Research

In an experimental lab we often have to set-up the infrastructure needed for measurements that we plan to do.

• I have built a set-up to do point contact measurements on systems from room temperature or higher down to 4.2 K. This is a variable temperature cryostat with nano-positioners and a conducting Pt tip inside to do current-voltage measurements locally in a system at various positions. The novelty of my set-up is that the sample can be loaded in an inert environment like in a glove box and kept in that atmosphere throughout the experiment. This is essential for systems that can degrade in oxygen atmosphere.

• Point contact measurements is a diagnostic tool in condensed matter physics where we bring a sharp conducting tip in contact to the sample. We record the voltage across the sample while applying current to the tip. The current-bias characteristics of the point contact region gives a plethora of information about the system like the local density of states, excitations responsible for electron scattering and so on . It has been widely used in superconductors to probe the superconducting energy gap. Using our built set-up we have done measurements on Pb film at low temperatures which show the superconducting gap of Pb . By varying the contact diameter we have been able to see various regimes of transport namely ballistic, thermal or diffusive. Using these set-up and measurement technique we can probe systems with high inhomogenity or instability to oxygen exposure.

• Low frequency fluctuations in electrical resistivity is a powerful tool to study the coupling between the electronic and structural degrees of freedom in a system. I have done 1/f noise measurements in Ti doped single crystal for ternary ruthenates which show metal-insulator transition accompanied by paramagnetic to antiferromagnetic transition. The magnitude of noise is proportional to the square of the local current density making the noise power proportional to the fourth power of the local current density. Consequently, the noise spectrum is extremely sensitive not only to the extent of structural disorder, but also to the slow time-dependent kinetics and rearrangements of the disorder. So by studying the noise spectrum across the metal-insulator transition of this material we are trying to understand the low frequency kinectis of the system.