speed electromagnetic guns for start to space of the heavy

useful loads. Analogous starting systems are applied for replacement of the

ﬁrst step of the multi-step rockets.

(2) Levitation systems.

The passive superconducting magnetic suspenders for contactless suspen-

sion of shafts may be used to stabilize satellites, but electromechanical storages

of energy to feed HTSC bearings.

(3) Electric motors, working on the principles of hysteresis and “freezed”

magnetic ﬂux.

The hysteresis motors developed consisting of cylindrical or disc HTSC

rotors are based on the use of two types of bulk superconducting ceram-

ics, namely (i) monocrystalline (YBCO) or bulk (BSCCO) elements and (ii)

melt-textured YBCO samples. The constructive elements of motors of the

synchronous–asynchronous type are the HTSC bulks, but ac-synchronous and

dc-unipolar electric machines use HTSC wires (from BSCCO).

The main directions of superconductivity applications in various transport

systems cover the following:

(1) High-speed trains and other kinds of ground transport on magnetic

suspension.

The superconducting (SC) electromagnetic systems (using linear electric

motors to speed up the truck) are applied in the development of high-speed

ground transportation based on the SC windings placed in the route and SC

magnets located in the vehicle. By this, in order to economically, accumulate

and use energy eﬀectively, the SC storages of electric energy that feed HTSC

bearings are applied. Magnetic levitation (MagLev) systems based on the use

of magnetic forces to “suspend” one object above another have been devel-

oped in Japan, the USA, Germany, France, Switzerland, China and Canada.

HTSC systems have been demonstrated in China during realization of Ger-

manic China project directed to create the levitated transportation mean.

During the last 25 years, great eﬀorts have been taken in Japan to develop

high-speed trains on magnetic suspension by the application of superconduct-

ing systems. In particular, for the passenger train on magnetic suspension,

caused by superconductivity, a speed of over 1000 km/h [898] has been demon-

strated! Today, an analogous train has been developed, called the Japanese

Linear Chuo Shinkansen Project (MLX) with nominal speed of 500 km/h.

At the same time, trains with superconducting magnetic suspension compete

with high-speed trains (e.g., France train TGV and German Transrapid Sys-

tem with speed of 420 km/h). The Inductrack MagLev System is developed in

the USA. The Swissmetro Project (speed of 320 km/h) should be noted. The

German Transrapid System is based on “classical” electromechanical technolo-

gies, requiring small air gap (< 12 mm) between the vehicle and the truck.

The Japanese MagLev is based on active superconductivity magnetic systems,

permitting large air gap (> 80 mm). The USA MagLev is based on passive

10 1 Superconductors and Superconductivity

superconductive magnets, also permitting large air gap (> 80 mm). Swiss-

metro presents a unique example of MagLev systems: it is designed to work

under partial vacuum (< 10 kPa). The vehicles run in tunnels of small inside

diameter (5 m), which require partial vacuum in order to reduce the aerody-

namic resistance. Independent magnetic systems permit to have medium air

gap of 20 mm. Thus, based on the melted HTSC ceramic, the superconducting

magnets are able to capture high magnetic ﬁelds (tens of Tesla) compared with

the classical magnets, and allow to create ecologically pure high-speed ground

transport systems with broadened air gap (the thickness of magnetic suspen-

sion). This deﬁnes the possibility to design railroads with lesser ﬁnancial and

operation expenses.

(2) Electromobiles and automobiles.

HTSC electric motors for electromobiles and automobiles act on the prin-

ciples of hysteresis and “freezed” magnetic ﬂow. The superconducting wires,

bulks and thick ﬁlms are used in construction. The next electric devices and

machines, using superconductivity, that are development under now are:

– ac-synchronous and dc-unipolar electric motors, using HTSC wires (from

BSCCO) and acting at the temperature of liquid hydrogen;

– hysteresis motors with cylindrical and disc YBCO rotors that are devel-

oped on the basis of monocrystalline YBCO- or BSCCO-ceramic, and also

melt-textured YBCO bulks;

– motors of synchronous–asynchronous type, consisting of HTSC bulks;

– motors with rotor from layered composites, namely YBCO bulks (thick

ﬁlms) with intermediate ferromagnetic inserts (steel plates);

– HTSC levitated systems, realized in electromechanical storages of energy

and levitated suspenders that use high-speed electromobiles.

(3) High-speed ships and Navy.

The linear synchronous electric motors are applied in starters of aircraft

carriers. The superconducting magneto-hydrodynamic systems are used in

Navy with the aim of decreasing the noise detection of motor in torpedoes

and in the development of high-eﬀective motors for fast-moving ships. There

are researches directed to the use of superconductivity in the ship impulse

source of energy, for example, for aircraft carrier. The Navy has intention

of creating a warship with unique superconducting equipment and apparatus

[356], including: (i) engines, (ii) magnetic mine-sweepings for ﬁshing out of

sea mines, (iii) board systems of feeding on the basis of inductive storage and

(iv) radio-locator, using superconducting magnet in the protection system of

the ship.

