Nonlinear conduction in a stable material with cheap components

Fe3O2BO3 is a ludwigite with a single type of metallic ion (Fe). The ludwigites belong to the family of oxyborates and are characterized by the presence of low dimensional sub-units in the form of three legged ladders (3LL) along the c-axis of their crystalline structure.  In a recent Journal of Physics: Condensed Matter paper, Mucio Continentino and his team investigate Charge Density Waves in single crystals. Read on to find out more in the authors’ own words.

Fe3O2BO3 presents a unique structural transition concomitant with the charge ordering (CO) of an itinerant electron in the rungs of a 3LL. This transition that occurs near room temperature is associated with the formation of a transverse charge-density wave (CDW) along the 3LL. It has been identified by several experimental techniques and as we show it is also found by specific heat measurements. It is signaled by a well-defined maximum that is insensitive to an applied magnetic field of 9 T, as expected for a structural transition.

When applying voltage in single crystals of Fe3O2BO3 near the temperature of the structural transition to explore the contribution of the CDW (CO) condensate to conduction, a very high current was liberated that melted the contacts and sometimes burned the sample. One way to avoid this problem was to use a current compliance. This approach allowed us to identify a first threshold voltage VT1, marking the beginning of the nonlinear behavior, and a second threshold voltage VT2 above which a sharp increase in the current was observed. This behavior was very well reproduced as could be seen cycling the voltage several times.

Current limited by a compliance of ±0.3 A (dashed lines) for a DC voltage applied perpendicular to the c axis of Fe3O2BO3 single crystal at 295 K. First, from −3 V to 3 V (open red squares), second, from −4 V to 4 V (blue stars) and third, from −5 V to 5 V (green crosses). The sharp increase in the current that defines VT 2 is also indicated. Taken from J. Phys. Cond. Mat. 205401 © IOP Publishing.

Besides, in the range VT1≤ V≤ 0.9 VT2, plotting the data as I x (V-VT1)/ VT1 we found out depinning characterized by power law scaling behavior with a critical exponent h»3/2. The behavior close to VT2 is in qualitative agreement with the theory of depinning with stress overshoot. Depinning with power law h»3/2 scaling was also revealed in real part of the AC conductivity when plotted as (s-sDC) x w/wP, with wP being a pinning frequency.

This work is part of a study that investigates the general physical properties of the oxyborates. Fe3O2BO3, so far, has revealed a unique and exciting material. It combines commonly available elements and its transport properties close to room temperature makes it very attractive for applications.

About the authors

Team in São Paulo

Éverton C. dos Santos is now a PhD student at Niels Bohr Institute, Denmark.
Everlin F. da Silva is now a PhD student at Universidade de São Paulo.
Lygia Walmsley is at Universidade Estadual Paulista (UNESP), Rio Claro.

Team in Rio

João Carlos Fernandes is at Universidade Federal Fluminense.
Luis Ghivelder is a Professor at the Federal University of Rio de Janeiro, with research interest in experimental condensed matter physics, on magnetism and superconductivity.
Daniele Freitas is now at Universidade Federal Fluminense.

Mucio Continentino is at Centro Brasileiro de Pesquisas Físicas and has recently published a book on Quantum Phase Transitions.

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Categories: Journal of Physics: Condensed Matter, JPhys+

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