Zero-resistance superconducting phase in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>BaFe</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mtext>As</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>under high pressure

Ishikawa, Fumihiro; Eguchi, Naoya; Kodama, Michihiro; Fujimaki, Koji; Einaga, Mari; Ohmura, Ayako; Nakayama, Atsuko; Mitsuda, Akihiro; Yamada, Yuh

doi:10.1103/physrevb.79.172506

Cited by 71 publications

(84 citation statements)

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“…[2][3][4][5][6][7][8][9][10][11][12][13] They exhibit SC with external pressure only, although many other families of Fe based superconductors require some form of chemical doping or deviation from stoichiometry to exhibit SC. 1 In particular, SrFe 2 As 2 (Sr122) and BaFe 2 As 2 (Ba122) show pressure-induced SC at relatively high temperatures of T c =34 K 5,7-9 and 28 K, 4,7,9,11 , respectively.…”

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Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

et al. 2013

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Optical reflectance R(ω) of a pressure-induced superconductor SrFe2As2 has been measured under external pressure to 6 GPa and at temperatures to 8 K. Optical conductivity σ(ω) has been derived from the measured R(ω). At ambient pressure, in the antiferromagnetic state below TN=198 K, a pronounced feature develops in σ(ω) due to the opening of a spin density wave (SDW) gap, as already reported in the literature. With increasing pressure, the SDW gap feature in σ(ω) is progressively suppressed. At 4 GPa, where the sample is superconducting, the SDW gap feature in σ(ω) is strongly reduced than that at ambient pressure, but is still clearly observed. At 6 GPa, the SDW gap is completely suppressed. The pressure evolutions of the SDW gap magnitude and the spectral weight closely follow the pressure evolution of TN. PACS numbers:Regarding the superconductivity (SC) exhibited by Fe-based compounds, 1 the pressure-induced SC exhibited by the stoichiometric "122" compounds AFe 2 As 2 (A=Ba, Ca, Sr, Eu) have attracted much interest. 2-13 They exhibit SC with external pressure only, although many other families of Fe based superconductors require some form of chemical doping or deviation from stoichiometry to exhibit SC. 1 In particular, SrFe 2 As 2 (Sr122) and BaFe 2 As 2 (Ba122) show pressure-induced SC at relatively high temperatures of T c =34 K 5,7-9 and 28 K, 4,7,9,11 , respectively. Interestingly, the 122 compounds also show SC with chemical doping, as shown by (Sr, K)Fe 2 As 2 , 14 Sr(Fe,Co) 2 As 2 , 15 and SrFe 2 (As, P) 2 . 16 At ambient pressure, the stoichiometric 122 compounds are antiferromagnetic (AFM), poor metals. For Sr122 and Ba122, the AFM transition temperature (T N ) is 198 K and 136 K, respectively. At T N , the resistivity [ρ(T )] shows a kink and rapid decrease with cooling below T N . With increasing pressure, T N is gradually lowered, and the kink in ρ(T ) becomes broadened. Above a critical pressure, the SC appears. Similar suppression of AFM and emergence of SC have also been observed with chemical doping. [14][15][16] In this regard, both methods have provided a lot of insight, but one advantage of the pressure technique compared with chemical doping is that the former does not cause disorder in the crystal lattice.However, there is an additional complication regarding the pressure-induced SC in the 122 compounds. Namely, it has been shown that the pressure evolutions of the AFM and SC states strongly depend on the hydrostaticity. 8,11,12 Here, hydrostaticity refers to how isotropic the pressure acting on the sample is. The hydrostaticity in a high pressure experiment depends on the types of pressure cell and pressure transmitting medium used. Figure 1 summarizes the results of high pressure studies on Sr122. 4,5,7-9 As discussed in detail later, these results show that the AFM state is suppressed and SC appears at lower pressure when the applied pressure is less hydrostatic (more uniaxial). This may indicate that a uniaxial stress promotes SC in the 122 compounds.To probe the microscopic elect...

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Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

et al. 2013

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“…Duncan et al have studied the difference of hydrostaticity in BaFe 2 As 2 using a piston cylinder cell, an alumina anvil cell with Daphne oil and a Bridgman anvil cell with solid steatite as pressure transmitting medium [21]. They reported that uniaxial stress strongly suppresses structural/AF ordering and induces superconductivity at lower pressure.We have studied difference of hydrostaticity in very highly hydrostatic pressure range since the confusing results appear in this region [11,12,[15][16][17]21]. We performed resistivity measurements using self-flux grown single crystals of BaFe 2 As 2 from the same batch up to 16 GPa with a cubic anvil apparatus and compared the results with those obtained with a Bridgman anvil cell containing liquid pressure transmitting medium.…”

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“…We have studied difference of hydrostaticity in very highly hydrostatic pressure range since the confusing results appear in this region [11,12,[15][16][17]21]. We performed resistivity measurements using self-flux grown single crystals of BaFe 2 As 2 from the same batch up to 16 GPa with a cubic anvil apparatus and compared the results with those obtained with a Bridgman anvil cell containing liquid pressure transmitting medium.…”

