Pressure Phase Diagram of 3d Itinerant System MnP

Transcription

1 PC-7-INV Pressure Phase Diagram of 3d Itinerant System MnP J. G. Cheng 1,2, K. Matsubayashi 1, M. Matsuda 3, F. Ye 3, S.E. Dissanayake 3, S. Chi 3, J. Ma 4, H. Zhou 4, J.Q. Yan 5,6, S. Kasamatsu 1, O. Sugino 1, T. Kato 1, Y. Uwatoko *,1 ( 1 ISSP, Univ. Tokyo Japan, 2 IOP, Chinese Academy of Sciences China, 3 QCMD, Oak Ridge Nat. Lab. USA, 4 Dep. Phys. Astro., Univ. Tennessee USA, 5 MSTD, Oak Ridge Nat. Lab. USA, 6 Dep. Mat. Sci. Eng., Univ. Tennessee USA) MnP is an interesting magnetic material that has been investigated since 1960 s [1,2]. At ambient pressure, it adopts an orthorhombic B31-type structure with space group Pnma. MnP is ferromagnetic between T c 291 K and T s 50 K, below which the magnetic structure changes from ferromagnetic into a double helical type with the Mn spins rotating in the a-b plan and propagating along the c axis [1,2]. Recently, we have performed comprehensive high-pressure studies on MnP single crystals up to 10 GPa with a suite of experimental probes, including resistivity, ac magnetic susceptibility, and neutron diffraction. We found that the MnP becomes superconducting with T sc 1 K when its long-range magnetic order is suppressed by the application of high pressure ~ 8 GPa.[3]. This is the first discovery of superconductivity among the Mn-based compounds, which were commonly believed to be antagonistic to superconductivity. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. A temperature-pressure phase diagram is shown in Fig. 1. With the application of external pressure, (1) both T c and T s decrease, and T s vanishes completely around 1.4 GPa; (2) a new antiferromagnetic (AFM) transition at T* appears around 2 GPa, rises quickly, and merges with T c around 3-4 GPa to convert the ferromagnetic transition at T c to an AFM one at T m ; (3) T m is continuously suppressed and eventually vanishes around P c = 8 GPa, where superconductivity with a maximum T sc 1K is observed. Exotic physical properties associated with the magnetic quantum critical point at P c are evidenced. Figure 1. A temperature-pressure phase diagram of MnP References [1] E. E. Huber, Jr. and D. H. Ridgley, Phys. Rev. 135, A1033 (1964). [2] G. P. Felcher, J. Appl. Phys., 37, 1056 (1966). [3] J.G. Cheng, et.al., Phys Rev Lett, 114, , 2015.

2 PC-8 Determination of crystal structure parameter important for the emergence of superconductivity in the BiCh 2 family Yoshikazu Mizuguchi 1 *, Kouhei Nagasaka 1, Joe Kajitani 1, Takafumi Hiroi 1, Osuke Miura 1, Akira Miura 2 ( 1 Tokyo Metropolitan University, 2 Hokkaido University) Since the discovery of superconductivity in BiS 2 -based layered compound, LaO 1-x F x BiS 2 [1], many studies have been dedicated to clarify superconductivity mechanisms and to discover new related (BiCh 2 -based; Ch = S, Se, Te) superconductors with high T c. So far, 10 parent compounds with 4 types of stacking structure have been discovered, and the highest transition temperature (T c ) recorded 11.5 K in the high-pressure phase of LaO 0.5 F 0.5 BiS 2. To attain the discovery of new BiCh 2 -based superconductor with a T c higher than the present record, strategy for materials design of BiCh 2 -based superconductor is needed. Therefore, we have investigated crystal structure of BiCh 2 -based superconductors to extract the crystal structure parameter which is essential for the emergence of superconductivity in the BiCh 2 family. Crystal structure analysis on two different systems, REO 0.5 F 0.5 BiS 2 and LaO 0.5 F 0.5 Bi(S 1-x Se x ) 2 revealed that the enhancement of in-plane chemical pressure is an important parameter for commonly understanding the emergence of superconductivity in these systems. Furthermore, we suggest that the evolution of T c for these respective systems could be plotted as a function of in-plane chemical pressure as shown in Fig. 1. On the basis of the relationship between superconductivity and in-plane chemical pressure, we discuss the correlation between superconductivity, crystal structure and/or carrier concentration. In addition, we will extend the discussion within two-dimensional Bi-Ch network to the discussion including one-dimensional Bi-Ch chains in the monoclinically distorted structure. [1] Y. Mizuguchi et al., J. Phys. Soc. Jpn. 81 (2012) [2] Y. Mizuguchi et al., J. Phys. Soc. Jpn. 83 (2014) [3] Y. Mizuguchi et al., arxiv: [4] A. Miura et al., J. Solid State Chem. 212 (2014) 213. Figure 1. Relationship between T c and in-plane chemical pressure calculated from in-plane Bi-Ch distance determined by synchrotron x-ray powder diffraction. The in-plane chemical pressure was defined (normalized) using the in-plane Bi-Ch distance of LaO 0.54 F 0.46 BiS 2 single crystal [4].

