Scanning tunneling spectroscopy of a 1DES
One-dimensional electron systems (1DES) are particularly interesting
since the electron-electron interaction in a 1DES is pathological.
Theory predicts that a single-particle description of the system
breaks down (at least close to the Fermi level) and many-particle
excitations are the only excitations. They are spin and charge
density waves with different Fermi velocities. Due to the
different velocities, one speaks about spin-charge separation and
the system is called a Luttinger liquid to distinguish it
from Fermi liquids still described within the single-particle
|Fig. 1: from left to right: first: STM image of a step edge; next: same image after
subtracting the average step edge showing the disorder as bright and dark spots;
next: resulting disorder potential; remaining: LDOS of the
1DES at different energies as indicated.
We investigated several 1DESs which are confined below charged step edges
One step edge is shown in the left column of Fig. 1.
This 1DES exhibits two-subbands, but others exhibit only one subband.
The determined subband energies in the displayed case
correspond to an average kinetic energy of 20 meV and to an average
electron-electron interaction strength of 25 meV within the 1DES. The 1DES is
to disorder, which has been determined and is shown in he third
column of Fig. 1. It exhibits fluctuations of a rms-value of 10 meV.
The other columns of Fig. 1 display the measured LDOS at the step edge
energies. Alignement of the LDOS with the potential disorder can be observed
e.g. at the potential valley marked by an arrow, where
a bright spot is found at -40 mV (resonant state).
|Fig. 2: left: Fourrier transforms of the measured LDOS of two different 1DES;
right: corresponding calculated Fourrier transforms.
Surprisingly the LDOS could be largely reproduced by a single-particle
calculation. This is demonstrated in Fig. 2, where Fourrier transforms
representing the k-space distribution of the states are shown for two
different step edgese with one and two subbands, respectively.
The yellow lines show the expected single-particle dispersion
of a not disordered system. Obviously the k-space distribution largely
follows the undisturbed dispersion with additional intensity within
the parabola. More importantly, the measured k-space distrĂbution
is very similar to the calculated one.
In particular, the k-value expected for the charge-density wave within the Luttinger
model, also indicated, exhibits no intensity.
This intriguing result is currently not completely understood, but might be a
good starting point for further investigations of the 1DES case.
Chr. Meyer, J. Klijn, M. Morgenstern, and R. Wiesendanger, Phys. Rev. Lett.:
Direct measurement of the local density of states of a disordered one-dimensional conductor.
Introduction to STM | Instrumentation | Results / Projects | Gallery | Publications | Team
impressum © copyright 2002 by group R - university of hamburg