JOINT ICTP/SISSA CONDENSED MATTER SEMINARS: "Re-Visiting Orbital Diamagnetism: A Surprise"

[Statistical Physics Group]

JOINT ICTP/SISSA CONDENSED MATTER SEMINARS



Seminar Room - ICTP Leonardo Building

(first floor)







Wednesday, 15 April -     4:00 p.m.


N. KUMAR

( Raman Research Institute, Bangalore )

"Re-Visiting Orbital Diamagnetism: A Surprise"

Abstract

It is  generally known that the orbital diamagnetism of a classical  
system of charged particles in thermal equilibrium is identically  
zero - the Bohr-van Leeuwen theorem. Physically, this null result  
derives from the exact cancellation of the orbital diamagnetic moment  
associated with the complete cyclotron orbits of the charged  
particles by the paramagnetic moment subtended by the incomplete  
orbits skipping the boundary in the opposite sense. Motivated by this  
crucial, but subtle role of the boundary, wed have simulated here the  
case of a finite but unbounded system, namely that of a charged  
particle moving on the surface of a sphere in the presence of an  
externally applied uniform magnetic field. Following a real space- 
time approach based on the classical Langevin equation, we have  
computed the orbital magnetic moment which now indeed turns out to be  
non-zero, and has the diamagnetic sign. To the best of our knowledge,  
this is the first report of the possibility of finite classical  
diamagnetism in principle, and it is due to the avoided cancellation