Biomedical subjects

T T Heikkilä

Publications and source records attributed to T T Heikkilä.

4 recordsLinked to original sources

PubMed2004

Observation of shot-noise-induced asymmetry in the Coulomb blockaded Josephson junction.

We have investigated the influence of shot noise on the IV curves of a single mesoscopic Josephson junction. We observe a linear enhancement of zero-bias conductance of the Josephson junction with increasing shot-noise power. Moreover, the IV curves become increasingly asymmetric. Our analysis on the asymmetry shows that the Coulomb blockade of Cooper pairs is strongly influenced by the non-Gaussian character of the shot noise.

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PubMed2004

Tailoring Josephson coupling through superconductivity-induced nonequilibrium.

The distinctive quasiparticle distribution existing under nonequilibrium in a superconductor-insulator-normal metal-insulator-superconductor mesoscopic line is proposed as a novel tool to control the supercurrent intensity in a long Josephson weak link. We present a description of this system in the framework of the diffusive-limit quasiclassical Green-function theory and take into account the effects of inelastic scattering with arbitrary strength. Supercurrent enhancement and suppression, including a marked transition to a pi junction, are striking features leading to a fully tunable structure.

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PubMed2004

Limitations in cooling electrons using normal-metal-superconductor tunnel junctions.

We demonstrate both theoretically and experimentally two limiting factors in cooling electrons using biased tunnel junctions to extract heat from a normal metal into a superconductor. First, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do not obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Second, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.

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PubMed2002

Direct observation of the transition from the conventional superconducting state to the pi state in a controllable Josephson junction.

We measure the full supercurrent-phase relation of a controllable pi junction around the transition from the conventional 0 state to the pi state. We show that around the transition the Josephson supercurrent-phase relation changes from I(sc) approximately I(c)sin((phi) to I(sc) approximately I(c)sin((2phi). This implies that, around the transition, two minima in the junction free energy exist, one at phi=0 and one at phi=pi, whereas only one minimum exists at the 0 state (at phi=0) and at the pi state (at phi=pi). Theoretical calculations based on the quasiclassical theory are in good agreement with the observed behavior.

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