Quasi-low-dimensional molecular materials
In the same way that a brick wall is built brick by brick, molecular
materials are assembled molecule by molecule. Molecular conductors and
magnets offer an promising alternative to traditional metals and rare-earth
magnets. The low cost, light weight, potentially high strength and
self-assembling nature of molecular conductors and magnets may lead to
applications ranging from flat-screen lap-top computer displays to electric
car batteries to nanoscale size magnetic recording devices.
Not surprisingly, the structural anisotropy of these materials also leads
to corresponding anisotropies in many other of their physical properties
(such as electrical conductivity). In particular, these electronically and
magnetically quasi-low dimensional materials are unusually susceptible to
dimensionally-driven phase transitions from normal conducting to novel
superconducting, insulating and magnetic states when perturbed by small
changes in pressure, magnetic field, crystal structure and chemical
composition.
Current research on these materials aims to indentify these
dimensionally-driven transitions and to understand their physical origin.
Research by Smith College students and myself on molecular materials
contributes towards these goals as follows:
1. Synthesis of molecular materials.
Electrically conducting molecular crystals can be economically synthesized
on a small table top by standard electrochemical techniques. We seek to
produce large, high purity, defect free molecular crystals both by
improving the standard electrochemical synthesis and by introducing
alternative small-scale synthesis methods. We have recently begun
video-microscopy-based studies designed to observe and control molecular
crystal growth modes in beta-(BEDT-TTF)_2 Cu (SCN)_2.
2. Anisotropic, quasi-low dimensional physics.
Once synthesized, we seek to characterize the anisotropic nature of these
crystalline molecular conductors by measurements of the anisotropy in
transport properties such as electrical conductivity and fundamental
thermodynamic properties such as the superconducting critical magnetic
field.
3. Collective phenomena and phase transitions.
The focus of our research is on thermodynamic measurements (specific heat,
magnetization and additional non-traditional thermal probes) of phase
transitions and changes in the effective dimensionality of well
characterized samples of electrically conducting and superconducting
molecular crystals. This entails measurements of the pressure, magnetic
field, structural and chemical dependence of the observed phase transitions
from conducting to magnetic and insulating states.
4.Development of sensors and techniques.
Overcoming technical challenges specific to experiments on these materials
requires the use of sensors and instrumentation not commercially available.
We design special purpose instrumentation and fabricate new low mass, rapid
thermal response resistive thin film thermal sensors that allow use to
perform measurements over a wide range of temperature, pressure and
magnetic field. We are currently developing polycrystalline AuGe thin films
for use in calorimetric measurements.
Representative publications
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