THz Investigations of Exotic Quantum States of Matter
"The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are ... completely known ..."
...or so was claimed in 1929 by P.A.M. Dirac shortly after the Schrodinger equation had been verified for few electron systems like H2 and He. Dirac continued that the difficulty in extending this success to larger systems is “only that the exact application of these laws leads to equations much too complicated to be soluble”. One could not have anticipated in 1929 that it is precisely this complexity and the resultant effects of 1024 particles acting in quantum mechanical unison that gives rise to a host of beautiful and striking phenomena like superconductivity and magnetism.
Like waves on the sea, these are collective phenomena not reducible to the properties of individual particles. Almost a century after Dirac, we know better; to paraphrase P. W. Anderson, more really IS different. The occurrence of novel quantum phenomena emergent on the longest length scales heightens the need for new experimental tools that probe finite, yet long time scales (compared to typical electronic ones). This talk will review recent advances in the area of THz spectroscopy and its application to exotic quantum states of matter. I will give examples on material systems as diverse as high-temperature cuprate superconductors, 1D quantum spin systems, “heavy-fermion” magnets, and topological insulators. A desire to characterize materials in a novel fashion and answer specific scientific questions is driving the technology forward, while new technology is changing the kinds of scientific questions we dare to ask.