Strong Electron–Phonon Coupling Superconductivity Induced by a Low-Lying Phonon in IrGe

Hirai, Daigorou; Ali, Mazhar N.; Cava, R. J.

doi:10.7566/jpsj.82.124701

Cited by 33 publications

(49 citation statements)

References 15 publications

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“…5 IrGe formula unit at the deep pseudogap inspired us to reinvestigate the electronic structure of superconductor IrGe, which has 13 valence electrons per formula unit. 22 Not surprisingly, a broad pseudogap in the DOS of IrGe is located above the Fermi level, also corresponding to 14 valence electrons. A new material with two fewer electrons per formula unit than TaIr 2 Ge 2 and the same crystal structure, if it could be synthesized, is expected to have its Fermi level quite close to a pseudogap in the density of states.…”

Section: Resultsmentioning

confidence: 99%

Superconductivity in a new intermetallic structure type based on endohedral Ta@Ir7Ge4 clusters

et al. 2017

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We report the observation of superconductivity at a temperature near 3.5 K for the previously unreported compound TaIr 2 Ge 2 . In addition to being a superconductor, this material displays a new crystal structure type that contains endohedral clusters, as determined by single crystal Xray diffraction structure refinement; the structure is more complex than those of the commonly observed tetragonal 122 intermetallic phases. Despite the strong metal-metal interactions, electronic structure calculations show the presence of a relatively simple set of states at the Fermi level, consisting mostly of Ta atom orbital contributions. The superconducting transition is characterized by temperature-dependent resistivity, magnetic susceptibility and specific heat measurements, and is of the weak coupling BCS type with ΔC/γT c =1.55. The upper critical field at 0 K is estimated to be 2 Tesla. Basic characterization of the superconductivity suggests that this material is similar to PbTaSe 2 , for which the effects of spin-orbit coupling may be important.2

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Section: Resultsmentioning

confidence: 99%

Superconductivity in a new intermetallic structure type based on endohedral Ta@Ir7Ge4 clusters

et al. 2017

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“…[1][2][3][4][5][6][7][8][9][10] Thus, engineering materials to produce low-lying phonons has become an important issue in superconductivity. A promising route to producing low-lying phonons is a local anharmonic vibration of the ion that is weakly bound in a cage-like structure.…”

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“…The MnP-type compound IrGe with T c = 4.7 K is a rare example that exhibits strong-coupling superconductivity with lowlying phonons but does not exhibit a structural phase transition. 10) Such superconductors suggest how low-lying phonons may be produced for enhancing superconductivity.…”

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Strong-Coupling Superconductivity in BaPd₂As₂ Induced by Soft Phonons in the ThCr₂Si₂-Type Polymorph

Kudo¹,

Yamada

Takeuchi

et al. 2017

J. Phys. Soc. Jpn.

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The specific heat of two polymorphs of BaPd 2 As 2 was measured. The ThCr 2 Si 2 -type polymorph (space group I4/mmm, D 17 4h , No. 139) is a previously reported superconductor with a transition temperature T c ≃ 3.5 K, while the CeMg 2 Si 2 -type polymorph (P4/mmm, D 1 4h , No. 123) is a normal metal and does not exhibit superconductivity down to 1.8 K. Our results revealed that the ThCr 2 Si 2 -type has an anomalously low Debye temperature, indicative of soft phonons, compared to the CeMg 2 Si 2 -type. Moreover, a large specific-heat jump at T c indicated that the superconductivity of ThCr 2 Si 2 -type is a strong-coupling type, which is likely derived from soft phonons.Energetically low-lying phonons often result in strongcoupling superconductivity with an enhanced superconducting transition temperature T c .1-10) Thus, engineering materials to produce low-lying phonons has become an important issue in superconductivity. A promising route to producing low-lying phonons is a local anharmonic vibration of the ion that is weakly bound in a cage-like structure. Such a vibration is called a rattling phonon and characterized by a lowfrequency Einstein mode. A remarkable example is the β-pyrochlore oxide KOs 2 O 6 with T c = 9.6 K, [1][2][3][4] as well as Ba 3 Ir 4 Ge 16 with T c ≃ 6 K. 5,6) Another route to producing low-lying phonons is structural instability that becomes evident from the occurrence of a structural phase transition due to applied pressure or chemical doping. Prominent examples of such superconductors include the 122-type pnictides BaNi 2 (As 1−x P x ) 2 with T c = 3.3 K, 7) BaNi 2 (Ge 1−x P x ) 2 with T c = 2.9 K, 8) and Ba(Ni 1−x Cu x ) 2 As 2 with T c = 3.2 K, 9) all of which exhibit strong-coupling superconductivity because of a structural phase transition and the subsequent phonon softening characterized by an anomalously low Debye frequency. The MnP-type compound IrGe with T c = 4.7 K is a rare example that exhibits strong-coupling superconductivity with lowlying phonons but does not exhibit a structural phase transition.10) Such superconductors suggest how low-lying phonons may be produced for enhancing superconductivity.The 12) The ThCr 2 Si 2 -type structure consists of PdAs 4 tetrahedra, while the CeMg 2 Si 2 -type consists of PdAs 4 planar squares, as shown in Figs. 1(a) and 1(b), respectively. The intergrowth structure, shown in Fig. 1(c), consists of Pd 4 As tetrahedra, which are characteristic of the CaBe 2 Ge 2 -type structure such as BaPt 2 As 2 , 13, 14) * E-mail: kudo@science.okayama-u.ac.jp † E-mail: nohara@science.okayama-u.ac.jp as well as PdAs 4 planar squares, which are characteristic of the CeMg 2 Si 2 -type structure. Guo et al. reported superconductivity at T c = 3.85 K for the ThCr 2 Si 2 -type structure. 15)This T c of BaPd 2 As 2 is anomalously high compared with T c = 1.27 and 0.92 K for CaPd 2 As 2 and SrPd 2 As 2 , respectively, 16) which are isoelectronic and isostructural with BaPd 2 As 2 of the ThCr 2 Si 2 -type structure. On the other hand, no bulk superconductiv...

