Thallium dopant in lead chalcogenides: investigation methods and peculiarities

Немов, С. А.; Ravich, Yu. I.

doi:10.1070/pu1998v041n08abeh000427

Cited by 107 publications

(100 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The matching between the L-pockets' Luttinger volumes and Hall numbers implies that PbTe, up to a carrier concentration of p H = (9.4 ± 0.6) × 10 19 cm −3 , is single band, that is, all the carriers contributing to conduction belong to the L band. This result implies that the band offset between the L and Σ valence band maxima is underestimated in our DFT calculations, as well as all previously published band-structure calculations 8,13,33,34,[42][43][44][45][46] , which predict the appearance of the Σ band at a hole concentration of the order of p ≈ 1 × 10 19 cm −3 . The evolution of the three high symmetry L-pocket cross-sectional areas, in frequency units (f min , f max and f [100] ), with Hall number is plotted in figure 13.…”

Section: A Fermi Surface Topologysupporting

confidence: 59%

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

et al. 2016

View full text Add to dashboard Cite

We present a combined experimental and theoretical study of the evolution of the low-temperature Fermi surface of lead telluride, PbTe, when holes are introduced through sodium substitution on the lead site. Our Shubnikov-de-Haas measurements for samples with carrier concentrations up to 9.4 × 10 19 cm −3 (0.62 Na atomic %) show the qualitative features of the Fermi surface evolution (topology and effective mass) predicted by our density functional (DFT) calculations within the generalized gradient approximation (GGA): we obtain perfect ellipsoidal L-pockets at low and intermediate carrier concentrations, evolution away from ideal ellipsoidicity for the highest doping studied, and cyclotron effective masses increasing monotonically with doping level, implying deviations from perfect parabolicity throughout the whole band. Our measurements show, however, that standard DFT calculations underestimate the energy difference between the L-point and Σ-line valence band maxima, since our data are consistent with occupation of a single Fermi surface pocket over the entire doping range studied, whereas the calculations predict an occupation of the Σ-pockets at higher doping. Our results for low and intermediate compositions are consistent with a non-parabolic Kane-model dispersion, in which the L-pockets are ellipsoids of fixed anisotropy throughout the band, but the effective masses depend strongly on Fermi energy.

show abstract

Section: A Fermi Surface Topologysupporting

confidence: 59%

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

et al. 2016

View full text Add to dashboard Cite

show abstract

“…23 Hole doping moves the Fermi energy deeper into the valence band, and earlier heat capacity data for double-doped systems indicate that the Fermi energy eventually resides in the resonant impurity levels for superconducting compositions. 3,15 Significantly, our measurements provide direct microscopic evidence for the anticipated spatial variation in DOS associated with such resonant impurity states. Moreover, we have shown that the nuclear spin dynamics are very different when the Fermi energy lies in the resonant impurity levels (i.e.…”

mentioning

confidence: 65%

Anomalous ¹²⁵Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb₁₋_xTl_xTe

et al. 2018

View full text Add to dashboard Cite

We report the results of a 125 Te NMR study of single crystalline Pb1−xTlxTe (x=0, 0.35, 1.0%) as a window on the novel electronic states associated with the thallium impurities in PbTe. The Knight shift is enhanced as x increases, corresponding to an increase in the average density of states (DOS) coupled to a strong spatial variation in the local DOS surrounding each Tl dopant. Remarkably, for the superconducting composition (x=1.0%), the 125 Te nuclear spin relaxation rate (1/T1T ) for Te ions that are close to the Tl dopants is unexpectedly enhanced in the normal state below a characteristic temperature of ∼10 K, below which the resistivity experiences an upturn. Such a simultaneous upturn in both the resistivity and (1/T1T ) was not suppressed in the high magnetic field. We suggest that these observations are consistently accounted for by dynamical charge fluctuations in the absence of paramagnetism, which is anticipated by the charge Kondo scenario associated with the Tl dopants. In contrast, such anomalies were not detected in the non-superconducting samples (x=0 and 0.35%), suggesting a connection between dynamical valence fluctuations and the occurrence of superconductivity in Pb1−xTlxTe.

