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Nernst effect

The Nernst effect, also known as the Nernst-Ettingshausen effect, is a thermomagnetic phenomenon observed in electrically conductive materials, where a temperature gradient along one direction (typically the x-axis) and a perpendicular magnetic field (along the z-axis) generate a transverse electric field or voltage (along the y-axis).^[1] This effect arises from the deflection of charge carriers by the Lorentz force in the presence of the temperature-induced carrier flow, resulting in a measurable Nernst voltage that depends on the material's properties, such as carrier density, mobility, and entropy per carrier.^[2] The Nernst coefficient N, which quantifies the effect, is defined as N = \frac{E_y}{B_z \nabla_x T}, where E_y is the transverse electric field, B_z is the magnetic field strength, and \nabla_x T is the temperature gradient.^[1] Discovered in 1887 by German physicists Walther Nernst and Albert von Ettingshausen following a theoretical suggestion by Ludwig Boltzmann, the effect was initially studied in metals and provided early insights into the interplay between heat, electricity, and magnetism.^[3] Nernst, a Nobel laureate in Chemistry (1920) for his work on thermochemistry, recognized its significance as part of the broader family of thermoelectric effects, including the Seebeck and Hall effects, with reciprocal relations formalized later by Lars Onsager in 1931.^[2] Early experiments focused on its magnitude in conventional conductors, where it is typically small, but theoretical frameworks like Bridgman's 1924 relations linked it to transverse entropy transport, emphasizing its role in revealing microscopic carrier dynamics.^[2] In modern research, the Nernst effect has gained renewed prominence for probing exotic states of matter, such as strange metals and high-temperature superconductors, where anomalously large signals indicate enhanced carrier entropy or vortex motion.^[4] For instance, colossal anomalous Nernst effects have been observed in correlated materials like Mn₃Sn, enabling applications in spin caloritronics and energy harvesting devices that convert thermal gradients into electrical power without mechanical parts.^[4] Recent advances, including electrically tunable giant Nernst responses in two-dimensional heterostructures and nonlinear variants in graphene, highlight its potential in quantum technologies and thermoelectric efficiency enhancement.^[5]^[6]

Introduction

Definition

The Nernst effect refers to the generation of a transverse electric field (or voltage) in a material when it is subjected to a longitudinal temperature gradient and a perpendicular magnetic field.^[7] This phenomenon arises in conducting materials where heat flow drives charge carriers, which are then deflected by the magnetic field.^[7] In the standard geometric setup, a temperature gradient is applied along the x-axis (∇T = -dT/dx), a magnetic field is oriented along the z-axis (B_z), and the resulting transverse electric field is measured along the y-axis (E_y).^[7] The Nernst signal is this transverse electric field E_y, while the Nernst coefficient ν quantifies the effect and is defined as

\nu = \frac{E_y}{B_z \left( -\frac{dT}{dx} \right)},

where B_z is the magnetic field strength.^[8] Qualitatively, the effect originates from the deflection of charge carriers—driven by the temperature gradient—via the Lorentz force in the presence of the magnetic field, leading to a buildup of charge separation transverse to both the gradient and field directions.^[9] This can be viewed as a magnetized variant of the Seebeck effect, where the transverse response emerges due to the magnetic field.^[7]

Historical development

The Nernst effect was discovered in 1886 by Walther Nernst, then a doctoral student, and his advisor Albert von Ettingshausen at the Technical University of Graz, following a theoretical suggestion by Ludwig Boltzmann to investigate thermoelectric phenomena under magnetic fields; their experiments observed a transverse voltage in bismuth samples with a temperature gradient perpendicular to the field.^[10]^[3] This finding built upon the broader thermoelectric history initiated by Thomas Seebeck's 1821 observation of the Seebeck effect in bimetallic junctions.^[11] Nernst's work established the effect as a thermomagnetic phenomenon distinct from the Hall effect, marking an early milestone in understanding coupled thermal and electrical transport under magnetic influence.^[12] In the early 20th century, the effect saw extensions to various solids and quantitative experimental validations, with Percy Bridgman conducting detailed measurements in metals and alloys around 1924, linking the Nernst coefficient to the Ettingshausen effect through thermodynamic relations.^[12] These developments were further solidified by Lars Onsager's 1931 formulation of reciprocal relations in irreversible thermodynamics, which provided a theoretical framework connecting the Nernst effect to other transport coefficients like the Seebeck and Peltier effects.^[12] Walther Nernst, recognized for his broader contributions to thermochemistry including the heat theorem (later the third law of thermodynamics), received the 1920 Nobel Prize in Chemistry, contextualizing his early thermoelectric discoveries within foundational physical chemistry.^[13] The mid-20th century brought a revival of interest in the Nernst effect, particularly in superconductors, where late-1960s experiments revealed its connection to vortex motion in the mixed state of type-II materials; for instance, Solomon and Otter in 1967 measured thermomagnetic responses in superconducting films, attributing transverse voltages to moving flux lines carrying entropy.^[12] This period highlighted the effect's utility in probing superconducting dynamics, with further studies by Lowell and others in 1967 confirming thermally induced voltages linked to vortex transport.^[12] Post-2000 research has emphasized the anomalous Nernst effect in ferromagnetic and antiferromagnetic materials, independent of external fields, with reports of colossal signals emerging in the 2010s; notably, in 2017, measurements in the noncollinear antiferromagnet Mn₃Sn demonstrated anomalous Nernst and Righi-Leduc effects dominated by Berry curvature contributions, yielding values far exceeding conventional expectations in metals.^[14] These advances have filled gaps in understanding magnetic analogs of the effect, extending its relevance to spintronics and topological materials.^[4]

