Hao Liu

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.

Spin-triplet pairing of superconductivity, drawing huge attention by enabling future technologies in quantum computing, spintronics, and other fields, can host unique transport phenomena. Here, we report gigantically enhanced nonreciprocal transport in the superconducting fluctuation regime of KTaO_{3}-based interface superconductors. Notably, the observed nonreciprocity undergoes a sign reversal compared to the normal state. Combining experimental observations with theoretical modeling, we identify its dominant mechanism as the vortex motion and parity mixing of spin-singlet and spin-triplet pairings. We also provide evidence for an attractive spin-triplet pairing interaction. Furthermore, the nonreciprocal response is highly tunable by orders of magnitude using electrostatic gating. These findings shed light on the pairing mechanisms in Rashba superconductors and offer new pathways for developing nonlinear superconducting devices.