Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
A new model of flow induced voltage generation in Carbon Nanotubes based on van der Waals friction K. Sathya Narayanan and A.K. Sood Department of Physics, Indian Institute of Science, Bangalore-560012, India. We present here a simple model to explain the plethora of experimental results concerning the flow induced voltage generation in carbon nanotubes which, thus far, have been only inadequately explained. To do this, we consider the zeroth order picture of the alignment of water molecules confined inside the nanotubes subject to the force field exerted by the imposed flow outside the tubes. These aligned water molecules polarize the nanotubes containing them, thereby inducing a potential difference across its length. Importantly, we model this force field as due to the van der Waals (VdW) frictional stress that exists between any two dissipating dielectric media in relative motion with each other, which, here, is between the confined water molecules and the flowing liquid. This simple model, surprisingly, captures the qualitative behavior observed in the experiments such as: induced voltage as a function of flow velocity, gate voltage and electrolyte concentration. Further, this also explains the apparently unrelated non-local voltage generation observed in isolated carbon nanotubes when filled with water vapor. We extend this even more to try and understand the intriguing phenomenon of flow induced voltage generation in carbon nanotubes trapped in Ice, wherein the flowing medium is well isolated from the nanotubes by a sufficiently thick layer of ice. We believe that this understanding is crucial to optimization of future energy harvesting devices.
Landau Level Spectroscopy of Broken Symmetry States in High Mobility Graphene on Boron Nitride Srijit Goswami, Paritosh Karnatak and Arindam Ghosh The presence of spin and valley degeneracy in graphene gives rise to four-fold degenerate Landau levels (LLs) in the presence of a magnetic field perpendicular to the plane of the graphene. Graphene devices on silicon oxide substrates typically exhibit very low mobility, resulting in significant broadening of LLs. As a result, any broken symmetry states are difficult to observe at reasonable magnetic fields. Placing graphene on atomically flat hexagonal Boron Nitride (BN) results in significantly higher carrier mobility. We have fabricated such high mobility graphene-BN heterostructures and show that the four-fold degeneracy of the LLs is completely lifted at moderate magnetic fields. Such broken symmetry states have been observed in a few studies previously, however their exact nature is still a matter of debate. We also show that charge transfer between graphene and a nearby defect site gives rise to discrete jumps in the resistance. In the presence of a magnetic field the size and nature of these resistance jumps is particularly sensitive to the position of the Fermi level. We discuss some preliminary results which indicate that such a graphene-defect system may allow for a more sensitive spectroscopy of the LLs, as compared to time averaged transport.
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Landau Level Spectroscopy <strong>of</strong> Broken Symmetry States in High Mobility<br />
Graphene on Boron Nitride<br />
Srijit Goswami, Paritosh Karnatak and Arindam Ghosh<br />
The presence <strong>of</strong> spin and valley degeneracy in graphene gives rise to four-fold degenerate<br />
Landau levels (LLs) in the presence <strong>of</strong> a magnetic field perpendicular to the plane <strong>of</strong> the<br />
graphene. Graphene devices on silicon oxide substrates typically exhibit very low mobility,<br />
resulting in significant broadening <strong>of</strong> LLs. As a result, any broken symmetry states are<br />
difficult to observe at reasonable magnetic fields.<br />
Placing graphene on atomically flat hexagonal Boron Nitride (BN) results in significantly<br />
higher carrier mobility. We have fabricated such high mobility graphene-BN<br />
heterostructures and show that the four-fold degeneracy <strong>of</strong> the LLs is completely lifted at<br />
moderate magnetic fields. Such broken symmetry states have been observed in a few<br />
studies previously, however their exact nature is still a matter <strong>of</strong> debate.<br />
We also show that charge transfer between graphene and a nearby defect site gives rise to<br />
discrete jumps in the resistance. In the presence <strong>of</strong> a magnetic field the size and nature <strong>of</strong><br />
these resistance jumps is particularly sensitive to the position <strong>of</strong> the Fermi level. We discuss<br />
some preliminary results which indicate that such a graphene-defect system may allow for a<br />
more sensitive spectroscopy <strong>of</strong> the LLs, as compared to time averaged transport.
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