Theoretical framework

Basic thermoelectric phenomena

Thermoelectric phenomena arise from the coupling between heat and charge transport in materials, primarily driven by the motion of charge carriers such as electrons or holes. The foundational effects were identified in the 19th century through experimental observations. The Seebeck effect, discovered by Thomas Johann Seebeck in 1821, describes the generation of an electric voltage across a material or junction of dissimilar materials subjected to a temperature gradient, with the voltage proportional to the temperature difference via the Seebeck coefficient \alpha.^[15] The Peltier effect, observed by Jean Charles Athanase Peltier in 1834, involves the absorption or release of heat at the junction of two dissimilar conductors when an electric current flows through it, quantified by the Peltier coefficient \Pi = \alpha T, where T is the absolute temperature.^[15] Complementing these, the Thomson effect, predicted and experimentally verified by William Thomson (Lord Kelvin) in 1851, accounts for the reversible heat production or absorption within a single material carrying current in the presence of a temperature gradient, governed by the Thomson coefficient \mu = T \frac{d\alpha}{dT}.^[15] In the presence of magnetic fields, these phenomena extend to magnetothermoelectric effects, where transverse responses emerge analogous to the Hall effect. The Hall effect, discovered by Edwin Hall in 1879, produces a transverse voltage perpendicular to both the current and an applied magnetic field due to the Lorentz deflection of charge carriers, providing a measure of carrier type and density.^[16] This transverse geometry sets the stage for related effects like the Nernst effect, which represents a transverse counterpart to the Seebeck effect under magnetic influence. At a fundamental level, these processes rely on the transport of entropy by charge carriers; in metals and semiconductors, electrons near the Fermi surface carry both charge and entropy, with the entropy per carrier s_e contributing to thermoelectric coefficients such as \alpha = s_e / q, where q is the carrier charge.^[17] The Fermi surface, defining the boundary of occupied electronic states at absolute zero, plays a crucial role in metals by determining the available carriers for transport, influencing the anisotropy and efficiency of heat and charge flow through the material's band structure.^[18] The interrelations among these effects are formalized by Onsager's reciprocal relations, derived from the principles of microscopic reversibility in linear irreversible thermodynamics. Lars Onsager established in 1931 that the thermoelectric transport coefficients form symmetric tensors, such that the Seebeck tensor \alpha_{ij} = \alpha_{ji} and the coupling between electric current \mathbf{J} and heat flux \mathbf{Q} satisfies \mathbf{J} = \sigma \mathbf{E} - \alpha \nabla T and \mathbf{Q} = T \alpha \mathbf{E} - \kappa \nabla T, where \sigma is electrical conductivity and \kappa is thermal conductivity, ensuring reciprocity like \Pi = \alpha T.^[19] These relations link the longitudinal effects (Seebeck, Peltier, Thomson) and underpin the theoretical framework for transverse magnetothermoelectric phenomena.

