Groundbreaking Discovery of Nonlinear Nernst Effect in Trilayer Graphene

In a significant advancement in the field of thermoelectric materials, researchers from Fudan University and Peking University have made the first experimental observation of a giant nonlinear Nernst effect (NNE) in an ABA trilayer graphene structure, without the need for an external magnetic field. This groundbreaking discovery, published in the esteemed journal Nature Nanotechnology on July 18, 2025, could revolutionize energy conversion technologies and has potential applications in various sectors, including space exploration and industrial energy recovery.

The Nernst effect, which generates a transverse voltage in response to a temperature gradient, has traditionally been observed in magnetic materials or under the influence of an external magnetic field. However, the recent theories posited that a nonlinear Nernst effect could occur in non-magnetic materials, which could simplify the integration of thermoelectric devices into compact systems.

Pan He, co-senior author of the study, explained, "Our research was inspired by the unique challenges and opportunities in the field of thermoelectricity. The conventional Nernst effect typically requires breaking time-reversal symmetry, often necessitating a magnetic field. This creates challenges for miniaturization and device integration. Our findings demonstrate that a nonlinear version of this effect can emerge in non-magnetic materials, potentially opening new avenues for thermoelectric applications."

To achieve this, the researchers fabricated high-quality Hall bar devices embedded with microheaters and thermometers. They applied a sinusoidal current to the heaters, inducing a fluctuating temperature gradient across the trilayer graphene. The NNE manifested as a fourth harmonic transverse voltage, indicative of a second-order response to the temperature gradient.

Remarkably, the team measured an effective Nernst coefficient of up to 300 µVK⁻¹ at 2 K, which is about two orders of magnitude larger than the highest values reported in magnetic materials under similar conditions. This unprecedented result offers a promising alternative for thermoelectric energy harvesting, eliminating the need for magnetic materials.

The implications of this discovery are vast. Not only does it pave the way for the development of more efficient thermoelectric devices, but it also suggests a pathway to achieving these effects at room temperature, which is crucial for practical applications. He remarked, "Our work opens several exciting directions for future research, including exploring other time-reversal invariant and non-centrosymmetric materials that might exhibit this effect at higher temperatures."

As researchers aim to optimize the nonlinear Nernst effect and explore its modulation through external magnetic fields, the potential applications in energy recovery from waste heat in industrial settings and enhanced energy generation in remote missions become increasingly viable. The future of thermoelectric technology may be significantly shaped by this innovative research, marking a pivotal moment in energy conversion science.