Amazing stuff! Graphene keeps on giving!
"... So far, the Nernst effect has been primarily demonstrated in time-reversal symmetry-breaking systems, either by applying an external magnetic field or by using magnetic materials. Yet recent physics theories have introduced the idea that a nonlinear Nernst effect (NNE) could arise in non-magnetic materials, crucially, under zero external magnetic field.
Researchers ... have now realized this idea in an experimental setting for the first time. Their paper ... reports the observation of a sizable nonlinear Nernst effect in an inversion symmetry-breaking form of trilayer graphene known as ABA trilayer graphene. ...
"The conventional Nernst effect, a thermoelectric phenomenon that generates a transverse voltage from a temperature gradient, typically requires breaking time-reversal symmetry, often with a magnetic field. This requirement poses a significant challenge for the miniaturization and integration of thermoelectric devices. Yet recently, theoretical predictions have suggested a new type of phenomenon called NNE." ..."
From the abstract:
"The Nernst effect, that is, the generation of a transverse voltage in response to a temperature gradient, enables thermoelectric energy conversion. In the absence of an external magnetic field, the linear Nernst effect is forbidden in non-magnetic materials because of time-reversal symmetry constraints, but the recently predicted nonlinear Nernst effect (NNE) is allowed.
Here we report the experimental observation of the NNE in non-magnetic ABA trilayer graphene, even in the absence of an external magnetic field. This effect is detected via electric harmonic measurements under an alternating temperature gradient at temperatures below 12 K.
The NNE exhibits a quadratic dependence on the temperature gradient. It is notably enhanced near the charge neutrality point and reaches a giant effective Nernst coefficient of up to 300 µV K−1 at 2 K, surpassing the linear coefficients of magnetic materials.
Moreover, we establish a scaling law between the NNE and the linear Seebeck effect, confirming the dominance of a skew scattering mechanism in driving the NNE. Our findings demonstrate an alternative approach for thermoelectric energy harvesting and cooling applications via nonlinear thermoelectric responses, which may, in the long run, offer alternative approaches towards the development of advanced thermoelectric devices."
Nonlinear Nernst effect in trilayer graphene at zero magnetic field (no public access)
a, The schematic diagram of nonlinear Nernst effect in non-magnetic materials at zero magnetic field. b, The Nernst coefficient obtained from nonlinear Nernst effect in trilayer graphene and anomalous Nernst effect in magnetic materials.
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