Electron Mass Enhancement near a Nematic Quantum Critical Point in NaFe1−xCoxAs

Abstract

A magnetic order can be completely suppressed at zero temperature (T ), by doping carriers or applying pressure, at a quantum critical point (QCP) , around which physical properties change drastically. However, the situation is unclear for an electronic nematic order that breaks rotation symmetry. Here we report nuclear magnetic resonance (NMR) studies on NaFe 1−x Co x As where magnetic and nematic transitions are well separated. The NMR spectrum is sensitive to inhomogeneous magnetic fields in the vortex state, which is related to London penetration depth λ L that measures the electron mass m * . We discovered two peaks in the doping dependence of λ 2 L (T ∼0); one at x M =0.027 where the spin-lattice relaxation rate shows quantum critical behavior, and another at x c =0.032 around which the nematic transition temperature extrapolates to zero and the electrical resistivity shows a T -linear variation. Our results indicate that a nematic QCP lies beneath the superconducting dome at x c where m * is enhanced. The impact of the nematic fluctuations on superconductivity is discussed.

Resistivity near a nematic quantum critical point: Impact of acoustic phonons

“…Recent experiments in several quantum materials have revealed the widespread presence of electronic nematicity, i.e. the lowering of the crystalline point-group symmetry by electronic degrees of freedom [1][2][3][4][5][6][7][8][9][10][11]. Assessing the impact of these nematic degrees of freedom on the normal-state and superconducting properties of these materials remains an important challenge, particularly near a putative nematic quantum critical point (QCP) [12][13][14][15][16][17][18][19][20].…”

Analysis of the London penetration depth in Ni-doped CaKFe4As4

“…On the other hand, in the clean limit, the absolute value of the London penetration depth depends only on the normal state properties, notably the effective electron mass λ 2 L (0) ∼ m * . Measurements of λ L (0) as a function of doping reveal a peak deep in the superconducting state due to the effective mass enhancement approaching a quantum phase transition [15][16][17][18]. Theoretically, London penetration depth can be computed on quite general grounds using the Eliashberg theory and, reproducing experimental data, one can discuss intrinsic quantities, such as the gap values and the coupling matrix coefficients [19][20][21][22].…”

Recent progress in NMR studies on high-<italic>T</italic><sub>c</sub> superconductors

“…(b) The temperature-dependent anisotropy in the 1/T 1 T is defined as Δ(1/T 1 T)=(1/T 1 T| H||a −1/T 1 T| H||b )/(1/T 1 T| H||a +1/T 1 T| H||b ) [135]. 于上临界磁场B c2 时, 由磁通引起的展宽∆f具体形式如 下 [148] : 磁共振峰, 其中测量温度都是在T=25 K [149] . 由于 [150] .…”

“…Ortho and Tetra denote the orthorhombic and tetragonal crystal structure, respectively. The parameter θ is obtained from the 1/T 1 T data [149]. [109,147] , 在FeSe 1−x S x 中也被强磁场电输运测量确认存 在 [108] , 这说明电子向列序量子临界点可能普遍存在于…”