Trends of Condensed Matter Science: A Personal View
A personal view on the development of the research activities in condensed matter sciences is presented, with special emphasis on the carrier doping into insulators, which have been classified into four categories: band insulators, Mott insulators, charge
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Summary: A personal view on the development of the research activities in condensed matter sciences is presented, with special emphasis on the carrier doping into insulators, which have been classified into four categories: band insulators, Mott insulators, charge ordering, and Anderson localization. Depending on these parent insulators, doped carriers behave essentially differently as typically seen in semiconductors (doped band insulators) in contrast to high Tc cuprates (doped Mott insulators) as bulk materials. Thanks to the establishment of experimental capabilities to probe local properties initiated by the success of scanning tunneling microscope (STM), more attentions are naturally being paid to local structures and associated electronic properties, spectroscopy in particular, which eventually govern material properties in macroscopic scales. Typical research targets from this viewpoint may include (1) strongly correlated electron systems, (2) surfaces, interfaces, and contacts, and (3) molecular assemblies. With more detailed explanation of the recent remarkable progress of the understanding of molecular solids belonging to above three, a hope is expressed that time is ripe to develop studies on bio-related materials, such as proteins and DNA, based on the well established technique in condensed matter science just as natural extensions of those on molecular solids. A tentative list of concrete research targets along this line of bio-material science has been proposed.
2.1 Introduction Progress in microscopic understanding of material properties is very impressive. Materials consist of atoms whose electronic states are simple and have been fully understood by now. However, properties of materials, which are condensed forms of atoms in one way or another, are “emergent” [1] in the sense that they are completely different from those of individual constituents and truly diverse and have infinite possibilities. This has been very properly phrased as “More is different” by Anderson [2]. An amazing fact is that the properties of crystals, which are typical forms of condensed matter with periodic array of atoms, are understood quantum mechanically based on the
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knowledge of each constituent and the spatial arrangements in unit cells (lattice structures). Here the existence of lattice periodicity and Bloch bands is crucial. Actually one sheet of paper showing a band structure has information of 1023 atoms. This procedure of band theory is to know 1023 atoms from one. (In Japanese, there is a saying for a very sharp person that he (she) understands 10 once he (she) hears one!) Thanks to the healthy relationship between experiments and theories in material science, which is not always the case in some of the disciplines of science now unfortunately, this powerful step bridging between microscopic and macroscopic scales differing more than 20 orders of magnitude in the number of constituents are exercised very commonly without noticing, i.e., theoretical predictions being checked by experiments and new e
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