EC NAPEP Project
Spintronics: New Tendency
in Electronics
Taryel Ismayilov
Oulu, 23-28 May, 2011
Spintronics: New Tendency
in Electronics
• Introduction
• Size quantization
• Spin-orbit interaction in semiconductors
• Spin-Hall Effect (SHE)
• Spin Dipole
• Detection of spin current: a nano-mechanical proposal
• Detection of spin current: by inverse SHE
• Spin injection
• Spin-orbit interaction at metal alloy surfaces
• Summary
 Semiconductor
 Electronics
Spintronics
for the 21st Century
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Conventional Electronics Charge Based on number of
charges and their energy
Performance limited in speed and dissipation
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Spintronics Spin
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Based on direction of spin and spin coupling
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Capable of much higher speed at very low power
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In March of 1959, Richard Feynman challenged his
listeners to build “Computers with wires no wider than 100
atoms, a microscope that could view individual atoms,
machines that could manipulate atoms 1 by 1, and circuits
involving quantized energy levels or the interactions of
quantized spins.”
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Richard Feynman - “There’s Plenty of Room at the
Bottom”, 1959 Annual Meeting of the American Physical
Society
Quantum computing
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Classical Bit (Boolean) 0 or 1 Two states
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Quantum Bit (Qubit) α|0>+ β|1> Infinite number of
states”
Where
Size Quantization
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Size Quantization
Frohlich (1937),
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I.M Lifshitz (1951, 1952)
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R.Kubo (1962)
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V.Sandomirskii (1962)
DOS in Low-Dimensional Electron Systems
Spherical Quantum Dot
Two-Dimensional Electron Systems
Low-Dimensional Electron Systems
Electron
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An electron has a charge (- e) and a spin (½)
-e
(spin) +
-e
(charge)
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Electronic industries have made good use of the charge
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But the electron spin has essentially been neglected
Application of spin current
 Electric
current -> electronics
 Spin current -> spintronics
What is the spin current?
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Electrons carry both charge and spin which may have
two components: up and down.
j   j
The electric current
J c  e  j  j   0
If the currents of electrons for different spins are not
equal,
The spin current
Js 

 j  j   0
2
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From the abstract of “Spintronics: Fundamentals and
applications” :
“Spintronics, or spin electronics, involves the study of
active control and manipulation of spin degrees of freedom
in solid-state systems”
Reviews of Modern Physics, vol. 76, p.323-410, 2004, by I.
Žutić, J. Fabian, and S. Das Sarma
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•
•
•
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Spintronics where magnetic material and
magnetic field is involved:
GMR: giant magnetoresistive effect
Memory / storage
TMR, CMR
Spin-based Quantum Computing: uses spin of
nuclei as qubits
• All electrical means of generation and manipulation
of spins: spin-polarized transport in
semiconductors spin FET, spin filter, logic /
storage
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The spin-orbit interaction is a relativistic correction to the
non-relativistic Pauli equation, which arises as a
combination of two effects: (i) the effective magnetic field
experienced in its rest frame by an electron moving in an
electric field and (ii) the Thomas precession of the rest
frame of an accelerated electron. It is derived from the
Dirac equation and expressed as
Here m is the free electron mass, P is the momentum
operator, e is the electronic charge,
σ =(σx , σy , σz) is the vector of Pauli matrices, V(r) is the
potential energy and ∇ stands for spatial gradient.

The Dirac equation describes a relativistic particle:
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Expansion of this equation in yields the single-particle
Schredinger equation, plus some spin-dependent terms
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The last term on the right hand side couples the spin to the
momentum in the presence of an electric field, hence the
name “spin-orbit coupling”
This effect is small in free space, but can be rather large in
semiconductors
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Spin-orbit coupling in semiconductors
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In a semiconductor heterostructures the spin-orbit
Hamiltonian is usually described by the Rashba form:
where α is proportional to the electric field, which is
perpendicular to the 2D electron gas formed in
semiconductor heterostructures.
The spin-Hall effect

It turns out that the RashbaHamiltonian gives rise to a
pure transverse spin current in response to a charge current
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2DEG
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The associated spin-Hall conductivity has a universal value
in the 2D plane, and is of much interest to the spintronics
community.

How does this effect manifest itself in quasi - 1D quantum
wires?
The spin-Hall effect –1D calculations
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Assume a quantum wire with confinement along the
x-axis and ballistic transport along the y-axis:
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Also assume hard-wall boundary conditions along x
With an electric field along the z-axis,the Schrodinger equation
becomes
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Write the wave function as
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Tranzistors
Spin transistor: Datta and Das (1990)
Working principe SFET

Physical origin of this large enhancement in the SO
coupling constant:
• a brief review of how SOI comes about, starting from the
Dirac equation.
• how does the SOI coupling constant gets enhanced in
semiconductors:
•k
p approach.
From micro to nanoelectronics
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The characteristic size of an element of 30 nanometers or less
Density more than 108 transistors on 1 sq. cm for logic
Density more than 1010 bits on 1 sq. cm for memory
The price less than 50 microcents for the transistor for logic
The price less than 660 nanocents for memory bit
Frequency of switching of 10 GHz
Low power consumption: 1.4 billion transistors of the
processor use less than 170 Watt
In 2005 for every second in the world it was made more than
2 billion transistors
The forecast for 2012
Spin-orbit coupling in semiconductors
Hamiltonian, describing this interaction, as it is known, is
from expansion of the of Dirac equation to within members
of an order and looks like:
Hamiltonian of Rashba describes spin-orbital interaction in
an asymmetrical potential hole (Rashba 1960)

Dresselhaus Hamiltonian is received for 3D semiconductor
crystals without the inversion centre (Дрессельхаус1955)
Spin-orbit coupling in semiconductors
Spin-orbit coupling in semiconductors
(Rashba 1960)
Spin-orbit coupling in semiconductors
Rashba-Dresselhaus

I. The Researches executed recently, have shown
that the spin Hall effect opens new possibilities in
management of electronic polarisation and
transport in nonmagnetic semiconductors for lack
of a magnetic field.