Superconducting electric engines have small sizes and weight, consume

small capacity. Their important advantage consists in the absence of mechan-

ical moving details that exclude acoustic noise at the ship movement. Fast

discharge is the advantage of superconducting storage of the electric energy,

which could be important for applications in guns, catapults, torpedoes with

electromagnetic launching. The clearance of the coastal waters from sea mines

1.2 Progress and Prognosis of Superconductivity Applications 11

is another important problem of the Navy. The mechanism of sea mine launch-

ing is connected with their sensitivity to the magnetic image of ship (i.e., with

perturbations of Earth’s magnetic ﬁeld under inﬂuence of magnetic mass of

the ship). Small ship with superconducting magnet can imitate the magnetic

image of moving ship, thus collecting the mines. Under large magnetic ﬁeld

(for this, the superconducting magnet is used) the mines can be blown up suf-

ﬁciently far from the magnet. Today, HTSC magnet, which may be placed in

helicopter and models ﬁelds, imitating moving ship, has been developed. With

the aim to ﬁnd and counteract small, low-ﬂying rockets, the Navy develops

powerful high-frequency radio-locator on the base of superconducting magnet.

In this case, interaction of electronic ray with magnetic ﬁeld creates electro-

magnetic radiation with frequency proportional to the magnetic ﬁeld.

IV. Medicine. At the top of our technological tree are seen beneﬁts, con-

nected with increase of human welfare and, especially, with development of

medicine. The main problem is to use the uniquely useful, ecologically safe and

energy-saving potential of superconducting materials and magnets. In partic-

ular, it relates to use of magnetic resonance imaging (MRI). This method

rapidly established itself as a new and virtually indispensable medical diag-

nostic tool. The perspectives of the method are caused by progress in the

technique of electronic image and cryogenic refrigeration. The base applica-

tion of MRI involves visualization of concentrations of “hydrogen molecules”

or “liquid” content of the various organs in the body. The use of even higher

ﬁeld superconducting magnets (so-called functional MRI) allows to state very

accurately the distribution of other chemical elements in the human body

that exist in much more limited concentrations than hydrogen. Another per-

spective direction is the use of SQUIDs that are the most sensitive detec-

tors of ﬂux or magnetic ﬁelds. SQUIDs are used to measure brain waves and

brain functions. Similar excitement surrounds the use of SQUIDs in cardi-

ology. Their other applications cover microbiology, biomedicine, high-energy

physics, nanoparticle magnetism, non-destructive control, archeology, geology

and SQUID microscopy. Medical HTSC tomographs can be used to control

the quality of goods, in particular of food products.

V. Mechanical systems. The application of superconducting motors shows

that such motors could be at least 20% more eﬃcient than typical present

products. The total energy saving on use of this technology could be enormous.

In particular, 5000 horsepower motors have been demonstrated [219]. Other

examples of superconductivity applications are the devices of energy accumu-

lation and storage based on the levitation phenomenon, high-ﬁeld magnets

for laboratory research, superconducting magnets for specialized fabrication

processes of the chemical and pharmaceutical products, industrial growing of

silicon crystals, material separation and so on.

VI. Scientiﬁc research. The application of superconducting magnets has

probably been the most radical event for high-energy physics. Note, in par-

ticular, most powerful in the world an accelerator of high-energetic charged

12 1 Superconductors and Superconductivity

particles (Large Hadron Collider), constructed in Europe by CERN

consor-

tium in 2007. In total, approximately 1200 tons of NiTi superconducting wires

and cables were required, which were supplied by several companies of Europe,

Japan and the USA.

Scanning HTSC SQUID microscopes have highest sensitivity to weak mag-

netic ﬁelds in broad frequency diapason. They are able to register magnetic

ﬁelds generated by vortex currents, magneto-tactile bacteria and currents of

leakage in integral schemes. Electron-ray origins of multi-charged ions are used

widely in laboratories. The parameters of HTSC origin [758] are suﬃcient to

create the multi-charged ions, namely, helium-like xenon and neon-like ura-

nium. It is used to study a surface modiﬁcation of diﬀerent materials by the

multi-charged ions, using the scanning probe microscope.

Record parameters of magnetic ﬁeld transducers (2006) [1192]:

(1) Sensitivity of LTSC and HTSC SQUIDs is equal to 10

−15

T/Hz

1/2

(1 Hz,

4 K, screened room) and 5 × 10

−14

T/Hz

1/2

(1 Hz, 77 K, screened room),

respectively.

(2) Sensitivity of giant magnetic resistance (GMR) spin valves is equal to

4×10

−10

T/Hz

1/2

(1 Hz, 300 K, without screening) and 4×10

−11

T/Hz

1/2

(1 Hz, 4.2 K, without screening).