Formulation of the Nernst effect

The Nernst effect is described within the framework of linear irreversible thermodynamics, where the electric current density \vec{J} and the heat current density \vec{J}_Q are linearly related to the electrochemical potential gradient and the temperature gradient in the presence of a magnetic field \vec{B}. The phenomenological transport equations take the form

\vec{J} = \hat{\sigma} \vec{E} - \hat{\alpha} \vec{\nabla} T,

\vec{J}_Q = \hat{\beta} \vec{E} - \hat{\kappa} \vec{\nabla} T,

where \hat{\sigma}, \hat{\alpha}, \hat{\beta}, and \hat{\kappa} are second-rank tensors incorporating the effects of \vec{B}, with \hat{\sigma} the electrical conductivity tensor, \hat{\alpha} the thermoelectric tensor (related to the Seebeck effect), \hat{\beta} the tensor for the Peltier effect (with \hat{\beta} = T \hat{\alpha} by Onsager reciprocity in the absence of magnetic field, modified in \vec{B}), and \hat{\kappa} the thermal conductivity tensor. The magnetic field introduces off-diagonal antisymmetric components (e.g., \sigma_{xy} = -\sigma_{yx}) due to the Lorentz force, leading to Hall-like terms in all coefficients.^[7] The Nernst-Ettingshausen coefficient \nu, which quantifies the transverse electric field induced by a longitudinal temperature gradient perpendicular to \vec{B}, is defined as \nu = \frac{E_y}{B_z (-\nabla_x T)} under open-circuit conditions (\vec{J} = 0) with \vec{B} = B_z \hat{z}, \vec{\nabla} T = \nabla_x T \hat{x}. In the low-magnetic-field limit, where \sigma_{xy} \ll \sigma_{xx}, this simplifies to \nu \approx \frac{\alpha_{xy}}{\sigma_{xx}}, with \alpha_{xy} the off-diagonal thermoelectric coefficient. More generally, solving for the electric field when J_x = J_y = 0 yields the full tensor expression for the transverse thermopower (Nernst thermopower) S_{xy} = \frac{E_y}{-\nabla_x T} = \frac{\alpha_{xy} \sigma_{xx} - \alpha_{xx} \sigma_{xy}}{\sigma_{xx}^2 + \sigma_{xy}^2}, so \nu = S_{xy} / B_z in the low-field regime where off-diagonals scale linearly with B_z. This relation highlights the interplay between the Seebeck tensor \hat{\alpha} and conductivity tensor \hat{\sigma}.^[7] Derivations of \nu often employ the Boltzmann transport equation in the relaxation-time approximation, assuming a single band of carriers with energy-independent scattering time \tau. For a degenerate electron gas, the Mott relation connects \alpha_{xx} = -\frac{\pi^2 k_B^2 T}{3 e} \left. \frac{\partial \ln \sigma(\varepsilon)}{\partial \varepsilon} \right|_{\varepsilon = \varepsilon_F} to the density of states at the Fermi energy \varepsilon_F, while the off-diagonal \alpha_{xy} arises from the cyclotron motion, yielding \nu \approx \frac{\pi^2 k_B^2 T}{3 e \varepsilon_F} \sigma_{xx} \tau \frac{\partial \ln \sigma / \partial \ln \varepsilon|_{\varepsilon_F}}{\sigma_{xx}} in the low-field limit (\omega_c \tau \ll 1, where \omega_c = e B / m^* is the cyclotron frequency). For non-degenerate statistics or energy-dependent \tau(\varepsilon), the expression generalizes to \nu = \alpha_0 (\mu_\beta - \mu_H), where \alpha_0 is the zero-field Seebeck coefficient, \mu_H = e \langle \tau \rangle / m^* the Hall mobility, and \mu_\beta = \frac{e}{m^*} \frac{\langle \tau^2 (\varepsilon - \varepsilon_F) \rangle}{\langle \tau (\varepsilon - \varepsilon_F) \rangle} the thermal mobility, capturing differences in energy weighting for thermal versus Hall transport.^[7]^[20] In tensor form, the antisymmetric components reverse sign under \vec{B} \to -\vec{B} by Onsager reciprocity (L_{ij}(B) = L_{ji}(-B)), ensuring \alpha_{xy}(B) = -\alpha_{yx}(-B). The field-dependent Nernst coefficient \nu(B) is approximately linear in B at low fields (\nu(B) \approx \nu_0), with the transverse electric field E_y \propto B_z, but deviates at higher fields due to the denominator in the transport integrals. For intermediate fields (\omega_c \tau \sim 1), \nu(B) follows \nu(B) = \alpha_0 (\mu_\beta - \mu_H) / [1 + (\mu_H B)^2], reflecting competition between deflection and scattering. In high magnetic fields (\omega_c \tau \gg 1), the Nernst signal E_y / (-\nabla_x T) saturates or decreases as $1/B_z, with \nu(B) \propto 1/B_z^2, as carriers complete many cyclotron orbits, suppressing transverse entropy transport; quantum oscillations may superimpose peaks when Landau levels cross \varepsilon_F. The distinction between isothermal (constant transverse temperature, allowing J_{Q,y} \neq 0) and adiabatic (no transverse heat flow, J_{Q,y} = 0) conditions is crucial: the isothermal Nernst coefficient \nu^T relates directly to \alpha_{xy}, while the adiabatic \nu^S (measured in insulated setups) is \nu^S = \nu^T (1 + \frac{\kappa_{xx}}{\kappa_{xy} \cot \theta}) or similar, enhanced by suppressed thermal diffusion across the sample, where \theta is the Hall angle and \hat{\kappa} the thermal tensor; this difference can be up to a factor of 2 in metals.^[7]

