Superconductivity and Structural Conversion with Na and K Doping of the Narrow-Gap Semiconductor CsBi₄Te₆

Abstract

The monoclinic narrow-gap (∼0.08 eV) semiconductor CsBi 4 Te 6 is a unique layered system which can be doped to achieve high thermoelectric performance as well as superconductivity. Here, we report superconductivity and structure change induced by alloying CsBi 4 Te 6 single crystals with Na and K. Substitution of Na in CsBi 4 Te 6 with doping levels ≥0.39 and of K with ≥0.63 transforms the original monoclinic structure (p-type) to the orthorhombic RbBi 3.67 Te 6 -type structure (n-type). When the K level is ≤0.18, the monoclinic structure type of CsBi 4 Te 6 is retained. Transport and magnetic measurements on all as-synthesized doped single crystals demonstrate type-II, bulk superconductivity. A maximal superconducting transition at 5.07 K, which is the highest temperature in bismuth chalcogenidebased superconductors, was obtained in Cs 0.82 K 0.18 Bi 4 Te 6 with a high upper critical field of ∼15 T. These findings suggest superconductivity may be induced by proper doping in narrow-gap semiconductors.

High Hole Mobility and Nonsaturating Giant Magnetoresistance in the New 2D Metal NaCu4Se4 Synthesized by a Unique Pathway

“…To evaluate the Debye temperature (Θ D ) and effective mass ( m *) of the holes in NaCu 4 Se 4 , the heat capacity ( C ) was measured. As shown in Figure , according to the formula C ( T ) = γ T + β 1 T 3 + β 2 T 5 in which γ T and β 1 T 3 + β 2 T 5 are the electron and phonon contributions, the calculated coefficients are γ = 6.8 mJ mol –1 K –2 , β 1 = 2.8 mJ mol –1 K –4 , and β 2 = 0.0085 mJ mol –1 K –6 , respectively . Θ D , calculated by Θ D = (12π 4 NR /5β) 1/3 , is determined to be ∼140 K. m * is found to be ∼3 m 0 , as estimated by the relationship with γ = π 2 /3κ B 2 N ( E F ) = 1.36 × 10 –4 × V mol 2/3 n γ 1/3 m */ m 0 , where V mol , n γ , and m */ m 0 are molar volume, carrier concentration per atom, and effective mass.…”

“…A number of crystals were manually selected and positioned on the sapphire platform using Apiezon N grease. It was measured in a temperature range of 4–10 K. The data are analyzed by the formula C ( T ) = γ T + β 1 T 3 + β 2 T 5 in which γ T and β 1 T 3 + β 2 T 5 are the electron and phonon contributions, respectively . The Debye temperature, Θ D , is calculated by Θ D = (12π 4 NR /5β) 1/3 in which N = 9 is the number of atoms per formula unit and R is the gas constant.…”

“…It was measured in a temperature range of 4  10 K. The data is analyzed by the formula C(T) = T + 1T 3 + 2T 5 in which T and 1T 3 + 2T 5 are the electron and phonon contributions, respectively. 39 The Debye temperature, D, is calculated by D = (12 4 NR/5β) 1/3 in which N = 9 is the number of atoms per formula unit and R is the gas constant. The effective mass m* is estimated by the relationship with 40 where Vmol, n, and m*/m0 are molar volume, carrier concentration per atom, and effective mass, respectively.…”

Modeling the Ternary Chalcogenide Na2MoSe4 from First-Principles

“…This, and the fact that they are well known ionic conductors, make them an attractive class of inorganic compounds [2,3]. In this scene, Kanatzadis and coworkers have shone light on the fundamental chemistry of these compounds, discovering systems as different as semi-and superconductors [4,5]. Regarding alkali metal transition selenides, partirularly, we highlight the discovery of the layered metal NaCu 6 Se 4 with mixed valency [6], the mixed-valent two-dimensional metal NaCu 4 Se 3 [7] and the two-dimensional metal NaCu 4 Se 4 , which presents high hole mobility and giant magnetoresistence [8].…”

One-Dimensional Frenkel Chain Defects in CsBi4Te6

“…CsBi 4 Te 6 is a narrow-gap semiconductor with luxuriant important applications, including cooling of electronic circuitry and fabrication of superconducting devices. − At low temperatures, hole-doped CsBi 4 Te 6 is a desirable candidate for thermoelectric materials with a high figure of merit ZT ≈ 0.82 at 225 K . However, balancing entangled thermoelectric parameters to optimize thermoelectric performances of narrow-gap semiconductors remains a critical challenge; for example, these thermoelectric parameters are determined by the electronic structures (band gap, band shape, and band degeneracy near the Fermi level ( E F )) and scattering of charge carriers. , Furthermore, superconductivity has been observed in Cs-deficient or Bi-rich CsBi 4 Te 6 with a transition temperature around 4.4 K, where the carrier concentration (≈10 19 cm –3 ) is much lower than the typical value of 10 22 cm –3 in traditional superconductors. ,− Therefore, further detailed understanding of their electronic structures will help to unveil the superconductivity mechanism such as how the superconducting Cooper pairs develop in those low carrier concentration compounds. Furthermore, the atomic-scale defects of superconductors have the ability to perturb the surrounding electronic environment. , It has been reported that the local pair strengthening by Frenkel defects may enhance superconductivity .…”