(3) Sensitivity of GMR spin valves with superconducting transformer of

ﬂux is equal to 10

−12

T/Hz

1/2

(1Hz,77K,withoutscreening)and

3 × 10

−13

T/Hz

1/2

(1 Hz, 4.2 K, without screening).

(4) Sensitivity of atomic magnetometer with sizes of microelectronic chip (at

minimal consumed capacity) is equal to 5 × 10

−11

T/Hz

1/2

(10 Hz)

VII. Electric power. The superconductivity could render potentially enor-

mous inﬂuence on the electric power industry, in particular, the power gen-

eration, power storage, power transformation and distribution and also the

improvement and assurance of power quality. Even though the eﬃciency of

power transmission lines, motor generators and especially electric transform-

ers is already very impressible, energy losses due to use of ordinary resistive

copper and aluminum conductors are enormous. Taking into account the basic

inﬂuence that energy renders on all economic sectors the use of superconduc-

tivity in this ﬁeld is connected with even more enormous perspectives. LTSC

superconducting windings for electric power generator equipment to reduce

energy losses have been carried out in a number of countries. While some very

challenging engineering problems were successfully overcome, the economics,

deﬁned by using liquid helium and existence of high magnetic ﬁelds, pose

extra challenges. In this case, the application of HTSC, which do not lose

their properties at liquid nitrogen temperature, provides, in perspective, con-

siderable advantages. For example, while the earlier approach involved the use

of homopolar machine design – to have the windings exposed to dc-magnetic

CERN is European Laboratory for Particle Physics.

1.2 Progress and Prognosis of Superconductivity Applications 13

ﬁelds only – the present HTSC design involves ac-synchronous approaches,

which also maintain dc-ﬁelds around the superconducting windings [220]. In

addition to lower losses, through the utilization of superconducting windings

instead of copper, the decrease of size andweightshouldalsoleadtolower

overall cost of product. Finally, greater reliability and potentially longer equip-

ment lifetimes can be expected due to a constant and much cooler operating

temperature environment.

The problems of thermonuclear energetic are directly connected with the

use of high-ﬁeld superconducting magnets (the proposals of TOKAMAK,

LHC, ITER

, etc.). While low-temperature superconductors will continue to

be employed initially, the potential applications of HTSC in this ﬁeld have

great perspectives.

A very attractive feature of superconducting magnets is the fact that they

canbeconsideredtobe“electromagnetic batteries.” They can store enormous

amounts of energy for long time suﬃciently. Compared to electrochemical

batteries, SMES

systems – although initially more costly – are considered to

be more eﬃcient, environmentally clean and less expensive for long term [100].

Successful feasibility demonstrations of superconducting transformers with

HTSC windings have been carried out in Japan, Germany and the USA [682].

The economic savings, operational reliability and environmental beneﬁts are

the main advantages of superconductors, used in this case. Because of HTSC

capabilities, they can readily and rapidly replace existing transformers, while

providing higher ratings, overload protection capability and smaller footprints

for equivalent ratings of conventional transformers. Superconducting cables

are of considerable interest to the electric industry because they oﬀer: (i)

eﬃciency gains in transmission lines, reducing resistive losses, and (ii) oppor-

tunities to replace existing underground cables with much higher capacity ca-

bles, than in existing pipelines, that also lead to their quantitative decrease.

The requirements to HTSC wires for diﬀerent electric technical devices are

presented in Table 1.2, and properties of main superconductors are shown in

Table 1.3.

Another unique application of superconductivity is the development

approaches for single-phase and multi-phase systems having signiﬁcant near-

term commercial potential. In particular, fault current limiters are devices uti-

lizing the ability of superconductors to act like a resistance “switch,” capable

of exhibiting zero resistance, when superconducting, but capable of returning

to a higher resistance state, when critical temperature, current or magnetic

ﬁeld limits are exceeded.

SuperFoam, synthesized from YBa

ceramic [878], may be ideal

material for the fault current limiters. Advantages of superconducting foam

under “tape” and “bulk” devices from BSCCO include the following ones

[772]: (i) it endures critical currents at T = 77 K, which are signiﬁcantly higher,

ITER is International Thermonuclear Energy Research.

SMES is superconducting magnetic energy storage.

