Evening out the spin and charge parity to increase T$_c$ in unconventional superconductor Sr_{2}RuO_{4}

Abstract

Unconventional superconductivity in Sr 2 RuO 4 has been intensively studied for decades. The origin and nature of the pairing continues to be widely debated, in particular, the possibility of a triplet origin of Cooper pairs. However, complexity of Sr 2 RuO 4 with multiple low-energy scales, involving subtle interplay among spin, charge and orbital degrees of freedom, calls for advanced theoretical approaches which treat on equal footing all electronic effects. Here we develop a novel approach, a detailed ab initio theory, coupling quasiparticle self-consistent GW approximation with dynamical mean field theory (DMFT), including both local and non-local correlations. We report that the superconducting instability has multiple triplet and singlet components. In the unstrained case the triplet eigenvalues are larger than the singlets. Under uniaxial strain, the triplet eigenvalues drop rapidly and the singlet components increase. This is concomitant with our observation of spin and charge fluctu-1

Magnetic response of Sr2RuO4 : Quasi-local spin fluctuations due to Hund's coupling

“…In contrast, these approximations yield an enhanced response at the X point and fail to account for the quasi-local response. The latter was not discussed in previous DMFT work [27], but noted in a recent DMFT+GW calculation [29]. Both the quasi-local response and the suppression of the X-point fluctuations are in qualitative agreement with the recent INS experiments [10].…”

“…A successful description of an extensive set of physical properties of Sr 2 RuO 4 has been obtained following this picture, supported by quantitative dynamical mean-field (DMFT) calculations. This includes the large mass enhancements of quasiparticles observed in de Haas-van Alphen experiments [17] and angle resolved photo-emission spectroscopy [18], as well as quasi-particle weights and lifetimes [15], nuclear magnetic resonance [15], optical conductivity [19,20], thermopower [21], Hall coefficient [22], quasiparticle dispersions [23][24][25], and magnetic response [26][27][28][29].…”

Consistent partial bosonization of the extended Hubbard model

“…Especially, it is an important problem for description of spin fluctuations and magnetic polarization in realistic systems [69,70] as they are not captured by a standard GW+DMFT scheme [35][36][37][38][39][40][41]. While the use of the fermion-boson vertex in a diagrammatic solution of multiband problems is possible [44], an inclusion of the fermion-fermion vertex in realistic calculations is extremely challenging and time consuming numerically [29][30][31][32][33][34]. The fermion-fermion vertex describes the full (renormalized) local fermion-fermion interaction, so it cannot be simply discarded.…”

“…For this reason, a number of proposed approaches that treat many-body excitations beyond DMFT grows as fast as a degree of their complexity [28]. These new methods provide a very accurate solution of model (single-band) problems, but are numerically very expensive for realistic multiband calculations [29][30][31][32][33][34].…”

Possible 3D nematic odd-parity pairing in Sr$_2$RuO$_4$: experimental evidences and predictions

“…For example, the indications of line-nodal gap structure [85][86][87] is inconsistent with the point-nodes of a simple nematic state. However, the highly anisotropic electronic structure could in principle generate line nodes unrelated to symmetry [21,88,89], or simply deep gap minima [54,90,91]. Nonetheless, more measurements, such as those proposed in Ref.…”