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Magnetism in
nanostructured
graphene
J. FernándezRossier
L. Brey
Juan José Palacios
Funding
MECSpainFIS200402356, MAT200765487,
and CONSOLIDER CSD20070010Generalitat Valenciana
Accomp07054
Dresden, May 29th, 2008
2 dimensional systems (topdown)graphene
Novoselov, K.S. et al. "Electric Field Effect in Atomically Thin Carbon Films", Science, Vol 306 (5696), 666, 2004
2 dimensional systems (bottomup)graphene
Vazquez de Parga et al., PRL (2008)
Ethylene decomposition
1 dimensional systems (topdown)graphene
Melinda Y. Han , Barbaros Oezyilmaz, Yuanbo Zhang, Philip Kim, Phys. Rev. Lett, 98, 206805 (2007)
1 dimensional systems (bottomup)graphene
Chemically Derived, Ultrasmooth Graphene Nanoribbon Semiconductors
Xiaolin Li,† Xinran Wang,† Li Zhang, Sangwon Lee, and Hongjie Dai*
Science Express (2008)
L. A. Ponomarenko, F. Schedin, M. I. Katsnelson, R. Yang, E. H. Hill, K. S. Novoselov, A. K.Geim, Science (2008)
0 dimensional systems (topdown)graphene
0 dimensional systems (bottomup)graphene
Vazquez de Parga et al., PRL (2008)
0 dimensional systems (bottomup)polycyclic aromatic hydrocarbons (PAH’s)
Naphthacene
Pentacene
Benzo[a]pyrene
Benz[a]ovalene
Benz[d]ovalene
Chrysene
Anthracene
Corannulene
Triphenylene
Pyrene
Coronene
Ovalene
0 dimensional systems (bottomup) disklike polycyclic aromatic hydrocarbons (PAH’s)
J. Wu, M. D. Watson, K. Müllen, Angew. Chem. Int. Ed. 42, 5329 (2003)
OutlineNanographenes
Vacancies and voids in graphene and graphene ribbons
J. FernándezRossier and J. J. Palacios, Phys. Rev. Lett. 99, 177204 (2007)
J. J. Palacios, J. FernándezRossier, and L. Brey, Phys. Rev. B 77, 195428 (2008)
OutlineNanographenes
Vacancies and voids in graphene and graphene ribbons
J. FernándezRossier and J. J. Palacios, Phys. Rev. Lett. 99, 177204 (2007)
J. J. Palacios, J. FernándezRossier, and L. Brey, Phys. Rev. B 77, 195428 (2008)
Theoretical description of graphene
0usually
neighborsfirst if eV 5.2
ˆˆˆˆ
=
==
+= ∑∑ +
i
ij
ijjiij
iii
tt
cctnH
ε
ε
A
B
t
B Bt t
Electronic structure of graphene
DOS
Band structure
Energy
Nanographenes
Nanographenes
Nanographenes
Nanographenes
Nanographenes
( ) ( )
( ) ( ) ( )
( ) ( )
A siteson only weight and 0 with states least At
?1 ifWhat
0ˆˆˆˆˆˆ
ˆ
:A siteson only ht with weigstate aconsider usLet 0 with state 1least At
?1 e.g., odd, ifWhat
ˆˆˆˆˆˆ
ˆˆˆ and ˆˆˆ
ˆˆˆˆˆ
ˆ ˆ
=−>−
=⇒
−=⇒−−=−
=
==−
−−=−=−
==
+=+
== ∑ ∑∈ ∈
ENN
NN
EEHPPEPPH
EH
E
NNN
PPEPPEPPH
PEPHPEPH
PPEPPH
jjPiiP
BA
BA
AAABAABA
AA
BA
BAABBA
ABBA
BABA
Ai BjBA
φφφφ
φφ
φφφ
φφφφ
φφ
Understanding the spectra
M. Inui, S. A. Trugman, and E. Abrahams
Phys. Rev. B 49, 3190 (1994)
( ) ( )
( ) ( ) ( )
( ) ( )
A siteson only weight and 0 with states least At
?1 ifWhat
0ˆˆˆˆˆˆ
ˆ
:A siteson only ht with weigstate aconsider usLet 0 with state 1least At
?1 e.g., odd, ifWhat
ˆˆˆˆˆˆ
ˆˆˆ and ˆˆˆ
ˆˆˆˆˆ
ˆ ˆ
=−>−
=⇒
−=⇒−−=−
=
==−
−−=−=−
==
+=+
== ∑ ∑∈ ∈
ENN
NN
EEHPPEPPH
EH
E
NNN
PPEPPEPPH
PEPHPEPH
PPEPPH
jjPiiP
BA
BA
AAABAABA
AA
BA
BAABBA
