1. 1/f-Noise in systems with multiple transport mechanisms K K Bardhan and C D Mukherjee Saha Institute of Nuclear Physics, India UPoN 5, Lyon, 5 June, 2008

2. Introduction Many condensed matter systems of recent interest (e.g. manganites, oxides, composites) exhibit multiple phases, often characterized by the behavior of conductance (or resistance) as a function of variables such as temperature or electric / magnetic field. Q. These transport phases are usually classified (e.g. by order) in the same manner as the thermal phases. How far such assumption is valid? Does the noise behave in the same manner as the resistance as far as the order of transition is concerned? For clarity, it is necessary to study the behavior of noise across transitions to obtain a comprehensive picture.

4. Noise and phase transition Previous studies are mostly around critical points of second order phase transitions. Examples: Metal-insulator transition (Si:P) Spin-glass transition Flux-lattice in superconductor Percolation threshold  Consistent with the phenomena of critical fluctuations resistance noise have been found to diverge at the critical point as e.g. in a composite system,  Noise tends to become non-gaussian Need to look at other properties of noise: β - bias exponent α - frequency exponent R- function of R

5. Composite (carbon-wax) and Phase diagram Why composites? A canonical example of a percolation system Many examples involving two phases, which invoke percolation for explanation Easy experimental access to compositional variable p to tune disorder No complex interactions as in manganites. Phases are well understood. percolation threshold p c - a non-thermodynamic critical point PRL 83 (1999) Tunneling: dR/dF<0 Joule: dR/dF>0

6. Measurements along path a second order first order!

7. Measurements along path b first order Open problem Phase diagram based upon noise data

8. Measurements along path b Kakalios et al., PRL (1991) Chitme et al., PRB 67 (2003) KKB, AIP Conf Proc 800 (2005) Variation in β (Open problem) appears to be a generic feature of disordered systems clearly disordered-induced, not field-driven sample-to-sample variation much larger than experimental error

9. Measurements along path a Noise power functional Tunneling phase: power-law KKB, Physica A 241(1997) Joule phase: polynomial

10. Conclusion Classification of transport (or non-thermodynamic) phases in terms of thermodynamic one is ambiguous Interpretation of experimental data in mixed phases require knowledge of pure ones