Photon Sidebands of the Ground State and First Excited State of a Quantum Dot

Abstract

We have measured photon-assisted tunneling through a quantum dot with zero dimensional (0D) states. For photon energies smaller than the separation between 0D states we observe photon sideband resonances of the ground state. When the photon energy exceeds the separation between 0D states we observe photon-induced excited state resonances. We identify the different resonances by studying their dependence on photon frequency and magnetic field. [S0031-9007(97)02424-1] PACS numbers: 73.20. Dx, 73.40.Gk, 73.50.Mx, 73.50.Pz In analogy to spectroscopy on atoms it is interesting to study the interaction between light and electrons confined in quantum dots. However, since it is difficult to realize identical quantum dots the response of an ensemble of quantum dots to light excitation is strongly averaged over sample differences. Despite this averaging, excitation studies on quantum dot arrays by far-infrared light have shown the spectrum of collective modes [1], and inelastic light scattering experiments have probed single particle excitations [2]. The latter technique has also probed excitons in a single quantum dot [3]. We have used microwaves with relatively low frequency to study the discrete electron excitation spectrum in the conduction band of a single quantum dot. In contrast to the light transmission or luminescence measurements of the above spectroscopy techniques, we measure the photoresponse in the dc current.Current can flow through a quantum dot when a discrete energy state is aligned to the Fermi energies of the leads. This current is carried by resonant elastic tunneling of electrons between the leads and the dot. An additional time-varying potential e V cos͑2pft͒ can induce inelastic tunnel events when electrons exchange photons of energy hf with the oscillating field. This inelastic tunneling with discrete energy exchange is known as photonassisted tunneling (PAT). PAT has been studied before in superconductor-insulator-superconductor tunnel junctions [4], in superlattices [5], and in quantum dots [6,7]. The quantum dots in Ref. [6] were rather large and effectively had a continuous density of states. So far, PAT through small quantum dots with discrete states has only been studied theoretically [8,9]. In this paper we show for the first time different types of PAT processes through a quantum dot with well resolved discrete 0D states. We first show that an elastic resonant tunneling peak in the current develops photon sideband resonances when we apply microwaves. We then use PAT as a spectroscopic tool to measure the energy evolution of the first excited state as a function of magnetic field [10].Transport through a quantum dot is dominated by Coulomb blockade effects [11]. The energy to add an extra electron to a quantum dot constitutes the charging energy E c for a single electron, and a finite energy difference D´arising from the confinement. A dot is said to have 0D states if D´is larger than the thermal energy k B T [11]. Assuming sequential tunneling of single electrons, the current can be cal...

Dissipation and noise in adiabatic quantum pumps

“…For certains pumps 23,24 the charge transferred in each cycle is quantized. Quantized charge pumping is most easily achieved in devices based on the Coulomb blockade effect [25][26][27][28][29][30] where the charge on a quantum dot is quantized. This is of considerable metrological interest 31,32 .…”

Influence of microwave fields on electron transport through a quantum dot in the presence of direct tunneling between leads

“…photon-assisted tunneling through small quantum dots with well-resolved discrete energy states [1,2,3], photon-electron pumps [4,5,6] and others. One can investigate the current flowing through a QD under periodic modulation of the QD electronic structure [7] or periodic (non-periodic) modulation of the tunneling barriers [6] and electron energy levels in both (left and right) electron reservoirs [8] (see also [9,10]).…”

Photon Assisted Tunneling in Quantum Dots

“…In 1993 PAT features were seen in the current-voltage characteristics of a GaAs/AlGaAs superlattice under THz irradiation from a free-electron laser [11]. Starting in 1994, PAT was also found in experiments on single-electron transport through semiconductor quantum dots [12][13][14][15][16]. The quantum dots in Ref.…”

“…Here, we focus on PAT processes through quantum dots with well-resolved, discrete energy states. For these small dots, the resonant tunneling peak in the current develops photon sideband resonances when we apply microwaves [16]. The energy separation between main peak and sidebands can be used as a spectroscopic measurement of the energy levels in the dot.…”