最近的激光角分辨光电子能谱研究已经建立了一个新的扭结的存在下，在低能量节分散的Bi $_2$ Sr $_2$ CaCu $_2$ O $+{8+δ}$（Bi-2212）。这种扭结的能量尺度（~8-15 meV）出现在超导能隙$δ_0$的最大值以下。因此，很难解释这个特点，在通常的耦合到一个尖锐的色散模式。在本文中，我们研究了电子-声子耦合的面内声学声子支所产生的屏蔽库仑势的调制。我们证明，这种耦合具有较强的前向散射峰，因此，在能量尺度被局部间隙$δ(k)$移动的情况下，色散中发生扭结。此外，考虑减少屏蔽与欠掺杂自然解释了所观察到的低能量扭结的掺杂依赖性。这些结果指向一个强耦合的声学分支，这是在前向散射方向达到峰值，并具有重要意义的运输和配对在高T $_c$铜酸盐。
英文摘要：
Recent laser angle-resolved photoemission spectroscopy studies have established the presence of a new kink in the low-energy nodal dispersion of Bi$_2$Sr$_2$CaCu$_2$O$+{8+δ}$ (Bi-2212). The energy scale (~8-15 meV) of this kink appears below the maximum of the superconducting gap $δ_0$. Therefore it is difficult to interpret this feature in terms of the usual coupling to a sharp dispersionless mode. In this paper we examine electron-phonon coupling to the in-plane acoustic phonon branch arising from the modulation of the screened Coulomb potential. We demonstrate that such a coupling has a strong forward scattering peak, and as a consequence, a kink occurs in the dispersion at an energy scale shifted by the local gap $δ(k)$. In addition, considerations for the reduction of screening with underdoping naturally explains the observed doping dependence of the low-energy kink. These results point to a strong coupling to the acoustic branch which is peaked in the forward scattering direction and has important implications for transport and pairing in the high-T$_c$ cuprates.
A softening of phonon-dispersion has been observed experimentally in under-doped cuprate superconductors at the charge-density wave (CDW) ordering wave vector. Interestingly, the softening occurs below the superconducting (SC) transition temperature T$_{c}$, in contrast to the metallic systems, where the softening occurs usually below the CDW onset temperature T$_{\text{CDW}}$. An understanding of the `anomalous' nature of the phonon-softening and its connection to the pseudo-gap phase in under-doped cuprates remain open questions. Within a perturbative approach, we show that a complex interpl…
Cuprates are promising candidates for study in developing higher temperature superconductors. A thorough understanding of a material's phonon modes enables further investigation of its emergent properties, however, no complete reference of the phonon modes exists. Here, using density functional theory, we evaluate the phonon frequencies and atomic displacements for $\text{La}_2\text{CuO}_4$, $\text{Bi}_2\text{Sr}_2\text{CuO}_6$, and $\text{Bi}_2\text{Sr}_2\text{CaCu}_2\text{O}_8$ in their tetragonal structures. The phonon modes for all materials agree with those expected from space group symme…
Investigation of fermionic pairing on two- dimensional tight binding lattice under phonon and electronic mechanisms within a simple Fermi liquid like scenario and beyond- possible consequences for superconductivity in overdoped cuprates
Distribution function of charge carriers in electron-phonon systems with spontaneously broken translational symmetry and 'vertical dispersion' in ARPES spectra of cuprates
Quantum phase transitions play an important role in shaping the phase diagram of high-temperature cuprate superconductors. These cuprates possess intertwined orders which interact strongly with superconductivity. However, the evidence for the quantum critical point associated with the charge order in the superconducting phase remains elusive. Here we show the short-range charge orders and the spectral signature of the quantum fluctuations in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) near the optimal doping using high-resolution resonant inelastic X-ray scattering. On performing calculations through a dia…
Large isotope effect on $T_c$ in cuprates despite of a small electron-phonon coupling
本文计算了含声子的t-J模型的平均场处理下超导临界温度$T_c$和赝能隙温度$T^\ast$的同位素系数$α$和$α^\ast$。在该模型中，赝能隙相被识别为$d$ -电荷密度波（$d$-CDW）相。使用小的电子-声子耦合常数$λ_d \sim 0.02$之前在LDA计算中获得的YBa $_2$ Cu $_3$ O $_7$，$α^{\ast}$是负的，但可以忽略不计的小，而$α$从最佳掺杂的约0.03增加到小掺杂的约1的值，这与在许多铜酸盐中观察到的一般趋势一致。使用一个简单的相位波动模型，其中的$d$ -CDW只有短程相关，它表明，大的增加$α$在低掺杂是相当普遍的，并不依赖于存在的赝能隙态的态密度的尖峰或特定值的声子截止。它是由$d$-CDW在低频处的频谱权重的大量耗尽引起的，因此也应该发生在伪带隙的其他实现中。
High temperature superconductivity due to the long-range electron-phonon interaction, application to isotope effects, thermomagnetic transport and nanoscale heterogeneity in cuprates
High Tc superconductors show a rich variety of phases associated with their charge degrees of freedom. Valence charges can give rise to charge ordering or acoustic plasmons in these layered cuprate superconductors. While charge ordering has been observed for both hole- and electron-doped cuprates, acoustic plasmons have only been found in electron-doped materials. Here, we use resonant inelastic X-ray scattering (RIXS) to observe the presence of acoustic plasmons in two families of hole-doped cuprate superconductors [La2-xSrxCuO4 (LSCO) and Bi2Sr1.6La0.4CuO6+d (Bi2201)], crucially completing t…
While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wavevectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here we investigate the temperature dependence of the low energy phonons in the canonical CDW ordered cuprate La$_{1.875}$Ba$_{0.125}$CuO$_{4}$. We discover that the phonon softening wavevector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wavevector of 0.238 reciprocal space units (r.l.u.) below the o…
Dynamic charge transfers, or charge fluxes, generated by anharmonic phonon couplings have previously shown some fundamental connections with the pseudogap phase and other important phases in cuprate superconductors. The anharmonicity here suggests the importance of nonadiabatic behaviors of charge fluxes in cuprates. These charge fluxes will result in the dynamic charge transfer that can be directly calculated by the charge difference induced by phonons in density functional theory simulations. However, retrieving the flux field from the calculated charge transfer is nontrivial. In this articl…
