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論文

Superconductivity in a multiorbital model for the $$Gamma_3$$ crystalline electric field state

久保 勝規

AIP Advances (Internet), 8(10), p.101313_1 - 101313_6, 2018/10

 被引用回数:3 パーセンタイル:24.63(Nanoscience & Nanotechnology)

A cubic system with the $$Gamma_3$$ cubic crystalline electric field (CEF) state is an ideal system to investigate multipole physics, since it does not have dipole but has higher-order multipoles such as quadrupole and octupole. In addition, superconductivity has been observed in PrT$$_2$$X$$_{20}$$ (T = Ir, Rh, X = Zn; T = Ti, V, X = Al) systems with the $$Gamma_3$$ CEF ground state. To approach these phenomena theoretically, we consider a model composed of f electrons with the total angular momentum $$j=5/2$$. From this model, we have derived multipole interactions for the $$Gamma_3$$ systems. In the present study, we investigate superconductivity in the same model. We apply random phase approximation for superconductivity in a multiorbital system to the present model. Then, we have obtained a d-wave spin-singlet state. We will discuss the relevance of the present theory to the PrT$$_2$$X$$_{20}$$ superconductors.

論文

Schottky specific heat of the lightly Mn-substituted electron-doped SrTiO$$_3$$

奥田 哲治*; 梶本 亮一; 野田 正亮*; 桑原 英樹*

AIP Advances (Internet), 8(10), p.101339_1 - 101339_5, 2018/10

 被引用回数:0 パーセンタイル:0(Nanoscience & Nanotechnology)

Large changes in the low-temperature specific heat (low-$$TC$$) by applying magnetic fields up to 9 Tesla were found in the lightly Mn-substituted electron-doped perovskites Sr$$_{1-x}$$La$$_{x}$$TiO$$_{3}$$. The changes in the low-$$TC$$ are qualitatively well explained by the Schottky specific heat ($$C_mathrm{Sch}$$) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. According to the analysis by using the conventional model, the doped Mn ions are apparently not Mn$$^{4+}$$ ($$S$$ = 3/2) ions, but are Jahn-Teller active Mn$$^{3+}$$ ($$S$$ = 2) ions or mixtures of Mn$$^{3+}$$ and Mn$$^{2+}$$ ions. However, the actual numbers of localized spins estimated from $$C_mathrm{Sch}$$ are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons, leading to the observed enhancement of the electronic specific heat coefficients.

論文

Effects of Fe doping on anomalous specific heat and XAFS oscillation in antiferromagnetic metal Mn$$_3$$Si

平賀 晴弘*; 大山 研司*; 小坂 昌史*; 松村 大樹

AIP Advances (Internet), 8(10), p.101424_1 - 101424_5, 2018/10

 被引用回数:0 パーセンタイル:0(Nanoscience & Nanotechnology)

The specific heat of Mn$$_{3-x}$$Fe$$_x$$Si was measured over a wide temperature range. Aside from the lattice and electronic specific heat components, another component had a significant contribution to the specific heat at low temperatures in the case of $$x$$ = 0.2; however, its contribution decreased when $$x$$ = 1.0. It is observed that the net component was retained at temperatures significantly higher than $$T_N$$ for both $$x$$. The XAFS spectra of the Mn $$K$$-edge for $$x$$ = 0 not only indicated a smooth structure near the edge, but also an unusually small amplitude in the extended high energy region; however, these features disappeared with Fe doping. The specific heat and XAFS data were discussed interms of the charge degree of freedom or electronic inhomogeneity.

口頭

Magnetic Bragg dip and Bragg edge in neutron transmission spectra of a typical spin order

間宮 広明*; 大場 洋次郎; 寺田 典樹*; 渡邉 騎通*; 廣井 孝介; 篠原 武尚; 及川 健一

no journal, , 

従来、スピン配列の解析には中性子回折法が利用されてきたが、中性子回折法ではできるだけ広い散乱角領域の測定が求められるため、試料環境機器の配置に制約が生じる原因となっていた。これを解決するため、我々は中性子透過率スペクトルに着目した。中性子透過率は、磁気回折による減少成分を含むため、回折成分と同様にスピン配列の情報を含む。中性子透過率は、散乱検出器を用いず透過率モニタのみで測定できるため、試料環境機器の配置が容易になると考えられる。そこで本研究では、酸化ニッケルの中性子透過率の測定を行った。その結果、磁気回折による中性子透過率の減少を観測することに成功した。

口頭

Ferromagnetic superconductivity mediated by pressure-enhanced spin fluctuation developed around the phase boundary of FM1 and FM2 in UGe$$_2$$

立岩 尚之; 芳賀 芳範; 山本 悦嗣

no journal, , 

ウラン系強磁性超伝導物質UGe$$_2$$の動的磁性に関する研究を行った。高橋らのスピンのゆらぎ理論を用いて磁化データを解析し、スピンのゆらぎのスペクトルの分布幅$$T_0$$, $$T_{rm A}$$を求めた。両方とも超伝導が現れる圧力領域で異常な増大を示す。この結果は、強磁性相FM1, FM2の相境界で発達する磁気的なゆらぎが超伝導出現に主要な役割を果たすことを意味する。

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