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How to formulate the $\mathbb{Z}_8$ topological invariant of Majorana fermion on the lattice
Authors:
Sho Araki,
Hidenori Fukaya,
Tetsuya Onogi,
Satoshi Yamaguchi
Abstract:
Topological invariants and their associated anomalies have played a crucial role in understanding low-energy phenomena in quantum field theories. In lattice gauge theory, the standard $\mathbb{Z}$-valued Atiyah-Singer index is formulated via the overlap Dirac operator through the Ginsparg-Wilson relation, but extensions to more general topological invariants have remained limited. In this work, we…
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Topological invariants and their associated anomalies have played a crucial role in understanding low-energy phenomena in quantum field theories. In lattice gauge theory, the standard $\mathbb{Z}$-valued Atiyah-Singer index is formulated via the overlap Dirac operator through the Ginsparg-Wilson relation, but extensions to more general topological invariants have remained limited. In this work, we propose a lattice formulation of the Arf-Brown-Kervaire (ABK) invariant, which takes values in $\mathbb{Z}_8$. The ABK invariant arises in Majorana fermion partition functions with reflection symmetry on two-dimensional non-oriented manifolds, and its definition involves an infinite sum over Dirac eigenvalues that must be properly regularized. By carefully treating the boundary conditions, with and without a domain-wall mass term, we demonstrate that the ABK invariant can be extracted from Pfaffians of the Wilson Dirac operator. We further provide numerical verification on two-dimensional lattices, showing that the $\mathbb{Z}_8$-valued results on the torus, Klein bottle, real projective plane, and Möbius strip agree with those in the continuum theory.
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Submitted 10 March, 2026;
originally announced March 2026.
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The Arf-Brown-Kervaire invariant on a lattice
Authors:
Sho Araki,
Hidenori Fukaya,
Tetsuya Onogi,
Satoshi Yamaguchi
Abstract:
We propose a lattice formulation of the Arf-Brown-Kervaire (ABK) invariant which takes values in $\mathbb{Z}_8$. Compared to the standard $\mathbb{Z}$-valued index, the ABK invariant is more involved in that it arises in Majorana fermion partition functions with reflection symmetry on two-dimensional non-orientable manifolds, and its definition contains an infinite sum over Dirac eigenvalues that…
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We propose a lattice formulation of the Arf-Brown-Kervaire (ABK) invariant which takes values in $\mathbb{Z}_8$. Compared to the standard $\mathbb{Z}$-valued index, the ABK invariant is more involved in that it arises in Majorana fermion partition functions with reflection symmetry on two-dimensional non-orientable manifolds, and its definition contains an infinite sum over Dirac eigenvalues that requires proper regularization. We employ the massive Wilson Dirac operator, with and without domain-walls, on standard two-dimensional square lattices, and use its Pfaffian for the definition. Twisted boundary conditions and cross-caps, which reverse the orientation, are introduced to realize nontrivial topologies equipped with nontrivial $\mathrm{Pin}^{-}$ structures of Majorana fermions. We verify numerically (and partly analytically) that our formulation on a torus, Klein bottle, real projective plane (as well as its triple connected sum), and two types of Möbius strip reproduces the known values in continuum theory.
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Submitted 25 December, 2025; v1 submitted 12 December, 2025;
originally announced December 2025.
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Topological Hall Effect in PrSb$_2$
Authors:
Shingo Araki,
Hinata Izumida,
Kazuto Akiba,
Tatsuo C. Kobayashi,
Takashi Kambe
Abstract:
PrSb$_2$ exhibits a charge-density wave (CDW) transition at $T_\mathrm{CDW} = 100$ K and antiferromagnetic (AFM) ordering at $T_\mathrm{N} = 5$ K at ambient pressure. Hall resistivity measurements revealed an anomalous feature within the AFM state, which was attributed to the topological Hall effect (THE), ruling out contributions from the ordinary and anomalous Hall effects. Significantly, the TH…
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PrSb$_2$ exhibits a charge-density wave (CDW) transition at $T_\mathrm{CDW} = 100$ K and antiferromagnetic (AFM) ordering at $T_\mathrm{N} = 5$ K at ambient pressure. Hall resistivity measurements revealed an anomalous feature within the AFM state, which was attributed to the topological Hall effect (THE), ruling out contributions from the ordinary and anomalous Hall effects. Significantly, the THE anomaly diminished with increasing pressure and almost vanished as the CDW transition was suppressed near the critical pressure $P_c$ = 1.0 GPa. These findings suggest a relationship between the CDW order and the appearance of the THE in PrSb$_2$.
