Two-loop approximation in the Coulomb blockade problem

We study Coulomb blockade (CB) oscillations in the thermodynamics of a metallic grain which is connected to a lead by a tunneling contact with a large conductance $g_0$ in a wide temperature range, $E_Cg_0^4 e^{-g_0/2}<T<E_C$, where $E_C$ is the charging energy. Using the instanton analysis and the renormalization group we obtain the temperature dependence of the amplitude of CB oscillations which differs from the previously obtained results. Assuming that at $T < E_Cg_0^4 e^{-g_0/2}$ the oscillation amplitude weakly depends on temperature we estimate the magnitude of CB oscillations in the ground state energy as $E_Cg_0^4 e^{-g_0/2}$.Comment: 10 pages, 3 figure

Conductance of the single-electron transistor: A comparison of experimental data with Monte Carlo calculations

We report on experimental results for the conductance of metallic single-electron transistors as a function of temperature, gate voltage and dimensionless conductance. In contrast to previous experiments our transistor layout allows for a direct measurement of the parallel conductance and no ad hoc assumptions on the symmetry of the transistors are necessary. Thus we can make a comparison between our data and theoretical predictions without any adjustable parameter. Even for rather weakly conducting transistors significant deviations from the perturbative results are noted. On the other hand, path integral Monte Carlo calculations show remarkable agreement with experiments for the whole range of temperatures and conductances.Comment: 8 pages, 7 figures, revtex4, corrected typos, submitted to PR

Einzelelektronentransistoren im Regime kleiner Widerstaende

In this thesis we report on the experimental investigation of Aluminum-Alumina-Aluminum single-electron transistors with tunnel junction resistances of the order of R_K and on the implementation of the measurement setup necessary for this. In the regime of low resistive tunnel junctions tunnel processes beyond the orthodox theory contribute clearly to the transport. The only two sample parameters which enter the theoretical descriptions are the charging energy E_c and the coupling strength #alpha# = R_K/R _p_a_r_a_l_l_e_l, where R _p_a_r_a_l_l_e_l denotes the parallel resistance of the junctions. The transistors investigated are fabricated with a special layout which allows the direct measurement of #alpha#. On such transistors with coupling strengths alpha from 0.8 to 6 the minimum and maximum linear-response conductance, G_m_i_n and G_m_a_x resp., were extracted from the coulomb oscillations as a function of temperature in the range from 28 mK to 18 K. The results are compared with the predictions of a second order perturbation theory, a semiclassical analytical description and quantum Monte-Carlo calculations (QMC). For G_m_a_x(T), a good agreement with the perturbation theory is found for samples with #alpha# &lt; 2. For higher #alpha# an increasing deviation is observed. For G_m_i_n(T) deviations are observed for all values of alpha which grow with increasing alpha. The semiclassical approach describes G_m_i_n(T) and G_m_a_x(T) at high temperatures well. For the QMC calculations good agreement is observed in the entire temperature range. (orig.)SIGLEAvailable from TIB Hannover: ZA 5141(6712) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman