Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Exploring Nanoscale Josephson Junctions in the Limits of High and Low Charging Energy.

Sueli Skinner Ramos, Rupert Lewis, William Kindel, Charles Thomas Harris

Published Oct 1, 2022• 0 citations
Publisher
DOI
10.2172/2005746

Related papers

Stacked Nanoscale Josephson Junction Arrays for High-Performance Voltage Standards

Samuel P. Benz, Paul D. Dresselhaus, Yonuk Chong +1 more

•Jan 1, 2002•1 citation

Two-Dimensional Arrays of Josephson Junctions with Controllable Charging Energy

Çağlıyan Kurdak, A. J. Rimberg, T. R. Ho +3 more

APS•Mar 1, 1998•0 citations

Circuit with small-capacitance high-quality Nb Josephson junctions

道生 渡部, Yasunobu Nakamura, Jaw-Shen Tsai

We have developed a fabrication process for nanoscale tunnel junctions which includes focused-ion-beam etching from different directions. By applying the process to a Nb/(Al–)Al2O3/Nb trilayer, we have fabricated a Nb single-electron transistor (SET), and characterized the SET at low temperatures, T=0.04–40 K. The superconducting gap energy and the transition temperature of the Nb SET agree with the bulk values, which suggests high quality Nb junctions. The single-electron charging energy of the SET is estimated to be larger than 1 K.

arXiv:cond-mat/0311332•Applied Physics Letters•Jan 13, 2004•23 citations

Transport properties of nanoscale Nb and NbN Josephson junctions fabricated by focused-ion-beam milling

Kazuaki Matsuba, 道生 渡部, Jaw-Shen Tsai

We have studied low-temperature electrical transport properties of nanoscale Nb∕(Al–)Al2O3∕Nb and NbN∕AlN∕NbN Josephson junctions (JJs) fabricated by focused-ion-beam (FIB) milling. This FIB fabrication process yields high-quality JJs whose superconducting gap energy agrees with the bulk value. In this paper, we report the improvement in the precision of the fabrication technology by employing a weaker ion beam current and by introducing a step of XeF2-gas-assisted milling, which allowed us to reduce the anodization voltage. For Nb JJs, we measured the current-voltage (I-V) characteristics of single-electron transistors (SETs) and examined the current observed within the superconducting energy gap. At finite voltages, we observed current peaks due to the Josephson-quasiparticle (JQP) cycle. Based on the JQP-peak positions, we estimated the charging energy Ec of the SETs. For all SETs, Ec∕kB is larger than 1K, which is consistent with 0.1×0.1μm2 junctions. We also analyzed the superconducting critical current at zero voltage. The ratio Ic∕Ic0 depended on the junction size, where Ic is the measured critical current and Ic0 is the theoretical one. The I-V curves of NbN single Josephson junctions also depended on the junction size, and they were qualitatively different, especially around the energy gap. We will discuss the possible origins for the junction-size dependence.

Journal of Applied Physics•Apr 1, 2008•2 citations

Quantum dynamics of the charge in Josephson tunnel junctions

Andrei D. Zaikin

Journal of Low Temperature Physics•Sep 1, 1990•28 citations

Quantum effects in nanoscale Josephson junction circuits

S. Corlevi

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.

•Jan 1, 2006•5 citations
We have developed a fabrication process for nanoscale tunnel junctions which includes focused-ion-beam etching from different directions. By applying the process to a Nb/(Al–)Al2O3/Nb trilayer, we have fabricated a Nb single-electron transistor (SET), and characterized the SET at low temperatures, T=0.04–40 K. The superconducting gap energy and the transition temperature of the Nb SET agree with the bulk values, which suggests high quality Nb junctions. The single-electron charging energy of the SET is estimated to be larger than 1 K.
We have studied low-temperature electrical transport properties of nanoscale Nb∕(Al–)Al2O3∕Nb and NbN∕AlN∕NbN Josephson junctions (JJs) fabricated by focused-ion-beam (FIB) milling. This FIB fabrication process yields high-quality JJs whose superconducting gap energy agrees with the bulk value. In this paper, we report the improvement in the precision of the fabrication technology by employing a weaker ion beam current and by introducing a step of XeF2-gas-assisted milling, which allowed us to reduce the anodization voltage. For Nb JJs, we measured the current-voltage (I-V) characteristics of single-electron transistors (SETs) and examined the current observed within the superconducting energy gap. At finite voltages, we observed current peaks due to the Josephson-quasiparticle (JQP) cycle. Based on the JQP-peak positions, we estimated the charging energy Ec of the SETs. For all SETs, Ec∕kB is larger than 1K, which is consistent with 0.1×0.1μm2 junctions. We also analyzed the superconducting critical current at zero voltage. The ratio Ic∕Ic0 depended on the junction size, where Ic is the measured critical current and Ic0 is the theoretical one. The I-V curves of NbN single Josephson junctions also depended on the junction size, and they were qualitatively different, especially around the energy gap. We will discuss the possible origins for the junction-size dependence.
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.