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“…These models are widely used to calculate the µ 0 H c2 (0) for a variety of intermetallics and oxide superconductors. 19,27,28,[30][31][32]35 Also, for a oneband superconductor, the orbital upper critical field derived from the slope k = dHc2 dT | T =Tc of the H-T phase boundary at T c is an indication of clean limit µ0Hc2 k Tc = −0.73 or dirty limit µ0Hc2 k Tc = −0.69 behav-ior. BaBi 3 has the µ0Hc2 k Tc = −0.74 value, therefore BaBi 3 is a type II BCS-superconductor that is close to the clean limit.…”

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confidence: 99%

“…This further confirms that the superconducting properties of this system are dominated by s-wave pairing symmetry. 27,29,30 Fig . 4 shows the analysis of the electronic density of states for BaBi 3 based on the electronic structure calculations.…”

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Superconducting properties of BaBi₃

Haldolaarachchige

Kushwaha

Gibson

et al. 2014

Supercond. Sci. Technol.

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We report the superconducting properties of single crystals of the intermetallic perovskite-related compound BaBi3. The superconducting transition temperature (Tc = 5.82 K) was obtained from heat capacity measurements. Using the measured values for the critical fields Hc1, Hc2, and the specific heat C, we estimate the thermodynamic critical field Hc(0), coherence length ξ(0), Debye temperature ΘD and coupling constant λep. ∆C/γTc and λep suggest that BaBi3 is a moderately coupled superconductor and γ suggests an enhanced density of states at the Fermi level. Electronic band structure calculations show a complex Fermi surface and a moderately high DOS at the Fermi level. Further analysis of the electronic specific heat shows that the superconducting properties are dominated by s-wave gap.

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Strong Electron–Phonon Coupling Superconductivity Induced by a Low-Lying Phonon in IrGe

Cited by 33 publications

References 15 publications

Superconductivity in a new intermetallic structure type based on endohedral Ta@Ir7Ge4 clusters

Superconductivity in a new intermetallic structure type based on endohedral Ta@Ir7Ge4 clusters

Strong-Coupling Superconductivity in BaPd₂As₂ Induced by Soft Phonons in the ThCr₂Si₂-Type Polymorph

Superconducting properties of BaBi₃

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Strong Electron–Phonon Coupling Superconductivity Induced by a Low-Lying Phonon in IrGe

Cited by 33 publications

References 15 publications

Superconductivity in a new intermetallic structure type based on endohedral Ta@Ir7Ge4 clusters

Superconductivity in a new intermetallic structure type based on endohedral Ta@Ir7Ge4 clusters

Strong-Coupling Superconductivity in BaPd2As2 Induced by Soft Phonons in the ThCr2Si2-Type Polymorph

Superconducting properties of BaBi3

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Strong-Coupling Superconductivity in BaPd₂As₂ Induced by Soft Phonons in the ThCr₂Si₂-Type Polymorph

Superconducting properties of BaBi₃