show abstract

“…Calculations by Weiser [12] indicate that Tl 1+ has a lower energy than Tl 3+ in the lattice. Tl impurities therefore initially act as acceptors, adding one hole per Tl to the valence band, as observed in Hall measurements [17]. However, the calculated energy difference between 1+ and 3+ impurity states, which can be modeled by δE = 2(ǫ 0 −µ)+U [4] (where ǫ 0 is the energy to remove an electron from the 6s orbital and U < 0), is very small [12].…”

mentioning

confidence: 99%

“…This results in a value of T K ∼ 6 K, with considerable uncertainty due to the crude estimate of ρ imp (0). Heat capacity measurements involving Na counterdoping allow an estimate for the range of µ * values for Tl impurities in PbTe, which is characterized by a width of 30 meV [17]. Assuming a Gaussian distribution of values of µ * centered at 200 meV and with a full width at half maximum of 30 meV, the fraction of Tl impurities for which the two valence states will be degenerate to within T K = 6 K is approximately 1%, corresponding to a concentration of 6 × 10 17 cm −3 .…”

mentioning

confidence: 99%

Evidence for Charge Kondo Effect in Superconducting Tl-Doped PbTe

et al. 2005

View full text Add to dashboard Cite

We report results of low-temperature thermodynamic and transport measurements of Pb1−xTlxTe single crystals for Tl concentrations up to the solubility limit of approximately x = 1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature TK ∼ 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high Tc values. The Kondo effect arises from the interaction of conduction electrons with degenerate degrees of freedom in a material and is usually associated with dilute magnetic impurities in a nonmagnetic host. In such cases, the two degenerate states correspond to the impurity spins oriented up or down. Second order scattering processes involving virtual intermediate states lead to the well-known logarithmic increase in resistivity at low temperatures, which saturates in the unitary scattering limit below a characteristic Kondo temperature [1]. However, other systems comprising two degenerate degrees of freedom can also lead to Kondo-like phenomena [2]. In particular, a "charge Kondo effect," corresponding to dilute impurities with two degenerate charge states, has been proposed in the negative-U Anderson model [3], though to date there has not been an experimental realization of such an effect. Significantly, the quantum valence fluctuations implicit in such a model, which involve pairs of electrons that tunnel on and off impurity sites, also provide an electronic pairing mechanism for superconductivity [4,5,6,7].Thallium is one of several elements that is known to skip valences, such that only Tl 1+ and Tl 3+ are observed in ionic compounds, corresponding to electron configurations 6s 2 and 6s 0 respectively. Compounds that one would otherwise expect to contain divalent Tl are found to disproportionate. For example, TlBr 2 is more specifically Tl I Tl III Br 4 , and TlS is likewise Tl I Tl III S 2 [8]. This effect is driven by the stability of a filled shell in conjunction with the polarizability of the material. In this case, Tl 2+ can be characterized by a negative effective U , where U n = (E n+1 − E n ) − (E n − E n−1 ) < 0 and n labels the valence state [9,10,11]. For this reason, valence-skipping elements provide experimental access to negative-U behavior and are therefore suitable candidate impurities for realizing a charge Kondo effect in a bulk material.

show abstract

Thallium dopant in lead chalcogenides: investigation methods and peculiarities

Cited by 107 publications

References 1 publication

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

Anomalous ¹²⁵Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb₁₋_xTl_xTe

Evidence for Charge Kondo Effect in Superconducting Tl-Doped PbTe

Contact Info

Product

Resources

About

Thallium dopant in lead chalcogenides: investigation methods and peculiarities

Cited by 107 publications

References 1 publication

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

Anomalous 125Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb1−xTlxTe

Evidence for Charge Kondo Effect in Superconducting Tl-Doped PbTe

Contact Info

Product

Resources

About

Anomalous ¹²⁵Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb₁₋_xTl_xTe