Projects

Research Topics

Quantum Magnetism:

2D spin-liquids - we are undertaking microscopic studies of the 2D frustrated spin-1/2 Heisenberg antiferromagnet, Cs2CuCl4. This material represents the first experimental realization of a 2D fractional quantum spin liquid.

We have carried out our first measurements at the National High Magnetic Field Laboratory, Tallahassee, FL. A detailed 133Cs NMR study down to 1.6 K shows that Cs-nuclei provides a useful probe for investigating magnetic properties in this material. An interesting field dependence both in the NMR rate and the shift has been observed. We will extend the measurements to below 1.6 K and to fields ranging from 2 - 15 T.

- High-magnetic field magnetization plateau in Cs2CuBr4.

NMR measurements are crucial for confirming the possible existence of deconfined fractionalized excitations (spinons) in frustrated quantum antiferromagnets; establishing whether there is a `small' ( ~ 200 mK) gap in the excitation spectrum of spinon quasiparticles; and, ascertaining their underlying statistics. In addition, we hope to unveil the low-energy mechanism governing the quantum phase transitions in Cs2CuCl4. Another strong motivation for the study of such systems comes from the observation of SC, possibly mediated by spin fluctuations, in doped materials with the same underlying lattice. This project is carried out in collaboration with R. Coldea (Oxford, UK), A. Reyes (NHMFL), and theory group of B. Marston (Brown). Unconventional Superconductivity (high-temperature, organic SC, and heavy-fermion SC) :
What is the role of magnetism in establishing unconventional superconductivity? We are investigating quantum critical phenomena and inhomogeneous SC state in heavy-fermion superconductor CeColn5 in collaboration with the NMR group at the Grenoble High Magnetic Field Laboratory (GHMFL), Grenoble, France, lead by Dr. C. Berthier.

		NMR study of FeSb2 Investigation on highly anisotropic magnetic behavior of FeSb2. Fern started working on this project in summer 2005 with the support of Royce Fellowship Program. The sample was made by Rongwei, who is working at Brookhaven National Laboratory. FeSb2 is a small gap semiconductor with highly anisotropic behaviors seen mainly from the esistivity and magneto-resistance measurements. Electrical transport measurements in bulk material have found that this material is a semiconductor along the a and c axes and exhibits metallic-semiconductor crossover along the b axis.
	In addition to strange magnetic behavior, measurements of the resistivity at low temperature show that FeSb2 exhibits the Kondo-like effect, that is the resistivity raise exponentially at low temperature. This shape of the resistivity curve is also similar to FeSi. FeSi has been under intense study. However, the real physical mechanism of its properties is not well understood. Understanding the physics of FeSb2 could shed light on the physics of narrow-gap semiconductors as well as the possibility to tune the properties of these exotic semi-conductors.

	NMR Probe Construction One of the most important appratus in NMR experiment is the NMR probe. Marc-Andre and Adam have been working on the design and the construction. They have built three probes so far.