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Submitted 7 October, 2025;
originally announced October 2025.
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Site Split of Antiferromagnetic $α$-Mn Revealed by $^{55}$Mn Nuclear Magnetic Resonance
Authors:
Masahiro Manago,
Gaku Motoyama,
Shijo Nishigori,
Kenji Fujiwara,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Kazuto Akiba,
Shingo Araki,
Tatsuo C. Kobayashi,
Hisatomo Harima
Abstract:
The magnetic structure of antiferromagnetic $α$-Mn has been unclarified for almost 70 years since its magnetism was discovered. We measured the zero-field nuclear magnetic resonance spectra of antiferromagnetic $α$-Mn to obtain further insight into magnetism below $T_{\text{N}} = 95$ K. The site II spectra split into two sites with five subpeaks owing to quadrupole interaction, and this shows that…
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The magnetic structure of antiferromagnetic $α$-Mn has been unclarified for almost 70 years since its magnetism was discovered. We measured the zero-field nuclear magnetic resonance spectra of antiferromagnetic $α$-Mn to obtain further insight into magnetism below $T_{\text{N}} = 95$ K. The site II spectra split into two sites with five subpeaks owing to quadrupole interaction, and this shows that the ordered moments at site II are slightly tilted from the $[001]$ direction. The site III spectra revealed that this site splits into four sites below $T_{\text{N}}$. These findings clearly demonstrate that the antiferromagnetic $α$-Mn symmetry is lower than previously considered.
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Submitted 6 October, 2022;
originally announced October 2022.
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Chirality-Controlled Enantiopure Crystal Growth of a Transition Metal Monosilicide by a Floating Zone Method
Authors:
Yusuke Kousaka,
Satoshi Iwasaki,
Taisei Sayo,
Hiroshi Tanida,
Takeshi Matsumura,
Shingo Araki,
Jun Akimitsu,
Yoshihiko Togawa
Abstract:
We performed a crystal growth to obtain chirality-controlled enantiopure crystals using a laser-diode-heated floating zone (LDFZ) method with a composition-gradient feed rod. It has been argued that the crystal handedness of $T$Si ($T$ : transition metal) is fixed depending on $T$ in the case of the ones grown by the conventional methods. We found that right-handed single crystals of CoSi and MnSi…
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We performed a crystal growth to obtain chirality-controlled enantiopure crystals using a laser-diode-heated floating zone (LDFZ) method with a composition-gradient feed rod. It has been argued that the crystal handedness of $T$Si ($T$ : transition metal) is fixed depending on $T$ in the case of the ones grown by the conventional methods. We found that right-handed single crystals of CoSi and MnSi were grown from the composition gradient feed rods that consist of FeSi--CoSi and FeSi--MnSi, respectively. The obtained CoSi and MnSi crystals inherit the chirality from the seed part of FeSi, which grows in a right-handed structure, and thus have the chirality opposite to that for the crystals in the literature. The LDFZ method with the feed rods with various combinations of $T$Si compounds enables a flexible control of the chirality of $T$Si and will be useful for clarifying the interplay between the crystalline chirality and chirality-induced physical responses.
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Submitted 23 January, 2022;
originally announced January 2022.
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Tailoring collective motion of kinesin-driven microtubules via topographic landscapes
Authors:
Shunya Araki,
Kazusa Beppu,
Arif Md. Rashedul Kabir,
Akira Kakugo,
Yusuke T. Maeda
Abstract:
Biomolecular motor proteins that generate forces by consuming chemical energy obtained from ATP hydrolysis are pivotal for organizing broad cytoskeletal structures in living cells. The control of such cytoskeletal structures benefits programmable protein patterning; however, our current knowledge is limited owing to the underdevelopment of an engineering approach for controlling pattern formation.…
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Biomolecular motor proteins that generate forces by consuming chemical energy obtained from ATP hydrolysis are pivotal for organizing broad cytoskeletal structures in living cells. The control of such cytoskeletal structures benefits programmable protein patterning; however, our current knowledge is limited owing to the underdevelopment of an engineering approach for controlling pattern formation. Here, we demonstrate the tailoring of assembled patterns of microtubules (MTs) driven by kinesin motors by designing the boundary shape in fabricated microwells. We found an MT bundle structure along the microwell wall and a bridging structure perpendicular to the wall. Corroborated by the theory of self-propelled rods, we further showed that the alignment of MTs defined by the boundary shape determined the transition of the assembled patterns, providing a blueprint to reconstruct bridge structures in microchannels. Our findings provide a geometric rule to tailor the self-organization of cytoskeletons and motor proteins for nanotechnological applications.
