Chemistry Reference
In-Depth Information
-k
F
k
F
3k
F
0
0.0
(a)
(b)
"spin"
~
(J)
-0.2
-0.4
"charge"
-0.6
~
(t)
-0.8
- /2
/2
-0.2
0.0
0.2
0.4
0
momentum along b* (Å
-1
)
momentum
Figure 6.13. (a) Schematic electron removal spectrum of the doped 1D Hubbard
model with band filling 1
3. The shaded region denotes the continuum
resulting from spin-charge separation. The solid curves indicate the dispersions of
the spin and charge singularity branches. (b) Theoretical spin and charge branch
dispersions of the 1D Hubbard model calculated for
U
/
2
<
N
at
<
2
/
=
1
.
96 eV,
W
=
1
.
6eV,
and
N
at
=
59 in comparison to the experimental ARUPS spectra. Reprinted with
permission from M. Sing, U. Schwingenschlolgl, R. Claessen, P. Blaha, J. M. P.
Carmelo, L. M. Martelo, P. D. Sacramento, M. Dressel and C. S. Jacobsen,
Physical
Review B
,
68
, 125111 (2003). Copyright (2003) by the American Physical Society.
0
.
200 cm
−
1
. These are the characteristics of a highly anisotropic interacting electron
system, with either a half- or a quarter-filled band. This leads to a Mott gap and,
at frequencies above the effective interchain transfer integral, to a Luttinger liquid
state. On the other hand, evidence for the separation of spin and charge in BFS has
been suggested based on thermal conductivity experiments, where it is shown that
spin excitations have a much larger thermal conductivity than charge excitations
(Lorenz
et al.
, 2002).
Electronic structure of unoccupied states
The unoccupied electronic states of a solid can be experimentally explored by
different techniques. The most commonly used are inverse photoemission, where
low-energy electrons impinge on the surface of the solid, and the photon-based
techniques ellipsometry, NEXAFS and constant-initial-state spectroscopy. Results
derived from inverse photoemission spectroscopy might be questionable unless
low-energy electrons (
c
. 10-20 eV) and low beam currents are used as in LEED
