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Phase-Charge duality of a Josephson junction in a fluctuating electromagnetic environment
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0001-8534-6577
2006 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 97, no 9Article in journal (Refereed) Published
Abstract [en]

We have measured the current-voltage characteristics of a single Josephson junction placed in a high impedance environment. The transfer of Cooper pairs through the junction is governed by overdamped quasicharge dynamics, leading to Coulomb blockade and Bloch oscillations. Exact duality exists to the standard overdamped phase dynamics of a Josephson junction, resulting in a dual shape of the current-voltage characteristic, with current and voltage changing roles. We demonstrate this duality with experiments which allow for a quantitative comparison with a theory that includes the effect of fluctuations due to the finite temperature of the electromagnetic environment.

Place, publisher, year, edition, pages
2006. Vol. 97, no 9
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5830DOI: 10.1103/PhysRevLett.97.096802ISI: 000240239000046Scopus ID: 2-s2.0-33748645370OAI: oai:DiVA.org:kth-5830DiVA: diva2:10341
Note
QC 20100920Available from: 2006-05-30 Created: 2006-05-30 Last updated: 2012-03-20Bibliographically approved
In thesis
1. Quantum effects in nanoscale Josephson junction circuits
Open this publication in new window or tab >>Quantum effects in nanoscale Josephson junction circuits
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents the results of an experimental study on single-charge effects in nanoscale Josephson junctions and Cooper pair transistors (CPTs).

In nanoscale Josephson junctions the charging energy EC becomes significant at sub-Kelvin temperatures and single-charge effects, such as the Coulomb blockade of Cooper pair tunneling, influence the transport properties. In order to observe charging effects in a single Josephson junction, the impedance of the electromagnetic environment surrounding the junction has to be larger than the quantum resistance (RQ=h/4e2≈6.45kΩ).

In this work the high impedance environment is obtained by biasing the sample under test (single Josephson junction or CPT) with four one-dimensional Josephson junction arrays having SQUID geometry. The advantage of this configuration is the possibility of tuning in situ the effective impedance of the electromagnetic environment. By applying a magnetic field perpendicular to the SQUID loops, the Josephson energy EJ of the SQUIDs is suppressed, resulting in an increase of the measured zero bias resistance of the arrays of several orders of magnitude (104< R0 (Ω) <109). This bias method enables the measurement of the same sample in environments with different impedance.

As the impedance of the environment is increased, the current-voltage characteristics (IVCs) of the single Josephson junction and of the CPT show a well defined Coulomb blockade feature with a region of negative differential resistance, signature of the coherent tunneling of single Cooper pairs.

The measured IVCs of a single Josephson junction with SQUID geometry in the high impedance environment show a qualitative agreement with the Bloch band theory as the EJ/EC ratio of the junction is tuned with the magnetic field. We also studied a single nontunable Josephson junction with strong coupling (EJ/EC > 1), where the exact dual of the overdamped Josephson effect is realized, resulting in a dual shape of the IVC, where the roles of current and voltage are exchanged. Here, we make for the first time a detailed quantitative comparison with a theory which includes the effect of fluctuations due to the finite temperature of the environment.

The measurements on CPTs in the high impedance environment showed that the Coulomb blockade voltage is modulated periodically by the gate-induced charge. The gate-voltage dependence of the CPT changes from e-periodic to 2e-periodic as the impedance of the environment is increased. The high impedance environment reduces quasiparticle tunneling rates, thereby restoring the even parity of the CPT island. This behavior suggests that high impedance leads can be used to effectively suppress quasiparticle poisoning.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 103 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:31
Keyword
Josephson junctions, Josephson junction arrays, electromagnetic environment, Cooper pair transistor, parity effects
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4004 (URN)91-7178-353-9 (ISBN)
Public defence
2006-06-09, FA32, Albanova University Centrum, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100928 Available from: 2006-05-30 Created: 2006-05-30 Last updated: 2010-09-28Bibliographically approved

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Haviland, David B.

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