176 research outputs found
Berezinskii-Kosterlitz-Thouless Type Scenario in Molecular Spin Liquid CrO
The spin relaxation in chromium spinel oxides CrO ( Mg,
Zn, Cd) is investigated in the paramagnetic regime by electron spin resonance
(ESR). The temperature dependence of the ESR linewidth indicates an
unconventional spin-relaxation behavior, similar to spin-spin relaxation in the
two-dimensional (2D) chromium-oxide triangular lattice antiferromagnets. The
data can be described in terms of a generalized Berezinskii-Kosterlitz-Thouless
(BKT) type scenario for 2D systems with additional internal symmetries. Based
on the characteristic exponents obtained from the evaluation of the ESR
linewidth, short-range order with a hidden internal symmetry is suggested.Comment: 7 pages, 4 figure
Nanoscale electronic inhomogeneity in FeSe0.4Te0.6 revealed through unsupervised machine learning
We report on an apparent low-energy nanoscale electronic inhomogeneity in FeSe0.4Te0.6 due to the distribution of selenium and tellurium atoms revealed through unsupervised machine learning. Through an unsupervised clustering algorithm, characteristic spectra of selenium- and tellurium-rich regions are identified. The inhomogeneity linked to these spectra can clearly be traced in the differential conductance and is detected both at energy scales of a few electron volts as well as within a few millielectronvolts of the Fermi energy. By comparison with ARPES, this inhomogeneity can be linked to an electron-like band just above the Fermi energy. It is directly correlated with the local distribution of selenium and tellurium. There is no clear correlation with the magnitude of the superconducting gap, however the height of the coherence peaks shows significant correlation with the intensity with which this band is detected, and hence with the local chemical composition.PostprintPeer reviewe
Evidence for Orbital Order and its Relation to Superconductivity in FeSe0.4Te0.6
The emergence of nematic electronic states accompanied by a structural phase
transition is a recurring theme in many correlated electron materials,
including the high-temperature copper oxide- and iron-based superconductors. We
provide evidence for nematic electronic states in the iron-chalcogenide
superconductor FeSe0.4Te0.6 from quasi-particle scattering detected in
spectroscopic maps. The symmetry-breaking states persist above Tc into the
normal state. We interpret the scattering patterns by comparison with
quasi-particle interference patterns obtained from a tight-binding model,
accounting for orbital ordering. The relation to superconductivity and the
influence on the coherence length are discussed.Comment: 5 pages, 5 figures, updated with published versio
Thermal decomposition of the Kitaev material α−RuCl3 and its influence on low-temperature behavior
We explore the effect of heat treatment in argon atmosphere under various temperatures up to 500∘C on single crystals of α−RuCl3 by the study of the mass loss, microprobe energy-dispersive x-ray spectroscopy, powder x-ray diffraction, and electrical resistance, as well as low-temperature magnetic susceptibility and specific heat. Clear signatures of dechlorination and oxidation of Ru appear for annealing temperatures beyond 300∘C. Analysis of the specific heat below 2 K reveals a RuO2 mass fraction of order 1% for pristine α−RuCl3 which increases up to 20% after thermal annealing, fully consistent with mass-loss analysis. The small RuO2 inclusions drastically reduce the global electrical resistance and may thus significantly affect low-temperature thermal transport and Hall effect
Atomic-scale coexistence of short-range magnetic order and superconductivity in FeSeTe
The ground state of the parent compounds of many high temperature
superconductors is an antiferromagnetically (AFM) ordered phase, where
superconductivity emerges when the AFM phase transition is suppressed by doping
or application of pressure. This behaviour implies a close relation between the
two orders. Understanding the interplay between them promises a better
understanding of how the superconducting condensate forms from the AFM ordered
background. Here we explore this relation in real space at the atomic scale
using low temperature spin-polarized scanning tunneling microscopy (SP-STM) and
spectroscopy. We investigate the transition from antiferromagnetically ordered
via the spin glass phase in
to superconducting
. In
we observe an
atomic-scale coexistence of superconductivity and short-ranged bicollinear
antiferromagnetic order.Comment: 7 pages, 6 figure
Orbital Freezing in FeCr2S4 Studied by Dielectric Spectroscopy
Broadband dielectric spectroscopy has been performed on single-crystalline
FeCr2S4 revealing a transition into a low-temperature orbital glass phase and
on polycrystalline FeCr2S4 where long-range orbital order is established via a
cooperative Jahn-Teller transition. The freezing of the orbital moments is
revealed by a clear relaxational behavior of the dielectric permittivity, which
allows a unique characterization of the orbital glass transition. The orbital
relaxation dynamics continuously slows down over six decades in time, before at
the lowest temperatures the glass transition becomes suppressed by quantum
tunneling.Comment: 4 pages, 4 figure
High-resolution neutron depolarization microscopy of the ferromagnetic transitions in NiAl and HgCrSe under pressure
We performed neutron imaging of ferromagnetic transitions in NiAl and
HgCrSe crystals. These neutron depolarization measurements revealed
bulk magnetic inhomogeneities in the ferromagnetic transition temperature with
spatial resolution of about 100~m. To obtain such spatial resolution, we
employed a novel neutron microscope equipped with Wolter mirrors as a neutron
image-forming lens and a focusing neutron guide as a neutron condenser lens.
The images of NiAl show that the sample does not homogeneously go through
the ferromagnetic transition; the improved resolution allowed us to identify a
distribution of small grains with slightly off-stoichiometric composition.
Additionally, neutron depolarization imaging experiments on the chrome spinel,
HgCrSe, under pressures up to 15~kbar highlight the advantages of the
new technique especially for small samples or sample environments with
restricted sample space. The improved spatial resolution enables one to observe
domain formation in the sample while decreasing the acquisition time despite
having a bulky pressure cell in the beam
Interplay between Superconductivity and Magnetism in Rb0.8Fe1.6Se2 under Pressure
High-pressure magnetization, structural and 57Fe M\"ossbauer studies were
performed on superconducting Rb0.8Fe1.6Se2.0 with Tc = 32.4 K. The
superconducting transition temperature gradually decreases on increasing
pressure up to 5.0 GPa followed by a marked step-like suppression of
superconductivity near 6 GPa. No structural phase transition in the Fe
vacancy-ordered superstructure is observed in synchrotron XRD studies up to
15.6 GPa, while the M\"ossbauer spectra above 5 GPa reveal the appearance of a
new paramagnetic phase and significant changes in the magnetic and electronic
properties of the dominant antiferromagnetic phase, coinciding with the
disappearance of superconductivity. These findings underline the strong
correlation between antiferromagnetic order and superconductivity in
phase-separated AxFe2-x/2Se2 (A = K, Rb, Cs) superconductors
Magnetic Excitations in the Multiferroic N\'eel-type Skyrmion Host GaVS
Broadband microwave spectroscopy has been performed on single-crystalline
GaVS, which exhibits a complex magnetic phase diagram including
cycloidal, N\'eel-type skyrmion lattice, as well as field-polarized
ferromagnetic phases below 13 K. At zero and small magnetic fields two
collective modes are found at 5 and 15 GHz, which are characteristic of the
cycloidal state in this easy-axis magnet. In finite fields, entering the
skyrmion lattice phase, the spectrum transforms into a multi-mode pattern with
absorption peaks near 4, 8, and 15 GHz. The spin excitation spectra in
GaVS and their field dependencies are found to be in close relation to
those observed in materials with Bloch-type skyrmions. Distinct differences
arise from the strong uniaxial magnetic anisotropy of GaV4S8 not present in
so-far known skyrmion hosts
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