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Submitted 12 October, 2021;
originally announced October 2021.
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Anomalous Hall effect triggered by pressure-induced magnetic phase transition in $α$-Mn
Authors:
Kazuto Akiba,
Kaisei Iwamoto,
Takaaki Sato,
Shingo Araki,
Tatsuo C. Kobayashi
Abstract:
Recent interest in topological nature in condensed matter physics has revealed the essential role of Berry curvature in anomalous Hall effect (AHE). However, since large Hall response originating from Berry curvature has been reported in quite limited materials, the detailed mechanism remains unclear at present. Here, we report the discovery of a large AHE triggered by a pressure-induced magnetic…
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Recent interest in topological nature in condensed matter physics has revealed the essential role of Berry curvature in anomalous Hall effect (AHE). However, since large Hall response originating from Berry curvature has been reported in quite limited materials, the detailed mechanism remains unclear at present. Here, we report the discovery of a large AHE triggered by a pressure-induced magnetic phase transition in elemental $α$-Mn. The AHE is absent in the non-collinear antiferromagnetic phase at ambient pressure, whereas a large AHE is observed in the weak ferromagnetic phase under high pressure despite the small averaged moment of $\sim 0.02 μ_B$/Mn. Our results indicate that the emergence of the AHE in $α$-Mn is governed by the symmetry of the underlying magnetic structure, providing a direct evidence of a switch between a zero and non-zero contribution of the Berry curvature across the phase boundary. $α$-Mn can be an elemental and tunable platform to reveal the role of Berry curvature in AHE.
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Submitted 16 October, 2020; v1 submitted 24 September, 2020;
originally announced September 2020.
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Pressure-Temperature Phase Diagram of $α$-Mn
Authors:
Takaaki Sato,
Kazuto Akiba,
Shingo Araki,
Tatsuo C. Kobayashi
Abstract:
Electrical resistivity and ac-susceptibility measurements under high pressure were carried out in high-quality single crystals of $α$-Mn. The pressure-temperature phase diagram consists of an antiferromagnetic ordered phase (0<$P$<1.4 GPa, $T<T_{\rm N}$), a pressure-induced ordered phase (1.4<$P$<4.2-4.4 GPa, $T<T_{\rm A}$), and a paramagnetic phase. A significant increase was observed in the temp…
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Electrical resistivity and ac-susceptibility measurements under high pressure were carried out in high-quality single crystals of $α$-Mn. The pressure-temperature phase diagram consists of an antiferromagnetic ordered phase (0<$P$<1.4 GPa, $T<T_{\rm N}$), a pressure-induced ordered phase (1.4<$P$<4.2-4.4 GPa, $T<T_{\rm A}$), and a paramagnetic phase. A significant increase was observed in the temperature dependence of ac-susceptibility at $T_{\rm A}$, indicating that the pressure-induced ordered phase has a spontaneous magnetic moment. Ferrimagnetic order and parasitic ferromagnetism are proposed as candidates for a possible magnetic structure. At the critical pressure, where the pressure-induced ordered phase disappears, the temperature dependence of the resistivity below 10 K is proportional to $T^{5/3}$. This non-Fermi liquid behavior suggests the presence of pronounced magnetic fluctuation.
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Submitted 24 September, 2020;
originally announced September 2020.
