Nano-Science Center > Seminarer og events > Electron-electron inte...

Electron-electron interactions in quantum point contacts and finite quantum wires

PhD defence by (Anders) Mathias Lunde, Nano-Science Center. 

Abstract
The presentation will be on the effect of electron-electron
interactions on the transport properties in long and short quantum
point contacts, i.e. in

(A) Finite length clean quantum wires and
(B) Point-like contacts.

In both situations, the system is perfectly connected to the leads
(integer transmission at zero temperature). The main difference is
that the point-like contacts are so short that they break the
translational invariance and hence the electron-electron
interaction processes do not have to conserve momentum (in
contrast to the finite quantum wires). Common for both cases is
that without interactions the conductance is 2e2/h times
the number of modes and the thermopower is exponentially
suppressed at low temperatures.

In the two cases, we find different features:

(A) In a single-mode finite quantum wire two-particle interactions
cannot change the distribution of electrons due to momentum and
energy conservation. Therefore multi-mode wires are considered and
we find that the interaction induced resonances in the conductance and thermopower at particular values of the Fermi level (i.e. gate voltage).

(B) For a point-like constriction, two-particle scattering can
change the current even for a single-mode. Therefore a weak
interaction V0 changes the current as I(T,V)/V=2e2/h-a |V0|2T2-b |V0|2V2 and the thermopower as S=c |V0|2T3 for low temperature
T and/or small bias V (a,b and c are constants). Furthermore, the noise is reduced compared to the single-particle case. In a large magnetic field, the interaction among electrons of equal spin suppress the low-temperature corrections to the transport properties by two extra powers of temperature. The conductance versus temperature (for B=0) beyond the perturbative regime was found in a self-consistent 2nd order approach. Based on numerical results, we conjecture that the conductance approach about e2/h for higher temperatures, however, still lower than the Fermi temperature. These results are all in qualitative agreement with experimental studies on the 0.7 anomaly in quantum point contacts.

The committee for the PhD defence is going to be:

Carlo Beenakker (Leiden),
Alexander Chudnovskiy (Hamburg),
Henrik Smith (Copenhagen) (Chairman).
------------------------------------------
Supervisor: Karsten Flensberg
------------------------------------------

After the defence there will be a RECEPTION on the second floor of
the D-building (HCØ), where you are most welcome (also if you
skipped the defence;-)).