Sum rule for transport in a Luttinger liquid with long range interaction in the presence of an impurity

We show that the non-linear dc transport in a Luttinger liquid with interaction of finite range in the presence of an impurity is governed by a sum rule which causes the charging energy to vanish.Comment: 5 pages, RevTeX, 1 figure, to be published in Europhysics Letter

Single-electron transistors in electromagnetic environments

The current-voltage (I-V) characteristics of single-electron transistors (SETs) have been measured in various electromagnetic environments. Some SETs were biased with one-dimensional arrays of dc superconducting quantum interference devices (SQUIDs). The purpose was to provide the SETs with a magnetic-field-tunable environment in the superconducting state, and a high-impedance environment in the normal state. The comparison of SETs with SQUID arrays and those without arrays in the normal state confirmed that the effective charging energy of SETs in the normal state becomes larger in the high-impedance environment, as expected theoretically. In SETs with SQUID arrays in the superconducting state, as the zero-bias resistance of the SQUID arrays was increased to be much larger than the quantum resistance R_K = h/e^2 = 26 kohm, a sharp Coulomb blockade was induced, and the current modulation by the gate-induced charge was changed from e periodic to 2e periodic at a bias point 0<|V|<2D_0/e, where D_0 is the superconducting energy gap. The author discusses the Coulomb blockade and its dependence on the gate-induced charge in terms of the single Josephson junction with gate-tunable junction capacitance.Comment: 8 pages with 10 embedded figures, RevTeX4, published versio

Mode-Locking in Quantum-Hall-Effect Point Contacts

We study the effect of an ac drive on the current-voltage (I-V) characteristics of a tunnel junction between two fractional Quantum Hall fluids at filling $\nu ^{-1}$ an odd integer. Within the chiral Luttinger liquid model of edge states, the point contact dynamics is described by a driven damped quantum mechanical pendulum. In a semi-classical limit which ignores electron tunnelling, this model exhibits mode-locking, which corresponds to current plateaus in the I-V curve at integer multiples of $I= e\omega /2\pi$, with $\omega$ the ac drive angular frequency. By analyzing the full quantum model at non-zero $\nu$ using perturbative and exact methods, we study the effect of quantum fluctuation on the mode-locked plateaus. For $\nu=1$ quantum fluctuations smear completely the plateaus, leaving no trace of the ac drive. For $\nu \ge 1/2$ smeared plateaus remain in the I-V curve, but are not centered at the currents $I=n e \omega /2\pi$. For $\nu < 1/2$ rounded plateaus centered around the quantized current values are found. The possibility of using mode locking in FQHE point contacts as a current-to-frequency standard is discussed.Comment: 12 pages, 8 figures, minor change

Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions

We have measured the current-voltage characteristics of small-capacitance single Josephson junctions at low temperatures (T < 0.04 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. We have clearly observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e^2 = 26 kohm. The negative differential resistance is evidence of coherent single-Cooper-pair tunneling in the single Josephson junction.Comment: RevTeX, 4 pages with 6 embedded figure

Cotunneling at resonance for the single-electron transistor

We study electron transport through a small metallic island in the perturbative regime. Using a recently developed diagrammatic technique, we calculate the occupation of the island as well as the conductance through the transistor in forth order in the tunneling matrix elements, a process referred to as cotunneling. Our formulation does not require the introduction of a cut-off. At resonance we find significant modifications of previous theories and good agreement with recent experiments.Comment: 5 pages, Revtex, 5 eps-figure

Quantum Conductance of the Single Electron Transistor

The quantum conductance of the single-electron tunneling (SET) transistor is investigated in this paper by the functional integral approach. The formalism is valid for arbitrary tunnel resistance of the junctions forming the SET transistor at any temperature. The path integrals are evaluated by the semiclassical method to yield an explicit non-perturbation form of the quantum conductance of the SET transistor. An anomaly of the quantum conductance is found if the tunnel resistances are much smaller than the quantum resistance. The dependence of the conductance on the gate voltage is also discussed.Comment: 4 pages including some mathe details of cond-mat/990806