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Ferrimagnetic States of Na-K Alloy Clusters in Zeolite Low-Silica X
Authors:
Takehito Nakano,
Shingo Araki,
Luu Manh Kien,
Nguyen Hoang Nam,
Duong Thi Hanh,
Akihiro Owaki,
Ken Goto,
Akira Matsuo,
Koichi Kindo,
Yasuo Nozue
Abstract:
In zeolite low-silica X (LSX), beta-cages with the inside diameter of approx 7 AA{} are arrayed in a diamond structure. Among them, supercages with the inside diameter of approx 13 AA{} are formed and arrayed in a diamond structure by the sharing of windows with the inside diameter of approx 8 AA{}. The chemical formula of zeolite LSX used in the present study is given by Na$_{x}$K$_{12-x}$Al…
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In zeolite low-silica X (LSX), beta-cages with the inside diameter of approx 7 AA{} are arrayed in a diamond structure. Among them, supercages with the inside diameter of approx 13 AA{} are formed and arrayed in a diamond structure by the sharing of windows with the inside diameter of approx 8 AA{}. The chemical formula of zeolite LSX used in the present study is given by Na$_{x}$K$_{12-x}$Al$_{12}$Si$_{12}$O$_{48}$ per supercage (or beta-cage), where Na$_{x}$K$_{12-x}$ and Al$_{12}$Si$_{12}$O$_{48}$ are the exchangeable cations of zeolite LSX and the aluminosilicate framework, respectively. Na-K alloy clusters are incorporated in these cages by the loading of guest K metal at $n$K atoms per supercage (or beta-cage). A N'eel's N-type ferrimagnetism has been observed at $n = 7.8$ for $x = 4$. In the present paper, optical, magnetic and electrical properties are studied in detail mainly for $x = 4$. Ferrimagnetic properties are observed at $6.5 < n < 8.5$. At the same time, the Curie constant suddenly increases. An optical reflection band of beta-cage clusters at 2.8 eV is observed at $n > 6.5$ in accordance with the sudden increase in the Curie constant. An electrical resistivity indicates metallic values at $n$ gtrapprox 6, because a metallic state is realized in the energy band of supercage clusters. The ferrimagnetism is explained by the antiferromagnetic interaction between the magnetic sublattice of itinerant electron ferromagnetism at supercage clusters and that of localized moments at beta-cage clusters. The electrical resistivity in ferrimagnetic samples at $n = 8.2$ for $x = 4$ increases extraordinarily at very low temperatures, such as approx $10^6$ times larger than the value at higher temperatures. Observed anomalies in the electrical resistivity resembles the Kondo insulator, but itinerant electrons of narrow energy band of supercage clusters are ferromagnetic.
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Submitted 12 September, 2020;
originally announced September 2020.
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Origin of magnetic moments and ferromagnetic properties of potassium clusters in zeolite A
Authors:
Takehito Nakano,
Shingo Araki,
Nguyen Hoang Nam,
Takashi Umemoto,
Kazushige Tsuchihashi,
Yosuke Kubo,
Akihiro Owaki,
Yasuo Nozue
Abstract:
K clusters arrayed in zeolite A are investigated in detail. K clusters are generated in regular alpha-cages of zeolite A by the loading of guest K metal at a loading density of K atoms per alpha-cage, $n$. The value of $n$ was changed from 0 to 7.2. It is known that this system shows ferromagnetic properties for $n > 2$, where the Curie temperature increases with $n$, has a peak of approx,8 K at…
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K clusters arrayed in zeolite A are investigated in detail. K clusters are generated in regular alpha-cages of zeolite A by the loading of guest K metal at a loading density of K atoms per alpha-cage, $n$. The value of $n$ was changed from 0 to 7.2. It is known that this system shows ferromagnetic properties for $n > 2$, where the Curie temperature increases with $n$, has a peak of approx,8 K at $n approx 3.6$, and decreases to 0 K at $n = 7.2$. The negative Weiss temperature is estimated from the Curie-Weiss law for $n > 2$. A spherical quantum-well (SQW) model for the K cluster with 1$s$, 1$p$, and 1$d$ quantum states has previously been proposed, and the ferromagnetic properties were explained as being due to $s$-electrons in 1$p$ states. A spin-cant model of Mott-insulator antiferromagnetism in a K cluster array has been proposed for the origin of the ferromagnetic properties. However, the SQW model cannot explain either the $n$-dependence of the Curie temperature or that of the Curie constant. In the present study, detailed measurements were made of the optical reflection, magnetic properties, electron spin resonance, and electrical resistivities. An optical reflection band at 0.7 eV is clearly observed for $2 < n < 6$ at low temperatures, and is assigned to the excitation of the sigma-bonding state between 1$p$-states in adjoining alpha-cages. The electrical resistivity indicates an insulating state continuously for $n$. We propose an advanced SQW model with consideration for sigma-bonding, the orbital orthogonality of 1$p$-hole states, and also the superlattice structure. We explain the observed electronic properties using this model based on a correlated polaron system. We propose an enhancement effect of the Dzyaloshinsky-Moriya (DM) interaction between adjoining $1p$ orbitals by the extension of the Rashba mechanism of spin-orbit interaction.