ABBA
BABA
Ai BjBA
φφφφ
φφ
φφφ
φφφφ
φφ
Understanding the spectra
M. Inui, S. A. Trugman, and E. Abrahams
Phys. Rev. B 49, 3190 (1994)
Understanding the spectra
( ) ( )
( ) ( ) ( )
( ) ( )
A siteson only weight and 0 with states least At
?1 ifWhat
0ˆˆˆˆˆˆ
ˆ
:A siteson only ht with weigstate aconsider usLet 0 with state 1least At
?1 e.g., odd, ifWhat
ˆˆˆˆˆˆ
ˆˆˆ and ˆˆˆ
ˆˆˆˆˆ
ˆ ˆ
=−>−
=⇒
−=⇒−−=−
=
==−
−−=−=−
==
+=+
== ∑ ∑∈ ∈
ENN
NN
EEHPPEPPH
EH
E
NNN
PPEPPEPPH
PEPHPEPH
PPEPPH
jjPiiP
BA
BA
AAABAABA
AA
BA
BAABBA
ABBA
BABA
Ai BjBA
φφφφ
φφ
φφφ
φφφφ
φφ
M. Inui, S. A. Trugman, and E. Abrahams
Phys. Rev. B 49, 3190 (1994)
Triangles vs. hexagons
Triangles vs. hexagons
Electronelectron interactions
Electronelectron interactions
Superatomic Hunds’s rule
Electronelectron interactions
( ) cteˆˆˆˆ Uˆˆˆ
:ionapproximat consistentself fieldMean
ˆˆ Uˆˆˆ
++++=
++=
∑∑∑
∑∑∑
↑↓↓↑+
↓↑+
iiiii
ijjiij
iii
iii
ijjiij
iii
nnnncctnH
nncctnH
σσσ
σσσ
σσσ
σσσ
ε
ε
Hubbard model
Density functional theory(GAUSSIAN03)
KohnSham equations (unrestricted)GGA (BLYP) approximation to the functional (avoid hybrids, e.g., B3LYP)Saturation of dangling bonds with H
DFT vs meanfield Hubbard
Hubbard model(U=3.85 eV, t=2.5 eV)
DFT
Ferromagnetic order
Lieb’s theorem/LonguetHiggins conjecture
LonguetHiggins, J. Chem. Phys. 18, 265 (1950)
(1) The number of unpaired electrons present in the ground state is at least as great as the number of carbon atoms having a deficiency of valence bonds in any principal resonance structure. (2) With a few special exceptions, these odd electrons are distributed over just those atoms which have a deficiency of valence bonds in one or more of the principal resonance structures. (3) In singly charged hydrocarbon anions or cations the ionic charge is located on just those atoms which bear charges in
the various principal resonance structures.
E. H. Lieb, Phys. Rev. Lett. 62, 1201 (1989)
Ferrimagnetic order
Ferrimagnetic order
OutlineNanographenes
Vacancies and voids in graphene and graphene ribbons
J. FernándezRossier and J. J. Palacios, Phys. Rev. Lett. 99, 177204 (2007)
J. J. Palacios, J. FernándezRossier, and L. Brey, Phys. Rev. B 77, 195428 (2008)
Vacancies = H adsorption
Jannik C. Meyer, C. O. Girit, M. F. Crommie, A. Zettl, arXiv:08053857
A few words about ribbons (armchair)
Son et al., Phys. Rev. Lett. 97, 216803 (2006)
Basic definitionsBA NN BA
44BA B 13BA
IBA NNN =− :charge imbalance Local
0=IN 1−=IN 2=IN
∑ ∑
∑ ∑−+
−+
+=
+=
α β
α β
βα
βα
)()(
)()(
max
min
IIZ
IIZ
NNN
NNN
Basic scenarios
well.as situations in these respin textu theascertain tonecessary be willnsCalculatio moments. magnetic uncoupled are theresince negligible is gap flipspin thecase, previous the
in as but,,2 has state ground The case. generalmost theis This not. some and
uncoupled are themof somebut sign,different of voidsare There: 4.
moments. magnetic uncoupled
are theresince negligible is gap flipspin but the , 2 has state ground The
uncoupled. and separated are typedifferent of voids theAll : 3.
