The activities of our faculty members in Condensed Matter Physics are quite varied, covering a full range of frontier issues.

Professor Joseph Birman carries out research in condensed matter theory on several topics. A major direction relates to symmetry and symmetry breaking in condensed matter. Both "geometrical" and "dynamical" symmetry play important roles. Geometrical symmetry gives rise to "go/no-go" selection rules for allowed/forbidden processes, phase transitions, and response functions. Dynamical symmetry is a powerful tool for the classification of the Hamiltonian of a many-body system. Techniques from Lie Algebras, supersymmetry, and more general algebraic structures are used to classify ground and excited states, transitions, and stability for interacting many-body systems. A continuing interest in Professor Birman's group is the prediction and analysis of optical properties of material systems. Examples include probing optical excitations in Bose-Einstein condensates, and "squeezing" of excitations in solids, analogous to quantum optics. Additional recent topics under active study include: magneto-acoustic transport theory for "composite fermions" in Quantum Hall Systems; nature of the excitations and their propagation in newly found atomic Bose-Einstein condensed systems; optical response of "quantum dot" systems. A recent experimental report on possible coexistence of competing effects such as superconductivity and ferroelectricity led us to the formulation of a new model based on "dynamical-symmetry" incorporating both effects, and our predictions of new effects when magnetic field and external pressure are applied.

Professor Herman Cummins directs a program of laser light-scattering studies of liquids and solids. His major effort is in the study of phase transitions and critical phenomena, most recently involving the liquid-glass transition, using Raman and Brillouin scattering and photon correlation spectroscopy. Professor Cummins also uses dielectric measurements and participates in neutron-scattering experiments at NIST and at Brookhaven National Laboratory.

Professor Harold Falk's research field is statistical mechanics. His work often uses spin-system techniques and focuses on mathematically exact results. Recently he has been studying the evolution of discrete-time, nonlinear and stochastic models.

Professor Joel Gersten's research deals with the properties of small solid-state particles and solid-state surfaces. The specific areas being investigated are the electromagnetic properties, electronic properties and the interaction of these particles and surfaces with atoms and molecules.

Professor Melvin Lax pursues theoretical research involving radiative and non-radiative interactions in ordered systems (semiconductor crystals, heterostructures, quantum wells), coherent systems (diffraction feedback semiconductor lasers), and disordered systems. The techniques involve (1) group theory in ordered systems, (2) random-process methods to deal with noise and partition fluctuations in lasers, and non-radiative, recombination-induced defect reactions, and (3) inverse scattering methods to deduce the nature of a scatterer by optical scattering techniques. (A related problem is the difficult one of character recognition.) Other applications of random-process techniques are light or radar scattering from a rough surface and infra-red scattering from the walls of an optical fiber.

Professor Myriam Sarachik does research in two areas of solid-state physics: doped semiconductors near the metal-insulator transition and macroscopic quantum tunneling of magnetization. The work on semiconductors includes studies in the hopping regime as well as in the metallic phase. The experiments yield information concerning the nature of the transition, the roles of disorder and correlations, and the effects of quantum interference, spin-orbit scattering, spin-flip scattering, and magnetic fields. A new effort is underway to establish the existence of macroscopic quantum tunneling of magnetization in small ferro-, antiferro-, and ferrimagnetic particles.
     Prof. Sarachik's laboratory has facilities for measuring transport, magnetic, and optical properties over a wide range of temperatures down to 0.04 K using a dilution refrigerator and magnetic fields as high as 90,000 gauss. For more information, visit the CCNY Low-Temperature Condense Matter Group Website.

Professor David Schmeltzer's research in condensed matter physics is devoted to studies of strongly correlated systems in low dimensions. Such systems include the Luttinger liquid in one dimension (quantum wires, spin ladders, edge states in the fractional hall effect) and (due to competing interactions) the Fermi-liquid--non-Fermi-liquid transition (high Tc), the superfluid-insulator transition and probably the metal-insulator transition in two dimensions. All these phenomena can be understood within a "quantum critical theory." Such a theory always emerges in the presence of competing interactions, giving rise to diverging correlation lengths.

Professor Frederick W. Smith concentrates his experimental condensed-matter research in two main areas:
     (1) Studies of the surface reactions of oxygen with crystalline SiC. This research involves the experimental investigation of the interactions of oxygen with the surfaces of single crystal SiC at high temperatures. The oxidation and etching reactions are being studied as a function of temperature and oxidant pressure with the goal of determining the critical conditions necessary for the oxidation of SiC. Extensive thermodynamic and kinetic modeling of these reactions is being carried out.
     (2) The preparation and characterization of a variety of crystalline and amorphous semiconductor and insulating films. The preparation of crystalline diamond and amorphous "diamond-like" carbon films is being carried out using a variety of deposition techniques. The goals are to prepare diamond films for use in wear-resistant, optical and possibly electronic applications. A thermodynamic model for the CVD of diamond has been developed which can explain the observed growth of diamond films. An in-situ measurement capability for determining the development of surface roughness of the growing diamond films has been established.