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Submitted 10 September, 2020;
originally announced September 2020.
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Two qualitatively different superconducting phases under high pressure in single-crystalline CeNiGe$_{3}$
Authors:
Shunsaku Kitagawa,
Shingo Araki,
Tatsuo C. Kobayashi,
Yoichi Ikeda
Abstract:
We have measured the temperature dependence of resistivity in single-crystalline CeNiGe$_{3}$ under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase $T_{\rm N1}$ = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at $\sim$ 3.0 GPa. Above 2.3 GPa, a clear zero-resistivi…
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We have measured the temperature dependence of resistivity in single-crystalline CeNiGe$_{3}$ under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase $T_{\rm N1}$ = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at $\sim$ 3.0 GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at $\sim$ 6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field $μ_0H_{\rm c2}$ and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds.
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Submitted 11 May, 2020;
originally announced May 2020.
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Helimagnetic Structure and Heavy-Fermion-Like Behavior in the Vicinity of the Quantum Critical Point in Mn$_3$P
Authors:
H. Kotegawa,
M. Matsuda,
F. Ye,
Y. Tani,
K. Uda,
Y. Kuwata,
H. Tou,
E. Matsuoka,
H. Sugawara,
T. Sakurai,
H. Ohta,
H. Harima,
K. Takeda,
J. Hayashi,
S. Araki,
T. C. Kobayashi
Abstract:
Antiferromagnet Mn$_3$P with Neel temperature $T_N=30$ K is composed of Mn-tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and r…
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Antiferromagnet Mn$_3$P with Neel temperature $T_N=30$ K is composed of Mn-tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at $\sim1.6$ GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn$_3$P, which is most likely effected by the underlying frustration effect.
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Submitted 28 January, 2020; v1 submitted 21 January, 2020;
originally announced January 2020.
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Field-angular Dependence of Pairing Interaction in URhGe: Comparison with UCoGe
Authors:
Yo Tokunaga,
Dai Aoki,
Hadrien Mayaffre,
Steffen Kramer,
Marc-Henri Julien,
Claude Berthier,
Mladen Horvatic,
Hironori Sakai,
Shinsaku Kambe,
Taisuke Hattori,
Shingo Araki
Abstract:
The field-angular dependence of Co-NMR spin-lattice relaxation rate 1/T1 has been measured for a 10% Co-doped single crystal of URhGe. The experiment revealed that spin fluctuations in ferromagnetic (FM) state of URhGe are robust against magnetic field below about 4 T, applied along any direction in the bc crystal plane. This is in clear contrast with the sister compound UCoGe, in which FM spin fl…
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The field-angular dependence of Co-NMR spin-lattice relaxation rate 1/T1 has been measured for a 10% Co-doped single crystal of URhGe. The experiment revealed that spin fluctuations in ferromagnetic (FM) state of URhGe are robust against magnetic field below about 4 T, applied along any direction in the bc crystal plane. This is in clear contrast with the sister compound UCoGe, in which FM spin fluctuations are rapidly suppressed by a tiny applied field along the c axis. We show that such a difference in the character of the spin fluctuations is reflected in their two distinct phase diagrams for the upper critical field Hc2, providing further support to the mechanism of superconductivity mediated by spin fluctuations in these materials.
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Submitted 1 October, 2019;
originally announced October 2019.
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Pressure-Induced Superconductivity from Doping-Induced Antiferromagnetic Phase of 112-type Ca$_{1-x}$La$_{x}$FeAs$_{2}$
Authors:
Shunsaku Kitagawa,
Taishi Sekiya,
Yo Fujiyoshi,
Shingo Araki,
Tatsuo C. Kobayashi,
Naoki Nishimoto,
Tasuku Mizukami,
Satoshi Ioka,
Kazunori Fujimura,
Kazutaka Kudo,
Minoru Nohara
Abstract:
The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca$_{1-x}$La$_{x}$FeAs$_{2}$ were studied, and the in-plane electrical resistivity $ρ_{ab}$ was measured with an indenter-type pressure cell. The AFM phase transition temperatures of $T_{\rm N}$ = 47, 63, and 63 K at ambient pressure for $x$ = 0.18, 0.21, and 0.26 was suppressed by applying pressur…
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The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca$_{1-x}$La$_{x}$FeAs$_{2}$ were studied, and the in-plane electrical resistivity $ρ_{ab}$ was measured with an indenter-type pressure cell. The AFM phase transition temperatures of $T_{\rm N}$ = 47, 63, and 63 K at ambient pressure for $x$ = 0.18, 0.21, and 0.26 was suppressed by applying pressure $P$, with superconductivity emerging at critical pressures of $P_{\rm c}$ $\simeq$ 0, 1.5, and 3.4 GPa, respectively. Correspondingly, the slope of $T_{\rm N}$ against $P$ decreased as $dT_{\rm N}/P$ $\simeq$ $-$15 and $-$2 K/GPa for $x$ = 0.21 and 0.26, respectively. Thus, although the AFM phase was stabilized with La doping $x$, the AFM phase was suppressed by pressure, and superconductivity eventually emerged.
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Submitted 1 November, 2017;
originally announced November 2017.
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Suppression of Nonmagnetic Insulating State by Application of Pressure in Mineral Tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$
Authors:
Shunsaku Kitagawa,
Taishi Sekiya,
Shingo Araki,
Tatsuo C. Kobayashi,
Kenji Ishida,
Takashi Kambe,
Takumi Kimura,
Naoki Nishimoto,
Kazutaka Kudo,
Minoru Nohara
Abstract:
The mineral tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$ exhibits a first-order metal--insulator transition (MIT) at $T_{\rm MI}$ = 85 K and ambient pressure. We measured the $^{63}$Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. $^{63}$Cu-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pres…
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The mineral tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$ exhibits a first-order metal--insulator transition (MIT) at $T_{\rm MI}$ = 85 K and ambient pressure. We measured the $^{63}$Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. $^{63}$Cu-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at $\sim1.0$ GPa. Two other anomalies are observed in the resistivity measurements, and the pressure -- temperature phase diagram of Cu$_{12}$Sb$_{4}$S$_{13}$ is constructed.
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Submitted 17 August, 2015;
originally announced August 2015.
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Suppression of superconductivity and structural phase transition against pressure in Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$
Authors:
Shunsaku Kitagawa,
Shingo Araki,
Tatsuo C. Kobayashi,
Hiroyuki Ishii,
Kazunori Fujimura,
Daisuke Mitsuoka,
Kazutaka Kudo,
Minoru Nohara
Abstract:
We measured the pressure dependence of in-plane resistivity $ρ_{ab}$ in the recently-discovered iron-based superconductor Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$, which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature $T_{\rm c}$ = 16 K and structural phase transition temperature $T_{\rm s}$…
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We measured the pressure dependence of in-plane resistivity $ρ_{ab}$ in the recently-discovered iron-based superconductor Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$, which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature $T_{\rm c}$ = 16 K and structural phase transition temperature $T_{\rm s}$ $\simeq$ 100 K at ambient pressure. $T_{\rm c}$ and $T_{\rm s}$ are suppressed on applying pressure and disappear at approximately 0.5 GPa, suggesting a relationship between superconductivity and structure. Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$ is a rather rare example in which the superconductivity appears only in a low-temperature ordered phase. The fact that the change in the crystal structure is directly linked with superconductivity suggests that the crystal structure as well as magnetism are important factors governing superconductivity in iron pnictides.
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Submitted 7 December, 2014;
originally announced December 2014.
