arXiv subjects

Takashi Kambe

Publications and source records attributed to Takashi Kambe.

12 recordsLinked to original sources

arXiv2025

$^{23}$Na-NMR study on the one-dimensional superoxide spin-chain compound NaO$_2$

We report $^{23}$Na-NMR study on a candidate one-dimensional quantum spin system NaO$_2$. The Knight shift, linewidth, and spin-lattice relaxation rate $1/T_1$ were investigated down to 0.3 K under fields up to 16 T. The results reveal the opening of a spin gap of $Δ(10.1 {\rm T}) \simeq$ 38 K below $T_{\rm S3} =$ 40 K, consistent with a spin-Peierls-like instability. The hyperfine coupling constant was found to drop sharply across the structural phase transition at $T_{\rm S2} =$ 215 K, highlighting the pronounced one-dimensional character of the system. These findings establish NaO$_2$ as a rare example of a $π$-orbital-based one-dimensional spin chain that exhibits a spin-gapped ground state.

cond-mat.str-el↗

arXiv2025

Topological Hall Effect in PrSb$_2$

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$_2$.

cond-mat.str-el↗

arXiv2023

Antiferromagnetic structure of alkali metal superoxide CsO$_2$

We have performed a powder neutron diffraction study on CsO$_2$, where the unpaired electron with $s=1/2$ in the $π^*$ orbital of the O$_2^-$ ion is responsible for the magnetism. The magnetic reflections 0 $\frac{1}{2}$ 0 and 0 $\frac{1}{2}$ 1 were observed below the Néel temperature of about 10 K. An antiferromagnetic structure with a propagation vector of (0 ,$\frac{1}{2}$, 0) and magnetic moments parallel to the $a$-axis is the most plausible. The magnitude of the ordered moment is about 0.2 $μ_B$, which is considered to be strongly suppressed due to the one-dimensionality of the system. We propose a possible $π^*$ orbital order that can explain the obtained magnetic structure, and discuss its relation to the one-dimensionality.

cond-mat.str-el↗

arXiv2021

Spin-gap formation due to spin-Peierls instability in $π$-orbital-ordered NaO$_2$

We have investigated the low-temperature magnetism of sodium superoxide (NaO$_{2}$), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at $T_{1}=220$ K and $T_{2}=190$ K, which correspond well to the structural phase transition temperatures, and a sudden decrease below $T_{3}=34$ K. At 4.2 K, the magnetization shows a clear stepwise anomaly around 30 T with a large hysteresis. In addition, the muon spin relaxation experiments indicate no magnetic phase transition down to $T=0.3$ K. The inelastic neutron scattering spectrum exhibits magnetic excitation with a finite energy gap. These results confirm that the ground state of NaO$_{2}$ is a spin-singlet state. To understand this ground state in NaO$_{2}$, we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below $T_{2}$ are observed. Furthermore, we find that several new peaks appear below $T_{3}$. This directly evidences the low crystal symmetry, namely, the presence of the phase transition at $T_{3}$. We conclude the singlet-ground state of NaO$_{2}$ due to the spin-Peierls instability.

cond-mat.str-el↗

arXiv2018

Magnetism and high-magnetic field magnetization in alkali superoxide CsO2

Alkali superoxide CsO2 is one of candidates for the spin-1/2 one-dimensional (1D) antiferromagnet, which may be sequentially caused by an ordering of the pi-orbital of O2- molecule below TS ~ 70 K. Here, we report on the magnetism in powder CsO2 and high-magnetic field magnetization measurements in pulsed-magnetic fields of up to 60 T. We obtained the low temperature phase diagram around the antiferromagnetic ordering temperature TN = 9.6 K under the magnetic field. At 1.3 K, remarkable up-turn curvature in the magnetization around a saturation field of ~ 60 T is found, which corresponds to the spin-1/2. We will compare it with the theoretical calculation.

cond-mat.mtrl-sci↗

arXiv2017

Phase Diagram and Soliton Picture of an Ideal Spin-Peierls Compound D-F$_{5}$PNN

We investigate magnetic properties of an $S$=1/2 quasi-one dimensional organic antiferromagnet, D-F$_{5}$PNN using magnetization measurements taken at temperatures as low as 0.5 K. Three distinct phases were observed consisting of uniform, dimerized (D), and incommensurate (I) spin structures in the magnetic field versus temperature plane, where a significant hysteresis appears between D-I transitions in the field scan measurements. A combination of magnon ($S$=1) and soliton ($S$=1/2) excitations have successfully reproduced the observed magnetic susceptibility. In addition, such excitations provide a reasonable interpretation of the temperature dependent electron spin resonance (ESR) spectra. By comparison with the theoretical study, we conclude that D-F$_{5}$PNN is an ideal compound for investigating the spin-Peierls transition.