Physical mechanisms

Classical description

The classical Nernst effect in non-magnetic materials originates from the thermal diffusion of charge carriers under a longitudinal temperature gradient, combined with the deflection induced by an external magnetic field. In metals and semiconductors, a temperature gradient applied along the x-direction drives a heat current carried primarily by electrons (or holes in p-type materials), with carriers diffusing from hot to cold regions due to their higher thermal velocity at elevated temperatures. The perpendicular magnetic field (along z) imposes a Lorentz force on these moving carriers, given by \mathbf{F} = -e (\mathbf{v} \times \mathbf{B}), which deflects them sideways along the y-direction. This deflection causes an accumulation of charge on one side of the sample, establishing a transverse electric field E_y that opposes further buildup, analogous to the Hall effect but driven by thermal rather than electrical current.^[9] The strength of the Nernst effect is intrinsically tied to carrier mobility \mu, as the transverse deflection depends on the mean free path \lambda = v_F \tau (where v_F is the Fermi velocity and \tau the relaxation time) and the magnetic field strength B. The Nernst signal scales as \propto \mu B, rendering the effect vanishingly small in insulators with negligible carrier mobility, while it becomes observable and significant in metals and semiconductors where mobile charge carriers enable substantial Lorentz deflection.^[21] In certain materials, particularly at low temperatures, a phonon-drag contribution enhances the Nernst response. Phonons, which carry entropy along the temperature gradient, transfer momentum to electrons through electron-phonon scattering; under the magnetic field, this drag induces a transverse electron motion, contributing to the overall signal and often resulting in a non-monotonic or peaked temperature dependence distinct from the pure carrier diffusion term.^[22] The semiclassical Boltzmann transport approach provides a rigorous framework for this mechanism, treating carriers as classical particles with wavevector \mathbf{k}. The nonequilibrium distribution function is expressed as f = f_0 - \left( \frac{\partial f_0}{\partial \varepsilon} \right) g, where f_0 is the equilibrium Fermi-Dirac distribution and g represents the deviation solved via the linearized Boltzmann equation, incorporating the driving terms from \nabla T and \mathbf{v} \times \mathbf{B}. This yields the transverse velocity components responsible for the charge separation, under the relaxation-time approximation where scattering is isotropic.^[21] This classical description breaks down in strong magnetic fields or low temperatures where quantum effects dominate, such as the formation of discrete Landau levels that quantize carrier orbits and lead to oscillatory Nernst signals when levels intersect the Fermi energy—phenomena unaccounted for in the semiclassical limit.^[23]

Anomalous Nernst effect

The anomalous Nernst effect (ANE) is a transverse thermoelectric phenomenon observed in ferromagnetic and antiferromagnetic materials, where a temperature gradient applied along one direction generates an electric field perpendicular to both the gradient and the magnetization direction, without requiring an external magnetic field. This effect originates from intrinsic spin-orbit coupling within the material's electronic band structure, which gives rise to a non-zero Berry curvature that influences carrier transport. Unlike the classical Nernst effect, the ANE is field-independent and stems from the topological properties of the Bloch wavefunctions.^[24]^[25] The mechanism of the ANE has a topological foundation, where the Berry phase acquired by electrons during their motion in k-space behaves as an effective magnetic field, deflecting carriers transversely under a thermal drive. This Berry curvature acts analogously to a monopole field in momentum space, contributing to the anomalous transverse response. The effect is particularly pronounced in non-collinear magnets, where the complex spin textures enhance the Berry curvature near the Fermi level; for instance, in the non-collinear antiferromagnet Mn₃Sn, a large ANE coefficient peaking at approximately 0.6 μV/K around 200 K (with ~0.35 μV/K at room temperature) has been measured.^[26]^[27] Theoretical descriptions of the ANE employ semiclassical transport theory, linking it directly to the Berry curvature distribution. A key formulation, developed by Xiao, Chang, and Niu, expresses the anomalous Nernst conductivity as

