How to Make Semiconductors Ferromagnetic: A First Course in Spintronics Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 1 Theories of ferromagnetic semiconductors (S. Das Sarma) • Weiss Mean Field Theory: Localized and Delocalized • Percolation Theory: Insulating DMS • Dynamical Mean Field Theory: Impurity Band extended and Localized • PRL87,227202(2001);PRL 88,247202(2002);PRB65,233206(2002)
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 1
Theories of ferromagnetic semiconductors (S. Das Sarma)
• Weiss Mean Field Theory: Localized and Delocalized
• Percolation Theory: Insulating DMS• Dynamical Mean Field Theory: Impurity
Band extended and Localized
• PRL87,227202(2001);PRL 88,247202(2002);PRB65,233206(2002)
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 2
Signatures of charge carrier localization
Ge1-xMnxGa1-xMnxAs
Bound magnetic polaron
localized hole
−−∝Ψ
Ba
rrr 0exp)(
magnetic impurities+
( )hi nn >>
hihi
ih sSJH�
�
∑=,
ˆ
−−=
B
hiih
a
rrJJ
2exp0
⇒lower T
T
AJar B
p0ln
2=
polaronradius:
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 3
Polaron percolation
Interaction of two polarons
)2/("")2/(1
12(1,2)int.reg. rJNJrJ
TNM ≈⇒≈
+=
T
Jna
T
Jar iB
B 030polaron lnln
2
1ln
2""
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 4
Percolation theory:the model of overlapping spheres
only one parameter: 3 nr
known characteristics: ( ) ( )333 ,,86.0)( nrVnrNnr crit =
Results
( )
−=
30
386.0
exphBh
ihBc
naJ
n
nnaT
matches mean-field result
0Jn
nT
h
ic = at 13 ≈hB na
+=
T
TnaV
M
TM chB ln86.0
)0(
)(3
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 5
Comparison with experimentsand numeric experiments
Ge1-xMnx (Park et al. (2002))
Also In1-xMnxAs, Ga1-xMnxSb, Ga1-xMnxAs (for x < 3%)
Monte-Carlo (Bhatt et al. (2000))
0.4�
;)()( � ≈−∝→ TTTTM cc
)0(1)0( 6
� 3
MTTMBian
−≈→
1.7�;)()(� � ≈−∝→ cc TTTT
Magnetization and susceptibility
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 6
M(T,B) and χ(T,B)
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 7
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 8
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 9
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 10
How to Make Semiconductors Ferromagnetic: A First Course in Spintronics
Dr. Sankar Das Sarma, Univ of Maryland (KITP Correlated Electrons 10/17/02) 11
Related Documents
