The thermopower properties of interacting systems

summary

The gist

The gist: Additional interaction scales can indeed enhance the Seebeck coefficient and further induce multiple sign changes as a function of doping Introduction and Motivation The Seebeck coefficient

In short

The study investigated how different interaction scales—attractive interactions, nearest-neighbor interactions, sublattice potentials, and electron-phonon coupling—affect the Seebeck coefficient in quantum systems. Results show these additional scales can enhance the Seebeck coefficient and cause multiple sign changes with doping. This anomalous behavior is linked to gap opening and Fermi surface reconstruction.

Key concepts

Seebeck Coefficient: This measures the voltage generated across a material when it's subjected to a temperature gradient. It is a key property for thermoelectric performance, indicating how efficiently heat can be converted into electrical energy.
Determinant Quantum Monte Carlo (DQMC): This is the computational method used to calculate thermodynamic properties like entropy from quantum mechanical simulations. It helps determine the density profiles and local density of states within complex interacting systems.
Fermi Surface Reconstruction (FSR): This refers to a change in the shape or topology of the electron's Fermi surface due to electronic interactions. A sign change in the Seebeck coefficient is often a direct signature that this reconstruction is occurring, indicating a shift in carrier type.
Electron-Phonon Coupling: This describes how electrons interact with lattice vibrations (phonons). Even without on-site repulsion, electron-phonon coupling alone can induce an anomaly in the Seebeck coefficient, suggesting that lattice interactions play a significant role alongside electronic ones.

Terminology used across episodes

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This episode discusses

The paper

The thermopower properties of interacting systems · Read on arXiv

M. A. Habitzreuter, Willdauany C. de Freitas da Silva, Rodrigo A. Fontenele, Natanael C. Costa, * and Thereza Paiva

International Institute of Physics, Universidade Federal do Rio Grande do Norte · Departamento de Física, Universidade Federal da Paraíba · Instituto de Física, Universidade Federal do Rio de Janeiro

The Seebeck coefficient quantifies the voltage generated across a material in response to a temperature gradient. Recent studies have shown that strong electronic correlations can enhance this coefficient, producing anomalous behavior near half-filling associated with the Mott plateau. This raises the possibility that other interaction scales, not necessarily originating in Mott physics, could give rise to similar enhancements. Here, we investigate the Seebeck coefficient in the presence of attractive interactions, nearest-neighbor interactions, sublattice potentials, and electron-phonon coupling. The Seebeck coefficient is obtained via the Kelvin formula, using entropy data derived from density calculations within determinant quantum Monte Carlo (DQMC). We find that these additional interaction scales can indeed enhance the Seebeck coefficient and further induce multiple sign changes as a function of doping. We show that this anomalous behavior is associated with the opening of a gap in the ground state, as computed via cluster perturbation theory (CPT). Moreover, electron-phonon coupling alone-even in the absence of on-site repulsion-can produce a Seebeck anomaly. We relate these sign changes to a restructuring of the Fermi surface and an accompanying change in its topology, an effect commonly observed in cuprates.

Transcript

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: I'm Kai, and with me are Mira and Lev, guest researcher.

Mira: Today's paper: "The thermopower properties of interacting systems".

Kai: The gist:

Mira: First, who's behind it and why it matters.

Title and authors: Kai: So the paper "The thermopower properties of interacting systems" by Habitzreuter, de Freitas da Silva, Fontenele, Costa and Paiva talks about how they use determinant quantum Monte Carlo to link interaction changes directly to electronic structure shifts.

Mira: The authors show that the Seebeck coefficient is obtained through the Kelvin formula using entropy data derived from density calculations. They are testing this across several interaction types like attractive interactions, nearest-neighbor interactions, sublattice potentials, and electron-phonon coupling.

Lev: From a quantum error correction standpoint, we have to ask how robust these findings are when you try to translate them to real hardware constraints because of the strong correlations they are studying.

Kai: It’s about seeing how adding these different interaction scales—like attractive versus repulsive interactions—actually changes the material's behavior near half-filling.