II. Interest to this problem is connected not only
with possible applications in the information
industry (for processing and information storage),
but also with statement of new problems in the
physics of the condensed matter.

Magnification of volumes and transfer velocity of
information comes nearer to a limit related with
the basic physical restrictions on
the further reduction of the sizes of active elements
of devices. For electronics development it is
necessary search of new solutions and principles.
The most perspective from directions "Spintronika". It is new field of a science and
technicians, in which not only a charge, but also a
spin of electron is used for storage and
transmission of information.
Spintronics history
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1988 - Giant Magnetoresistive Effect (GME) discovered by Albert Fert and Peter Gruenberg.
1989 - IBM scientists made a string of key discoveries about the “GMR" effect in thin-film structures.
1997 - first GMR (Giant magnetoresistive) Harddisk head introduced by IBM.
2000 - University of Buffalo get 10$ million to develop specific ferromagnetic materials for use in "spintronics
2001 - University of Arkansas physicists have successfully injected a stream of electrons with identical spins
into a semiconductor.
2002 - A new device allows the polarization of an electron to determine the switching of the device
2002 - Plastic Shows Promise For Spintronics, Magnetic Computer Memory
2003 - M Ouyang and D Awschalom of the University of California at Santa Barbara have transferred
electron spins across molecular ‘bridges’ between quantum dots for the first time.
2004 The Korea Institute of Science and Technology (KIST) and MIT's Francis Bitter Magnet Laboratory
have launched a 10-year program in spintronics.
IBM scientists view a single electron spin with a special atomic force microscope
2005 New Spintronic Speed Record - 2GHz MRAM devised.
2006
January - Researchers at the University of Michigan created a computer chip based on the
esoteric science of quantum mechanics.
July - Freescale begins selling 4-Mbit MRAM.
September - Spin Hall effect detected at room temperature.
2007
February - New European Initiative To Develop Spintonics Computing Devices
April - University of Delaware receives $1.9 million for new spintronics center
Furdyna JAP 1988
Heterostructure: Two-Dimensional
System
Spin Hall effect. Mechanism.
(Sinova, et al, 2004)
In presence of electric field Ex , when Fermi distribution of electrons is shifted along px ,
electron spins with py>0 are turned up, but electron spins with py<0 are turned down.
How to produce a non-equilibrium spin
population
Injection from a ferromagnet to a normal metal or
semiconductor, through an interface; via electrical
currents, or optical excitation.
 Creation of electron-hole pairs by circularly polarized light
above the band gap of semiconductor.
 Electrical transport through a quantum dot in an applied
 magnetic field
 Use of electrical currents to generate spin currents and
 polarization without magnetic fields or ferromagnets, via
spin-orbit coupling.
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Reference
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Spin Physics in Semiconductors Editor: M.I. Dyakonov, Springer Series in Solid
State Sciences, Springer-Verlag Berlin Heidelberg, 2008
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S. Murakami, N.Nagaosa, S.C. Zhang, Science 301, 1348 (2003), Phys. Rev. B 69,
235206 (2004)
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J. Sinova et al., Phys. Rev. Lett. 92, 126603 (2004)
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J. Wunderlich et al, Phys. Rev. Lett. 94, 047204 (2005)
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Y.K. Kato et al., Science 306, 1910 (2004)
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Shih et al. Naturephysics, October (2005)
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Э. Рашба, ФТТ, 2,1224 (1960)
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G. Dresselhaus, Phys. Rev. 100, 580 (1955)
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M.I. Dyakonov, V.I. Perel, Phys. Lett. 35A, 459 (1971)
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J.E. Hirsch, Phys. Rev. Lett. 83, 1834(1999)
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S.-Q. Shen, Phys. Rev. B 70, 081311(R)(2004)
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S.-Q. Sheng, Phys. Rev. B 70, 081311(R) (2004)
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E.G. Mishenko, A.V. Shytov, and B.I. GalperinPhys. Rev. Lett. 93, 226602 (2004)
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J. Schliemann, D. Loss, Phys. Rev. B 69, 165315 (2004).
SPINTRONICS: PYSICAL BASIS AND APPLICATIONS
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• D.D. Awshalom, D.Loss, N.Samarth, Semiconductor spintronics and
quantum computing. Springer.
• S.D. Ganichev, W. Prettl, Spin photocurrents in quantum wells. 2003
• T. Jungwirth, J. Sinova, J.Masek, J. Kuchera, A.H.MacDonald
Theory of ferromagnetic (III, Mn)V semiconductors. 2006
• Ohno H. Toward Functional Spintronics. 2001.
• Žutić I., Fabian О., Das Sarma S. Spintronics: Fundamentals and applications.2004.
• Захарченя Б.П., Коренев В.Л. Интегрируя магнетизм в полупроводниковую
электронику. // УФН. 2005.
• C. Timm, Disorder effects in dilute magnetic semiconductors, 2003
• T. Dietl, Ferromagnetic semiconductors
• Bibes, Bartolomey, Oxide spintronics, cond mat 2007
• B.A. Aronzon, S.V. Kapelnitsky and A.S. Lagutin, Transport and Magnetic
Properties of Nanogranular Magnetic Metals, Elsiever 2007
Научиться воздействовать на спин, как на заряд, током, магнитным полем,
светом. Переход от малой области (магнитный домен) к отдельному спину
Thank you for attention!