Below is a selection of publications representing our research interests.
- Specific Heat of CsNiF3: Evidence for Spin Solitons, Phys. Rev. Lett. 49, 227 (1983): Discovered sine-Gordon soliton contribution to specific heat in the quasi-1D, spin-1 ferromagnet CsNiF3.
- Specific Heat of Defects in Haldane Systems Y2BaNiO5 and NENP - Absence of Free Spin-1/2 Excitations, Phys. Rev. Lett. 72, 3108 (1994): Demonstrated that the specific heat of uncompensated spins at the ends of s=1 antiferromagnetic chains in Y2BaNiO5 are not described by s=1/2 as expected from the Haldane effect, but rather by s=1 Schottky anomalies.
- Strongly Geometrically Frustrated Magnets, Annu. Rev. Mater. Sci. 24, 453 (1994): Introduced the criterion of strong frustration (θw/Tc > 10) to define a class of geometrically frustrated magnets.
- Strong Frustration and Dilution-Enhanced Spin Glass Order in a Quasi-2D Antiferromagnet, Phys. Rev. Lett. 64, 2070 (1990): Identified a new liquid-like phase of the antiferromagnetic Heisenberg kagome system SrCr9Ga3O19.
- Zero Point Entropy in Spin-Ice, Nature 399, 527 (1999): Discovered zero-point entropy in the pyrochlore Dy2Ti2O7, demonstrating the spin-ice ground state.
- Phonon Density of States and Negative Thermal Expansion in ZrW2O8, Nature 396, 147 (1998) & Giant Dielectric Constant Response in a Copper-Titanate, Solid State Commun. 115, 217 (2000): Identified the role of geometrical frustration for understanding non-magnetic phenomena, specifically negative thermal expansion in ZrW2O8, and large dielectric response in CaCu3Ti4O12.
- Quasispin Glass in a Geometrically Frustrated Magnet, Phys. Rev. Lett. 110, 017203 (2013): Discovered, in the vacancy-doped spinel ZnCr2O4, evidence for freezing among quasi-spins with range-independent interactions.
- Electronic Properties of La2-xSrxCuO4 High-Tc Superconductors, Phys. Rev. B 35, 5347 (1987): Performed first measurement of the specific heat jump at Tc in cuprate superconductors, in La2-xSrxCuO4.
- Superconductivity at 18K in Potassium-doped C60, Nature 350, 600 (1991): Co-discovered superconductivity in A3C60.
- Isotope Effect in Superconducting Rb3 C60, Phys. Rev. Lett. 68, 1058 (1992): Determined the carbon isotope Tc-shift in A3C60, demonstrating a phonon-mediated process.
- Specific Heat Jump at Tc and Normal State Susceptibility of A3C60, Phys. Rev. Lett. 69, 1687 (1992): Performed the only measurement to date of the specific heat jump at Tc in A3C60 (for A = K); showed consistency among ωph, λ, and μ for phonon-mediated pairing.
- Fermi-Liquid Renormalization in the Superconducting State of UBe13, Phil. Mag. 79, 111 (1999): Found the Fermi-liquid effect, known for 3He, in a superconductor, the heavy fermion system UBe13.
- Low Temperature Magnetoresistance and the Magnetic Phase Diagram of La1-xCaxMnO3, Phys. Rev. Lett 75, 3336 (1995): Determined the first complete phase diagram for a CMR system, La1-xCaxMnO3.
- Magnetic Field Dependent Specific Heat of V3Si -- Downward Curvature as a General Feature of Superconductivity, Physics Letters A 211, 59 (1996) & Thermal Conductivity of Manganite Perovskites, Phys. Rev. Lett. 78, 3947 (1997): Demonstrated coupling of the lattice to magnetism using sound velocity and thermal conductivity.
- Large Enhancement of Magnetoresistance in Tl2Mn2O7 : Pyrochlore vs. Perovskite, Science 277, 546 (1997) & Colossal Magnetoresistance in Cr-Chalcogenide Spinels, Nature 386, 166 (1997): Demonstrated CMR in a Mn-containing non-perovskite and a non-Mn containing spinel.
2-Dimensional Hole Gas
- Nonmonotonic Temperature-Dependent Resistance in Low Density 2D Hole Gases, Phys. Rev. Lett. 83, 2805 (1999): Demonstrated scaling of non-monotonic insulating-to-metallic crossover in a high mobility 2d hole-gas.
- Magnetically Driven Ferroelectric Order in Ni3V2O8, Phys. Rev. Lett. 95, 087205 (2005): Discovered multiferroic behavior in the kagome staircase compound Ni3V2O8.
- Cupric Oxide as an Induced-Multiferroic with High Tc, Nature Materials 7, 291 (2008): Co-discovered multiferroic behavior at 230K in cupric oxide.
- Bias-Dependent Generation and Quenching of Defects in Pentacene, Phys. Rev. Lett. 93, 076601 (2004): Found that deep traps in pentacene are due to formation of meta-stable hydrapentacene impurities.
- Dependence of Mobility on Density of Gap States in Organics by GAME(a)S-Gate Modulated Activation Energy Spectroscopy, J. Appl. Phys. 104, 054512 (2008): Developed simple spectroscopy, Gate Modulated Activation Energy Spectroscopy (GAMES) for study of deep and shallow trap states.
- Mobility-independent doping in crystalline rubrene field-effect transistors, Solid State Commun. 142, 483 (2007): co-discovered a method for doping organic crystals – i.e. changing carrier density without changing mobility (patented).
- Mechanism for Oxygen-Enhanced Photoconductivity in Rubrene: Electron Transfer Doping, Chem. Mat. 21, 5519 (2009): Co-discovered mechanism for oxygen-induced doping in rubrene.