48 research outputs found
Giant stress response of terahertz magnons in a spin-orbit Mott insulator
Open Access funding enabled and organized by Projekt DEAL.Magnonic devices operating at terahertz frequencies offer intriguing prospects for high-speed electronics with minimal energy dissipation However, guiding and manipulating terahertz magnons via external parameters present formidable challenges. Here we report the results of magnetic Raman scattering experiments on the antiferromagnetic spin-orbit Mott insulator Sr2IrO4 under uniaxial stress. We find that the energies of zone-center magnons are extremely stress sensitive: lattice strain of 0.1% increases the magnon energy by 40%. The magnon response is symmetric with respect to the sign of the applied stress (tensile or compressive), but depends strongly on its direction in the IrO2 planes. A theory based on coupling of the spin-orbit-entangled iridium magnetic moments to lattice distortions provides a quantitative explanation of the Raman data and a comprehensive framework for the description of magnon-lattice interactions in magnets with strong spin-orbit coupling. The possibility to efficiently manipulate the propagation of terahertz magnons via external stress opens up multifold design options for reconfigurable magnonic devices.Publisher PDFPeer reviewe
Dependence of T of YBa Cu O on in-plane uniaxial stress
We probe the effect on of in-plane uniaxial stress applied to the high-temperature superconductor . We find a highly anisotropic response. Under compression along the axis, which reduces the orthorhombicity of the planes, is broadly flat for stresses up to at least 1.7 GPa. Under compression along the axis, decreases steeply. For stresses beyond GPa the decrease is quasilinear. We hypothesize that superconductivity is suppressed by competition with uniaxial charge density wave order, which has been found to onset at GPa
Paramagnons and high-temperature superconductivity in a model family of cuprates
Cuprate superconductors have the highest critical temperatures (Tc) at ambient pressure, yet
a consensus on the superconducting mechanism remains to be established. Finding an
empirical parameter that limits the highest reachable Tc can provide crucial insight into this
outstanding problem. Here, in the first two Ruddlesden-Popper members of the model Hg-
family of cuprates, which are chemically nearly identical and have the highest Tc among all
cuprate families, we use inelastic photon scattering to reveal that the energy of magnetic
fluctuations may play such a role. In particular, we observe the single-paramagnon spectra to
be nearly identical between the two compounds, apart from an energy scale difference of
~30% which matches their difference in Tc. The empirical correlation between paramagnon
energy and maximal Tc is further found to extend to other cuprate families with relatively high
Tc’s, hinting at a fundamental connection between them
Resonant Inelastic X-ray Scattering from Electronic Excitations in -RuCl Nanolayers
We present Ru -edge resonant inelastic x-ray scattering (RIXS)
measurements of spin-orbit and d-d excitations in exfoliated nanolayers of the
Kitaev spin-liquid candidate RuCl. Whereas the spin-orbit excitations are
independent of thickness, we observe a pronounced red-shift and broadening of
the d-d excitations in layers with thickness below 7 nm. Aided by model
calculations, we attribute these effects to distortions of the RuCl
octahedra near the surface. Our study paves the way towards RIXS investigations
of electronic excitations in various other 2D materials and heterostructures
Structural, Electronic and Magnetic Properties of a Few Nanometer-Thick Superconducting NdBa₂Cu₃O₇ Films
Abstract: Epitaxial films of high critical temperature (Tc) cuprate superconductors preserve
their transport properties even when their thickness is reduced to a few nanometers. However,
when approaching the single crystalline unit cell (u.c.) of thickness, Tc decreases and eventually,
superconductivity is lost. Strain originating from the mismatch with the substrate, electronic
reconstruction at the interface and alteration of the chemical composition and of doping can be
the cause of such changes. Here, we use resonant inelastic x-ray scattering at the Cu L3 edge to study
the crystal field and spin excitations of NdBa2Cu3O7x ultrathin films grown on SrTiO3, comparing
1, 2 and 80 u.c.-thick samples. We find that even at extremely low thicknesses, the strength of the
in-plane superexchange interaction is mostly preserved, with just a slight decrease in the 1 u.c. with
respect to the 80 u.c.-thick sample. We also observe spectroscopic signatures for a decrease of the
hole-doping at low thickness, consistent with the expansion of the c-axis lattice parameter and oxygen
deficiency in the chains of the first unit cell, determined by high-resolution transmission microscopy
and x-ray diffraction
High Tc superconductivity in superlattices of insulating oxides
We report the occurrence of superconductivity, with maximum Tc = 40 K, in
superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3.
In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block,
which is an antiferromagnetic insulator. Superconductivity, confined within few
unit cells at the CaCuO2/SrTiO3 interface, shows up only when the SLs are grown
in a highly oxidizing atmosphere, because of extra oxygen ions entering at the
interfaces. Evidence is reported that the hole doping of the CuO2 planes is
obtained by charge transfer from the interface layers, which act as charge
reservoir.Comment: 18 pages, 8 figure