44 research outputs found
Interplay of electronic correlations and lattice instabilities in BaVS3
The quasi-one-dimensional metallic system BaVS3 with a metal-insulator
transition at T_MI=70 K shows large changes of the optical phonon spectrum, a
central peak, and an electronic Raman scattering continuum that evolve in a
three-step process. Motivated by the observation of a strongly fluctuating
precursor state at high temperatures and orbital ordering and a charge gap at
low temperatures we suggest a concerted action of the orbital, electronic, and
lattice subsystems dominated by electronic correlations.Comment: 4 pages, 4 figure
Interplay of thermal and quantum spin fluctuations on the kagome lattice
We present a Raman spectroscopic investigation of the Herbertsmithite
ZnCu3(OH)6Cl2, the first realization of a Heisenberg s=1/2 antiferromagnet on a
perfect kagome lattice. The magnetic excitation spectrum of this compound is
dominated by two components, a high temperature quasi elastic signal and a low
temperature, broad maximum. The latter has a linear low energy slope and
extends to high energy. We have investigated the temperature dependence and
symmetry properties of both signals. Our data agree with previous calculations
and point to a spin liquid ground state.Comment: 5 figure
Crossover from coherent to incoherent scattering in spin-orbit dominated Sr2IrO4
Strong spin-orbit interaction in the two dimensional compound Sr2IrO4 leads
to the formation of Jeff=1/2 isospins with unprecedented dynamics. In Raman
scattering a continuum attributed to double spin scattering is observed. With
higher excitation energy of the incident Laser this signal crosses over to an
incoherent background. The characteristic energy scale of this cross over is
identical to that of intensity resonance effects in phonon scattering. It is
related to exciton-like orbital excitations that are also evident in resonant
X-Ray scattering. The crossover and evolution of incoherent excitations are
proposed to be due to their coupling to spin excitations. This signals a
spin-orbit induced entanglement of spin, lattice and charge degrees of freedoms
in Sr2IrO4.Comment: 20 pages, 7 figure
Spatially resolved penetration depth measurements and vortex manipulation in the ferromagnetic superconductor ErNi2B2C
We present a local probe study of the magnetic superconductor,
ErNiBC, using magnetic force microscopy at sub-Kelvin temperatures.
ErNiBC is an ideal system to explore the effects of concomitant
superconductivity and ferromagnetism. At 500 mK, far below the transition to a
weakly ferromagnetic state, we directly observe a structured magnetic
background on the micrometer scale. We determine spatially resolved absolute
values of the magnetic penetration depth and study its temperature
dependence as the system undergoes magnetic phase transitions from paramagnetic
to antiferromagnetic, and to weak ferromagnetic, all within the superconducting
regime. In addition, we estimate the absolute pinning force of Abrikosov
vortices, which shows a position- and temperature dependence as well, and
discuss the possibility of the purported spontaneous vortex formation
Linear scaling relationship of N\'{e}el temperature and dominant magnons in pyrochlore ruthenates
We present a systematic Raman spectroscopy study on a series of pyrochlore
ruthenates, a system which is not yet clearly settled on its magnetic origin
and structure. Apart from the Raman-active phonon modes, new peaks that appear
in the energy range of 15 - 35 meV below the N\'{e}el temperature are assigned
as one-magnon modes. The temperature evolution of one-magnon modes displays no
significant thermal dependence in mode frequencies while the intensities
decrease monotonically. Remarkably, one-magnons from all compounds show similar
characteristics with a single dominant peak at lower energy and weaker side
peaks at a couple of meV higher energy. Most importantly, we uncover a striking
proportionality between the dominant magnon mode energies and the N\'{e}el
temperatures. Our results suggest the Ru ions may have similar or the same
magnetic phase in all pyrochlore ruthenates of our study. We have thus found an
avenue for directly tuning the magnetic exchange interaction by the selection
of the -site ion
Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: the Cr based dimer system Sr3Cr2O8
We report on an extended fluctuation regime in the spin dimer system Sr3Cr2O8
based on anomalies in Raman active phonons and magnetic scattering. The
compound has two characteristic temperatures, TS = 275 K, related to a
Jahn-Teller transition with structural distortions and orbital ordering and a
second, T*= 150 K, which is due to further changes in the orbital sector. Below
TS quasielastic scattering marks strong fluctuations and in addition phonon
anomalies are observed. For temperatures below T* we observe an exponential
decrease of one phonon linewidth and determine a gap of the orbital
excitations. At low temperatures the observation of two- and three-magnon
scattering allows the determination of the spin excitation gap.Comment: 7 pages, 4 figures, 1 tabl