Related papers: Van Vleck excitons in Ca$_{2}$RuO$_{4}$
High resolution neutron scattering measurements on a single crystal of SrCu(2-x)Mgx(BO3)2 with x=0.05 reveal the presence of new spin excitations within the gap of this quasi-two dimensional, singlet ground state system. Application of a…
TlCuCl$_3$ has a singlet ground state with the excitation gap $\Delta =0.65$ meV. The magnetic excitations in TlCuCl$_3$ have been investigated by means of neutron inelastic scattering experiments. The constant-$\it{\pmb Q}$ energy scan…
The concept of the entanglement between spin and orbital degrees of freedom plays a crucial role in understanding various phases and exotic ground states in a broad class of materials, including orbitally ordered materials and spin liquids.…
Excited states of the hydrogen molecule subject to a homogeneous magnetic field are investigated for the parallel configuration in the complete regime of field strengths B=0-100a.u.. Up to seven excitations are studied for gerade as well as…
We show that, as in Hartree Fock theory, the orbitals for excited state mean field theory can be optimized via a self-consistent one-electron equation in which electron-electron repulsion is accounted for through mean field operators. In…
The one dimensional Heisenberg model in the presence of orbital degeneracy is studied at the SU(4) symmetric viewpoint by means of Bethe ansatz. Following Sutherland's previous work on an equivalent model, we discuss the ground state and…
Artificial moir\'e superlattices in 2d van der Waals heterostructure is a new venue for realizing and controlling correlated electronic phenomena. Recently, twisted bilayer WSe$_2$ emerged as a new robust moir\'e system hosting a correlated…
We use perturbative series expansions about a staggered dimerized ground state to compute the ground state energy, triplet excitation spectra and spectral weight for a one-dimensional model in which each site has an $S=\case 1/2$ spin ${\bf…
When the gauge fields have derivative couplings to scalars, like in the case of the relativistic theory of Van der Waals (or Casimir-Polder) interactions, conformal invariance is broken but the magnetic and electric susceptibilities are not…
Single crystals of the spin-gap system $\rm (VO)_2P_2O_7$ have been investigated by means of Raman scattering. At temperatures below T=75 K~$\approx 2\Delta_{01}({\bf k}=0)$, with $\Delta_{01}$ the singlet-triplet gap, a shoulder appears at…
We present comprehensive electron spin resonance (ESR) studies of in-plane oriented single crystals of $\alpha$-RuCl$_3$, a quasi-two-dimensional material with honeycomb structure, focusing on its high-field spin dynamics. The measurements…
Orbitally degenerate systems provide a promising platform for realizing novel quantum phases driven by spin-orbital exchange interactions, as described by the Kugel-Khomskii model. Spinel vanadates, in which orbital degrees of freedom…
We study the elementary excitations in 5d transition metal oxideSr$_2$IrO$_4$ by calculating the particle-hole Green's function within the random phase approximation on an antiferromagnetic ground state in the two-dimensional multi-orbital…
A spin-rotation symmetry in spin-orbit coupled two-dimensional electron systems gives rise to a long-lived spin excitation that is robust against short-range impurity scattering. The influence of a constant in-plane electric field on this…
The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin…
Investigation of elementary excitations has advanced our understanding of many-body physics governing most physical properties of matter. Recently spin-orbit excitons have drawn much attention, whose condensates near phase transitions…
Theoretical models of the spin-orbital liquid (SOL) FeSc$_2$S$_4$ have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the…
We study the interplay of crystal field splitting and Hund coupling in a two-orbital model which captures the essential physics of systems with two electrons or holes in the e_g shell. We use single site dynamical mean field theory with a…
We report on the magnetic excitation spectrum of the coupled spin tetrahedral system Cu$_{2}$Te$_{2}$O$_{5}$Cl$_{2}$ using Raman scattering on single crystals. The transition to an ordered state at T$_{N}^{Cl}$=18.2 K evidenced from…
The possible role of the van Hove singularity (vHs) in stabilizing the low-temperature orthorhombic (LTO) phase transition in La$_{2-x}$\-Sr$_x$\-CuO$_ 4$ (LSCO) is discussed. It is found that the vHs can drive a structural distortion in…