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Register a new userSpin Blockade in Capacitively Coupled Quantum Dots
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We present transport measurements on a lateral double dot produced by combining local anodic oxidation and electron beam lithography. We investigate the tunability of our device and demonstrate, that we can switch between capacitive and tunnel coupling. In the regime of capacitive coupling we observe the phenomenon of spin blockade in a magnetic field and analyze the influence of capacitive interdot coupling on this effect.
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We present measurements on gate-defined double quantum dots in Ge-Si core-shell nanowires, which we tune to a regime with visible shell filling in both dots. We observe a Pauli spin blockade and can assign the measured leakage current at low magnetic fields to spin-flip cotunneling, for which we measure a strong anisotropy related to an anisotropic g-factor. At higher magnetic fields we see signatures for leakage current caused by spin-orbit coupling between (1,1)-singlet and (2,0)-triplet states. Taking into account these anisotropic spin-flip mechanisms, we can choose the magnetic field direction with the longest spin lifetime for improved spin-orbit qubits.
We propose a nanoscale device consisting of a double quantum dot with strong intra- and inter- dot Coulomb repulsions. In this design, the current can only flow through the lower dot, but is triggered by the gate-controlled occupancy of the upper dot. At low temperatures, our calculations predict the double dot to pass through a narrow Kondo regime, resulting in highly sensitive switching characteristics between three well-defined states : insulating, normal conduction and resonant conduction.
We report Pauli spin blockade in an impurity defined carbon nanotube double quantum dot. We observe a pronounced current suppression for negative source-drain bias voltages which is investigated for both symmetric and asymmetric coupling of the quantum dots to the leads. The measured differential conductance agrees well with a theoretical model of a double quantum dot system in the spin-blockade regime which allows us to estimate the occupation probabilities of the relevant singlet and triplet states. This work shows that effective spin-to-charge conversion in nanotube quantum dots is feasible and opens the possibility of single-spin readout in a material that is not limited by hyperfine interaction with nuclear spins.
We investigate the influence of thermal energy on the current flow and electron spin states in double quantum dots in series. The quadruplet Pauli spin blockade, which is caused by the quadruplet and doublet states, occurs at low temperatures affecting the transport properties. As the temperature increases, the quadruplet Pauli spin blockade occurs as a result of the thermal energy, even in regions where it does not occur at low temperatures. This is because the triplet state is formed in one dot as a result of the gradual change of the Fermi distribution function of the electrodes with increasing temperature. Moreover, the thermally assisted Pauli spin blockade results in coexistence of the Coulomb and Pauli spin blockades. Conversely, for the standard triplet Pauli spin blockade, which occurs as a result of the triplet and singlet states, the current through the double dots monotonously smears out as the temperature increases. Therefore, the thermally assisted Pauli spin blockade is not clearly observed. However, the coexistence of the Coulomb and triplet Pauli spin blockades as a result of the thermal energy is clearly obtained in the calculation of the probability of the spin state in the double dots.
We demonstrate double quantum dots fabricated in undoped Si/SiGe heterostructures relying on a double top-gated design. Charge sensing shows that we can reliably deplete these devices to zero charge occupancy. Measurements and simulations confirm that the energetics are determined by the gate-induced electrostatic potentials. Pauli spin blockade has been observed via transport through the double dot in the two electron configuration, a critical step in performing coherent spin manipulations in Si.
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