本文报道了用单晶Raman散射研究耦合自旋四面体体系Cu $_{2}$ Te $_{2}$ O $_{5}$ Cl $_{2}$的磁激发谱。从热力学数据证明T $_{N}^{Cl}$ =18.2 K时向有序状态的转变导致叠加了宽的最大值的不同的低能磁激发的演变。这些模式被归因于具有不同程度的本地化和两个磁振子连续的磁振子。两个模式开发一个实质性的能量转移，降低温度类似的序参量的其他Neel有序系统。其他两种模式只显示出可以忽略不计的温度依赖性和溶解在一个连续的激发在有限的能量的有序温度以上。这些观测结果表明，四面体内部和内部的磁性自由度之间存在微妙的相互作用，并且在描述自旋动力学时单线态波动具有重要意义。
英文摘要：
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 thermodynamic data leads to the evolution of distinct low-energy magnetic excitations superimposed by a broad maximum. These modes are ascribed to magnons with different degree of localization and a two-magnon continuum. Two of the modes develop a substantial energy shift with decreasing temperature similar to the order parameter of other Neel ordered systems. The other two modes show only a negligible temperature dependence and dissolve above the ordering temperature in a continuum of excitations at finite energies. These observations point to a delicate interplay of magnetic inter- and intra-tetrahedra degrees of freedom and an importance of singlet fluctuations in describing a spin dynamics.
We report numerical calculations of the collective excitation spectrum and the speed of sound of the superfluid phase of an atomic Fermi-Fermi mixture of population-imbalanced Lithium-6 and Potassium-40 atoms in a square lattice. It is predicted that in the exotic states of matter, known as the Fulde-Ferrell phase, an anomalous dispersion of the collective modes may be realized at some values of polarization, interacting strength and temperature, i.e. the collective-mode dispersion initially bends upward before bending over as the quasimomentum increases.
The spectrum of collective excitations in Weyl materials is studied by using consistent hydrodynamics. The corresponding framework includes the vortical and chiral anomaly effects, as well as the dependence on the separations between the Weyl nodes in energy $b_0$ and momentum $\mathbf{b}$. The latter are introduced via the Chern-Simons contributions to the electric current and charge densities in Maxwell's equations. It is found that, even in the absence of a background magnetic field, certain collective excitations (e.g. the helicon-like modes and the anomalous Hall waves) are strongly affec…
Collective Spin Excitations in Correlated Moiré Chern Ferromagnets
Condensed Matter Theory Center, Department of Physics, University of Maryland（马里兰大学凝聚态理论中心）；Department of Physics, The University of Texas at Dallas（德克萨斯大学达拉斯分校物理系）
Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La$_{2-x}$Sr$_x$CuO$_4$
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Magnetic collective mode in underdoped cuprates: a phenomenological analysis
动态自旋磁化率相关的欠掺杂铜酸盐内的记忆功能（MeF）的方法进行了分析。一个唯象的阻尼函数结合一个$T$独立的求和规则被用来描述异常的正常状态和超导态的共振峰，特别是它的位置和它的相对强度的正常状态。与随机相位近似的关系进行了讨论。为了与$_2$、$_3$ O $_{6+x}$的非弹性中子散射实验进行比较，将MeF方法推广到双层膜系统，并进行了定量比较。在这种情况下，失踪的综合光谱强度在实验上可访问的能量窗口的问题也进行了讨论。
We theoretically investigate the Heisenberg antiferromagnet on a triangular lattice doped with nonmagnetic impurities. Two nontrivial effects resulting from collective impurity behavior are predicted. The first one is related to presence of uncompensated magnetic moments localized near vacancies as revealed by the low-temperature Curie tail in the magnetic susceptibility. These moments exhibit an anomalous growth with the impurity concentration, which we attribute to the clustering mechanism. In an external magnetic field, impurities lead to an even more peculiar phenomenon lifting the classic…
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We study in detail the transverse collective modes of simple holographic models in presence of electromagnetic Coulomb interactions. We render the Maxwell gauge field dynamical via mixed boundary conditions, corresponding to a double trace deformation in the boundary field theory. We consider three different situations: (i) a holographic plasma with conserved momentum, (ii) a holographic (dirty) plasma with finite momentum relaxation and (iii) a holographic viscoelastic plasma with propagating transverse phonons. We observe two interesting new features induced by the Coulomb interactions: a mo…
Motivated by recent experimental measurements, we study the quasiparticle spectra and the collective excitations in doped Sr$_2$IrO$_4$, in which the interesting interplay between the electronic correlations and strong spin-orbital coupling (SOC) exists. To include the SOC, we use the Hugenholtz diagrams to extend the fluctuation exchange (FLEX) approach to the case where the SU(2) symmetry can be broken. By using this generalized FLEX method, we find a weak pseudogap behavior near $(π,0)$ in the slightly electron-doped system, with the corresponding Fermi arc formed by the partial destruction…
Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator Ta$_2$NiSe$_5$. Below 328 K, we observe the anomalous micrometer-scale propagation of coherent modes at velocities of the order of $\sim10^5$ m/s, which we attribute to the hybridization be…
We study the response of a Dirac fluid to electric fields and thermal gradients at finite wave-numbers and frequencies in the hydrodynamic regime. We find that non-local transport in the hydrodynamic regime is governed by infinite set of kinetic modes that describe non-collinear scattering events in different angular harmonic channels. The scattering rates of these modes $τ_{m}^{-1}$ increase as $\|m\|$, where $m$ labels the angular harmonics. In an earlier publication, we pointed out that this dependence leads to anomalous, Lévy-flight-like phase space diffusion (Phys. Rev. Lett. 123, 195302 …
Recent spectroscopic measurements in a number of strongly correlated metals that exhibit non-Fermi liquid like properties have observed evidence of anomalous frequency and momentum-dependent charge-density fluctuations. Specifically, in the strange metallic regime of the cuprate superconductors, there is a featureless particle-hole continuum exhibiting unusual power-laws, and experiments suggest that the plasmon mode decays into this continuum in a manner that is distinct from the expectations of conventional Fermi liquid theory. Inspired by these new experimental developments, we address the …
Clapping modes, which are relative amplitude and phase modes between two chiral components of Cooper pairs, are bosonic collective modes inherent to chiral superconductors. These modes behave as long-lived bosons with masses smaller than the threshold energy, $2|Δ|$, for decay into unbound fermion pairs. Here, we clarify that the real/imaginary clapping modes in chiral superconductors directly couple to acoustic wave propagation when the weak particle-hole asymmetry of the normal state quasiparticle dispersion is taken into account. The clapping modes driven by an acoustic wave generate an alt…
The charge-density wave (CDW) phase is often accompanied by the condensation of a soft acoustic phonon mode, giving rise to lattice distortion and charge density modulation. This picture was challenged for the recently discovered kagome metal CsV$_3$Sb$_5$, based on the evidence of absence of soft phonons. Here we report the observation of Raman-active CDW amplitude modes in this material, which are collective excitations typically thought to emerge out of frozen soft phonons. The amplitude modes strongly hybridize with other superlattice modes, imparting them with clear temperature-dependent …
