Development of a New Approach to Contactless Transport Measurements at Cryogenic Temperatures

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

Advances both in the development of new materials and in fundamental understanding of new physics are often coupled to advances in experimental technology. This work extends such technology via an instrument permitting conventional transport style measurements to be made without the use of ohmic contacts. The approach is based on the use of capacitive coupling to samples. Such a system, while involving significant experimental challenges, offers considerable promise for the investigation of physical phenomena where conventional ohmic contacts can either not be used, or are unreliable to use. Examples of such areas of investigation include 2-D electron systems with extremely low electron densities, for which the relative importance of electron interaction are greatly enhanced, and low density samples at very high magnetic fields, where ohmic contacts can be notoriously difficult. Another area is the study of the metal insulator transition, where the combined effects of low densities, disorder, and magnetic field effects can combine to make ohmic contacts unreliable. These measurement capabilities will also benefit the investigation of new materials, since transport measurements can be used as a diagnostic tool without the considerable effort often necessary to develop ohmic contacts. The unique requirements of a capacitively-based measurement approach requires the development of new electronic and cryogenic techniques and instrumentation. Combined with the prospect for exploration of important topics in physics, its development will provide valuable training and experience for graduate students. Experience has demonstrated that pushing at extremes of temperature, magnetic field, or other measurement parameters, has exposed inadequacies in our knowledge of materials. Exploring such areas has often led to new and fundamental advances in our understanding of materials and their physics, and even to the development of new materials. This work will extend experimental capabilities by the creation of an instrument for making contact-less electrical measurements of electronic materials in cryogenic environments. The measurement system will provide experimental access to a number of areas, areas for which the difficulty of making conventional electrical contacts effectively prevents investigation. The instrument itself represents a technical challenge, involving low-noise measurements and complex sample environments, and its use will involve technologically important materials. It provides a valuable arena for the training of graduate students in both advanced technology and fundamental physics, whose training is a cornerstone of our technological infrastructure.