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Inelastic neutron scattering measurements of magnetic excitations in the charge-ordered state of ${\mathrm{Yb}}_{4}{\mathrm{As}}_{3}$ have been performed under magnetic field up to about 6 T. By applying a magnetic field, the spectrum at the one-dimensional wave vector $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ [ $\ensuremath{\pi}/d$] changes drastically from a broad one corresponding to the spinon excitation continuum of the one-dimensional $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\frac{1}{2}$ spin system to a sharp one at a finite energy, indicating the opening of an energy gap in the system. The magnetic field dependence of the gap is well fitted by the power law ${H}^{2/3}$. The experimental result gives strong evidence for the existence of a staggered field alternating along ${\mathrm{Yb}}^{3+}$ chains induced by the Dzyaloshinsky-Moriya interaction.

We report low-temperature measurements of the specific heat, thermal expansion, and thermal conductivity on the quasi-one-dimensional, effective $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\frac{1}{2}$ Heisenberg antiferromagnet ${\mathrm{Yb}}_{4}{\mathrm{As}}_{3}$. Distinct field-induced anomalies were found in the above quantities which are well described by the classical sine-Gordon soliton solution for an easy-plane Heisenberg antiferromagnet. Our findings strongly suggest that ${\mathrm{Yb}}_{4}{\mathrm{As}}_{3}$ represents the first example of an antiferromagnetic $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\frac{1}{2}$ spin-chain system where this type of nonlinear excitation could be identified.

The sequence of prominent fractional quantum Hall states up to $\nu$=5/11 around $\nu$=1/2 in a high mobility two-dimensional electron system confined at oxide heterointerface (ZnO) is analyzed in terms of the composite fermion model. The temperature dependence of $\Rxx$ oscillations around $\nu$=1/2 yields an estimation of the composite fermion effective mass, which increases linearly with the magnetic field. This mass is of similar value to an enhanced electron effective mass, which in itself arises from strong electron interaction. The energy gaps of fractional states and the temperature dependence of $\Rxx$ at $\nu$=1/2 point to large residual interactions between composite fermions., Comment: 5 pages, 4 Figures

We report the measurements of the de Haas--van Alphen (dHvA) effect for field ranges below and above the metamagnetic transition field (${\mathit{H}}_{\mathit{m}}$) in ${\mathrm{CeRu}}_{2}$${\mathrm{Si}}_{2}$. The dHvA frequency branches and the effective masses ranging from 1.5${\mathit{m}}_{0}$ to 120${\mathit{m}}_{0}$ observed below ${\mathit{H}}_{\mathit{m}}$ agree with the predictions of the itinerant f electron model, whereas those above ${\mathit{H}}_{\mathit{m}}$ can be explained well with the localized f electron model. All the dHvA frequencies change abruptly around ${\mathit{H}}_{\mathit{m}}$. The effective masses decrease considerably around ${\mathit{H}}_{\mathit{m}}$ and then continue to decrease with increasing field.

We have used the magneto-oscillatory behavior of the quasi-two-dimensional orbits in the charge-transfer organic salt (BEDT-TTF${)}_{2}$KHg(SCN${)}_{4}$ to probe its underlying magnetic ground states, which arise from the coexisting quasi-one-dimensional nature of the material. The complex nature of the oscillations results from the field dependence of these states. Our results allow comparison between several competing models which have attempted to describe the unusual properties of this material.

Angle-resolved photoelectron spectroscopy in the Ce $3d\ensuremath{\rightarrow}4f$ excitation region was measured for the paramagnetic state of ${\mathrm{CeRu}}_{2}{\mathrm{Si}}_{2}$, ${\mathrm{CeRu}}_{2}({\mathrm{Si}}_{0.82}{\mathrm{Ge}}_{0.18}{)}_{2}$, and ${\mathrm{LaRu}}_{2}{\mathrm{Si}}_{2}$ to investigate the changes of the $4f$ electron Fermi surfaces around the quantum critical point. While the difference of the Fermi surfaces between ${\mathrm{CeRu}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{LaRu}}_{2}{\mathrm{Si}}_{2}$ was experimentally confirmed, a strong $4f$-electron character was observed in the band structures and the Fermi surfaces of ${\mathrm{CeRu}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{CeRu}}_{2}({\mathrm{Si}}_{0.82}{\mathrm{Ge}}_{0.18}{)}_{2}$, consequently indicating a delocalized nature of the $4f$ electrons in both compounds. The absence of Fermi surface reconstruction across the critical composition suggests that SDW quantum criticality is more appropriate than local quantum criticality in ${\mathrm{CeRu}}_{2}({\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}{)}_{2}$.

We report the pressure-induced superconductivity in the noncentrosymmetric heavy-fermion ${\mathrm{CeRhSi}}_{3}$. The superconductivity emerges above about 12 kbar even though the antiferromagnetic ordering persists. Furthermore, another anomaly is observed in the superconducting phase. The anomalous magnetic field-temperature phase diagram with a high upper critical field suggests that an unconventional superconductivity is realized in ${\mathrm{CeRhSi}}_{3}$.

We have studied the field and spin dependences of the effective masses in ${\mathrm{C}\mathrm{e}\mathrm{I}\mathrm{n}}_{3}$ as a function of pressure via the de Haas--van Alphen (dHvA) effect. The effective mass increases with the field at pressures up to about 10 kbar and then decreases with the field. The spin direction of the dominant dHvA oscillation is likely to be reversed across the same pressure. The dHvA frequency changes significantly at the pressure ${P}_{c}$ for the antiferromagnetic quantum critical point and two neighboring pressures ${P}_{2}$ and ${P}_{4}$ below and above ${P}_{c}$. The spin and field dependences rapidly diminish across ${P}_{c}$ and finally disappear above ${P}_{4}$. These observations are discussed in conjunction with relevant observations and theories.

We report measurements of the de Haas-van Alphen effect in ZrZn 2 under hydrostatic pressures up to 21 kbar where the Curie temperature vanishes. The exchange splitting of a Fermi surface changes in behavior with increasing magnetic field, which is qualitatively consistent with the behavior of the high-field magnetization, suggesting the existence of a crossover between two distinct magnetic states. These and previously unexplained findings may be understood in terms of a p-T-B phase diagram qualitatively similar to that of the ferromagnetic superconductor UGe 2 .

The magnetic structure of the localized-5f uranium intermetallic compound U3Pd20Si6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling.