Thursday's seminar

[CM ICTP - Trieste]

Sseminar on  Disorder and strong electron correlations


Thursday, 22 May      -  11:00 a.m.



Seminar Room,  Leonardo Bldg.- first floor





G. SENATORE ( Università degli Studi di Trieste & INFM-CNR Democritos )


"Modeling the two-dimensional electron gas in solid state devices"



Abstract

The electron gas (EG), a collection of point charges moving in a 
homogeneous neutralizing background, provides a far reaching paradigm 
underlying our current understanding of electronic systems.  Nowadays,  
quasi two-dimensional electron gases of exceedingly high mobility are 
routinely available in the best laboratories around the world.  This 
allows for the experimental investigation of the two-dimensional 
electron gas  (2DEG) in the strong coupling regime, where the interplay 
between interaction and disorder scattering has unexpected effects, 
such as an apparent metal to insulator transition (MIT) which has 
attracted a considerable experimental and theoretical interest.  
Evidently, fine details of the devices hosting the quasi 2DEG play an 
important role in determining its properties and should be accounted 
for by theory. In actual solid-states realizations the 2DEG (i) has a 
finite transverse thickness, (ii) suffers scattering by a number of 
sources (scattering which in fact determines its mobility), and 
depending on the system (iii)  occupies one or two valleys; moreover, 
(iv) in certain AlAs quantum wells it may have an in plane anisotropic 
kinetic energy (mass tensor).  A property of the 2DEG that has recently 
received a lot of attention in connection with the MIT is the spin 
susceptibility. This measures the linear response of the electrons to 
an applied magnetic field that couples to the electron spin, causing a 
net spin polarization. We demonstrate that the EG model is perfectly 
capable of describing the available experimental evidence for spin 
susceptibility once two conditions are met:  relevant device details 
are included in the theoretical description and strong correlation 
effects are dealt with by a sufficiently accurate technique, such as 
quantum Monte Carlo simulations (QMC).  In particular,  we show that a 
perturbative account of disorder, based on the  QMC predictions for the 
clean interacting 2DEG, yields for two-valley systems a divergence of 
spin susceptibility with lowering the density in excellent agreement 
with the available  experimental evidence for Si-MOSFETs.