摘要
研究人员利用偏振超快泵浦-探测光谱，对比研究了常压下双层La3Ni2O7和三层La4Ni3O10单晶的正常态电子动力学。两种材料均表现出密度波转变并伴随准粒子弛豫瓶颈的打开，但其电子响应具有显著不同的对称性：三层La4Ni3O10在整个温区内保持光学各向同性，而双层La3Ni2O7在低温下则展现出明显的二重（C2）旋转对称性破缺，即电子向列性。这种向列性体现在准粒子慢弛豫动力学和有效能隙尺度的各向异性中，并且其在115 K以下与一个次级各向同性序相互竞争，导致向列信号随温度呈非单调变化。该工作揭示了双层镍酸盐中电子向列涨落的存在，而三层体系中并未出现这一现象，暗示了电子向列性与La3Ni2O7高压超导配对之间可能存在的紧密关联，为深入理解这类镍基超导体的微观机制提供了关键信息。
材料
方法
- Polarized ultrafast pump-probe spectroscopy
- Rothwarf-Taylor model fitting
- polarized ultrafast pump-probe spectroscopy
关键词
- electronic nematicity
- density wave transition
- quasiparticle relaxation bottleneck
- twofold rotational symmetry breaking
- c2 symmetry
- c2 anisotropy
亮点
- The presence of macroscopic electronic anisotropy in the bilayer system, and its absence in the trilayer system, suggests an intimate relation between electronic nematic fluctuations and superconducting pairing in La3Ni2O7.
- This nematicity manifests as a significant anisotropy in the slow quasiparticle relaxation dynamics and effective gap scales.
- Electronic nematicity revealed by polarized ultrafast spectroscopy in bilayer La3Ni2O7.
- The twofold anisotropy and competition with isotropic order provide deeper exploration for superconducting pairing.
结论
- La3Ni2O7 exhibits a pronounced rotational-symmetry-breaking electronic response with twofold anisotropy, indicating electronic nematicity.
- The non-monotonic temperature dependence of the nematic signal indicates its competition with a secondary, isotropic density-wave-like order below 115 K.
- La4Ni3O10 maintains a robustly isotropic optical response over the entire temperature range, showing no nematicity.
- La4Ni3O10 maintains an isotropic optical response across the entire temperature range.
- La3Ni2O7 exhibits a pronounced twofold (C2) anisotropy in its low-temperature electronic dynamics.
- This electronic nematicity competes with a secondary isotropic order emerging below 115 K.
- The presence of macroscopic electronic anisotropy in the bilayer system and its absence in the trilayer system suggests an intimate relation between electronic nematic fluctuations and superconducting pairing in La3Ni2O7.
主要论断
- Bilayer La3Ni2O7 exhibits electronic nematicity with twofold (C2) rotational symmetry breaking at low temperatures, while trilayer La4Ni3O10 remains isotropic.
- 证据: Abstract: 'La3Ni2O7 shows clear twofold (C2) rotational symmetry breaking—i.e., electronic nematicity—at low temperatures'
- The nematicity competes with a secondary isotropic order emerging below 115 K, leading to a non-monotonic temperature dependence of the nematic signal.
- 证据: Abstract: 'below 115 K it competes with a secondary isotropic order, leading to a non-monotonic temperature dependence of the nematic signal'
- La3Ni2O7 exhibits a pronounced twofold (C2) anisotropy in its low-temperature electronic dynamics, indicative of electronic nematicity.
- 证据: Normalized transient reflectivity (ΔR/R)_Norm shows clear deviation between φ=0° and φ=90° below T_SDW.,Polar plots of τ_s show isotropic at 160 K, two-fold at 115 K and 70 K.,Difference plot τ_ani = τ_s0 - τ_s90 peaks near 115 K.
- The electronic nematicity in La3Ni2O7 competes with a secondary isotropic order emerging below 115 K.
- 证据: τ_ani shows non-monotonic behavior: increases below T_SDW, peaks near 115 K, then decreases upon further cooling.,Optical measurements report opening of an energy gap below 115 K, possibly associated with CDW order.
- La4Ni3O10 maintains an isotropic optical response across the entire temperature range, showing no rotational symmetry breaking.
- 证据: (ΔR/R)_Norm curves for φ=0° and φ=90° completely overlap at all temperatures.,Polar plots of τ_s remain circular at all measured temperatures (130 K, 115 K, 70 K).
- The presence of electronic nematicity in bilayer La3Ni2O7 and its absence in trilayer La4Ni3O10 suggests an intimate relation between nematic fluctuations and superconducting pairing in La3Ni2O7.
- 证据: Nematicity in iron-based and cuprate superconductors is linked to enhanced Tc near a nematic quantum critical point.,The observed anisotropy is spin-driven (SDW gap) and may provide additional attractive interaction for pairing.
研究流程
- Sample preparation
- 材料: La3Ni2O7 and La4Ni3O10 single crystals
- 方法: Vertical optical image floating-zone method; Cleavage of (001) planes
- 观察: High-quality single crystals with well-defined surfaces
- Ultrafast pump-probe spectroscopy
- 材料: Single crystals
- 方法: Polarized ultrafast pump-probe measurement; Rotation of half-wave plate and polarizer
- 观察: Normalized transient reflectivity along 0° and 90°
- Data analysis — Bilayer exhibits electronic nematicity that competes with isotropic order below 115K
- 材料: Transient reflectivity data
- 方法: Two-exponential decay model; Rothwarf-Taylor model
- 观察: La3Ni2O7 shows C2 rotational symmetry breaking below SDW transition; La4Ni3O10 remains isotropic
- sample_preparation
- 材料: La3Ni2O7 single crystals; La4Ni3O10 single crystals
- 方法: vertical optical image floating-zone method
- measurement
- 材料: single crystals of La3Ni2O7 and La4Ni3O10
- 方法: polarized ultrafast pump-probe spectroscopy
- 观察: normalized transient reflectivity (ΔR/R)_Norm measured as function of delay time; angular dependence of (ΔR/R)_Norm and relaxation times
- analysis
- 材料: measured ΔR/R data
- 方法: two-exponential decay model fitting; Rothwarf-Taylor (RT) model fitting for gap extraction
- 观察: τ_f and τ_s extracted for both polarizations; temperature dependence of τ_f and τ_s; difference plots (ΔR/R)_ani and τ_ani = τ_s0 - τ_s90
- interpretation — La3Ni2O7 exhibits electronic nematicity (C2 rotational symmetry breaking) in its low-temperature electronic dynamics, while La4Ni3O10 remains isotropic.
- 方法: comparison of symmetry properties between La3Ni2O7 and La4Ni3O10; analysis of rotational symmetry using polar plots of τ_s
- 观察: La4Ni3O10: isotropic response across all temperatures; La3Ni2O7: isotropic at high T, pronounced two-fold (C2) anisotropy below T_SDW ≈140K; non-monotonic τ_ani peaking near 115 K, suppressed by secondary isotropic order below 115K