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A Study of Ni-Substitution Effects on Heavy-Fermion CeCu2Si2 - Similarities between Ni Substitution and High-Pressure Effects -
Authors:
Yoichi Ikeda,
Shingo Araki,
Tatsuo C. Kobayashi,
Yusei Shimizu,
Tatsuya Yanagisawa,
Hiroshi Amitsuka
Abstract:
The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by specific heat and electrical resistivity measurements. The specific heat measurement has revealed that the enhanced quantum fluctuations around an antiferromagnetic quantum critical point are markedly suppressed by Ni substitution, and that the Fermi liquid state recovers in the Nirich region (x > 0.12). The characteristic T-l…
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The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by specific heat and electrical resistivity measurements. The specific heat measurement has revealed that the enhanced quantum fluctuations around an antiferromagnetic quantum critical point are markedly suppressed by Ni substitution, and that the Fermi liquid state recovers in the Nirich region (x > 0.12). The characteristic T-linear dependence of the resistivity has been observed at approximately x ~ 0.10 together with a sign of superconductivity. The variation of n in the form of rho - rho0 = aT^n against Tmax^1, at which the resistivity peaks, coincides with the case of high-pressure experiments on pure CeCu2Si2. The anomalous T-linear behavior appears to occur in the crossover region from the Kondo regime to the valence fluctuation regime rather than in the conventional antiferromagnetic quantum critical region.
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Submitted 25 June, 2012;
originally announced June 2012.
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Iron-platinum-arsenide superconductors Ca10(PtnAs8)(Fe2-xPtxAs2)5
Authors:
Minoru Nohara,
Satomi Kakiya,
Kazutaka Kudo,
Yoshihiro Oshiro,
Shingo Araki,
Tatsuo C. Kobayashi,
Kenta Oku,
Eiji Nishibori,
Hiroshi Sawa
Abstract:
An overview of the crystal structures and physical properties of the recently discovered iron-platinum-arsenide superconductors, Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3 and 4), which have a superconducting transition temperature up to 38 K, is provided. The crystal structure consists of superconducting Fe2As2 layers alternating with platinum-arsenic layers, PtnAs8. The upper critical field Hc2, hydrosta…
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An overview of the crystal structures and physical properties of the recently discovered iron-platinum-arsenide superconductors, Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3 and 4), which have a superconducting transition temperature up to 38 K, is provided. The crystal structure consists of superconducting Fe2As2 layers alternating with platinum-arsenic layers, PtnAs8. The upper critical field Hc2, hydrostatic pressure dependence of superconducting transition temperature Tc, and normal-state magnetic susceptibility are reported.
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Submitted 5 March, 2012;
originally announced March 2012.
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Interplay of Superconductivity and Fermi-Liquid Transport in Rh-Doped CaFe2As2 with Lattice-Collapse Transition
Authors:
Masataka Danura,
Kazutaka Kudo,
Yoshihiro Oshiro,
Shingo Araki,
Tatsuo C. Kobayashi,
Minoru Nohara
Abstract:
Ca(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ undergoes successive phase transitions with increasing Rh doping in the $T$ $=$ 0 limit. The antiferromagnetic-metal phase with orthorhombic structure at 0.00 $\le$ $x$ $\le$ 0.020 is driven to a superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020 $\le$ $x$ $\le$ 0.024; a non-superconducting collapsed-tetragonal (cT) phase takes over at $x$…
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Ca(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ undergoes successive phase transitions with increasing Rh doping in the $T$ $=$ 0 limit. The antiferromagnetic-metal phase with orthorhombic structure at 0.00 $\le$ $x$ $\le$ 0.020 is driven to a superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020 $\le$ $x$ $\le$ 0.024; a non-superconducting collapsed-tetragonal (cT) phase takes over at $x$ $\geq$ 0.024. The breakdown of Fermi-liquid transport is observed in the ucT phase above $T_{\rm c}$. In the adjacent cT phase, Fermi-liquid transport is restored along with a disappearance of superconductivity. This interplay of superconductivity and Fermi-liquid transport suggests the essential role of magnetic fluctuations in the emergence of superconductivity in doped CaFe$_2$As$_2$.
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Submitted 9 September, 2011;
originally announced September 2011.
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Pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3: An 115In-NQR study under pressure
Authors:
S. Kawasaki,
M. Yashima,
Y. Kitaoka,
K. Takeda,
K. Shimizu,
Y. Oishi,
M. Takata,
T. C. Kobayashi,
H. Harima,
S. Araki,
H. Shishido,
R. Settai,
Y. Onuki
Abstract:
We report on the pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature and pressure dependences of the NQR spectra have revealed a first-order quantum-phase transition (QPT) from an AFM to PM at a critical pressure Pc=2.46 GPa. Despite the lack of an AFM…
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We report on the pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature and pressure dependences of the NQR spectra have revealed a first-order quantum-phase transition (QPT) from an AFM to PM at a critical pressure Pc=2.46 GPa. Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that the unconventional SC occurs in both phases of the AFM and PM. The nuclear spin-lattice relaxation rate 1/T1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T1 decreases without the coherence peak just below Tc, followed by a power-law like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, Tc has a peak around Pc in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of Tc = 230 mK around Pc, indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, Pc = 2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical point from the AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations.
