K. Tshoo, Y. Satou, H. Bhang, S. Choi, T. Nakamura, Y. Kondo, S. Deguchi, Y. Kawada, N. Kobayashi, Y. Nakayama, K. N. Tanaka, N. Tanaka, N. Aoi, M. Ishihara, T. Motobayashi, H. Otsu, H. Sakurai, S. Takeuchi, Y. Togano, K. Yoneda, Z. H. Li, F. Delaunay, J. Gibelin, F. M. Marqués, N. A. Orr, T. Honda, M. Matsushita, T. Kobayashi, Y. Miyashita, T. Sumikama, K. Yoshinaga, S. Shimoura, D. Sohler, T. Zheng, Z. X. Cao
The unbound excited states of the neutron drip-line isotope 24O have been investigated via the 24O(p,p')23O+n reaction in inverse kinematics at a beam energy of 62 MeV/nucleon. The decay energy spectrum of 24O* was reconstructed from the momenta of 23O and the neutron. The spin-parity of the first excited state, observed at Ex = 4.65 +/- 0.14 MeV, was determined to be Jpi = 2+ from the angular distribution of the cross section. Higher lying states were also observed. The quadrupole transition parameter beta2 of the 2+ state was deduced, for the first time, to be 0.15 +/- 0.04. The relatively high excitation energy and small beta2 value are indicative of the N = 16 shell closure in 24O.
J. S. White, T. Honda, K. Kimura, T. Kimura, Ch. Niedermayer, O. Zaharko, A. Poole, B. Roessli, M. Kenzelmann
The olivine compound Mn2GeO4 is shown to feature both a ferroelectric polarization and a ferromagnetic magnetization that are directly coupled and point along the same direction. We show that a spin spiral generates ferroelectricity (FE), and a canted commensurate order leads to weak ferromagnetism (FM). Symmetry suggests that the direct coupling between the FM and FE is mediated by Dzyaloshinskii-Moriya interactions that exist only in the ferroelectric phase, controlling both the sense of the spiral rotation and the canting of the commensurate structure. Our study demonstrates how multi-component magnetic structures found in magnetically-frustrated materials like Mn2GeO4 provide a new route towards functional materials that exhibit coupled FM and FE.
T. Okudaira, T. Oku, T. Ino, H. Hayashida, H. Kira, K. Sakai, K. Hiroi, S. Takahashi, K. Aizawa, H. Endo, S. Endo, M. Hino, K. Hirota, T. Honda, K. Ikeda, K. Kakurai, W. Kambara, M. Kitaguchi, T. Oda, H. Ohshita, T. Otomo, H. M. Shimizu, T. Shinohara, J. Suzuki, T. Yamamoto
We are developing a neutron polarizer with polarized $^3$He gas, referred to as a $^3$He spin filter, based on the Spin Exchange Optical Pumping (SEOP) for polarized neutron scattering experiments at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). A $^3$He gas-filling station was constructed at J-PARC, and several $^3$He cells with long spin relaxation times have been fabricated using the gas-filling station. A laboratory has been prepared in the MLF beam hall for polarizing $^3$He cells, and compact pumping systems with laser powers of 30~W and 110~W, which can be installed onto a neutron beamline, have been developed. A $^3$He polarization of 85% was achieved at a neutron beamline by using the pumping system with the 110~W laser. Recently, the first user experiment utilizing the $^3$He spin filter was conducted, and there have been several more since then. The development and utilization of $^3$He spin filters at MLF of J-PARC are reported.
