Chemistry Reference
In-Depth Information
Figure 1.19. Generic
T-P
phase diagram for BFS. The origin on the pressure axis is
arbitrarily set for (TMTTF)
2
PF
6
. MH, Mott-Hubbard; M, Metal; SP, Spin-Peierls;
AF, Antiferromagnetic; SDW, Spin-Density-Wave; SC, Superconductor. Adapted
from Auban-Senzier & Jerome, 2003.
salts undergo MH-Spin-Peierls (SP) and M-spin-density-wave (SDW) transitions.
In both cases
E
t
=
0, which becomesmore evident for the (TMTSF)
2
Xsalts because
of the metal to semiconductor transition. The most salient feature of this generic
phase diagram is the existence of a wide variety of ground states below
c
.20K.
(TMTTF)
2
PF
6
is the only known system that can be driven through the entire series
of ground states: SP, AF, SDW and SC by applying an external pressure, deserving
selection as origin of the pressure axis in Fig. 1.19. The case of (TMTSF)
2
ClO
4
is
also important since it is the onlymaterial that becomes a superconductor at ambient
pressure. The generic M region should in fact be divided into Fermi liquid and
Luttinger liquid regions, a point that will be briefly discussed in Sections 1.7 and 6.1.
The series of 2D superconductors based on the BEDT-TTFmolecule is extremely
rich because of the large number of polymorphs and because, to date, they exhibit
the highest
T
c
values with
T
c
-(BEDT-TTF)
2
Cu[N(CN)
2
]Cl (see
Table 1.8). Figure 1.20 shows different arrangements of the BEDT-TTF layers
for the
12
.
8 K for
κ
,
,
α
,
β
,
β
β
γ
,
δ
,
κ
and
θ
crystallographic phases. The
α
-phase exhibits
a herringbone arrangement, similar to the
-structure found in fused-ring aro-
matic hydrocarbons, as discussed in Section 1.4. The
γ
θ
-phase can be regarded as