cond-mat.str-el↗

arXiv2015

Suppression of Nonmagnetic Insulating State by Application of Pressure in Mineral Tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$

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.

cond-mat.str-el↗

arXiv2013

Co-intercalation of Ammonia molecules between FeSe layers in Ba-doped FeSe superconductor

We have synthesized a Ba-doped FeSe superconductor using liquid ammonia, and investigated in detail the structure and composition of the Ba-FeSe phase. In the superconducting phase, both the Tc and the shielding fraction are almost unchanged even if the nominal composition of Ba is varied in the region from 0.3 to 0.7. The optimized Tc is 38.8 K. We have determined the structure of the superconducting phase with X-ray powder diffraction (using synchrotron radiation) and here describe the co-intercalation of Ba and NH3 molecules between the FeSe layers.

cond-mat.supr-con↗

arXiv2013

Magnetoelectric Effect driven by Magnetic Domain Modification in LuFe2O4

Magneto-capacitance effect was investigated using the impedance spectroscopy on single crystals of LuFe2O4. The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below TFerri ~ 240 K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of dielectric property related to the motion of nano-sized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe2O4.

cond-mat.str-el↗

arXiv2012

Investigation on synthesis and physical properties of metal doped picene solids

We report electronic structure and physical properties of metal doped picene as well as selective synthesis of the phase exhibiting 18 K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules. The charge transfer leads to a softening of Raman scattering peaks, which enables us to determine the number of transferred electrons. From this we have identified that three electrons are transferred to each picene molecule in the superconducting doped-picene solids. Second, we report the pressure dependence of Tc in 7 and 18 K phases of K3picene. The 7 K phase shows a negative pressure-dependence, while the 18 K phase exhibits a positive pressure-dependence which cannot be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a new synthesis method for superconducting K3picene by a solution process with monomethylamine, CH3NH2. This method enables one to prepare selectively the K3picene sample exhibiting 18 K superconducting transition. The discovery of suitable way for preparing K3picene with Tc = 18 K may facilitate clarification of the mechanism of superconductivity.

cond-mat.supr-con↗

arXiv2007

Antiferromagnetic order driven by the molecular orbital order of C$_{60}$ in $α'$--tetra--$kis$--(dimethylamino)--ethylene--C$_{60}$

We have studied the ground state of a fullerene--based magnet, the $α'$--phase tetra--$kis$--(dimethylamino)--ethylene--C$_{60}$ ($α'$--TDAE--C$_{60}$), by electron spin resonance (ESR) and magnetic torque measurements. Below T$_N=7$ K, non--paramagnetic field dependent resonances with a finite excitation gap (1.7 GHz) are observed along the $a$--axis. Strong enhancement in their intensity as temperature is decreased is inconsistent with excitation from a singlet state, which had been proposed for the $α'$--phase ground state. Below T$_N$, non--quadratic field dependence of magnetic torque signal is also observed in contrast to quadratic field dependence in the paramagnetic phase. The angle--dependent torque signals below T$_N$ indicate the existence of an anisotropy of the bulk magnetization. From both experiments, we propose an antiferromagnetic ground state driven by the cooperative orientational ordering of C$_{60}$ in the $α'$--TDAE--C$_{60}$.

cond-mat.mtrl-sci↗

arXiv2002

The polymer phase of the TDAE-C$_{60}$ organic ferromagnet

The high-pressure Electron Spin Resonance (ESR) measurements were preformed on TDAE-C$_{60}$ single crystals and stability of the polymeric phase was established in the $P - T$ parameter space. At 7 kbar the system undergoes a ferromagnetic to paramagnetic phase transition due to the pressure-induced polymerization. The polymeric phase remains stable after the pressure release. The depolymerization of the pressure-induced phase was observed at the temperature of 520 K. Below room temperature, the polymeric phase behaves as a simple Curie-type insulator with one unpaired electron spin per chemical formula. The TDAE$^+$ donor-related unpaired electron spins, formerly ESR-silent, become active above the temperature of 320 K and the Curie-Weiss behavior is re-established.

cond-mat.str-el↗