K. Tshoo, Y. Satou, C. A. Bertulani, H. Bhang, S. Choi, T. Nakamura, Y. Kondo, S. Deguchi, Y. Kawada, Y. Nakayama, K. N. Tanaka, N. Tanaka, Y. Togano, N. Kobayashi, N. Aoi, M. Ishihara, T. Motobayashi, H. Otsu, H. Sakurai, S. Takeuchi, K. Yoneda, F. Delaunay, J. Gibelin, F. M. Marqués, N. A. Orr, T. Honda, T. Kobayashi, T. Sumikama, Y. Miyashita, K. Yoshinaga, M. Matsushita, S. Shimoura, D. Sohler, J. W. Hwang, T. Zheng, Z. H. Li, Z. X. Cao
One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at Edecay=50$\pm$3 keV, corresponding to an excited state in 23O at 2.78$\pm$0.11 MeV, as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d -wave neutron knockout, providing support for a Jπ assignment of 5/2+. The associated spectroscopic factor was deduced to be C2S(0d5/2)=4.1$\pm$0.4 by comparing the measured cross section (View the MathML source) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2 orbital is in line with the N=16 shell closure in 24O.
X. G. Zheng, M. Hagihala, I. Yamauchi, E. Nishibori, T. Honda, T. Yuasa, C. -N. Xu
The newly identified field-induced up-up-down order in Ba$_3$CoSb$_2$O$_9$ etc. renewed attention on exotic phases in spin-1/2 triangular-lattice antiferromagnets. Here, we report a unique zero-field noncoplanar up,up,down, down,down,up Kagome spin order in spin-1/2 antiferromagnet Clinoatacamite, Cu$_4$(OH)$_6$Cl$_2$, which consists of weakly-coupled Kagome layers and was known as the parent compound for the most researched spin liquid candidate Herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$. The two-dimensional uud-ddu Kagome order develops below T$_{N1}$ = 18.1 K in Clinoatacamite before a further transition into a three-dimensional magnetic order at low temperatures below T$_{N2}$ ~ 6.4 K with persistent spin fluctuations. The present work reveals a new unpredicted Kagome order in a readily accessible temperature range in the parent compound of a well-studied spin liquid. In addition, it has also solved a puzzling issue for a mysterious magnetic phase.
T. Kawarabayashi, T. Honda, H. Aoki, Y. Hatsugai
The effect of disorder on the Landau levels of massless Dirac fermions is examined for the cases with and without the fermion doubling. To tune the doubling a tight-binding model having a complex transfer integral is adopted to shift the energies of two Dirac cones, which is theoretically proposed earlier and realizable in cold atoms in an optical lattice. In the absence of the fermion doubling, the $n=0$ Landau level is shown to exhibit an anomalous sharpness even if the disorder is uncorrelated in space (i.e., large K-K' scattering). This anomaly occurs when the disorder respects the chiral symmetry of the Dirac cone.
T. H. Oosterkamp, J. W. Janssen, L. P. Kouwenhoven, D. G. Austing, T. Honda, S. Tarucha
We have measured electron transport through a vertical quantum dot containing a tunable number of electrons between 0 and 40. Over some region in magnetic field the electrons are spin polarized and occupy successive angular momentum states, i.e. the maximum density droplet (MDD) state. The stability region where the MDD state is the ground state, decreases for increasing electron number. The instability of the MDD is accompanied by a redistribution of charge which increases the area of the electron droplet.
L. P. Kouwenhoven, T. H. Oosterkamp, M. W. S. Danoesastro, M. Eto, D. G. Austing, T. Honda, S. Tarucha
We study ground states and excited states in semiconductor quantum dots containing 1 to 12 electrons. For the first time, it is possible to identify the quantum numbers of the states in the excitation spectra and make a direct comparison to exact calculations. A magnetic field induces transitions between excited states and ground state. These transitions are discussed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. Our impurity-free quantum dots allow for atomic physics experiments in magnetic field regimes not accessible for atoms.
