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Resonant tunneling of fluctuation Cooper pairs.

Galda A, Mel'nikov AS, Vinokur VM - Sci Rep (2015)

Bottom Line: According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc.This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors.Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.

View Article: PubMed Central - PubMed

Affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.

ABSTRACT
Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.

No MeSH data available.


Related in: MedlinePlus

I–V characteristics for 1D and 3D SIS junctions in fluctuation regime.(a) Tunneling current through the 1D junction develops resonant spikes at resonant values , which grow sharper upon approaching Tc due to increasing lifetime of fluctuation Cooper pairs. At higher dc bias voltages the current decreases monotonically as a function of V0. System parameters used for the calculation: , . (b) Tunneling current in the 3D model. For the resonant spikes in the 3D setup to be visible, one requires higher ratios of  as compared to the 1D system. Parameters used: , , which is equivalent to Tc = 10 K, microwave frequency of 1 THz and V1 = 6.6 mV.
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f3: I–V characteristics for 1D and 3D SIS junctions in fluctuation regime.(a) Tunneling current through the 1D junction develops resonant spikes at resonant values , which grow sharper upon approaching Tc due to increasing lifetime of fluctuation Cooper pairs. At higher dc bias voltages the current decreases monotonically as a function of V0. System parameters used for the calculation: , . (b) Tunneling current in the 3D model. For the resonant spikes in the 3D setup to be visible, one requires higher ratios of as compared to the 1D system. Parameters used: , , which is equivalent to Tc = 10 K, microwave frequency of 1 THz and V1 = 6.6 mV.

Mentions: In Fig. 3 we plot the I–V characteristics for 1D and 3D setups, illustrating that the effect of resonant fluctuation Cooper pair tunneling should be observable across all effective dimensionalities of the SIS junction. The total current in the 3D case, depicted in Fig. 3b, is normalized by the characteristic number of fluctuation modes . As can be seen from the expression for the current in 3D (see Methods), ωτGL is no longer a single parameter defining the shape of the resonances. Instead, the ratio now determines how well pronounced the spikes around can be upon approaching the critical temperature, i.e. lowering . In order to clearly observe sharp Shapiro resonances in the Gaussian fluctuation regime for a 3D junction, much higher values of are required as compared to the 1D case, by an order of magnitude or more, assuming the same range of temperatures. This is due to the fact that the slope of Shapiro spikes in 3D is much less sensitive to as one approaches Tc. In fact, in close vicinity of each resonant value the tunneling current takes the following form:where Jn is the Bessel function of the first kind and d is the effective dimensionality of the junction. While for 1D junctions Shapiro peaks should be observable at frequencies of tens of GHz and just fractions of a Kelvin away from a typical critical temperature Tc ~ 10 K, in order to produce reasonably sharp resonant features in the 3D regime, one would need to use frequencies of at least hundreds of GHz – several THz and be able to measure temperature with almost millivolt precision.


Resonant tunneling of fluctuation Cooper pairs.

Galda A, Mel'nikov AS, Vinokur VM - Sci Rep (2015)

I–V characteristics for 1D and 3D SIS junctions in fluctuation regime.(a) Tunneling current through the 1D junction develops resonant spikes at resonant values , which grow sharper upon approaching Tc due to increasing lifetime of fluctuation Cooper pairs. At higher dc bias voltages the current decreases monotonically as a function of V0. System parameters used for the calculation: , . (b) Tunneling current in the 3D model. For the resonant spikes in the 3D setup to be visible, one requires higher ratios of  as compared to the 1D system. Parameters used: , , which is equivalent to Tc = 10 K, microwave frequency of 1 THz and V1 = 6.6 mV.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4321188&req=5

f3: I–V characteristics for 1D and 3D SIS junctions in fluctuation regime.(a) Tunneling current through the 1D junction develops resonant spikes at resonant values , which grow sharper upon approaching Tc due to increasing lifetime of fluctuation Cooper pairs. At higher dc bias voltages the current decreases monotonically as a function of V0. System parameters used for the calculation: , . (b) Tunneling current in the 3D model. For the resonant spikes in the 3D setup to be visible, one requires higher ratios of as compared to the 1D system. Parameters used: , , which is equivalent to Tc = 10 K, microwave frequency of 1 THz and V1 = 6.6 mV.
Mentions: In Fig. 3 we plot the I–V characteristics for 1D and 3D setups, illustrating that the effect of resonant fluctuation Cooper pair tunneling should be observable across all effective dimensionalities of the SIS junction. The total current in the 3D case, depicted in Fig. 3b, is normalized by the characteristic number of fluctuation modes . As can be seen from the expression for the current in 3D (see Methods), ωτGL is no longer a single parameter defining the shape of the resonances. Instead, the ratio now determines how well pronounced the spikes around can be upon approaching the critical temperature, i.e. lowering . In order to clearly observe sharp Shapiro resonances in the Gaussian fluctuation regime for a 3D junction, much higher values of are required as compared to the 1D case, by an order of magnitude or more, assuming the same range of temperatures. This is due to the fact that the slope of Shapiro spikes in 3D is much less sensitive to as one approaches Tc. In fact, in close vicinity of each resonant value the tunneling current takes the following form:where Jn is the Bessel function of the first kind and d is the effective dimensionality of the junction. While for 1D junctions Shapiro peaks should be observable at frequencies of tens of GHz and just fractions of a Kelvin away from a typical critical temperature Tc ~ 10 K, in order to produce reasonably sharp resonant features in the 3D regime, one would need to use frequencies of at least hundreds of GHz – several THz and be able to measure temperature with almost millivolt precision.

Bottom Line: According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc.This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors.Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.

View Article: PubMed Central - PubMed

Affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.

ABSTRACT
Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.

No MeSH data available.


Related in: MedlinePlus