Enhanced Superconductivity in Close Proximity to the Structural Phase Transition of Sr1−xBaxNi2P2

Kudo, Kazuhiro; Kitahama, Yutaka; Iba, Keita; Takasuga, Masaya; Nohara, M.

doi:10.7566/jpsj.86.035001

Cited by 3 publications

(3 citation statements)

References 15 publications

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“…Similarly, a miscibility gap of the phosphorus content existed above x = 0.13 for BaNi 2 (As 1−x P x ) 2 [7]. Superconductivity at T c = 2.5 K appeared when arsenic was completely replaced by phosphorus in BaNi 2 P 2 [10,11,16,18], but it was weak-coupling type superconductivity as demonstrated in BaNi 2 (Ge 1−x P x ) 2 [18].…”

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confidence: 90%

“…Nickel-based 122-type compounds, such as BaNi 2 As 2 [1][2][3][4][5][6][7][8], SrNi 2 As 2 [9], BaNi 2 P 2 [10,11], SrNi 2 P 2 [12][13][14][15][16], BaNi 2 Ge 2 [17,18], and SrNi 2 Ge 2 [19] are nonmagnetic analogs of iron-based superconductors. Some of these compounds have provided opportunities for investigating the interplay between structural instability and superconductivity upon chemical doping [7,15,16,18].…”

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confidence: 99%

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Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

Kudo,

Takasuga,

Nohara

2017

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The effects of copper doping on the structural and superconducting phase transitions of Ba(Ni1−xCux)2As2 were studied by examining the resistivity, magnetic susceptibility, and specific heat. We found an abrupt increase in the superconducting transition temperature Tc from 0.6 K in the triclinic phase with less copper (x ≤ 0.16) to 2.5-3.2 K in the tetragonal phase with more copper (x > 0.16). The specific-heat data suggested that doping-induced phonon softening was responsible for the enhanced superconductivity in the tetragonal phase. All of these observations exhibited striking similarities to those observed in the phosphorus doping of BaNi2(As1−xPx)2 [K. Kudo et al., Phys. Rev. Lett. 109, 097002 (2012).], which markedly contrast the behavior of phosphorus and copper doping of the iron-based superconductor BaFe2As2.

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Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

Kudo,

Takasuga,

Nohara

2017

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“…2 As 2 -SrPd 2 As 2 -BaPd 2 As 2 . However, this trend was less apparent in SrNi 2 P 2 -BaNi 2 P 2 and SrNi 2 As 2 -BaNi 2 As 2 likely as a result of the structural phase transition and resultant structural distortion of SrNi 2 P 223,26) and BaNi 2 As 2 7,27). However, the substitution of tiny amount of P for As in BaNi 2 As 2…”

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

Kudo,

Yamada,

Takeuchi

et al. 2017

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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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Enhanced Superconductivity in Close Proximity to the Structural Phase Transition of Sr₁₋_xBa_xNi₂P₂

Cited by 3 publications

References 15 publications

Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

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

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

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Enhanced Superconductivity in Close Proximity to the Structural Phase Transition of Sr1−xBaxNi2P2

Cited by 3 publications

References 15 publications

Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

Copper Doping of BaNi$_{2}$As$_{2}$: Giant Phonon Softening and Superconductivity Enhancement

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

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

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Enhanced Superconductivity in Close Proximity to the Structural Phase Transition of Sr₁₋_xBa_xNi₂P₂

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