Wed-Thurs seminars

[Cond.Matt. & Stat.Mech.Section]

JOINT ICTP/SISSA   COLLOQUIUM    ON CONDENSED MATTER PHYSICS

 

Wednesday, 9 March -  4:30 p.m.

  

Luigi Stasi Seminar Room - ICTP Leonardo Building (1st floor)

  

Paolo POSTORINO   (University of Rome "La Sapienza')

 

" Tuning lattice distortion by pressure: The insulator to metal transition and the onset of phase separated states"

 

Abstract

 The experimental accessibility of high density phases in condensed matter systems, thanks to the advances of high pressure techniques over the last years, has switched pressure from being a less common external perturbation probe into an increasingly versatile tool in materials research.  Here, I want to focus on some selected pressure-induced effects in crystalline systems, in particular on how the natural effect of promoting more symmetric structure upon compressing the lattice can be worked out into a tuning of local and extended lattice distortions arising from charge-lattice coupling.  This is the exemplary case of the spontaneous symmetry breaking occurring in Jahn-Teller and Peierls systems.  The physics of these correlated materials is quite complex and typically characterized by a delicate interplay among different interactions at the same energy scale.  Applying pressure, over even a relatively small range (0-40 GPa), causes these systems to reach new, and sometimes unconventional, states but it also enables to disentangle the effects of the different coupling mechanisms thus gaining a deeper knowledge of the  ambient conditions phases.  As an example of a Jahn-Teller system I present an extended experimental study of La-Ca manganites (La1-xCaxMnO3) under high pressure (range 0-30 GPa), with particular attention to the parent LaMnO3 compound and the LaMn1-xGaxO3 family.  Recent high pressure experiments (range 0-20 GPa) on several Vanadium oxides with special focusing to the case of VO2 (Peierls system) is also discussed.  We will see that, apart from the characterization of the new higher density phases, the high pressure studies provide key information on the physics of these systems at ambient pressure which stimulates their theoretical modeling.



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SEMINAR on  Disorder and strong electron correlations

  

Thursday, 10 March -  11:30 a.m.

 

Luigi Stasi Seminar Room,  Leonardo Building - first floor

 

Valentin Y. KACHOROVSKII     ( A.F. Ioffe Physical-Technical Institute, St. Petersburg )

  

"Aharonov-Bohm conductance through   a single-channel quantum ring"

 

Abstract

We study the effect of electron-electron interaction on transport through a tunnel-coupled single-channel ring. We find that the conductance as a function of magnetic flux shows a series of interaction-induced resonances that survive thermal averaging.  The period of the series is given by the interaction strength alpha.  The physics behind this behavior is the blocking of the tunneling current by the circular current.  The main mechanism of dephasing is due to circular-current fluctuations.  The dephasing rate is proportional to the tunneling rate and does not depend on alpha.