Computer simulation of tunneling characteristics of superconducting - - PowerPoint PPT Presentation

Computer simulation of tunneling characteristics of superconducting nanostructures

Supervisor: Dr. Yury Shukrinov Co-supervisors: Ilhom Rahmonov Kirill Kulikov Laboratory of Theoretical Physics

Students: Aleš Popelka, Czech Technical University in Prague, Czech Republic Martin Synek, Czech Technical University in Prague, Czech Republic Vlad-Stefan Raducanu, University of Bucharest, Romania

Outline

I. The effect of Josephson II. Intrinsic Josephson junctions

• III. Shapiro steps
• IV. Model and method of simulation

V. Results

• VI. Conclusions

The effect of Josephson

Shapiro steps

Bi2Sr2CaCu2O8+δ

Intrinsic Josephson junctions

► The layered high-Tc superconducting materials as Bi2Sr2CaCu2O8+δ can be considered as a stack of Josephson junctions. In this system the intrinsic Josephson effect was

• bserved.

► This system can be used as a terahertz electromagnetic radiation sources.

Stack of Josephson junctions

• We solved the differential equations system with the Runge-Kutta method of order 4,

for fixed value of the current I.

• We obtained the voltage – time dependence at the fixed current.
• We calculated the average value of the voltage over time and put the point on the CVC

at the corresponding fixed current value.

• We computed the charge density as being proportional to the voltage difference

between two neighbor layers.

• We repeated this procedure by increasing and decreasing the current in small steps.

Results for single JJ without external radiation

β=1.5

FFT analysis for sinusoidal voltage

Results for single JJ with external radiation

Results for stack JJ without external radiation

Results for stack JJ with external radiation

Results for stack JJ with external radiation

Conclusions

• The mathematical modeling of the system gave us some of the physical

properties: calculate CVC, demonstration of Josephson oscillations, Shapiro steps on the CVC, parametric resonance and longitudinal plasma wave in the stack of Josephson junctions.

• Was demonstrated the possibility of realization of parametric resonance

in the stack of Josephson junctions.

• In the parametric resonance region and nearby some Shapiro steps is
• bserved existence of the longitudinal plasma wave. There are regions

where charge is nonzero.

• In the presence of radiation the wavelength of the plasma wave changes.

Thank you for your attention ! Q&A