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Register a new userExistence of Fine Structure inside Spin Gap in CeRu2Al10
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We investigate the magnetic field effect on the spin gap state in CeRu2Al10 by measuring the magnetization and electrical resistivity. We found that the magnetization curve for the magnetic field H//c shows a metamagnetic-like anomaly at H*~4 T below T_0=27 K, but no anomaly for H//a and H//b. A shoulder of the electrical resistivity at Ts~5 K for I//c is suppressed by applying a longitudinal magnetic field above 5 T. Many anomalies are also found in the magnetoresistance for Hkc below ~5 K. The obtained magnetic phase diagram consists of at least two or three phases below T_0. These results strongly indicate the existence of a fine structure at a low energy side in a spin gap state with the excitation energy of 8 meV recently observed in the inelastic neutron scattering experiments.
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Spin dynamics in the new Kondo insulator compound CeRu2Al10 has been studied using unpolarized and polarized neutron scattering on single crystals. In the unconventional ordered phase forming below T0 = 27.3 K, two excitation branches are observed with significant intensities, the lower one of which has a gap of 4.8 +/- 0.3 meV and a pronounced dispersion up to about 8.5 meV. Comparison with RPA magnon calculations assuming crystal-field and anisotropic exchange couplings captures major aspects of the data, but leaves unexplained discrepancies, pointing to a key role of direction-specific hybridization between 4f and conduction band states in this compound.
The magnetization measurements of CexLa1-xRu2Al10 (x = 1, 0.75) under the high magnetic field were performed in order to obtain the information for the long-range order (LRO) in CeRu2Al10. We successfully obtained the magnetic phase diagram of these two compounds for the applied magnetic field along the a-axis which is the magnetization easy axis, and found that the LRO for x = 1 disappears at ~50 T which is the critical field to the paramagnetic phase. For x = 0.75, the critical magnetic field decreases to ~37 T by La substitution. The magnetic phase diagram and magnetization curve are qualitatively consistent with the recent Hanzawas mean field calculation results obtained by assuming the dimer of Ce ions whose crystalline electric field ground state has a large magnetic anisotropy. These results support the singlet pair formation scenario recently proposed by Tanida et al.. We also pointed out the possibility of the appearance of the field-induced magnetic phase between ~40 T and ~50 T for x = 1.
Condensed matter systems provide alternative `vacua exhibiting emergent low-energy properties drastically different from those of the standard model. A case in point is the emergent quantum electrodynamics (QED) in the fractionalized topological magnet known as quantum spin ice, whose magnetic monopoles set it apart from the familiar QED of the world we live in. Here, we show that the two greatly differ in their fine-structure constant $alpha$, which parametrizes how strongly matter couples to light: $alpha_{mathrm{QSI}}$ is more than an order of magnitude greater than $alpha_{mathrm{QED}} approx 1/137$. Furthermore, $alpha_{mathrm{QSI}}$, the emergent speed of light, and all other parameters of the emergent QED, are tunable by engineering the microscopic Hamiltonian. We find that $alpha_{mathrm{QSI}}$ can be tuned all the way from zero up to what is believed to be the textit{strongest possible} coupling beyond which QED confines. In view of the small size of its constrained Hilbert space, this marks out quantum spin ice as an ideal platform for studying exotic quantum field theories and a target for quantum simulation. The large $alpha_{mathrm{QSI}}$ implies that experiments probing candidate condensed-matter realizations of quantum spin ice should expect to observe phenomena arising due to strong interactions.
The photoconductivity spectra of NbS_3 (phase I) crystals are studied. A drop of photoconductivity corresponding to the Peierls gap edge is observed. Reproducible spectral features are found at energies smaller the energy gap value. The first one is a peak at the energy 0.6 eV that is close to the midgap one. It has a threshold-like dependence of the amplitude on the electrical field applied. Another feature is a peak at the energy 0.9 eV near to the edge of the gap. We ascribe the origin of this peak to the stacking faults. The third one are continuous states between these peaks at energies 0.6-0.8 eV. We observed bleaching of the photoconductivity even below zero at this energies in the high electric field (700 V/cm) and under additional illumination applied.
We have succeeded in synthesizing two types of new organic radical crystals 3-I-V [= 3- (3-iodophenyl)-1,5-diphenylverdazyl] and 3-Br-4-F-V [= 3-(3-bromo-4-fluorophenyl)-1,5- diphenylverdazyl]. Their crystal strucutures are found to be isomorphous to that of previously reported spin ladder 3-Cl-4-F-V. Through the quantitative analysis of their molecular arrangements and magnetic properties, we confirm that these materials form ferromagnetic chain-based spin ladders with slightly modulated magnetic interactions. These results present the first quantitative demonstration of the fine-tuning of magnetic interactions in the molecular- based materials.
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