.situations in these
respin textu theascertain tonecessary be willnsCalculatio state. 2 a yielding
interact, andproximity in aresign different of voids theAll : 2.
coupling. voidinter on the depend willstatesspin smaller
with splitting The .2 is state ground theofspin theand ticferromagne always
is embetween th coupling The sign. same theof are voids theAll : 1.
min
maxmin
min
maxmin
min
maxmin
maxmin
Z
ZZZ
Z
ZZZ
Z
ZZZ
Z
ZZZ
NS
NNN
NS
NNN
NS
NNN
NS
NNN
=
<<
=
=<
=
<=
=
==
Basic scenarios
well.as situations in these respin textu theascertain tonecessary be willnsCalculatio moments. magnetic uncoupled are theresince negligible is gap flipspin thecase, previous the
in as but,,2 has state ground The case. generalmost theis This not. some and
uncoupled are themof somebut sign,different of voidsare There: 4.
moments. magnetic uncoupled
are theresince negligible is gap flipspin but the , 2 has state ground The
uncoupled. and separated are typedifferent of voids theAll : 3.
.situations in these
respin textu theascertain tonecessary be willnsCalculatio state. 2 a yielding
interact, andproximity in aresign different of voids theAll : 2.
coupling. voidinter on the depend willstatesspin smaller
with splitting The .2 is state ground theofspin theand ticferromagne always
is embetween th coupling The sign. same theof are voids theAll : 1.
min
maxmin
min
maxmin
min
maxmin
maxmin
Z
ZZZ
Z
ZZZ
Z
ZZZ
Z
ZZZ
NS
NNN
NS
NNN
NS
NNN
NS
NNN
=
<<
=
=<
=
<=
=
==
Basic scenarios
well.as situations in these respin textu theascertain tonecessary be willnsCalculatio moments. magnetic uncoupled are theresince negligible is gap flipspin thecase, previous the
in as but,,2 has state ground The case. generalmost theis This not. some and
uncoupled are themof somebut sign,different of voidsare There: 4.
moments. magnetic uncoupled
are theresince negligible is gap flipspin but the , 2 has state ground The
uncoupled. and separated are typedifferent of voids theAll : 3.
.situations in these
respin textu theascertain tonecessary be willnsCalculatio state. 2 a yielding
interact, andproximity in aresign different of voids theAll : 2.
coupling. voidinter on the depend willstatesspin smaller
with splitting The .2 is state ground theofspin theand ticferromagne always
is embetween th coupling The sign. same theof are voids theAll : 1.
min
maxmin
min
maxmin
min
maxmin
maxmin
Z
ZZZ
Z
ZZZ
Z
ZZZ
Z
ZZZ
NS
NNN
NS
NNN
NS
NNN
NS
NNN
=
<<
=
=<
=
<=
=
==
Basic scenarios
well.as situations in these respin textu theascertain tonecessary be willnsCalculatio moments. magnetic uncoupled are theresince negligible is gap flipspin thecase, previous the
in as but,,2 has state ground The case. generalmost theis This not. some and
uncoupled are themof somebut sign,different of voidsare There: 4.
moments. magnetic uncoupled
are theresince negligible is gap flipspin but the , 2 has state ground The
uncoupled. and separated are typedifferent of voids theAll : 3.
.situations in these
respin textu theascertain tonecessary be willnsCalculatio state. 2 a yielding
interact, andproximity in aresign different of voids theAll : 2.
coupling. voidinter on the depend willstatesspin smaller
with splitting The .2 is state ground theofspin theand ticferromagne always
is embetween th coupling The sign. same theof are voids theAll : 1.
min
maxmin
min
maxmin
min
maxmin
maxmin
Z
ZZZ
Z
ZZZ
Z
ZZZ
Z
ZZZ
NS
NNN
NS
NNN
NS
NNN
NS
NNN
=
<<
=
=<
=
<=
=
==
Single vacancy: A
Single vacancy: A
∑=Σi
im2
∑=i
v i4
)(φη
Spincharge separation
0=Q
1=Q
Charge Spin
A and A2
Two vacancies
A+A
A+B
Two vacancies: A and B(no interactions)
Two voids: A2 and B2(no interactions)
Large voids with NI=0
Two notches
Single vacancy in bulk graphene
20 )(irrR v
ii φ∑ −=
Bd
Add
iBAi
iBA
d
MMM
mrrM
+=
−= ∑∈ )(
0)(
Single vacancy in bulk graphene
Finite density of vacancies: Compensated graphene (NI=0)
Future work Magnetic structure of more generic PAH’s or nanographenes Thermal fluctuations: Superparamagnetism Stability of open shell structures (radicals) Change of properties when deposited on surfaces Devices
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