Mira: They specifically noted that in the attractive and noninteracting cases, the only sign change in the Seebeck coefficient occurs at half-filling because of particle-hole symmetry.

The paper's summary: Kai: The paper "The thermopower properties of interacting systems" summarizes their findings by showing how they systematically control inherent approximations by increasing computational effort, specifically by reducing the Trotter decomposition error to less than or equal to zero point one in their simulations.

Mira: They also showed that when you use the Hubbard-Stratonovich transformation, which turns many-particle terms into single-particle quadratic ones, they can use discrete real fields that take values of plus or minus one for ea, which simplifies things computationally <ref:2605.14225#pg3>.

Lev: From an engineering standpoint we need to know if that reduced error level is actually enough to see the physical effects they are looking for, like those subtle Fermi surface reconstructions.

Kai: The paper links the sign change in the Seebeck coefficient directly to a Fermi surface reconstruction when they analyze spectral functions at zero frequency, A(k, omega = zero) <ref:2605.14225#pg3>. That's how they diagnose what's happening in the electronic structure.

Mira: And they show that this hole-like FS behavior persists for other values of U and temperature, which suggests this isn't just a fluke in the parameters they chose.

The paper's improvements: Kai: To wrap up on "The thermopower properties of interacting systems," these results show that the Seebeck coefficient is a very sensitive probe for interaction-driven changes in electronic structure, including Mott gap formation and Fermi surface reconstruction.

Mira: The key points are that additional interaction scales can significantly enhance the thermopower response, with nearest-neighbor interactions really amplifying the anomaly near half-filling in the extended Hubbard model.

Lev: What this means for running things is that we need to focus on how these insulating behaviors and metal-insulator boundaries are connected, because that’s where the Seebeck anomaly starts showing up.

Kai: Right, so if we can tune these interaction scales correctly, we can get a much stronger voltage response from a material. We’ll be looking at spin Seebeck effect next.

Mira: Yeah, this paper opens the door to thinking about how CDW physics and other electronic interactions can be used as tunable ingredients in designing efficient low-temperature thermoelectric materials.

Conclusion: Kai: So we've been talking about "The thermopower properties of interacting systems" by Habitzreuter et al. and how they use determinant quantum Monte Carlo to link interaction changes directly to electronic structure shifts.

Mira: And the key is that they found attractive interactions can lead to things like a supersolid phase at half-filling or s-wave superconductivity away from it. That really connects the voltage anomaly we measure in thermopower to some deep structural physics happening in the material itself.

Lev: From an engineering standpoint, we're still looking at whether those specific interaction scales actually translate into something measurable on real hardware because of how much error is involved in simulating those strong correlations.

Kai: Exactly Lev, it’s about tuning the system using attractive versus repulsive interactions and seeing if that leads to a sign change in the Seebeck coefficient, which is what makes this paper interesting for thermoelectric design.

Mira: And they also looked at nearest-neighbor repulsion in the extended Hubbard model and saw that it tends to localize pairs on one sublattice, producing a charge density wave pattern when you're near half-filling. That CDW pattern is something we need to keep an eye on because it could potentially open up a gap that makes the material insulating, which is good for some thermoelectric applications.

Lev: So if we can confirm that spectral shift pattern across different interaction scales is robust, it gives us confidence that the physics they are seeing isn't just a fluke in the model setup.

Kai: Right, so to wrap up on "The thermopower properties of interacting systems," these results show that the Seebeck coefficient is a very sensitive probe for interaction-driven changes in electronic structure, including Mott gap formation and Fermi surface reconstruction.

Kai: Right, so if we can tune these interaction scales correctly, we can get a much stronger voltage response from a material. We'll be looking at spin Seebeck effect next.

Lev: I just want to say that confirming these specific mechanisms is what will tell us if we can actually engineer a material with a measurable enhancement on our current platforms.

Kai: We'll keep building on this, but for now, that’s where we are with this paper on "The thermopower properties of interacting systems."

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