J. S. White, T. Honda, R. Sibille, N. Gauthier, V. Dmitriev, Th. Strässle, Ch. Niedermayer, T. Kimura, M. Kenzelmann
At ambient pressure (P) and below 5.5 K, olivine-type Mn2GeO4 hosts a multiferroic (MF) phase where a multicomponent, i.e., multi-k magnetic order generates spontaneous ferromagnetism and ferroelectricity (FE) along the c axis. Under high P the FE disappears above 6 GPa, yet the P evolution of the magnetic structure remained unclear based on available data. Here we report high P single crystal neutron diffraction experiments in theMF phase at T = 4.5 K.We observe clearly that the incommensurate spiral component of the magnetic order responsible for FE varies little with P up to 5.1 GPa. With support from high P synchrotron x-ray diffraction measurements at room temperature (T), the P driven suppression of FE is proposed to occur as a consequence of a crystal structure transition away from the olivine structure. In addition, in the low T neutron scattering experiments an emergent nonhydrostatic P component, i.e., a uniaxial stress, leads to the selection of certain multi-k domains. We use this observation to deduce a double-k conical magnetic structure for the ambient P ground state, this being a key ingredient for a model description of the MF phase.
T. Honda, J. S. White, A. B. Harris, L. C. Chapon, A. Fennell, B. Roessli, O. Zaharko, Y. Murakami, M. Kenzelmann, T. Kimura
Despite remarkable progress in developing multifunctional materials, spin-driven ferroelectrics featuring both spontaneous magnetization and electric polarization are still rare. Among such ferromagnetic ferroelectrics are conical spin spiral magnets with a simultaneous reversal of magnetization and electric polarization that is still little understood. Such materials can feature various multiferroic domains that complicates their study. Here we study the multiferroic domains in ferromagnetic ferroelectric Mn$_{2}$GeO$_{4}$ using neutron diffraction, and show that it features a double-Q conical magnetic structure that, apart from trivial 180 degree commensurate magnetic domains, can be described by ferromagnetic and ferroelectric domains only. We show unconventional magnetoelectric couplings such as the magnetic-field-driven reversal of ferroelectric polarization with no change of spin-helicity, and present a phenomenological theory that successfully explains the magnetoelectric coupling. Our measurements establish Mn$_{2}$GeO$_{4}$ as a conceptually simple multiferroic in which the magnetic-field-driven flop of conical spin spirals leads to the simultaneous reversal of magnetization and electric polarization.
D. Q. Fang, Y. G. Ma, X. Y. Sun, P. Zhou, Y. Togano, N. Aoi, H. Baba, X. Z. Cai, X. G. Cao, J. G. Chen, Y. Fu, W. Guo, Y. Hara, T. Honda, Z. G. Hu, K. Ieki, Y. Ishibashi, Y. Ito, N. Iwasa, S. Kanno, T. Kawabata, H. Kimura, Y. Kondo, K. Kurita, M. Kurokawa, T. Moriguchi, H. Murakami, H. Ooishi, K. Okada, S. Ota, A. Ozawa, H. Sakurai, S. Shimoura, R. Shioda, E. Takeshita, S. Takeuchi, W. D. Tian, H. W. Wang, J. S. Wang, M. Wang, K. Yamada, Y. Yamada, Y. Yasuda, K. Yoneda, G. Q. Zhang, T. Motobayashi
The proton-proton momentum correlation functions ($C_{pp}(q)$) for kinematically complete decay channels of $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne have been measured at the RIKEN RI Beam Factory. From the very different correlation strength of $C_{pp}(q)$ for $^{23}$Al and $^{22}$Mg, the source size and emission time information were extracted from the $C_{pp}(q)$ data by assuming a Gaussian source profile in the correlation function calculation code (CRAB). The results indicated that the mechanism of two-proton emission from $^{23}$Al was mainly sequential emission, while that of $^{22}$Mg was mainly three-body simultaneous emission. By combining our earlier results of the two-proton relative momentum and the opening angle, it is pointed out that the mechanism of two-proton emission could be distinguished clearly.