\alpha_{xy} = \frac{1}{e} \int d\varepsilon \left( \frac{\partial f}{\partial \varepsilon} \right) \frac{\sigma_{xy}(\varepsilon)}{T},

where e is the electron charge, f(\varepsilon) is the Fermi-Dirac distribution function, \sigma_{xy}(\varepsilon) is the energy-resolved anomalous Hall conductivity given by \sigma_{xy}(\varepsilon) = \frac{e^2}{\hbar} \int \frac{d\mathbf{k}}{(2\pi)^d} \Omega_z(\mathbf{k}) \delta(\varepsilon - \varepsilon(\mathbf{k})), and T is the temperature. In the low-temperature limit, this approximates to \alpha_{xy} \approx -\frac{\pi^2 k_B^2 T}{3e} \left. \frac{\partial \sigma_{xy}}{\partial \varepsilon} \right|_{\varepsilon=\mu}. This expression highlights the ANE's connection to the anomalous Hall effect, as both arise from the same Berry phase contributions, with the ANE being sensitive to the energy dependence of the curvature near the Fermi surface.^[28]^[29] The ANE's magnitude exhibits strong dependence on temperature, often peaking near magnetic phase transitions due to band structure modifications that amplify the Berry curvature. Doping can tune the Fermi level position relative to high-curvature regions, further modulating the response; in Weyl semimetals, the presence of Weyl nodes—sources of monopole-like Berry flux—leads to exceptionally enhanced ANE values. Post-2010 investigations into correlated oxide systems, such as manganites, have revealed how strong electron interactions can boost the intrinsic Berry contributions, providing deeper insights into the effect's microscopic origins.^[26]^[27]^[30]

Material-specific behaviors

In normal metals and semiconductors

In normal metals, the Nernst coefficient ν is typically small, on the order of nanovolts per kelvin per tesla (nV/KT), primarily due to the high carrier density that suppresses the transverse thermoelectric response. For example, in copper (Cu), experimental measurements yield ν values below 3 nV/KT across a wide temperature range, reflecting the dominance of short carrier mean free paths relative to the Fermi wavelength in such dense Fermi liquids. In contrast, semimetals like bismuth (Bi), with lower carrier densities around 3 × 10^{17} cm^{-3}, exhibit enhanced Nernst signals, reaching up to 40 μV/KT at low temperatures near 4.7 K, where the effect is amplified by the material's large effective mass and low Fermi energy.^[31] This enhancement arises from the deflection of charge carriers in the presence of a magnetic field, amplifying the transverse voltage despite the material's metallic character. In semiconductors, the Nernst effect is generally larger owing to lower carrier densities and higher mobilities, which increase the sensitivity to thermal gradients and magnetic fields. Doping plays a crucial role in tuning both the sign and magnitude of ν; for instance, in n-type indium antimonide (InSb), values up to approximately 30 μV/KT have been observed at 77 K under fields of 1.2 T, making it a promising material for thermomagnetic applications. Similarly, in doped strontium titanate (SrTiO₃) with carrier densities around 5.5 × 10^{17} cm^{-3}, the Nernst coefficient aligns closely with theoretical expectations based on carrier deflection models, emphasizing the role of reduced Fermi energies in boosting the effect. These behaviors stem from the classical mechanism of carrier Lorentz deflection, where low carrier concentrations allow for greater transverse displacement under combined thermal and magnetic influences. The temperature dependence of the Nernst coefficient in these materials often features a peak at intermediate temperatures, resulting from the competition between increasing carrier mobility and rising scattering rates. At low temperatures, an anomalous rise in ν can occur in certain systems due to phonon-drag enhancement, as seen in Bi where the signal peaks around 4 K from phonon-carrier interactions. In heavy-fermion compounds like YbRh₂Si₂, similar low-temperature upturns have been linked to phonon-drag effects amid quantum critical scattering, contributing to enhanced transverse responses below 10 K. Regarding magnetic field dependence, the Nernst signal is linear at low fields (B ≲ 1 T), reflecting perturbative carrier orbits, but saturates or exhibits nonlinearities at higher fields where cyclotron motion dominates. The Fermi surface geometry plays a key role here; in materials with open or anisotropic surfaces, such as Bi, the response can peak near the quantum limit (around 9 T), influenced by the interplay of orbit sizes and scattering. Semimetals like graphene and Weyl materials further illustrate amplified Nernst effects through quantum phenomena. In graphene, the diffusive Nernst response shows strong quantum oscillations versus magnetic field, with signals peaking near charge neutrality and exhibiting field-dependent sign changes up to 3 T, driven by Landau level formation.^[32] In Weyl semimetals such as NdAlSi, high-mobility carriers lead to giant enhancements, with ν reaching several μV/KT, further amplified by quantum oscillations that probe the chiral Fermi arcs and topological band structure.

