Superconductivity in the solid phases of Bi. Is Bi-IV a superconductor? (original) (raw)

Possible superconductivity in the Bismuth IV solid phase under pressure

Scientific Reports, 2018

The first successful theory of superconductivity was the one proposed by Bardeen, Cooper and Schrieffer in 1957. This breakthrough fostered a remarkable growth of the field that propitiated progress and questionings, generating alternative theories to explain specific phenomena. For example, it has been argued that Bismuth, being a semimetal with a low number of carriers, does not comply with the basic hypotheses underlying BCS and therefore a different approach should be considered. Nevertheless, in 2016 based on BCS we put forth a prediction that Bi at ambient pressure becomes a superconductor at 1.3 mK. A year later an experimental group corroborated that in fact Bi is a superconductor with a transition temperature of 0.53 mK, a result that eluded previous work. So, since Bi is superconductive in almost all the different structures and phases, the question is why Bi-IV has been elusive and has not been found yet to superconduct? Here we present a study of the electronic and vibra...

A facile approach to calculating superconducting transition temperatures in the bismuth solid phases

Scientific Reports, 2019

All solid phases of bismuth under pressure, but one, have been experimentally found to superconduct. From Bi-I to Bi-V, avoiding Bi-IV, they become superconductors and perhaps Bi-IV may also become superconductive. To investigate the influence of the electronic properties N(E) and the vibrational properties F(ω) on their superconductivity we have ab initio calculated them for the corresponding experimental crystalline structures, and using a BCs approach have been able to determine their critical temperatures T c obtaining results close to experiment: For Bi-I (The Wyckoff Phase) we predicted a transition temperature of less than 1.3 mK and a year later a T c of 0.5 mK was measured; for Bi-II T c is 3.9 K measured and 3.6 K calculated; Bi-III has a measured T c of 7 K and 6.5 K calculated for the structure reported by Chen et al., and for Bi-V T c ~ 8 K measured and 6.8 K calculated. Bi-IV has not been found to be a superconductor, but we have recently predicted a T c of 4.25 K.

The effect of negative pressures on the superconductivity of amorphous and crystalline bismuth

Scientific Reports, 2022

Materials may behave in non-expected ways when subject to unexpected conditions. For example, when Bi was turned into an amorphous phase (a-Bi) unexpectedly it became a superconductor at temperatures below 10 K. Using the superconductivity of the amorphous phase we provided an explanation as to why crystalline bismuth (c-Bi) had not been found to superconduct, and even predicted an upper limit for its superconducting transition temperature T c. This was experimentally corroborated within the following year. We now decided to investigate what happens to the crystalline, Wyckoff structure, and amorphous Bi when pressures below the atmospheric are applied. Here it is shown that, within the BCS approach, under expansion the Wyckoff c-Bi increases its superconducting transition temperature minimally, whereas the amorphous phase decreases its T c. The electron densities of states (eDoS), the vibrational densities of states (vDoS) and the Debye temperatures (θ D) are calculated to perform this qualitative evaluation. Expansion can be obtained in the laboratory by chemically etching Bi-based alloys, for example, a process also known as dealloying. The quest for a room temperature superconductor has permeated the field for decades. Patents and claims have come and gone 1,2 and with the advent of laboratory equipment that produces very high pressures for very short periods of time the quest has increased. Recently, a (controversial) claim, portrayed in a paper on carbonaceous sulfur hydride 3 that supposedly is a room temperature superconductor under very high pressures, provoked an optimism that gave hope to accomplish this quest for more accessible pressures. However, the high pressures required thermalize the original optimism since the difficulties involved in the process are considerable, and it does not seem possible to develop a room temperature superconductor at reasonable pressures yet. These experimental results were questioned by some researchers who did not give credit to the claim 4 (see Ref. 5 also), disbelieve that has not been fully clarified. But, going high in pressure is the only resource to investigate high T c superconductivity? In principle other alternatives should be explored. Faced with the above controversy and searching for other alternatives it seemed natural "to look the other way" and start studying the effect on the electronic structure and vibrational properties of materials when pressures below atmospheric are applied, ("negative" pressures). Since one of the superconductors better investigated is bismuth in its solid phases, both at atmospheric pressure and also at high pressures, it was decided to undertake its study under pressures below the atmospheric, although being a heavy element no record-breaking changes in T c were expected. It happens that when a new field of research is developed other lines are essentially forgotten and that is why, in this work, we are looking the other way to search for interesting properties or results with the hope of catalyzing developments hitherto minimized. Bismuth is an interesting material since it is one of the few elements that maintains some properties, like superconductivity, under varied circumstances. Bismuth was first found to be a superconductor when in the amorphous phase at ambient pressure 6,7 , with a superconducting transition temperature of ∼ 6 K. Then, when the Wyckoff crystalline phase (a rhombohedral structure with the R-3 m space group, at room temperature and atmospheric pressure) was subjected to positive pressures it changed crystalline structures but maintained the superconducting properties for most of the new topologies (see Refs. 8,9 , and references contained therein). However, the possible superconductivity of c-Bi in the Wyckoff structure had not been found so we decided to

