Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Increasing the ν = 5/2 gap energy: an analysis of MBE growth parameters

Abstract: The fractional quantized Hall state at the filling factor = 5/2 is of special interest due to its possible application for quantum computing. Here we report on the optimization of growth parameters that allowed us to produce twodimensional electron gases (2DEGs) with a 5/2 gap energy up to 135mK. We concentrated on optimizing the molecular beam epitaxy (MBE) growth to provide high 5/2 gap energies in ‘as-grown’ samples, without the need to enhance the 2DEGs properties by illumination or gating techniques. Our findings allow us to analyse the impact of doping in narrow quantum wells with respect to conventional DX-doping in AlxGa1 xAs. The impact of the setback distance between doping layer and 2DEG was investigated as well. Additionally, we found a considerable increase in gap energy by reducing the amount of background impurities. To this end growth techniques like temperature reductions for substrate and effusion cells and the reduction of the Al mole fraction in the 2DEG region were applied.

Nagaoka ferromagnetism observed in a quantum dot plaquette

Abstract: Engineered, highly-controllable quantum systems hold promise as simulators of emergent physics beyond the capabilities of classical computers. An important problem in many-body physics is itinerant magnetism, which originates purely from long-range interactions of free electrons and whose existence in real systems has been subject to debate for decades. Here we use a quantum simulator consisting of a four-site square plaquette of quantum dots to demonstrate Nagaoka ferromagnetism. This form of itinerant magnetism has been rigorously studied theoretically but has remained unattainable in experiment. We load the plaquette with three electrons and demonstrate the predicted emergence of spontaneous ferromagnetic correlations through pairwise measurements of spin. We find the ferromagnetic ground state is remarkably robust to engineered disorder in the on-site potentials and can induce a transition to the low-spin state by changing the plaquette topology to an open chain. This demonstration of Nagaoka ferromagnetism highlights that quantum simulators can be used to study physical phenomena that have not yet been observed in any system before. The work also constitutes an important step towards large-scale quantum dot simulators of correlated electron systems.

Anisotropic reversible mixed-state properties of superconducting carbon-doped Mg ( B 1 − x C x ) 2 single crystals

Abstract: We report on magnetic and torque measurements on carbon-doped $\mathrm{Mg}{({\mathrm{B}}_{1\ensuremath{-}x}{\mathrm{C}}_{x})}_{2}$ single crystals with $x=0.038$, 0.066, and 0.095. One-band Ginzburg Landau (GL) and London theories are applied to derive the reversible parameters: i.e., the upper critical fields ${H}_{c2}$, the coherence lengths $\ensuremath{\xi}$, the penetration depths $\ensuremath{\lambda}$, the anisotropy $\ensuremath{\gamma}$, the lower critical fields ${H}_{c1}$, and the GL parameter $\ensuremath{\kappa}$ for fields parallel and perpendicular to the crystallographic $ab$ plane. Due to the persistence of two-band superconductivity in the investigated doping range, these parameters turn out to depend not only on temperature, as in the case of one-band superconductors, but also on field. Therefore, the evaluation was carried out separately for two field regions: first for fields near ${H}_{c1}$ and second close to ${H}_{c2}$. In general, the upper critical field increases and the anisotropy decreases upon carbon doping. All further reversible parameters are significantly modified as well. These modifications are compared for single crystals with different carbon concentration.

A Sensitive Inexpensive SAW Sensor for Wide Range Humidity Measurement

Abstract: The dynamic range of humidity measurement is very large. The conventional relative humidity sensor suffers from low dynamic range, particularly below 20%RH and the sensor is also relatively costlier. This paper presents fabrication of inexpensive humidity sensor over wide dynamic range using surface acoustic wave resonators of 433.92 MHz frequency. Three sets, each are having three sensors have been fabricated by varying coating thickness of poly vinyl alcohol (PVA) sensing film. Experiments have been conducted to observe the resonant frequency shift with the variation of humidity in the range of 0 to 99%RH using HP 8753C VNA. All the sensors show significant frequency shift for the full span. The maximum sensitivity of the 5% PVA coated sensor for 0-30%RH is 3.72 kHz/%RH. Performance parameters of the sensors are compared with other polymer SAW sensors. The fabricated sensors compare well with the sensors reported in the literature. Important features of the sensors are wide dynamic range, inexpensive fabrication and high sensitivity.