![]() ![]() Our results have revealed interesting routes by which magnetic and orbital frustration can be tuned with field or pressure and show the connection between orbital/spin frustration and highly tunable properties of matter.įield- and pressure-tuned melting of orbital order in correlated materials Our current efforts include using various single crystal growth methods to grow geometically frustrated materials, and then applying field- and pressure-dependent optical spectroscopy to study orbital- and spin-disordered phases in several classes of materials, including the layered ruthenates, spinels such as Mn 3O 4, iridates like Sr 2IrO 4, and vanadates such as Ni 3V 2O 8. This interest is motivated by the novel low temperature phase behavior frustrated materials have been proposed to exhibit - including orbital- and spin-liquid phases - and by a desire to elucidate the connection between frustration and exotic properties such as colossal magnetoresistance, and multiferroic and magnetodielectric behavior. ![]() ![]() We are interested in growing - using float zone and other growth techniques - and spectroscopically studying materials in which structural geometry and competing interactions conspire to frustrate the onset of long range magnetic and/or orbital order, even down to T=0 K. The development at low temperatures of some form of long-range order - such as magnetism, orbital-order, charge-order, or superconductivity - is ubiquitous in materials, and reflects the tendency of a material to lower its ground state degeneracy near T=0 K. Documentsįield- and pressure-tuned spectroscopy of magnetically frustrated and strong spin-lattice coupled materials Lance Cooper also runs a Physics Grad Student Blog with job, fellowship, academic deadline, and other information of interest to graduate students the Physics Careers seminar, in which Physics PhDs - mostly Illinois alumni - describe their jobs and the importance of a physics PhD and their grad school experiences to their careers and a Physics Grad Student Travel Award program. The Cooper group has used floating zone, vapor transport, evaporative, and other methods to grow high quality single crystals, including spinel materials such as Mn 3O 4 and CoCr 2O 4, orbital ordering materials such as KCuF 3, layered chalcogenide materials such as TiSe 2, and topological insulators like Bi 2Se 3. His group has also shown that magnetic fields can be used both to control the elastic properties of materials (e.g., "magnetic field induced shape memory") and to thwart long-range order down to T=0 K. More recently, his group has studied how high pressures "melt" charge- and orbital-ordered insulating states, even at T=0 K, creating novel metallic phases. The Cooper group's first accomplishment with its "extreme conditions" optical spectroscopy capability was a study of the evolution of the crystal lattice ("phonon") and atomic spin dynamics through the pressure-tuned destruction of the insulating state of layered ruthenate materials. The Cooper group's Raman spectroscopy experiments have shed light on the behavior of matter through various pressure- and magnetic-field-tuned quantum (T~0 K) phase transitions. His group has developed particular expertise in light-scattering experiments on materials under extreme conditions of low temperature, high pressure, and high magnetic field. The Cooper group uses optical spectroscopy to reveal the properties of and excitations in novel states of matter in strongly correlated materials. From 1993-1995, he was a member of the Defense Science Study Group (DSSG), a Divisional Associate Editor for Physical Review Letters from 2006-2011, and the Secretary-Treasurer for the Division of Condensed Matter Physics of the American Physical Society from 2015-2019. After a two-year postdoctoral appointment at AT&T Bell Labs, Professor Cooper joined the UIUC faculty in 1990. in Physics summa cum laude from the University of Virginia in 1982 and a Ph.D in Physics from the University of Illinois in 1988. ![]()
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