In superconductors

In superconductors, the Nernst effect displays temperature-dependent characteristics relative to the critical temperature T_c. Above T_c, in the normal state, it manifests as a conventional signal akin to that in nonsuperconducting materials. Below T_c, the signal vanishes in the Meissner state due to magnetic field expulsion and the lack of Lorentz deflection on charge carriers. In type-II superconductors subjected to applied magnetic fields that form a vortex lattice, however, the Nernst effect reappears as a signature of the mixed state.^[33] The underlying mechanism in this vortex regime stems from thermally induced vortex motion. A longitudinal thermal gradient applies a Magnus-like force to the vortices, prompting their flow across the sample, while dissipative processes in the quasiparticle cores generate the transverse voltage. This phenomenon is captured by the Bardeen-Stephen model, which approximates the Nernst coefficient \nu as

\nu \approx \frac{\Phi_0}{B} \frac{\sigma_n}{n e^2},

where \Phi_0 is the magnetic flux quantum, B is the applied magnetic field, \sigma_n is the normal-state electrical conductivity, n is the carrier density, and e is the elementary charge.^[34]^[33] Proximal to T_c, the Nernst signal exhibits a giant enhancement driven by Gaussian superconducting fluctuations, where transient Cooper pairs contribute to transverse thermoelectric transport even in zero resistivity. In high-T_c cuprates like YBa_2Cu_3O_7 (YBCO), this amplified effect extends above T_c and serves as an indicator of the pseudogap phase, distinguishing it from simple paraconductivity.^[35]^[36] This behavior is especially pronounced in type-II high-T_c superconductors, where the Nernst effect enables estimation of carrier density through vortex fluidity analysis and probes pairing symmetry via the sign and magnitude of the fluctuation signal, supporting d-wave pairing in cuprates.^[33] Studies in the 2020s on iron-based superconductors have uncovered anomalous Nernst effect-like signals, potentially arising from magnetic pairing or nontrivial topology. For instance, in Fe_{1+y}Te_{1-x}Se_x, a spontaneous Nernst response reveals unconventional vortex dynamics in an s-wave superconductor.^[37]^[38]

Experimental methods and applications

Measurement techniques

The measurement of the Nernst effect typically employs a bar or Corbino disk geometry to detect the transverse electric field E_y generated perpendicular to both the applied temperature gradient \nabla_x T and magnetic field B_z. In the standard bar geometry, the sample is mounted between a heater and a heat sink to establish the longitudinal temperature gradient, with voltage probes attached along the edges to capture the transverse voltage while minimizing current flow. The Corbino disk configuration, involving radial temperature gradients and concentric electrodes, is particularly useful for isolating intrinsic contributions by suppressing Hall currents. Magnetic fields up to 10-20 T are applied using superconducting electromagnets, with the field oriented perpendicular to the sample plane. To isolate the Nernst signal from confounding Hall and Seebeck effects, multi-probe configurations are used, such as attaching three or more copper wires via spot-welding or silver paste to measure voltages under reversed field polarities and subtract longitudinal thermoelectric contributions. Adiabatic mounting on low-thermal-conductivity substrates like glass or sapphire reduces parasitic heat leaks, while isothermal conditions at the contacts prevent spurious gradients. Alternating current (AC) heating at low frequencies (1-2 Hz) with lock-in detection at twice the frequency (2ω) enhances sensitivity by rejecting DC offsets and thermoelectric noise from lead wires, achieving sub-nanovolt resolution in thin films. For low-temperature studies down to millikelvin ranges, dilution refrigerators are employed to reach base temperatures of ~70 mK, enabling precise control of electron temperatures and integration with on-chip thermometers like indium oxide for superconducting samples. High-field measurements beyond steady-state limits utilize pulsed magnets, achieving fields up to 58 T for brief durations to probe extreme regimes without sample heating. These setups often incorporate one-heater-two-thermometer configurations on microfabricated chips to maintain uniform gradients in two-dimensional materials. Data analysis involves plotting the transverse electric field E_y versus magnetic field B to extract the Nernst coefficient \nu = E_y / (B \nabla T) from the linear slope at low fields, with antisymmetrization across B to eliminate offsets. Error sources, such as probe misalignment or thermal leaks from wiring, are mitigated by calibrating against known Seebeck values and monitoring gradient stability, ensuring uncertainties below 10% in typical setups. Advanced post-2015 techniques include scanning near-field optical microscopy leveraging the anomalous Nernst effect for local mapping of transverse voltages in magnetic heterostructures with nanometer resolution. For thin films, AC on-chip methods with integrated heaters and thermometers provide high-throughput characterization of two-dimensional systems, isolating the effect from substrate influences. Recent 2025 studies have demonstrated on-chip measurements of giant nonlinear Nernst effects in trilayer graphene, achieving enhanced sensitivity in 2D van der Waals heterostructures.^[39]

