Chemistry Reference
In-Depth Information
and Doniach [40] confirmed our findings in a detailed and systematic mean
field theory and discovered an important result for the order parameter
symmetry. They found that the lowest energy mean field solution corre-
sponds to
d
+
id
symmetry, an unconventional order parameter, rather than
the extended-
s
solution. The value of mean field
T
c
obtained was an order
of magnitude larger than room temperature!
Although results of the mean-field theory are encouraging, it is far from
certain that the superconducting ground state is stable to quantum fluctua-
tions. In particular, our Hamiltonian does not include
which inhibits local
number fluctuations. In the more basic Hubbard model, a superconduct-
ing state will suffer further quantum mechanical phase fluctuations since
U
U
inhibits local number fluctuations. The key question therefore is does the
singlet promotion arising out of the local correlation physics strong enough
to resist the destruction of superconductivity arising out of quantum phase
fluctuations induced by
U
?
6
4
2
0
0
0.1
0.2
0.3
Doping, x
Fig. 8. Strength of superconducting order parameter, as extracted from the Cooper
pair correlation function.
To investigate the possibility of superconductivity in doped graphene we
construct a variational ground state and optimize it using variational quan-
tum Monte Carlo (VMC).
[
46
]
Thegroundstateweconstructismotivated
by the mean-field theory of our model
ε
)
=
k
a
k
σ
b
k
σ
+h. c.)
MF
GB
a
k
σ
b
k
σ
H
(
k
)(
− µ
f
(
n
+
n
a
k
↑
b
†
−
k
↓
− a
k
↓
b
†
−
k
↑
−
∆(
k
)(
)+h. c.
k