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“…(Dated: January 16,2018) We have performed electrical resistivity measurements on single crystal BaFe2As2 under high pressure P up to 16 GPa with a cubic anvil apparatus, and up to 3 GPa with a modified Bridgman anvil cell. The samples were obtained from the same batch, which was grown with a self-flux method.…”

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“…This has a great advantage over chemical doping since the ground state of the system can be tuned without introducing any disorder. Hence, many high pressure measurements have been performed in iron pnictides [11][12][13][14][15][16][17][18][19][20][21]. However, contradicting results were reported in the 1-2-2 compound up to now.…”

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Appearance of pressure-induced superconductivity inBaFe2As2under hydrostatic conditions and its extremely high sensitivity to uniaxial stress

et al. 2010

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We have performed electrical resistivity measurements on single crystal BaFe2As2 under high pressure P up to 16 GPa with a cubic anvil apparatus, and up to 3 GPa with a modified Bridgman anvil cell. The samples were obtained from the same batch, which was grown with a self-flux method. A cubic anvil apparatus provides highly hydrostatic pressure, and a modified Bridgman anvil cell, which contains liquid pressure transmitting medium, provides quasi hydrostatic pressure. For highly hydrostatic pressure, the crystal phase and magnetic transition temperature decreases robustly with P and disappears at around 10 GPa. The superconducting phase appears adjacent to magnetic phase in narrow pressure region between 11 and 14 GPa. The tiny difference of hydrostaticity between the cubic anvil apparatus and modified Bridgman anvil cell induces a drastic effect on the phase diagram of BaFe2As2. This result indicates that small uniaxial stress along c-axis strongly suppresses the structural/antiferromagnetic ordering and stabilizes superconductivity at much lower pressure. . The common feature of the new superconductors is existence of iron pnictide layers, which is analogous to CuO 2 planes of the cuprate superconductors. After extensive investigations, high temperature superconductivity with a transition temperature T c of 56 K was observed in rare earth iron oxypnictides (1-1-1-1 compound) [3,4]. Members of superconducting iron family were observed one after another in oxygen free compounds such as BaFe 2 As 2 having ThCr 2 As 2 type crystal structure (1-2-2 compound) [5,6], LiFeAs (1-1-1 compound) [7] and FeSe (1-1 compound) [8]. New compounds having a thick perovskite layer were also reported recently [9]. Among them, the 1-2-2 compound AEFe 2 As 2 (AE =Ba, Ca and Sr) occupies a singular position, which is particularly suitable for precise physical property measurements, since high quality large single crystals can be grown in the congruent melting condition. The 1-2-2 compounds have a first order antiferromagnetic AF transition on cooling at moderately high temperature, which always accompanied by a phase transition from tetragonal to orthorhombic structure. In the case of BaFe 2 As 2 , the crystal structure/magnetic phase transition occurs at 141 K [10]. The carrier doping of K for Ba, or Co for Fe strongly suppresses the transition in BaFe 2 As 2 . The highest T c of 38 K in the 1-2-2 compounds is obtained in a K doped material located adjacent to AF state [6].Another method to suppress AF ordering is applying pressure P . This has a great advantage over chemical doping since the ground state of the system can be tuned without introducing any disorder. Hence, many high pressure measurements have been performed in iron pnictides [11][12][13][14][15][16][17][18][19][20][21]. However, contradicting results were reported in the 1-2-2 compound up to now. The simplest reason is sample quality difference. Polycrystalline samples are inhomogeneous and have broader phase transitions than single crystals. Even in single crystals...

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Hydrostatic and Uniaxial Pressure Tuning of Iron‐Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

Gati

Bud’ko

et al. 2020

Annalen der Physik

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Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic, and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to as nematic transition. Nematicity is therefore a prominent feature of these materials, which signals the importance of the coupling of electronic and lattice properties. Correspondingly, these systems are particularly susceptible to tuning via pressure (hydrostatic, uniaxial, or some combination). Efforts to probe the phase diagrams of pressure-tuned iron-based superconductors are reviewed with a strong focus on recent insights into the phase diagrams of several members of this material class under hydrostatic pressure. These studies on FeSe, Ba(Fe 1−x Co x) 2 As 2 , Ca(Fe 1−x Co x) 2 As 2 , and CaK(Fe 1−x Ni x) 4 As 4 are, to a significant extent, made possible by advances of what measurements can be adapted to their use under differing pressure environments. The potential impact of these tools for the study of the wider class of strongly correlated electron systems is pointed out.

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Zero-resistance superconducting phase inBaFe2As2under high pressure

Cited by 71 publications

References 14 publications

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

Appearance of pressure-induced superconductivity inBaFe2As2under hydrostatic conditions and its extremely high sensitivity to uniaxial stress

Hydrostatic and Uniaxial Pressure Tuning of Iron‐Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

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Zero-resistance superconducting phase inBaFe2As2under high pressure

Cited by 71 publications

References 14 publications

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe2As2

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe2As2

Appearance of pressure-induced superconductivity inBaFe2As2under hydrostatic conditions and its extremely high sensitivity to uniaxial stress

Hydrostatic and Uniaxial Pressure Tuning of Iron‐Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

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Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂

Pressure Suppression of Spin-Density-Wave Gap in the Optical Conductivity of SrFe₂As₂