RESUMEN
We investigate magnetic excitations in the spin-ladder compound Sr_{14}Cu_{24}O_{41} using high-resolution Cu L_{3} edge resonant inelastic x-ray scattering (RIXS). Our findings demonstrate that RIXS couples to two-triplon collective excitations. In contrast to inelastic neutron scattering, the RIXS cross section changes only moderately over the entire Brillouin zone, revealing high sensitivity also at small momentum transfers, allowing determination of the two-triplon energy gap as 100 +/- 30 meV. Our results are backed by calculations within an effective Hubbard model for a finite-size cluster, and confirm that optical selection rules are obeyed for excitations from this spherically symmetric quantum spin-liquid ground state.
RESUMEN
We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material (C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered phase and at high fields in the saturated phase contrast sharply with a spinon continuum at intermediate fields characteristic of the Luttinger-liquid phase. By tuning the magnetic field, we drive the fractionalization of magnons into spinons and, in this deconfined regime, observe both commensurate and incommensurate continua.
RESUMEN
The phase diagram in temperature and magnetic field of the metal-organic, two-leg, spin-ladder compound (C5H12N)2CuBr4 is studied by measurements of the specific heat and the magnetocaloric effect. We demonstrate the presence of an extended spin Luttinger-liquid phase between two field-induced quantum critical points and over a broad range of temperature. Based on an ideal spin-ladder Hamiltonian, comprehensive numerical modeling of the ladder specific heat yields excellent quantitative agreement with the experimental data across the entire phase diagram.
RESUMEN
Various nerve conduction velocities, the terminal latency (TL) of facial nerve, the trigeminofacial reflex and fast auditory evoked potentials (FAEP) were investigated in 26 patients with peroneal muscular atrophy (22 with HMSN I and 4 with HMSN II). With the brain nerve status revealing no clinical abnormalities, 85.7% of HMSN I patients showed a longer-than-normal TL of the facial nerve, 66.6% had a prolonged early reflex component of trigeminofacial reflex and 22.7% pathological FAEPs. Normal neurophysiologic findings were obtained for brain nerves of HMSN II subjects. Subclinical involvement of the mid-group of brain nerves did not at all correlate with the impairment of extremity nerves and the duration of the disease. The present results reflect the heterogeneity of HMSN.
