### About the Group

Supriyo Datta started his research career in the field of ultrasonics, but after joining the Purdue faculty in 1981, has largely focused on the problem of understanding the flow of electrical current through very small conductors.

The basic problem is a familiar one: A voltage _V_ is applied across two contacts (\“source\” and \“drain\” ) made to a conductor (\“channel\”). How do we calculate the current _I_, as the length of the channel _L_ is made shorter and shorter, down to a few atoms? Twenty years ago, such a question was largely academic, but today experimentalists are actually making current measurements through \“channels\” that are only a few atoms long. Indeed, this is also a question of great interest from an applied point of view, since every laptop computer contains about one billion transistors, each of which is basically a conductor whose resistance (V/I) can be controlled with an additional terminal.

As the channel length _L_ is reduced from macroscopic dimensions (such as millimeters) to atomic dimensions (such as nanometers), the nature of electron transport—that is, current flow—changes significantly. At one end, it is described by a diffusion equation in which electrons are viewed as particles that are repeatedly scattered by various obstacles as they perform a \“random walk\” from the source to the drain. At the other end, there is the regime of quantum transport. There, wavelike interference effects play an important role, leading to such non-intuitive behavior as two resistors in series having less resistance than either one alone. However, this wave behavior is also interlinked fundamentally with the particle nature of electrons, and a proper description of current flow on this scale requires a model that accounts for _both_. Quantum transport far from equilibrium remains one of the most challenging problems in physics although there has been significant progress in our understanding over the last twenty years. Broadly speaking, this is what Prof. Datta\‘s research is about.

Interestingly, this research activity has also had a significant impact on teaching and curriculum development. While developing an undergraduate course on nanoelectronics, it seemed that the typical \“top-down\” approach that starts from the macroscopic limit (large _L_) was not very effective in conveying our latest understanding to students. Instead, we found a \“bottom-up\” view starting from the atomic limit (small _L_) that was far more effective. The \“top-down\” approach that is so common in education is used primarily for historical reasons—after all, 20 years ago, no one knew what the resistance was for an atomic scale conductor, or if it even made sense to ask about its resistance. But now that the bottom-line is known, the \“bottom-up\” approach is needed at least to complement the existing \“top-down\” curriculum and at Purdue we have developed a unique set of undergraduate and graduate courses based on the text: S. Datta, \“Quantum Transport: Atom to Transistor\”:http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=0521631459, Cambridge (2005).