Gen Shirane

A brief review of his career at the time of his 65th birthday in 1989

by John Axe and Steve Shapiro

Shortly after the discovery of the neutron in 1932 it was demonstrated that the neutron could be diffracted by a solid.  After WW II, when research reactors were built, there was a burst of activity in neutron scattering and the present age dawned in the mid-60's with the arrival of high flux reactors such as the High Flux Beam Reactor at Brookhaven.  Gen Shirane's remarkable 30 year career in neutron scattering spans the entire period of high flux reactors, and he is unequivocally recognized as the world's leading expert in utilizing neutron scattering in probing problems in solid state physics.  In that period he has published nearly 500 scientific papers, many of them seminal in nature.  His contributions to Solid State Physics were recognized in 1973 when he was awarded the Oliver E. Buckley Prize, the most prestigious award in condensed matter science given by the American Physical Society, and the Warren Award presented by the American Crystallographic Association. Most recently (April, 1989), he was honored by being elected to the National Academy of Science.

The underlying theme of Gen's work has been the study of phase transitions.  This concerns the study of solids which undergo changes of symmetry as the temperature, pressure, or field (electric or magnetic) is changed.  It is worthwhile to note, here, that prior to the 1950's solids were generally studied in terms of single particle effects and from that period on physicists began to view interactions in solids in terms of cooperative, many-body phenomena.  Neutron scattering had already been shown to be uniquely capable of measuring collective effects in solids, and Gen's early experiments on phase transitions provided many convincing examples of cooperative behavior of atoms in solids.  His first work focused on phase transitions in ferroelectric materials where he collaborated extensively with Chalmers Frazer (now at DOE). These materials have important technological applications because the lower symmetry in the ferrolectric phase allows for piezoelectricity and non-linear optical properties.  Gen co-authored a book entitled "Ferroelectric Crystals" which is now considered a classic and is still used extensively by researchers.  These studies led to Gen's experimentation in other structural phase transitions in the mid-60's and 70's. The soft mode theory of P. W. Anderson (1960) and W. Cochran (1959) predicted that the frequency of a lattice vibrational mode would tend to zero as the transformation temperature is approached, and the solid would distort to a new state of lower symmetry.  The elegant experiments performed by Gen and his collaborators, notably J. D. Axe (BNL) and Y. Yamada (ISSP), confirmed this theory on a wide variety of systems and discovered new features which were not envisioned in the theory, such as incommensurate structures.  Simultaneously, Gen was studying critical pehnomena in magnetic systems and providing a wealth of trusted experimental data that served as a test of any theory.  In this area, as well as others, Gen interacted closely with the BNL Solid State theory group, most notably, M. Blume and V. J. Emery.  The beneficial interaction continues to this day.

In the early sixties, Gen started using the Brookhaven graphite reactor and became interested in the magnetic structure of solids.  He performed the definitive measurements of the collective motions of magnetic moments in a magnetically ordered solid such as iron.  These excitations, called spin waves, contain the microscopic information about the magnetic interactions in the solid.  Knowledge about their energy and dispersion is necessary for an understanding of magnetism.  His early experiments in Fe, Ni, and Co formed the basis of our present understanding of magnetism in these elemental solids.  Gen returned to this field in the mid-80's when questions were raised about the nature of the paramagnetic state, that is, the state existing at high enough temperatures where the thermal energy destroys the ordered arrangement of the magnetic moments.  The groups of experiments performed at Brookhaven are accepted by the scientific community as being the most thorough and definitive.

Another theme of Gen' s work is his study of magnetic and structural properties of lower dimensional systems.  Although we live in a three dimensional world, special solids can be prepared with very anisotropic interactions such that their properties resemble a one- or two-dimensional material.  Frequently, detailed calculations are much easier in one- or two- dimensions than they are in three-dimensions.  In addition, the cooperative effects depend fundamentally on the dimensionality of the solid.  In the 70's Gen formed a close collaboration with R. J. Birgeneau (then at Bell Labs, now at MIT) and extensively studied one- and two-dimensional magnets with a wide variety of different types of interactions.  At about the same time he began his studies on structural transformations in lower dimensional systems along with R. Comes (Orsay) where the electron-lattice interactions are fundamental.  It is widely recognized that his results provided the experimental basis for our understanding of lower dimensional systems.

Around the same period Gen, Bob Birgeneau, along with Roger Cowley (Oxford), performed some seminal experiments on the study of random magnetic impurities in antiferromagnetic systems.  These experiments showed that when a non-magnetic atom is placed in an ordered magnetic solid, the magnetic properties are altered in a very surprising way.  The experiments performed at BNL with Gen's help proved the most reliable in deciding between different and often conflicting theories.

Another unifying thread in Gen's body of work involves the study of the properties of superconductors.  He performed the first measurements with neutrons on the effect of the energy gap on phonon linewidths in strong-coupling superconductors.  This is a direct measure of the amount of electron-lattice coupling which is one of the key parameters in the Bardeen-Cooper-Schrieffer theory of superconductivity.  He subsequently collaborated on neutron studies of the interplay of superconductivity and magnetism in rare earth ternary solids where the magnetism and the superconductivity are due to different electronic states.  These experiments demonstrated that magnetic order and superconductivity are not always incompatible, contrary to prevailing wisdom.  This was a very important finding.

Currently Gen is actively involved in the study of the new high-Tc superconductors.  All of his past experiences in magnetism, structural phase transitions in perovskites, lower dimensional phenomena, and superconductivity come together beautifully in the series of experiments he has performed in this rapidly advancing and exciting field.  This is, perhaps, the pinnacle of his long and distinguished career.  Gen and his collaborators succeeded (while others have failed!) in detecting magnetic fluctuations in theYBa2Cu3O7 (called 123) and La2CuO4 (called 214) superconductors.  The significance of his results is that they essentially define the nature of the charge carriers and, possibly, the mechanism describing the superconductivity in these high-Tc materials.  In addition, his studies of the magnetism in the above compounds provide the first information about the quantum mechanical effects on the dynamics of lower dimensional solids.

It is important to emphasize the totality and consistency of Gen Shirane's scientific output over his entire scientific career.  His energy has never lagged nor have his scientific standards been compromised: only superior science is acceptable to him.  Gen has served as head of the Neutron Scattering Group within the Physics Department at BNL and has trained numerous young neutron scatterers who struggled to meet his standards.  Only the best succeeded, and they now populate the world-wide neutron research centers, as well as some of the top universities.  Gen Shirane has few equals!

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Last Modified: Wednesday, 26-Jan-2005 16:39:26 EST

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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