Effect of quantum noise on Coulomb blockade in normal tunnel junctions at high voltages

We have investigated asymptotic behavior of normal tunnel junctions at voltages where even the best ohmic environments start to look like RC transmission lines. In the experiments, this is manifested by an exceedingly slow approach to the linear behavior above the Coulomb gap. As expected on the basis of the quantum theory taking into account interaction with the environmental modes, better fits are obtained using 1/sqrt{V}- than 1/V- dependence for the asymptote. These results agree with the horizon picture if the frequency-dependent phase velocity is employed instead of the speed of light in order to determine the extent of the surroundings seen by the junction.Comment: 9 pages, 4 figures, submitted to Phys. Rev.

Tunneling between two Luttinger liquids with long range interaction

The non linear charge transfer through a tunnel junction between two Luttinger systems is studied for repulsive, finite range interaction between electrons on the same, V_{11}, and on different,V_{12}, sides of the junction. Features of the Coulomb blockade effect are observed if V_{12}=0. We predict a novel interaction induced enhancement of the current if V_{12}>0. When V_{12}=V_{11}, the current is suppressed at small bias, but the ``charging energy'', obtained from the asymptotic behavior at high bias voltage, vanishes.Comment: 4 pages, RevTeX, to be published in Physical Review B (Brief Report

Charging Ultrasmall Tunnel Junctions in Electromagnetic Environment

We have investigated the quantum admittance of an ultrasmall tunnel junction with arbitrary tunneling strength under an electromagnetic environment. Using the functional integral approach a close analytical expression of the quantum admittance is derived for a general electromagnetic environment. We then consider a specific controllable environment where a resistance is connected in series with the tunneling junction, for which we derived the dc quantum conductance from the zero frequency limit of the imaginary part of the quantum admittance. For such electromagnetic environment the dc conductance has been investigated in recent experiments, and our numerical results agree quantitatively very well with the measurements. Our complete numerical results for the entire range of junction conductance and electromagnetic environmental conductance confirmed the few existing theoretical conclusions.Comment: 7 pages, 3 ps-figure

The value of real-world testing: a qualitative feasibility study to explore staff and organisational barriers and strategies to support implementation of a clinical pathway for the management of anxiety and depression in adult cancer patients.

Background: Effective translation of evidence-based research into clinical practice requires assessment of the many factors that can impact implementation success. Research methods that draw on recognised implementation frameworks, such as the Promoting Action Research in Health Services (PARiHS) framework, and that test feasibility to gain information prior to full-scale roll-out, can support a more structured approach to implementation. Objective: This paper presents qualitative findings from a feasibility study in one cancer service of an online portal to operationalise a clinical pathway for the screening, assessment and management of anxiety and depression in adult cancer patients. The aim of this study was to explore staff perspectives on the feasibility and acceptance of a range of strategies to support implementation in order to inform the full-scale roll-out. Methods: Semi-structured interviews were conducted with fifteen hospital staff holding a range of clinical, administrative and managerial roles, and with differing levels of exposure to the pathway. Qualitative data were analysed thematically, and themes were subsequently organised within the constructs of the PARiHS framework. Results: Barriers and facilitators that affected the feasibility of the online portal and implementation strategies were organised across eight key themes: staff perceptions, culture, external influences, attitudes to psychosocial care, intervention fit, familiarity, burden and engagement. These themes mapped to the PARiHS framework's three domains of evidence, context and facilitation. Conclusions: Implementation success may be threatened by a range of factors related to the real-world context, perceptions of the intervention (evidence) and the process by which it is introduced (facilitation). Feasibility testing of implementation strategies can provide unique insights into issues likely to influence full-scale implementation, allowing for early tailoring and more effective facilitation which may save time, money and effort in the long-term. Use of a determinant implementation framework can assist researchers to synthesise and effectively respond to barriers as they arise. While the current feasibility study related to a specific implementation, strategies such as regular engagement with local stakeholders, and discussion of barriers arising in real-time during early testing is likely to be of benefit to all researchers and clinicians seeking to maximise the likelihood of long-term implementation success