Impact of defect layers on superconductivity in Bi-O-S compounds

Newly discovered Bi-S-O compounds remain an enigma in attempts to establish a coherent understanding of their electronic, structural and underlying emergent superconducting properties. Recent extensive chemical study of Bi$_{4}$O$_{4}$S$_{3}$ has shown this compound to be actually a mixture of two phases, Bi$_{2}$OS$_{2}$ and Bi$_{3}$O$_{2}$S$_{3}$, and only the latter being the superconducting one. Here we explore, using density functional theory calculations, the electronic structure of both the phases, as well as the effect of the introduction of stacking faults in the latter compound. Our results demonstrate that the S$_{2}$ layers in Bi$_{3}$O$_{2}$S$_{3}$ are responsible for the electron doping of the BiS$_{2}$ bands, and that the electrons are actually accumulated in the BiS planes. We also show that the introduction of defects in the stacking diminishes the effects of doping which would suppress superconductivity.

Structural and electronic inhomogeneity of superconducting Nb-doped Bi2Se3

Physical Review B

The crystal structure, electronic structure, and transport properties of crystals with the nominal composition Nb 0.25 Bi 2 Se 3 are investigated. X-ray diffraction reveals that the as-grown crystals display phase segregation and contain major contributions of BiSe and the superconducting misfit layer compound (BiSe) 1.1 NbSe 2. The inhomogeneous character of the samples is also reflected in the electronic structure and transport properties of different single crystals. Angle-resolved photoemission spectroscopy (ARPES) reveals an electronic structure that resembles poor-quality Bi 2 Se 3 with an ill-defined topological surface state. High-quality topological surface states are instead observed when using a highly focused beam size, i.e., nanoARPES. While the superconducting transition temperature is found to vary between 2.5 and 3.5 K, the majority of the bulk single crystals does not exhibit a zero-resistance state suggesting filamentary superconductivity in the materials. Susceptibility measurements of the system together with the temperature dependence of the coherence length extracted from the upper critical field are consistent with conventional BCS superconductivity of a type II superconductor.

Superconductivity in Bi 2223 compound: physics and potential applications

FIZIKA A, 1995

The main results of the systematic study of the electron transport properties and AC susceptibility in Pb-doped, almost single phase, Bi 2223 ceramic samples and Ag-clad Bi 2223 tape, are presented. Whereas the results for the ceramic samples can only be used for the study of ...

Local structure of Nb in superconducting Nb-doped Bi2Se3

Physical Review B

In the prospect of realizing bulk superconductivity in a topological insulator, metal-doped Bi 2 Se 3 has been investigated with increased interest, where the Cu-, Sr-, and Nb-doped systems appear particularly promising. It is generally assumed that metal intercalation into the van der Waals (vdW) gap is responsible for the superconductivity. We have investigated the local structure of Nb in samples with nominal composition Nb 0.25 Bi 2 Se 3 and Nb 0.25 Bi 1.75 Se 3 using the x-ray absorption fine structure technique. It is found that that Nb is primarily located in a local environment consistent with that of the misfit layered structure (BiSe) 1+δ NbSe 2 , which has a δ-dependent superconducting transition in the same temperature range. We explore the possibility of Nb occupancy on various sites in the Bi 2 Se 3 structure, but neither intercalation nor substitution lead to physically meaningful improvements of the models. Furthermore, we report single crystal x-ray diffraction analysis of Nb-doped Bi 2 Se 3. Difference density maps are found to show negligible occupancy in the vdW gap. The misfit layer compound has recently been suggested as an alternative origin for superconductivity in the Nb-doped Bi 2 Se 3 system, in good agreement with the present study. Our findings stress the necessity of thorough structural characterization of these samples. In more general terms, it raises the question of whether metal intercalation is responsible for the superconductivity in the Cu-and Sr-doped Bi 2 Se 3 systems or phase segregation plays a role as well.

Superconductivity in Bismuth Oxysulfide Bi 4 O 4 S 3

Journal of the Physical Society of Japan, 2013

Bismuth oxysulfide Bi 4 O 4 S 3 , which has recently been claimed to be an exotic superconductor (T c ¼ 4:5 K), was investigated by magnetic susceptibility and electrical resistivity measurements as well as by electron probe microanalysis. Single-phase Bi 4 O 4 S 3 was successfully prepared by a high-pressure method, and its lattice parameters and normal-state resistivity, as well as the density of states at the Fermi level, were found to be comparable to those determined earlier. However, the observed superconductivity was most likely impurity-driven, strictly contradictory to the observations in ongoing experiments. The present results indicate that the superconductivity of Bi 4 O 4 S 3 does not truly reflect the bulk nature of the BiS 2 layered phase, regardless of the manner in which Bi 4 O 4 S 3 is synthesized. We discuss possible superconducting impurities.