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We demonstrate sensitive detection of single charges using a planar tunnel junction 8.5nm wide and 17.2nm long defined by an atomically precise phosphorus doping profile in silicon. The conductance of the junction responds to a nearby gate potential and also to changes in the charge state of a quantum dot patterned 52nm away. The response of this detector is monotonic across the entire working voltage range of the device, which will make it particularly useful for studying systems of multiple quantum dots. The charge sensitivity is maximized when the junction is most conductive, suggesting that more sensitive detection can be achieved by shortening the length of the junction to increase its conductance.
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We consider a tunnel junction formed between a fixed electrode and an oscillating one. Accumulation of the charge on the junction capacitor induces a force on the nano-mechanical oscillator. The junction is voltage biased and connected in series with an impedance $Z(omega)$. We discuss how the picture of Coulomb blockade is modified by the presence of the oscillator. Quantum fluctuations of the mechanical oscillator modify the $I$-$V$ characteristics particularly in the strong Coulomb blockade limit. We show that the oscillator can be taken into account by a simple modification of the effective impedance of the circuit. We discuss in some details the case of a single inductance $Z(omega)=iLomega$ and of a constant resistance $Z(omega)=R$. With little modifications the theory applies also to incoherent transport in Josephson junctions in the tunneling limit.
The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal | single molecule | metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference.
Large magnetoresistance effect controlled by electric field rather than magnetic field or electric current is a preferable routine for designing low power consumption magnetoresistance-based spintronic devices. Here we propose an electric-field controlled antiferromagnetic (AFM) tunnel junction with structure of piezoelectric substrate/Mn3Pt/SrTiO3/Pt operating by the magnetic phase transition (MPT) of antiferromagnet Mn3Pt through its magneto-volume effect. The transport properties of the proposed AFM tunnel junction have been investigated by employing first-principles calculations. Our results show that a magnetoresistance over hundreds of percent is achievable when Mn3Pt undergoes MPT from a collinear AFM state to a non-collinear AFM state. Band structure analysis based on density functional calculations shows that the large TMR can be attributed to the joint effect of significant different Fermi surface of Mn3Pt at two AFM phases and the band symmetry filtering effect of the SrTiO3 tunnel barrier. In addition, other than single-crystalline tunnel barrier, we also discuss the robustness of the proposed magnetoresistance effect by considering amorphous AlOx barrier. Our results may open perspective way for effectively electrical writing and reading of the AFM state and its application in energy efficient magnetic memory devices.
Inspired by a recent experiment, we study the influence of thermal fluctuations on the $I$-$V$ characteristics of a Josephson junction, coupled to a strongly resistive environment. We obtain analytical results in the limit where the Josephson energy is larger than the charging energy and quasiparticles are absent.
We theoretically investigate the critical current of a thermally-biased SIS Josephson junction formed by electrodes made by different BCS superconductors. The response of the device is analyzed as a function of the asymmetry parameter, $r=T_{c_1} /T_{c_2}$. We highlight the appearance of jumps in the critical current of an asymmetric junction, namely, when $r eq1$. In fact, in such case at temperatures at which the BCS superconducting gaps coincide, the critical current suddenly increases or decreases. In particular, we thoroughly discuss the counterintuitively behaviour of the critical current, which increases by enhancing the temperature of one lead, instead of monotonically reducing. In this case, we found that the largest jump of the critical current is obtained for moderate asymmetries, $rsimeq3$. In view of these results, the discussed behavior can be speculatively proposed as a temperature-based threshold single-photon detector with photon-counting capabilities, which operates non-linearly in the non-dissipative channel.
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