Thermopower in an anisotropic two-dimensional Weyl semimetal

Mandal, Ipsita; Saha, Kush

doi:10.1103/physrevb.101.045101

“…The strength of S x x and N reflects the efficiency of the thermoelectric materials regarding the conversion of heat into electrical power. In condensed matter physics, the Seebeck effect and the Nernst effect have been studied in various solid state matters, such as semiconductors [54], Bismuth [55], graphene [56][57][58] and Weyl semimetal [59,60]. The Seebeck coefficient and the Nernst coefficient have also been estimated in hot and dense hadronic matter at zero magnetic field [61] as well as at nonzero magnetic field [62].…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric properties of the (an-)isotropic QGP in magnetic fields

Zhang

¹

,

Kang

²

,

Zhang

³

2021

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The Seebeck effect and the Nernst effect, which reflect the appearance of electric fields along x-axis and along y-axis ($$E_{x}$$ E x and $$E_{y}$$ E y ), respectively, induced by the thermal gradient along x-axis, are studied in the QGP at an external magnetic field along z-axis. We calculate the associated Seebeck coefficient ($$S_{xx}$$ S xx ) and Nernst signal (N) using the relativistic Boltzmann equation under the relaxation time approximation. In an isotropic QGP, the influences of magnetic field (B) and quark chemical potential ($$\mu _{q}$$ μ q ) on these thermoelectric transport coefficients are investigated. In the presence (absence) of weak magnetic field, we find $$S_{xx}$$ S xx for a fixed $$\mu _{q}$$ μ q is negative (positive) in sign, indicating that the dominant carriers for converting heat gradient to electric field are negatively (positively) charged quarks. The absolute value of $$S_{xx}$$ S xx decreases with increasing temperature. Unlike $$S_{xx}$$ S xx , the sign of N is independent of charge carrier type, and its thermal behavior displays a peak structure. In the presence of strong magnetic field, due to the Landau quantization of transverse motion of (anti-)quarks perpendicular to magnetic field, only the longitudinal Seebeck coefficient ($$S_{zz}$$ S zz ) exists. Our results show that the value of $$S_{zz}$$ S zz at a fixed $$\mu _{q}$$ μ q in the lowest Landau level (LLL) approximation always remains positive. Within the effect of high Landau levels, $$S_{zz}$$ S zz exhibits a thermal structure similar to that in the LLL approximation. As the Landau level increases further, $$S_{zz}$$ S zz decreases and even its sign changes from positive to negative. The computations of these thermoelectric transport coefficients are also extended to a medium with momentum-anisotropy induced by initial spatial expansion as well as strong magnetic field.

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“…[6][7][8][9][10][11][12][13][14][15][16], which is an organic charge-transfer complex with two-dimensional conduction sheets consisting of a self-aggregated donor molecule (D) sublattice (Figure 1a). The α-ET2I3 is now known as a zero-gap semiconductor with Dirac cones under high pressure (>15 kbar) [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. However, many of the experiments are very challenging or impossible to perform under such high pressures.…”

Section: Introductionmentioning

confidence: 99%

Band Structure and Physical Properties of α-STF2I3: Dirac Electrons in Disordered Conduction Sheets

Naito

¹

,

Doi

²

2020

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The compound being investigated is an organic charge-transfer complex of the unsymmetrical donor STF with I3 [STF = bis(ethylenedithio)diselenadithiafulvalene], which is isostructural with α-ET2I3 and α-BETS2I3 [ET = bis(ethylenedithio)tetrathiafulvalene, BETS = bis(ethylenedithio)tetraselenafulvalene]. According to recent studies, the calculated band structure should represent a zero-gap semiconductor at 1 bar that is similar to α-ET2I3 under high pressure (>15 kbar). Such materials have attracted extensive interest because the electrons at the Fermi level can be massless Dirac fermions (MDFs), with relativistic behaviors like those seen in graphene. In fact, α-STF2I3 exhibited nearly temperature-independent resistivity, ρ, (~100–300 K), a phenomenon that is widely observed in zero-gap semiconductors. The non-Arrhenius-type increase in ρ (<~100 K) was consistent with the characteristics of interacting MDFs. The paramagnetic susceptibility, χ, (2–300 K)—as well as the reflectivity, R and optical conductivity, σ, (25–300 K; 400–25,000 cm−1)—were also almost temperature independent. Furthermore, σ was practically independent of wavenumber at ~6000–15,000 cm−1. There was no structural transition based on X-ray studies (90–300 K). Considering all the electrical, magnetic, optical and structural properties of α-STF2I3 at 1 bar, it was concluded that the salt possesses a band structure characterized with Dirac cones, which was consistent with the calculation.

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“…In this paper, we will focus on calculating two central transport coefficients: the thermal conductivity and the thermoelectric response (see Refs. [51][52][53][54][55] in the context of other closely-related systems). The thermal conductivity is naturally related to the ability of a material to conduct heat under an applied temperature gradient, while the thermoelectric response describes the resulting voltage generation due to a temperature gradient.…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric and thermal properties of the weakly disordered non-Fermi liquid phase of Luttinger semimetals

Freire,

Mandal

2021

Preprint

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We compute the thermoelectric and thermal transport in the weakly disordered non-Fermi liquid phase of the Luttinger semimetals at zero doping, where the decay rate associated with the (strong) Coulomb interactions is much larger than the electron-impurity scattering rate. To this end, we implement the Mori-Zwanzig memory matrix method, that does not rely on the existence of longlived quasiparticles in the system. We find that the thermal conductivity at zero electric field scales as κ ∼ T −n (with 0 n 1) at low temperatures, whereas the thermoelectric coefficient has the temperature dependence given by α ∼ T p (with 1/2 p 3/2). These unconventional properties turn out to be key signatures of this long sought-after non-Fermi liquid state in the Luttinger semimetals, which is expected to emerge in strongly correlated spin-orbit coupled materials like the pyrochlore iridates. Finally, our results indicate that these materials might be good candidates for achieving high figure of merit for thermoelectric applications.

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Thermopower in an anisotropic two-dimensional Weyl semimetal

Cited by 41 publications

References 53 publications

Thermoelectric properties of the (an-)isotropic QGP in magnetic fields

Thermoelectric properties of the (an-)isotropic QGP in magnetic fields

Band Structure and Physical Properties of α-STF2I3: Dirac Electrons in Disordered Conduction Sheets

Thermoelectric and thermal properties of the weakly disordered non-Fermi liquid phase of Luttinger semimetals

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