14 1 Superconductors and Superconductivity

Table 1.2. The requirements of HTSC wires for diﬀerent electric technical devices [761]

Device J

(A/cm

)

Field (T) Working

temperature

(K)

(A) Wire length

(m)

Strain

(%)

Twisting

radius (m)

Cost ($/kA m)

Fault

current

limiters

− 10

0.1 − 3 20–77 10

− 10

1000 0.2 0.1 10–100

Big motors 10

4.5 20–77 500 1000 0.2–0.3 0.05 10

Generators 10

4–5 20–50 > 1000 1000 0.2 0.1 10

SMES 10

5–10 20–77 10

1000 0.2 1 10

Cables 10

–10

< 0.2 65–77 100 per

strand

100 0.4 2 (in

cable)

10–100

Transformers 10

0.1–0.5 65–77 10

–10

1000 0.2 1 10

1.2 Progress and Prognosis of Superconductivity Applications 15

Table 1.3. Main superconductors and their properties [761]

Material Crystalline

structure

Anisotropy T

(K) H

(T) H

∗

(T) ξ(nm) λ(0)(nm) De-pairing

current density,

at 4.2 K (A/cm

)

Critical current

density (A/cm

)

ρT

(μΩcm)

NbTi

(Nb, 47

wt%)

b.c.c. Neglected 9 12 (4 K) 10.5 (4 K) 4 240 3.6 × 10

4 × 10

(5 T) 60

Sn A-15, cubic Neglected 18 27 (4 K) 24 (4 K) 3 65 7.7 × 10

∼ 10

MgB

P6/mmm,

hexagonal

2–2.7 39 15 (4 K) 8 (4 K) 6.5 140 7.7 × 10

∼ 10

0.4

YBCO Orthorhombic,

layered

perovskite

792> 100 (4 K) 5–7

(77 K)

1.5 150 3 × 10

∼ 10

∼ 40–60

Bi-2223 Tetragonal,

layered

perovskite

50–100 108 > 100 (4 K) 0.2

(77 K)

1.5 150 3 × 10

∼ 10

∼ 150–800

16 1 Superconductors and Superconductivity

compared to Bi-2212 phase, having problems with pinning centers at this

“high” temperatures, (ii) it has suﬃciently high electric resistance at room

temperature in order to dissipate in heat an energy of supercurrent and (iii)

it switches rapidly from and in superconducting state. The last two properties

are forced in signiﬁcant degree due to the foam includes open pores, in which

there is cryogenic cooler. This provides continuously a directed contact with

liquid nitrogen, compensating bad heat capacity of ceramics in the bulks.

1.3 Superconductivity Phenomena

1.3.1 Critical Field

Not only thermal ﬂuctuations destroy superconductivity eﬀect, but a suﬃ-

ciently intense magnetic ﬁeld can restore resistance and return the supercon-

ductor to its normal, that is, resistive state. This ﬁeld is called the critical ﬁeld

of bulk material, H

, or the thermodynamic critical ﬁeld. The temperature

dependence of H

is well described by the empirical formula:

(T )=H

(0)[1 − (T/T

)

] . (1.1)

This dependence is shown in Fig. 1.5a, which essentially represents the H–T

phase diagram of the superconducting state. Within area of S,anypointin

H–T plane corresponds to the superconducting state. The critical ﬁeld can

be related to the critical temperature T

. Since the critical ﬁeld is zero at

, then in this case there is a second order phase transition. The entropy is

continuous at T

in zero magnetic ﬁeld, but the speciﬁc heat is discontinuous.

When H = 0, transition takes place at T<T

and becomes of ﬁrst order.

The zero resistance state can also be destroyed by large enough electrical

currents, stated by the Silsbee criterion [989]. It deﬁnes an existence of critical

current, the application of which through bulk superconductor causes initia-

tion on its surface of the critical magnetic ﬁeld, destroying superconductivity.

1.3.2 Josephson Eﬀects

The quantum nature of superconductivity is provided by the so-called weak

superconductivity, or Josephson eﬀects [500]. They were predicted in 1962 and

soon veriﬁed experimentally. The term “weak superconductivity” refers to

situation in which two superconductors are coupled together by a weak link.

There are two Josephson eﬀects, namely stationary (dc) and non-

stationary (ac).

dc-Josephson eﬀect. Let us apply a current through a weak link (or so-

called Josephson junction). If the current is small enough, it passes through

the weak link without resistance, even if the material of the weak link itself

is not superconducting (e.g., it is an insulator in a tunnel junction). Through

the weak link, the electrons of the two superconductors merge into a single

1.3 Superconductivity Phenomena 17

T/T

1.2

1.0

0.8

0.6

0.4

0.2

0.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0.0

0.2 0.4 0.6 0.8 1.0 1.2

(0)

λ / λ(0)

(a)

(b)

Fig. 1.5. Temperature dependence of the critical ﬁeld, H

(a); temperature

dependence of penetration depth, λ (b)

quantum body. In other words, all superconducting electrons on both sides of

the weak link are described by the same wave function. The presence of the

weak link should not change signiﬁcantly the wave functions on the two sides,

compared to what they had been before the link was established.

ac-Josephson eﬀect. Let us increase the dc- current through the weak link

until a ﬁnite voltage appears across the junction. Then, in addition to a