Large enhancement of thermopower at low magnetic field in compensated semimetals

Feng, Xiaozhou; Skinner, B. F.

doi:10.1103/physrevmaterials.5.024202

Cited by 7 publications

(2 citation statements)

References 33 publications

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“…Therefore our results strongly suggest that bismuth is a perfectly compensated material. This implies that, contrary to what is sometimes assumed [47], absence of compensation is not a prerequisite for a large Seebeck effect.…”

Section: Discussioncontrasting

confidence: 68%

“…Although the Umkehr effect has been known in principle for decades [5,6,27], it seems to us as this knowledge has got lost in parts of the community. Feng and Skinner recently wrote that because of Onsager reciprocity "the value of the Seebeck coefficient is independent of the sign of the magnetic field" [47]. As we saw above, this is not the case here and in perfect agreement with Onsager reciprocity.…”

Section: Discussionsupporting

confidence: 62%

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Magneto-Seebeck effect in bismuth

Spathelf,

Fauqué,

Behnia

2022

Preprint

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Thermoelectricity was discovered almost two centuries ago in bismuth. The large and negative Seebeck coefficient of this semimetal remains almost flat between 300 K and 100 K. This striking feature can be understood by considering the ratio of electron and hole mobilities and the evolution of their equal densities with temperature. The large and anisotropic magneto-Seebeck effect in bismuth, on the other hand, has not been understood up to the present day. Here, we report on a systematic study of the thermopower of bismuth from room temperature down to 20 K upon the application of a magnetic field of 13.8 T in the binary-bisectrix plane. The amplitude of the Seebeck coefficient depends on the orientation of the magnetic field and the anisotropy changes sign with decreasing temperature. The magneto-Seebeck effect becomes non-monotonic at low temperatures. When the magnetic field is oriented along the binary axis, the Seebeck coefficient is not the same for positive and negative fields. This so-called Umkehr effect arises because the high symmetry axes of the Fermi surface ellipsoids are neither parallel to each other nor to the high symmetry axes of the lattice. The complex evolution of thermopower can be accounted for in a large part of the (T, B, Θ)-space by a model based on semiclassical transport theory and incorporating Landau quantization. The employed energy dependence of the scattering time is compatible with electronacoustic phonon scattering. We find that the transverse Nernst response plays an important role in setting the amplitude of the longitudinal magneto-Seebeck effect. Furthermore, Landau quantization significantly affects thermoelectricity up to temperatures as high as 120 K.

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Section: Discussioncontrasting

confidence: 68%

Section: Discussionsupporting

confidence: 62%

Magneto-Seebeck effect in bismuth

Spathelf,

Fauqué,

Behnia

2022

Preprint

View full text Add to dashboard Cite

show abstract

Evidence of compensated semimetal with electronic correlations at charge neutrality of twisted double bilayer graphene

Ghosh,

Chakraborty,

Ghorai

et al. 2023

Commun Phys

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Recently, magic-angle twisted bilayer graphene (MATBLG) has emerged with various interaction-driven novel quantum phases at the commensurate fillings of the moiré superlattice, while the charge neutrality point (CNP) remains mostly a trivial insulator. Here, we show an emerging phase of compensated semimetallicity at the CNP of twisted double bilayer graphene (TDBLG), a close cousin of MATBLG, with signatures of electronic correlation. Using electrical and thermal transport, we find two orders of magnitude enhancement of the thermopower at magnetic fields much smaller than the extreme quantum limit, accompanied by large magnetoresistance ( ~ 2500%) at CNP, providing strong experimental evidence of compensated semimetallicity at CNP of TDBLG. Moreover, at low temperatures, we observe unusual sublinear temperature dependence of resistance. A recent theory1 predicts the formation of an excitonic metal near CNP, where small electron and hole pockets co-exist. We understand this sublinear temperature dependence in terms of critical fluctuations in this theory.

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Controllable Nernst and Seebeck effects in graphene with O-shaped Kekulé structure

Zhang,

Wang,

et al. 2023

Applied Physics Letters

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The Nernst and Seebeck effects in graphene with uniform Kekulé lattice distortion have been studied using the tight-binding model combined with the nonequilibrium Green's function method. Numerical results of this work showed that due to the electron–hole symmetry, the Nernst coefficient is an even function of the Fermi energy, while the Seebeck coefficient is an odd function regardless of the magnetic field. The Nernst and Seebeck coefficients show peaks when the Fermi energy crosses the Landau levels at high magnetic fields or crosses the transverse subbands at the zero magnetic fields. The peak height can be very large when the Fermi energy approaches the Dirac point, the Seebeck coefficient can reach about 0.78 mV/K, and the Nernst coefficient can reach about 0.95 mV/K at the corresponding hopping energy modification parameter δ=0.03 and T=0.009t/kB≈288 K. When δ=0.08 and T=0.024t/kB≈766 K, the Seebeck coefficient (or Nernst coefficient) is still up to about 0.78 mV/K (or 0.95 mV/K). This suggests that tunable Seebeck and Nernst coefficients can be achieved because the bandgap is a function of the corresponding hopping energy modification parameter δ. Experimentally, δ can be modulated by changing the type and amount of atoms adsorbed on graphene. In strong magnetic fields, the Nernst coefficient does not depend on the chirality of the nanoribbon.

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Large enhancement of thermopower at low magnetic field in compensated semimetals

Cited by 7 publications

References 33 publications

Magneto-Seebeck effect in bismuth

Magneto-Seebeck effect in bismuth

Evidence of compensated semimetal with electronic correlations at charge neutrality of twisted double bilayer graphene

Controllable Nernst and Seebeck effects in graphene with O-shaped Kekulé structure

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