3 PC-9-INV New electronic phase diagram of iron-chalcogenide superconductor ~ Suppression of phase separation using film fabrication ~ Yoshinori Imai (Dept. of Basic Science, the University of Tokyo) To clarify the mechanism of superconductivity of iron-based superconductors, it is crucial to investigate superconductivity of FeSe 1-xTe x, which has the simplest crystal structure. There is, however, a serious obstacle to the understanding of its superconductivity; phase separation by spinodal decomposition occurs in the region of 0.1 < x < 0.4[1] and thus a whole phase diagram has not been available. In general, the process of film deposition involves crystal growth in a thermodynamically non-equilibrium state. Thus, film deposition provides an avenue for the synthesis of a material with a metastable phase. In this talk, we report the fabrication of epitaxial thin films of FeSe 1-xTe x with 0 < x < 1, including the region of 0.1 < x < 0.4 where a phase separation is observed, on CaF 2 substrates[2]. All of the FeSe 1-xTe x (x=0-1) films in this study were grown by the pulsed laser deposition method using a KrF laser[3,4]. Polycrystalline pellets with a nominal composition of FeSe 1-xTe x (x = 0-1) were used as the targets. Single crystals of the CaF 2(100), which is one of the most preferred materials for the thin-film growth of FeSe 1-xTe x [5-7], were used as the substrates. From the x-ray diffraction measurements of resultant films, we confirm the suppression of the phase separation in the region of 0.1 < x < 0.4. FeSe 1-xTe x films on CaF 2 substrates show superconductivity except for x=1. Surprisingly the optimal composition to achieve the highest superconducting transition temperature, T c, was found onset in this phase separation region; T c reaches 23 K at x = 0.2[2]. This value is approximately 1.5 times as high as those of bulk crystals of FeSe 1-xTe x with the optimal composition, x 0.5[1]. Using the data of T c, we present a whole phase diagram in this system, which provides a new perspective for the superconductivity of this material. ACKNOWLEDGMENTS. This work has been done in collaboration with Mr. Yuichi Sawada, Dr. Fuyuki Nabeshima, and Prof. Atsutaka Maeda. This work was partially supported by Strategic International Collaborative Research Program (SICORP), Japan Science and Technology Agency. [1] M. H. Fang et al.: Phys. Rev. B 78 (2008) [2] Y. Imai et al.: Proc. Natl. Acad. Sci. USA 112 (2015) [3] Y. Imai et al.: Jpn. J. Appl. Phys. 49 (2010) [4] Y. Imai et al.: Appl. Phys. Express 3 (2010) [5] F. Nabeshima et al.: Appl. Phys. Lett. 103 (2013) [6] A. Maeda et al.: Appl. Sur. Sci. 312 (2014) 43. [7] I. Tsukada et al.: Appl. Phys. Express 4 (2011)

4 PC-10 Superconductivity in Iron Chalcogenide compounds Induced by Battery-like Reaction Aichi Yamashita *,1, 2, Satoshi Demura 1,2, Masashi Tanaka 1, Hiroshi Hara 1,2, Kouji Suzuki 1,2, Saleem J. Denholme 1, Hiroyuki Okazaki 1, Masaya Fujioka 1, Takahide Yamaguchi 1, Hiroyuki Takeya 1, Yoshihiko Takano 1,2 ( 1 National Institute for Materials Science, 2 University of Tsukuba) Iron chalcogenides superconductors (termed the 11-system) have the simplest crystal structure among the iron-based superconductors. The iron chalcogenides have only superconducting layers without blocking layers, which indicates that this system is suitable to clarify the mechanism of iron-based superconductivity. However, several studies have found that a small amount of excess Fe is trapped between the layers during the synthesis. Excess Fe suppresses superconductivity by supplying a substantial amount of electrons to the conducting layers and its magnetic moment. To remove excess Fe from the interlayers and to induce superconductivity, an attention was focused on the chemical reaction which takes place in battery such as a typical Li-ion battery. Recently, we have reported that to induce superconductivity excess Fe in FeTe 0.8 S 0.2 sample was electrochemically removed, (i.e. de-intercalated), by applying voltage to the citric acid solution. We report the results of an electrochemical reaction that successfully induced superconductivity in Iron chalcogenide superconductors. [1] Aichi Yamashita et al., Solid State Communications 200, (2014) [2] Aichi Yamashita et al., J. Phys. Soc. Jpn. 84, (2015)