Practical applications

The Nernst effect finds practical utility in thermometry and magnetometry, particularly in environments requiring precise mapping of magnetic fields or temperature gradients under extreme conditions. In high-energy-density plasmas relevant to inertial confinement fusion, the Nernst effect enables diagnostics of magnetic field dynamics through techniques like proton radiography, which visualize field advection and compression driven by thermal gradients.^[40] Additionally, atomic force microscopy combined with the anomalous Nernst effect (ANE) allows high-resolution imaging of magnetic domains in materials, serving as a nanoscale magnetometer for ferromagnetic nanostructures.^[41] These applications leverage the transverse voltage generated by the interplay of temperature gradients and magnetic fields, providing non-invasive probes in cryogenic setups like cryostats for low-temperature material studies.^[42] Beyond sensing, the Nernst effect serves as a powerful tool for material characterization, revealing insights into carrier mobility, Fermi surface topology, and phase transitions. In topological semimetals and high-mobility materials, the Nernst signal probes the Berry curvature and band structure away from the Fermi level, enabling characterization of nontrivial electronic states without direct Fermi surface imaging.^[43] For instance, large Nernst responses in Weyl semimetals correlate with high carrier mobility and small Fermi energies, allowing quantification of transport parameters in semimetallic systems.^[44] In superconductors, the Nernst effect detects the onset of superconducting fluctuations through vortex-like excitations, with signal peaks indicating the pseudogap or critical temperature well above Tc, as observed in high-Tc cuprates where the onset reaches ~125 K.^[33] This makes it invaluable for identifying phase transitions in correlated electron materials.^[35] In energy harvesting, the transverse geometry of the Nernst effect facilitates compact thermoelectric generators that convert waste heat to electricity without needing external magnets in ANE-based designs. Proof-of-concept devices using ferromagnetic materials like L10-ordered FePt demonstrate scalable voltage output in thermopile configurations, achieving theoretical power densities up to 120 nW/cm² under a 1 K/mm gradient.^[25] Antiferromagnetic Weyl materials such as Mn3Sn exhibit room-temperature ANE suitable for these generators, with Nernst coefficients around 0.35 µV/K, though current figures of merit (ZT) remain low at ≈ 4 × 10^{-6}, limiting efficiency.^[25] Emerging technologies harness the Nernst effect in spin-caloritronics for low-power electronics and waste-heat recovery, capitalizing on its spin-dependent transport. Flexible films incorporating ANE materials enable transverse spin currents for energy-efficient devices, with recent advancements showing ~70% enhancement in Nernst coefficients to 3.7 µV/K in hybrid structures.^[45] Colossal ANE in antiferromagnets like YbMnBi2, with thermopowers up to 6 µV/K and conductivities of 10 A m⁻¹ K⁻¹ near room temperature, promises high ZT values for flexible waste-heat recovery modules, benefiting from low thermal conductivity and minimal magnetic interference.^[27] Despite these advances, practical deployment faces challenges, including weak signals at ambient conditions due to modest Nernst coefficients and low ZT values, which hinder competitive energy conversion efficiencies compared to longitudinal thermoelectrics.^[25] Scalability issues arise from material synthesis complexities and integration into devices, necessitating further optimization of Berry curvature hotspots and carrier mobilities in non-magnetic or antiferromagnetic hosts.^[27]

