ﻻ يوجد ملخص باللغة العربية
The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart of the mystery of the cuprates cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}. In bulk cuprates such as LCO{}, the presence of a weak interlayer coupling stabilizes 3D N{e}el order up to high temperatures. In a truly 2D system however, thermal spin fluctuations melt long range order at any finite temperature cite{Mermin1966}. Further, quantum spin fluctuations transfer magnetic spectral weight out of a well-defined magnon excitation into a magnetic continuum, the nature of which remains controversial cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the spin response of emph{isolated one-unit-cell thick layers} of LCO{}. We show that coherent magnons persist even in a single layer of LCO{} despite the loss of magnetic order, with no evidence for resonating valence bond (RVB)-like spin correlations cite{Anderson1987,Hsu1990,Christensen2007}. Thus these excitations are well described by linear spin wave theory (LSWT). We also observe a high-energy magnetic continuum in the isotropic magnetic response. This high-energy continuum is not well described by 2 magnon LSWT, or indeed any existing theories.
We use femtosecond resonant soft x-ray scattering to measure the ultrafast optical melting of charge-order correlations in La$_{1.875}$Ba$_{0.125}$CuO$_4$. By analyzing both the energy-resolved and energy-integrated order parameter dynamics, we find
Charge order is universal among high-T$_c$ cuprates but its relevance to superconductivity is not established. It is widely believed that, while static order competes with superconductivity, dynamic order may be favorable and even contribute to Coope
The magnetic excitations in the cuprate superconductors might be essential for an understanding of high-temperature superconductivity. In these cuprate superconductors the magnetic excitation spectrum resembles an hour-glass and certain resonant magn
The transition temperature $T_textrm{c}$ of unconventional superconductivity is often tunable. For a monolayer of FeSe, for example, the sweet spot is uniquely bound to titanium-oxide substrates. By contrast for La$_{2-mathrm{x}}$Sr$_mathrm{x}$CuO$_4
Kitaev interactions underlying a quantum spin liquid have been long sought, but experimental data from which their strengths can be determined directly is still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality