Tunneling resonances in quantum dots: Coulomb interaction modifies the width

Single-electron tunneling through a zero-dimensional state in an asymmetric double-barrier resonant-tunneling structure is studied. The broadening of steps in the $I\text{−}V$ characteristics is found to strongly depend on the polarity of the applied bias voltage. Based on a qualitative picture for the finite-lifetime broadening of the quantum dot states and a quantitative comparison of the experimental data with a nonequilibrium transport theory, we identify this polarity dependence as a clear signature of Coulomb interaction.

Figure 1

(a) Schematic energy diagram of the asymmetric double-barrier device under finite bias. (b) First current step in negative bias direction. (c) Comparison of the full width half maximum (FWHM) value of the differential-conductance peaks for both bias polarities at base temperature $(T=20\mathrm{mK})$.

Figure 2

Sketch of our device in a noncharging direction. The electronic structure of the dot is given by the spectral density $\rho \left(\omega \right)$, which is shifted and broadened with respect to the bare level ${\epsilon }_0+(1-{\alpha }_{+})eV$ (solid line) as reflected in the real part and imaginary part of the self-energy $\Sigma$, respectively.

Figure 3

Experimental (solid lines) and theoretical (dashed lines) differential conductance for the (a) charging and (b) noncharging direction at base temperature $(T=20\mathrm{mK})$.

Figure 4

(a) Temperature dependence of the resonance width $\Delta V$ at $B=0\mathrm{T}$ for both polarities, open circles $V>0$, filled squares $V<0$, continuous lines theoretical simulations. (b) Resonance width $\Delta V$ at base temperature $(T=20\mathrm{mK})$ as a function of $B$ field in direction $B\Vert I$ for both polarities of applied voltage.