Incommensurate Phonon Anomaly and the Nature of Charge Density Waves in Cuprates

Abstract

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 La1.875Ba0.125CuO4. We discover that the phonon softening wavevector associated with CDW correlations becomes temperature dependent in the hightemperature precursor phase and changes from a wavevector of 0.238 reciprocal space units (r.l.u.) below the ordering transition temperature up to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that "214"-type cuprates can host CDW correlations at a similar wavevector to previously reported CDW correlations in non-"214"-type cuprates such as YBa2Cu3O 6+δ . This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low temperature ordering wavevectors. arXiv:1712.04554v2 [cond-mat.supr-con]

Formation of Incommensurate Charge Density Waves in Cuprates

“…While unidirectional charge density waves (CDWs), also known as stripes, have been theoretically predicted for doped Mott insulators [3][4][5][6] and experimentally discovered in La-based cuprates over two decades ago [7], a full CDW phase diagram for different cuprate systems, as shown schematically in Fig. 1(a), was only established very recently [8][9][10][11][12][13][14][15][16][17][18]. Consistent results are also found in state-of-the-art numerical calculations of realistic 2D t − J and Hubbard models near 1/8 doping, where stripe ordering or fluctuations are found to be one of the leading electronic instabilities of the ground state [19][20][21].…”

“…In this picture, when both CDW and SDW are static, the CDW wavevector is expected to follow the SDW with a simple |Q CDW | = 2δ SDW relation that is observed in Labased cuprates at low temperature and reconfirmed in our RIXS study. When the SDW is dynamic with a spin gap and no magnetic Bragg peak, the CDW wavevector is expected to unlock from the spin correlations with nearly degenerate wavevectors [16,17,20,21,36]. In the FS-based mechanism, the CDW is determined by FS portions with large density-of-states (DOS), and the free energy is minimized by reducing the DOS near the FS.…”

Orbital Symmetry and Orbital Excitations in High-Tc Superconductors

“…These phenomena follow in a natural way from orbital pseudo-degeneracy [57], and these ideas were further developed in [58][59][60][61][62]. Support for the relevance of electron-phonon interaction comes from the observation of the isotope effect on the pseudogap temperature T * [63], from strong renormalization of certain phonons by doped holes [64], and from recently observed phonon anomalies in charge density wave states in cuprates [65,66].…”

Phononic Helical Nodal Lines with PT Protection in MoB2

“…where Q = q + τ , q, and τ are the total momentum transfer, reduced momentum transfer in the first BZ and the reciprocal lattice vector, respectively. ω qj is the jth energy of phonon mode at momentum q [34,35]. |F (τ, q, j)| 2 is given by…”

“…Having experimentally established the topologically non-trivial band crossings along the high-symmetry lines, S(q,ω) (Counts/sec) 35 30 25 Energy (meV) #1 #2 #3 (7,7,7) (8,8,8) (7,7,7) (7,7.5,6.5) (7.5,7.5,7.5) (7.5,8,7)…”