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Submitted 15 February, 2008;
originally announced February 2008.
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New Superconducting and Magnetic Phases Emerge on the Verge of Antiferromagnetism in CeIn$_3$
Authors:
Shinji Kawasaki,
Takeshi Mito,
Yu Kawasaki,
Hisashi Kotegawa,
Guo-qing Zheng,
Yoshio Kitaoka,
Hiroaki Shishido,
Shingo Araki,
Rikio Settai,
Yoshichika Ōnuki
Abstract:
We report the discovery of new superconducting and novel magnetic phases in CeIn$_3$ on the verge of antiferromagnetism (AFM) under pressure ($P$) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a $P$-induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in…
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We report the discovery of new superconducting and novel magnetic phases in CeIn$_3$ on the verge of antiferromagnetism (AFM) under pressure ($P$) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a $P$-induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in $P=2.28-2.5$ GPa to coexist with AFM that is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.
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Submitted 16 April, 2004;
originally announced April 2004.
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^{115}In-NQR evidence for unconventional superconductivity in CeIn_3 under pressure
Authors:
S. Kawasaki,
T. Mito,
Y. Kawasaki,
G. -q. Zheng,
Y. Kitaoka,
H. Shishido,
S. Araki,
R. Settai,
Y. Onuki
Abstract:
We report evidence for unconventional superconductivity in CeIn_3 at a pressure P = 2.65 GPa above critical pressure (P_c ~ 2.5 GPa) revealed by the measurements of nuclear-spin-lattice-relaxation time (T_1) and ac-susceptibility (ac-chi). Both the measurements of T_1 and ac-chi have pointed to a superconducting transition at T_c = 95 mK, which is much lower than an onset temperature T_{onset} =…
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We report evidence for unconventional superconductivity in CeIn_3 at a pressure P = 2.65 GPa above critical pressure (P_c ~ 2.5 GPa) revealed by the measurements of nuclear-spin-lattice-relaxation time (T_1) and ac-susceptibility (ac-chi). Both the measurements of T_1 and ac-chi have pointed to a superconducting transition at T_c = 95 mK, which is much lower than an onset temperature T_{onset} = 0.15 K at zero resistance. The temperature dependence of 1/T_1 shows no coherence peak just below T_c, indicative of an unconventional nature for the superconductivity induced in CeIn_3.
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Submitted 11 August, 2002;
originally announced August 2002.
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Pressure-Temperature Phase Diagram of Antiferromagnetism and Superconductivity in CeRhIn5 and CeIn3 : In-NQR Study under Pressure
Authors:
S. Kawasaki,
T. Mito,
G. -q. Zheng,
C. Thessieu,
Y. Kawasaki,
K. Ishida,
Y. Kitaoka,
T. Muramatsu,
T. C. Kobayashi,
D. Aoki,
S. Araki,
Y. Haga,
R. Settai,
Y. Onuki
Abstract:
We report the novel pressure($P$) - temperature($T$) phase diagram of antiferromagnetism and superconductivity in CeRhIn$_5$ and CeIn$_3$ revealed by the $^{115}$In nuclear-spin-lattice-relaxation ($T_1$) measurement. In the itinerant magnet CeRhIn$_5$, we found that the Néel temperature $T_N$ is reduced at $P \geq$ 1.23 GPa with an emergent pseudogap behavior. In CeIn$_3$, the localized magneti…
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We report the novel pressure($P$) - temperature($T$) phase diagram of antiferromagnetism and superconductivity in CeRhIn$_5$ and CeIn$_3$ revealed by the $^{115}$In nuclear-spin-lattice-relaxation ($T_1$) measurement. In the itinerant magnet CeRhIn$_5$, we found that the Néel temperature $T_N$ is reduced at $P \geq$ 1.23 GPa with an emergent pseudogap behavior. In CeIn$_3$, the localized magnetic character is robust against the application of pressure up to $P \sim$ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.
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Submitted 30 October, 2001;
originally announced October 2001.