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Transport Function Analysis of Thermoelectric Properties
This is important for thermoelectrics because the Fermi Surface of conducting electrons typically contains many separate pockets, large anisotropy and/or ...Missing: entropy | Show results with:entropy
[18]
Reciprocal Relations in Irreversible Processes. I. | Phys. Rev.
Reciprocal relations for heat conduction in an anisotropic medium are derived from the assumption of microscopic reversibility, applied to fluctuations.
[19]
Nernst effect beyond the relaxation-time approximation | Phys. Rev. B
Jul 29, 2011 · Boltzmann equation. We start from the semiclassical Boltzmann transport equation for quasiparticles (charge e ) in a weak magnetic field B ...Missing: classical | Show results with:classical
[20]
Current stripes, large Nernst effect, and influence of electron ...
Nov 6, 2020 · The Nernst voltage due to phonon drag appears already in the classical transport regime and can be comparable with the Seebeck voltage, while ...
[21]
Nernst effect and dimensionality in the quantum limit | Nature Physics
Nov 8, 2009 · The Nernst effect has recently emerged as a very sensitive, yet poorly understood, probe of electron organization in solids.
[22]
Simultaneous achievement of large anomalous Nernst effect and ...
Sep 1, 2025 · The anomalous Nernst effect (ANE) refers to the conversion of a longitudinal heat current into a transverse electric field in a magnetic ...
[23]
Energy-harvesting materials based on the anomalous Nernst effect
Another notable advantage of the Nernst effect is that the observed Nernst voltage is governed by not the temperature difference but the temperature gradient.
[24]
[PDF] Large anomalous Nernst effect at room temperature in a chiral ...
Sep 20, 2017 · The inverse triangular spin structure for Mn3Sn reduces the lattice symmetry from six fold to two fold in the plane and. 6. Page 7. thus based ...Missing: colossal | Show results with:colossal
[25]
Giant anomalous Nernst signal in the antiferromagnet YbMnBi 2
Nov 22, 2021 · Anomalous Nernst and Righi-Leduc effects in Mn3Sn: Berry curvature and entropy flow. ... Colossal anomalous Nernst effect in a correlated ...
[26]
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[27]
Berry phase effects on electronic properties | Rev. Mod. Phys.
Jul 6, 2010 · The anomalous velocity can also be understood as due to the Berry curvature of the Bloch states, which exist in the absence of the external ...
[28]
Skew scattering dominated anomalous Nernst effect in La1 ...
Apr 17, 2019 · ... anomalous Nernst effect (ANE),3,4 ... Although manganites have been extensively investigated over the last three decades for their colossal ...
[29]
https://link.aps.org/doi/10.1103/RevModPhys.82.1959
[30]
https://pubs.aip.org/aip/jap/article/125/15/153902/308614/Skew-scattering-dominated-anomalous-Nernst-effect
[31]
Nernst effect in high- superconductors | Phys. Rev. B
Jan 24, 2006 · In the Nernst experiment, the flow of vortices and antivortices down the gradient generates signals of opposite signs. Hence the observed e N s ...
[32]
Theory of the Motion of Vortices in Superconductors | Phys. Rev.
The theory of the motion of vortex lines in the mixed state of type II superconductors is derived on the basis of a local model that is a generalization of the ...
[33]
Observation of the Nernst signal generated by fluctuating Cooper pairs
Sep 10, 2006 · We resolved a Nernst signal, which persists deep inside the normal state. Its amplitude is in excellent agreement with the theoretical prediction.
[34]
Giant Nernst Effect due to Fluctuating Cooper Pairs in ...
Feb 9, 2009 · A theory of the fluctuation-induced Nernst effect is developed for a two-dimensional superconductor in a perpendicular magnetic field.Missing: YBCO | Show results with:YBCO
[35]
Spontaneous Nernst effect in the iron-based superconductor
To study the field dependence of the Nernst effect, we measured the Seebeck and Nernst signal simultaneously in a magnetic field up to 14 T. Figure 2(a) shows ...Abstract · Article Text · ACKNOWLEDGMENTS · APPENDICES
[36]
Large anomalous Nernst effect and nodal plane in an iron-based ...
Jan 14, 2022 · Anomalous Nernst effect (ANE), converting a heat flow to transverse electric voltage, originates from the Berry phase of electronic wave ...
[37]
Proton imaging of high-energy-density laboratory plasmas
Dec 28, 2023 · These experiments also showed that the magnetic field is rapidly convected by the heat flux via the Nernst effect, which was ∼ 10 times faster ...
[38]
Anomalous Nernst Effect-Based Near-Field Imaging of Magnetic ...
Nov 5, 2024 · The anomalous Nernst effect (ANE) gives rise to an electrical response transverse to magnetization and an applied temperature gradient in a magnetic metal.
[39]
Magnetic imaging by the anomalous Nernst effect using atomic force ...
We report a method to visualize magnetic domains based on the anomalous Nernst effect in a nanowire of Co2MnGa using atomic force microscopy.
[40]
Characterization of topological band structures away from the Fermi ...
Dec 13, 2018 · This work demonstrates that anomalous Nernst measurements can be an effective tool for the characterization of topological band structures.
[41]
https://pubs.acs.org/doi/10.1021/acsnano.4c09749
[42]
Creation of flexible spin-caloritronic material with giant transverse ...
Mar 27, 2024 · We demonstrate a remarkable ~ 70% improvement in the anomalous Nernst coefficients (reaching ~ 3.7 µVK−1) and a significant ~ 200% enhancement ...