5 PC-11 Fabrication and Transport Properties of FeSe/FeTe Superlattice Thin Films Fuyuki Nabeshima *,1, Daisuke Asami 1, Yuichi Sawada 1, Yoshinori Imai 1, Masafumi Hanawa 2, Ataru Ichinose 2, Ichiro Tsukada 2, and Atsutaka Maeda 1 ( 1 The University of Tokyo, 2 Central Research Institute of Electric Power Industry) It is well known that T c of cuprate superconductors rises as the number of conducting planes per unit cell, n, increases from 1 to 3. Iron-based superconductors (FeSC) comprise conducting planes similar to cuprates, and the similar behavior can be expected. However, FeSC with n 2 have not been discovered. Therefore, we focused on Fe(Se,Te), which is composed of only conducting planes, and grew FeSe/FeTe superlattice thin films by pulsed laser deposition in order to artificially synthesize new materials with different n. By XRD and TEM observations, we confirmed that the grown films have periodic layered structure. The films show superconducting transition and T c zero reaches 12.5 K, which is higher than those of FeSe bulk crystals and films on CaF 2 [1]. However considerable amount of Se/Te interdiffusion was observed. At this moment it is not clear whether the origin of the enhancement of T c is an effect of Se/Te interdiffusion or superlattice effects including an effect of having different n values. In the presentation we will also report on the anisotropy of H c2 of the films. This work is partially supported by Strategic International Collaborative Research Program (SICORP) of Japan Science and Technology Agency. [1] F. Nabeshima et al., APL 103 (2013)

6 PC-12-INV Superconductivity in alkali-metal- and organic-molecule-intercalated FeSe Y. Koike *, T. Hatakeda, S. Hosono, T. Noji, T. Kawamata, M. Kato (Department of Applied Physics, Tohoku University, Sendai , Japan) The simple layered compound FeSe has attracted great interest, because the superconducting transition temperature, T c, dramatically increases from 8 K to ~ 45 K through the co-intercalation of alkali or alkali-earth metal and ammonia or organic molecules between FeSe layers. We have succeeded in the synthesis of several FeSe-based intercalation superconductors where both alkali metal and linear organic-molecule (ethylenediamine (C 2 H 8 N 2 ), hexamethylenediamine (C 6 H 16 N 2 )) are co-intercalated. The T c is 45 K in A x (C 2 H 8 N 2 ) y Fe 2-z Se 2 (A = Li, Na) with the interlayer spacing between neighboring Fe layers, d, of 10.4 A and 11.0 A, respectively [1,2], and 38 K in Li x (C 6 H 16 N 2 ) y Fe 2-z Se 2 with d = 16.2 A [3]. This d value is the longest among the FeSe-based intercalation superconductors. In Li x (C 6 H 16 N 2 ) y Fe 2-z Se 2, a different phase with d = 10 A and T c = 41 K has also been obtained through the annealing in vacuum. It has been concluded that T c increases with increasing d, is saturated at about 45 K for d > 9 A, and then decreases in the FeSe-based intercalation superconductors. In A x (C 2 H 8 N 2 ) y Fe 2-z Se 2 (A = Li, Na), we have succeeded in observing zero-resistivity, using the sintered pellet samples [4]. It has been found that the electrical resistivity in the normal state is metallic and that the superconducting onset-temperature is as high as 57 K, which may be due to the large superconducting-fluctuation. To the surprise, moreover, it has been found that both the crystal structure and superconductivity of the pellet sample of Li x (C 2 H 8 N 2 ) y Fe 2-z Se 2 are resistant to the atmospheric exposure at least up to several days in spite of the inclusion of alkali metal [4]. [1] T. Hatakeda et al., J. Phys. Soc. Jpn. 82, (2013). [2] T. Noji et al., Physica C 504, 8 (2014). [3] S. Hosono et al., J. Phys. Soc. Jpn. 83, (2014). [4] T. Hatakeda et al., J. Phys.: Conf. Ser. 568, (2014).