Investigation of exotic electronic properties on rare-earth & actinide compounds under high pressure
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Investigation of exotic electronic properties on rare-earth & actinide compounds under high pressure Fuminori Honda1, Dexin Li1, Keigo Okauchi2, Yoshiya Homma1, Ai Nakamura1, and Dai Aoki1 Institute for Materials Research, Tohoku University, Oarai, Ibaraki, 311-1313, Japan 2 Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan 1
ABSTRACT We have synthesized and investigated electronic properties of several noncentrosymmetric actinide compounds, which do not have an inversion center in the crystal structure “globally” or “locally”, under high pressure. The Néel temperature of an antiferromagnet UIrSi3 with “globally” non-centrosymmetric structure increases with increasing pressure at a rate of 2.5 K/GPa up to 5 GPa. On the other hand, TNs of U2Rh3Si5 and U2Ir3Si5, which are “locally” non-centrosymmetric compounds, decrease with -1 K/GPa and -0.5 K/GPa with increasing pressure, respectively. Here, U2Ir3Si5 is a new antiferromagnet crystallizing in the U2Co3Si5-type of orthorhombic structure. Below TN = 36.5 K, U2Ir3Si5 shows magnetic order-order transition at T0 = 26.1 K with a first-order nature. Electrical resistivity in U2Ir3Si5 shows semiconducting-like behavior due to the formation of the super-zone gap in the antiferromagnetic state. TN and T0 as well as semi-conducting-like behavior in resistivity are suppressed by external pressure. INTRODUCTION The wide variety of electronic properties in f-electron compounds provides ample opportunity for systematic studies from both the fundamental interest and application points of view. This variety is a consequence of the competitive interactions between f-electrons and hybridizations with surrounded ligands of d- and/or p-electrons. Furthermore, the f-electrons play an important role in the heavy-fermion character, magnetic and multipolar orderings, and unconventional superconductivity. For a systematic understanding of the nature of f-electrons, we are focusing on the compounds having non-centrosymmetric crystal structure and started investigation of their electronic properties. The compounds without inversion symmetry in the crystal structure has been receiving increasing attention in these days, since the lack of inversion symmetry yields unique physical properties, such as skirmion [1], chiral magnetism [2], spin-Hall effect [3,4], superconductivity with parity mixing [5], etc. One of the typical example studied recently is a RTX3 (R: actinide or rare-earth, T: transition metal, X: metalloid) system which crystallizes in the BaNiSn3 typetetragonal structure as shown in Fig. 1(a). This crystal structure consists of layers of R, T, X elements stacking along the crystallographic c-axis in R-T-X-R-T-X-… manner. This structure is simple, but there is no inversion symmetry. In particular, there is a potential gradient ▽V, which is parallel to the [001] direction in this structure, due to the lack of mirror symmetry along the [001] direction. In such case, one should consider antisymmetric spin-or
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