Y. G. Ma, D. Q. Fang, X. Y. Sun, P. Zhou, Y. Togano, N. Aoi, H. Baba, X. Z. Cai, X. G. Cao, J. G. Chen, Y. Fu, W. Guo, Y. Hara, T. Honda, Z. G. Hu, K. Ieki, Y. Ishibashi, Y. Ito, N. Iwasa, S. Kanno, T. Kawabata, H. Kimura, Y. Kondo, K. Kurita, M. Kurokawa, T. Moriguchi, H. Murakami, H. Ooishi, K. Okada, S. Ota, A. Ozawa, H. Sakurai, S. Shimoura, R. Shioda, E. Takeshita, S. Takeuchi, W. D. Tian, H. W. Wang, J. S. Wang, M. Wang, K. Yamada, Y. Yamada, Y. Yasuda, K. Yoneda, G. Q. Zhang, T. Motobayashi
Two-proton relative momentum ($q_{pp}$) and opening angle ($θ_{pp}$) distributions from the three-body decay of two excited proton-rich nuclei, namely $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp}\sim20$ MeV/c as well as a peak in $θ_{pp}$ around 30$^\circ$ are seen in the two-proton break-up channel from a highly-excited $^{22}$Mg. In contrast, such peaks are absent for the $^{23}$Al case. It is concluded that the two-proton emission mechanism of excited $^{22}$Mg is quite different from the $^{23}$Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.
S. K. Dey, K. Ishida, H. Okabe, M. Hiraishi, A. Koda, T. Honda, J. Yamaura, H. Kageyama, R. Kadono
The magnetic ground state of oxynitride pyrochlore Lu$_2$Mo$_2$O$_{5-y}$N$_2$, a candidate compound for the quantum spin liquid ($S=1/2$, Mo$^{5+}$), was studied by muon spin rotation/relaxation experiment. In contrast to Lu$_2$Mo$_2$O$_7$ ($S=1$, Mo$^{4+}$) which exhibits the spin-glass behavior with a freezing temperature $T_g\simeq16$ K, no such spin freezing or long range magnetic order was observed down to 0.3 K. Moreover, two separate magnetic domains were detected below $\sim$13 K, which were characterized by differences in spin dynamics. The first is the "sporadic" spin fluctuation seen in frustrated antiferromagnets, where the amplitude of the hyperfine fields suggests that the excitation comprises a local cluster of unpaired spins. The other is rapid paramagnetic fluctuation, which is only weakly suppressed at low temperatures. In place of the paramagnetic fluctuation, the volume fraction for the sporadic fluctuation steadily increases with decreasing temperature, indicating the formation of an excitation gap with a broad distribution of the gap energy involving null gap.
T. Honda, H. Honjo, H. Katsuragi
We studied dendritic side-branching mechanism in the experiment of anisotropic viscous fingering. We measured the time dependence of growth speed of side-branch and the envelop of side-branches. We found that the speed of side-branch gets to be faster than one of the stem and the growth exponent of the speed changes at a certain time. The envelope of side-branches is represented as Y ~ X^1.47.
J. Yoneda, K. Takeda, T. Otsuka, T. Nakajima, M. R. Delbecq, G. Allison, T. Honda, T. Kodera, S. Oda, Y. Hoshi, N. Usami, K. M. Itoh, S. Tarucha
Recent advances towards spin-based quantum computation have been primarily fuelled by elaborate isolation from noise sources, such as surrounding nuclear spins and spin-electric susceptibility, to extend spin coherence. In the meanwhile, addressable single-spin and spin-spin manipulations in multiple-qubit systems will necessitate sizable spin-electric coupling. Given background charge fluctuation in nanostructures, however, its compatibility with enhanced coherence should be crucially questioned. Here we realise a single-electron spin qubit with isotopically-enriched phase coherence time (20 microseconds) and fast electrical control speed (up to 30 MHz) mediated by extrinsic spin-electric coupling. Using rapid spin rotations, we reveal that the free-evolution dephasing is caused by charge (instead of conventional magnetic) noise featured by a 1/f spectrum over seven decades of frequency. The qubit nevertheless exhibits superior performance with single-qubit gate fidelities exceeding 99.9% on average. Our work strongly suggests that designing artificial spin-electric coupling with account taken of charge noise is a promising route to large-scale spin-qubit systems having fault-tolerant controllability.