Understanding low-temperature bulk transport in samarium hexaboride without relying on in-gap bulk states

Rakoski, Alexa; Eo, Yun Suk; Sun, Kai; Kurdak, Çağlıyan

doi:10.1103/physrevb.95.195133

Cited by 15 publications

(14 citation statements)

References 45 publications

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“…However (as pointed out in Ref. 23), attempting to directly apply this description to MVIs can give nonsensical results, including an ionization energy that is either unreasonably large or unreasonably small, depending on whether one uses the heavy (" f -band") mass or the light ("d-band") mass. The issue is that the conduction and valence bands at low temperature arise from hybridization between coexisting light and heavy bands, and the resulting hybridized bands have a "Mexican hat" shape (as pointed out, for example, in Ref.…”

Section: Introductionmentioning

confidence: 99%

Properties of the donor impurity band in mixed valence insulators

Skinner

2019

Phys. Rev. Materials

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In traditional semiconductors with large effective Bohr radius, an electron donor creates a hydrogen-like bound state just below the conduction band edge. The properties of the impurity band arising from such hydrogenic impurities have been studied extensively during the last 70 years. In this paper we consider whether a similar bound state and a similar impurity band can exist in mixed-valence insulators, where the gap arises at low temperature due to strong electron-electron interactions. We find that the structure of the hybridized conduction band leads to an unusual bound state that can be described using the physics of the one-dimensional hydrogen atom. The properties of the resulting impurity band are also modified in a number of ways relative to the traditional semiconductor case; most notably, the impurity band can hold a much larger concentration without inducing an insulator-to-metal transition. We estimate the critical doping associated with this transition, and then proceed to calculate the dc and ac conductivities and the specific heat. We discuss our results in light of recent measurements on the mixed-valence insulator SmB 6 , and find them to be consistent with the experiments.

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Section: Introductionmentioning

confidence: 99%

Properties of the donor impurity band in mixed valence insulators

Skinner

2019

Phys. Rev. Materials

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“…A general model of impurities used in semiconductors and other materials is the effective mass approximation, in which the impurity is treated hydrogenically, with an effective Bohr radius and binding energy [69]. In SmB 6 , the conditions for standard hydrogenic impurities are not satisfied when the model for semiconductors is used [49]. However, the model introduced by Skinner [48] demonstrated that the effective mass approximation can be modified for SmB 6 .…”

Section: Resultsmentioning

confidence: 99%

“…Historically, hydrogenic in-gap impurity states like those found in doped semiconductors were proposed in SmB 6 . This model is unjustified in SmB 6 [49], one reason being that the standard hydrogenic impurity model relies on a parabolic band structure. Instead, Ref.…”

Section: Introductionmentioning

confidence: 99%

Bulk transport paths through defects in floating zone and Al flux grown SmB6

Rakoski

Sinha

et al. 2021

Phys. Rev. Materials

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We investigate the roles of disorder on low-temperature transport in SmB 6 crystals grown by both the Al flux and floating zone methods. We used the inverted resistance method with Corbino geometry to investigate whether low-temperature variations in the standard resistance plateau arise from a surface or a bulk channel in floating zone samples. The results show significant sample-dependent residual bulk conduction, in contrast to smaller amounts of residual bulk conduction previously observed in Al flux grown samples with Sm vacancies. We consider hopping in an activated impurity band as a possible source for the observed bulk conduction, but it is unlikely that the large residual bulk conduction seen in floating zone samples is solely due to Sm vacancies. We therefore propose that one-dimensional defects, or dislocations, contribute as well. Using chemical etching, we find evidence for dislocations in both flux and floating zone samples, with higher dislocation density in floating zone samples than in Al flux grown samples. In addition to the possibility of transport through one-dimensional dislocations, we also discuss our results in the context of recent theoretical models of SmB 6 .

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“…[48] Historically, hydrogenic in-gap impurity states as are found in doped semiconductors were proposed in SmB 6 . This model is unjustified in SmB 6 , [49], one reason being that the standard hydrogenic impurity model relies on a parabolic band structure. Instead, Ref.…”

Section: Introductionmentioning

confidence: 99%

Bulk transport paths through defects in floating zone and Al flux grown SmB$_6$

Eo,

Rakoski,

Sinha

et al. 2020

Preprint

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We investigate the roles of disorder on low-temperature transport in SmB 6 crystals grown by both the Al flux and floating zone methods. We used the inverted resistance method with Corbino geometry to investigate whether low-temperature variations in the standard resistance plateau arises from a surface or a bulk channel in floating zone samples. The results show significant sampledependent residual bulk conduction, in contrast to smaller amounts of residual bulk conduction previously observed in Al flux grown samples with Sm vacancies. We consider hopping in an activated impurity band as a possible source for the observed bulk conduction, but it is unlikely that the large residual bulk conduction seen in floating zone samples is solely due to Sm vacancies.We therefore propose that one-dimensional defects, or dislocations, contribute as well. Using chemical etching, we find evidence for dislocations in both flux and floating zone samples, with higher dislocation density in floating zone samples than in Al flux grown samples. In addition to the possibility of transport through one-dimensional dislocations, we also discuss our results in the context of recent theoretical models of SmB 6 .

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Understanding low-temperature bulk transport in samarium hexaboride without relying on in-gap bulk states

Cited by 15 publications

References 45 publications

Properties of the donor impurity band in mixed valence insulators

Properties of the donor impurity band in mixed valence insulators

Bulk transport paths through defects in floating zone and Al flux grown SmB6

Bulk transport paths through defects in floating zone and Al flux grown SmB$_6$

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