[seminar] Seminar na IF-u, 18. rujna 2014. u 15:00h

[Niksa Krstulovic]

Institut za fiziku, Bijenička cesta 46, 

predavaonica u zgradi Mladen Paić četvrtak, 18. rujna 2014., u 15:00 sati 


FINGERPRINTS OF HOPPING CONDUCTIVITY IN DISORDERED CHARGE DENSITY WAVE SYSTEMS 

Dr. Damir Dominko 



Institut za fiziku, Zagreb E-mail: ddominko at ifs.hr 



Electric conductivity of charge density wave (CDW) systems exhibits rich variety of behavior; thermal activation across the gap at low fields below transition temperature T P , collective contribution (nonlinear conductivity channel) above the threshold field (E T ) and variable range hopping (VRH) at low temperatures 1 and in granulated thin films in the whole temperature range 2 . Particularly the origin of the hopping conductivity is still unclear. 

We have investigated the influence of disorder on conductivity phenomena in CDW systems TaS 3 and blue bronze (BB: K 0.3 MoO 3 ) in a wide range of temperatures and electric fields using both the DC and pulse measurements at low and high fields respectively. Disorder has been introduced in several ways: (1) synthesis of TaS 3 samples doped with Nb, (2) irradiation of nominally pure TaS 3 samples and (3) deposition of granular thin BB films by pulsed laser deposition (PLD). 

Our results show that the nonlinear conductivity can be described by VRH already below 50 K in contrast to the linear channel, where it appears only below 20 K 1 . Moreover, the point defects in TaS3 introduced by doping and irradiation have no effect on VRH behavior. Together with the dielectric data, we will reevaluate microscopic picture of soliton hopping in CDW at low temperatures 1,2,3 . In granular thin BB films, on the other hand, the influence of grain boundaries is overwhelming even above T P , which is in contrast to the previous experiments on thin BB films 5 . The results can be understood by applying recent theoretical results for Beloborodov's Efros-Shlovskii VRH in granular materials 6 . 




[1] M. E. Itkis, F. Ya. Nad, and P. Monceau, J. Phys. Cond. Matt. 2 (1990) 8327 

[2] M. Đekić et al, Vacuum 98 (2013) 93-99 

[3] W. F. Pasveer, P. A. Bobbert, and M. A. J. Michels, Phys. Rev. B 74 (2006) 165209 

[4] A. S. Rodin and M. M. Fogler, Phys. Rev. B 80 (2009) 155435 

[5] O. C. Mantel, C. A. W. Bal, C. Langezaal, C. Dekker and H. S. J. Van Der Zant, J. App. Phys. 86, 4440 (1999) [6] I. Beloborodov, A. Lopatin, V. Vinokur, and K. B. Efetov, Rev. Mod. Phys. 79 ( 2007) 469-518 



Voditelji seminara IF-a: Nikša Krstulović i Osor Bari šić 


************************* 
Nikša Krstulović, PhD 
Research associate 

Institute of Physics 
Bijenicka 46 
HR-10000 Zagreb, Croatia 

Phone: 00385 1 4698 872 
00385 1 4698 851 
Fax: 00385 1 4698 889 

http://www.ifs.hr/ 
http://spectra.ifs.hr/ 
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