Charge-induced nematicity in FeSe

Abstract

The spontaneous appearance of nematicity, a state of matter that breaks rotation but not translation symmetry, is one of the most intriguing properties of the iron-based superconductors (Fe SC), and has relevance for the cuprates as well. Establishing the critical electronic modes behind nematicity remains a challenge, however, because their associated susceptibilities are not easily accessible by conventional probes. Here, using FeSe as a model system, and symmetry-resolved electronic Raman scattering as a probe, we unravel the presence of critical charge nematic fluctuations near the structural/nematic transition temperature, T S ∼ 90 K. The diverging behavior of the associated nematic susceptibility foretells the presence of a Pomeranchuk instability of the Fermi surface with d-wave symmetry. The excellent scaling between the observed nematic susceptibility and elastic modulus data demonstrates that the structural distortion is driven by this d-wave Pomeranchuk transition. Our results make a strong case for chargeinduced nematicity in FeSe.nematicity | superconductivity | Raman scattering

Nematic fluctuations and phase transitions in LaFeAsO: A Raman scattering study

“…3(a,c)) are consistent with 75 As NMR measurements that show coexisting AFM and paramagnetic regions in this T -interval , [40]; the paramagnetic regions are expected to host the residual nematic fluctuations observed here. Intriguingly, the temperature where the QEP area and height are maxima, T max , does not coincide with the bulk-average T S , contrary to other parent FeSCs [4,26]. This deviation is likely related to the broad T interval where tetragonal and orthorhombic domains coexist and fluctuate [41].…”

“…In A(Fe 1−x Co x ) 2 As 2 (A = Ca, Sr, Ba, Eu) [1, 4,19,21,22,24,25], Ba 1−p K p Fe 2 As 2 [25], FeSe [26,27] and NaFe 1−x Co x As [28], a quasi-elastic peak (QEP) with B 2g symmetry (considering the 2 Fe tetragonal cell, see Fig. 1(a)) has been observed and interpreted in terms of either charge/orbital [21,22,24,26,29] or spin [4,25,30,31] nematic fluctuations. An unambiguous experimental identification of the nature of the fluctuations generating the B 2g Raman QEP (charge/orbital or magnetic) is challenging due to the inherent coupling between the corresponding degrees of freedom.…”

“…R a m a n S h i f t ( c m -1 ) As for the other FeSCs [4,21,22,[24][25][26][29][30][31], we ascribe the B 2g QEP in LFAO to electronic nematic fluctuations. In principle, the Raman intensity may be dominated either by charge/orbital or spin nematic fluctuations.…”

Fermi Surface, Pressure-Induced Antiferromagnetic Order, and Superconductivity in FeSe

“…13) The enhancement explains the elastic constants in ultrasonic experiments 19) and the susceptibility in Raman scattering experiments. 20) In Sect. 3, we present the pressure dependence of the spin and orbital fluctuations and the superconductivity using the RPA calculation.…”

Possible nematic spin liquid in spin-1 antiferromagnetic system on the square lattice: Implications for the nematic paramagnetic state of FeSe

“…Besides, FeSe possesses an electronic nematic order after a tetragonal-to-orthorhombic structural transition at T s 90K [19][20][21][22] . Although the primary origin of this nematic order is still unclear [23][24][25][26][27][28][29][30][31][32][33][34] , neutron scattering measurements indicate the important role of spin degree of freedom 24,25 . These novel properties have triggered wide interests in the magnetic ground state of FeSe [35][36][37][38][39][40][41][42][43][44][45] .…”