Observation of nuclear-spin Seebeck effect

TL;DR

This paper reports the discovery of a nuclear-spin Seebeck effect in MnCO₃, enabling thermoelectric generation at ultralow temperatures through nuclear spin excitations, expanding thermoelectric science beyond electronic systems.

Contribution

It introduces the nuclear-spin Seebeck effect in a solid, demonstrating thermoelectric generation caused by nuclear spins at millikelvin temperatures, supported by theoretical modeling.

Findings

Observation of thermoelectric signals down to 100 mK.

Quantitative agreement between experiment and theory.

Potential for ultralow-temperature thermoelectric applications.

Abstract

Thermoelectric effects have been applied to power generators and temperature sensors that convert waste heat into electricity. The effects, however, have been limited to electrons to occur, and inevitably disappear at low temperatures due to electronic entropy quenching. Here, we report thermoelectric generation caused by nuclear spins in a solid: nuclear-spin Seebeck effect. The sample is a magnetically ordered material MnCO$_{3}$ having a large nuclear spin ($I = 5/2$) of $^{55}$Mn nuclei and strong hyperfine coupling, with a Pt contact. In the system, we observe low-temperature thermoelectric signals down to 100 mK due to nuclear-spin excitation. Our theoretical calculation in which interfacial Korringa process is taken into consideration quantitatively reproduces the results. The nuclear thermoelectric effect demonstrated here offers a way for exploring thermoelectric science and technologies at ultralow temperatures.