Lattice-shifted nematic quantum critical point in FeSe1−xSx

AbstractWe report the evolution of nematic fluctuations in FeSe1−xSx single crystals as a function of Sulfur content x across the nematic quantum critical point (QCP) xc ~ 0.17 via Raman scattering. The Raman spectra in the B1g nematic channel consist of two components, but only the low energy one displays clear fingerprints of critical behavior and is attributed to itinerant carriers. Curie–Weiss analysis of the associated nematic susceptibility indicates a substantial effect of nemato-elastic coupling, which shifts the location of the nematic QCP. We argue that this lattice-induced shift likely explains the absence of any enhancement of the superconducting transition temperature at the QCP. The presence of two components in the nematic fluctuations spectrum is attributed to the dual aspect of electronic degrees of freedom in Hund’s metals, with both itinerant carriers and local moments contributing to the nematic susceptibility.

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First-Order Superconducting Transition near a Ferromagnetic Quantum Critical Point

Physical Review Letters ◽

10.1103/physrevlett.90.077002 ◽

2003 ◽

Vol 90 (7) ◽

Cited By ~ 54

Author(s):

Andrey V. Chubukov ◽

Alexander M. Finkel’stein ◽

Robert Haslinger ◽

Dirk K. Morr

Keyword(s):

Critical Point ◽

Quantum Critical Point ◽

Superconducting Transition ◽

First Order ◽

Quantum Critical

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Superconductivity mediated by polar modes in ferroelectric metals

Nature Communications ◽

10.1038/s41467-020-18438-0 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

C. Enderlein ◽

J. Ferreira de Oliveira ◽

D. A. Tompsett ◽

E. Baggio Saitovitch ◽

S. S. Saxena ◽

...

Keyword(s):

Critical Point ◽

Energy Gap ◽

Quantum Critical Point ◽

Quantitative Model ◽

Superconducting Transition ◽

Pairing Interaction ◽

Optimal Doping ◽

Occurrence Of Superconductivity ◽

Quantum Critical ◽

Dynamical Screening

Abstract The occurrence of superconductivity in doped SrTiO3 at low carrier densities points to the presence of an unusually strong pairing interaction that has eluded understanding for several decades. We report experimental results showing the pressure dependence of the superconducting transition temperature, Tc, near to optimal doping that sheds light on the nature of this interaction. We find that Tc increases dramatically when the energy gap of the ferroelectric critical modes is suppressed, i.e., as the ferroelectric quantum critical point is approached in a way reminiscent to behaviour observed in magnetic counterparts. However, in contrast to the latter, the coupling of the carriers to the critical modes in ferroelectrics is predicted to be small. We present a quantitative model involving the dynamical screening of the Coulomb interaction and show that an enhancement of Tc near to a ferroelectric quantum critical point can arise due to the virtual exchange of longitudinal hybrid-polar-modes, even in the absence of a strong coupling to the transverse critical modes.

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Quantum critical point in the superconducting transition on the surface of a topological insulator

Physical Review B ◽

10.1103/physrevb.90.054517 ◽

2014 ◽

Vol 90 (5) ◽

Cited By ~ 11

Author(s):

Dingping Li ◽

Baruch Rosenstein ◽

B. Ya. Shapiro ◽

I. Shapiro

Keyword(s):

Critical Point ◽

Topological Insulator ◽

Quantum Critical Point ◽

Superconducting Transition ◽

Quantum Critical

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SUPERFLUID TO BOSE METAL TRANSITION IN SYSTEMS WITH RESONANT PAIRING

International Journal of Modern Physics B ◽

10.1142/s0217979208050139 ◽

2008 ◽

Vol 22 (25n26) ◽

pp. 4379-4385

Author(s):

JULIUS RANNINGER

Keyword(s):

Critical Point ◽

Exchange Coupling ◽

Degrees Of Freedom ◽

Fundamental Problem ◽

Spatial Scales ◽

Phase Locking ◽

Quantum Critical Point ◽

Zero Temperature ◽

Pair Exchange ◽

Quantum Critical

Experiments in thin films whose thickness can be modified and by this way induce a superconductor to insulator transition, seem to suggest that in the quantum critical regime of this phase transition there might be a Bose metal, i.e., uncondensed bosonic carriers with a finite dissipation. This poses a fundamental problem as to our understanding of how such a state could be justified. On the basis of a simple Boson-Fermion model, where bosonic and fermionic degrees of freedom are strongly inter-related via a Boson-Fermion pair exchange coupling g, we illustrate how such a bosonic metal phase could possibly come about. We show that, as we approach the quantum critical point at some critical gc from the superfluid side, the superfluid phase locking is sustained only for longer and longer spatial scales. On a finite spatial scale, the boson have a quasi-free itinerant behavior with metallic features. At the quantum critical point the systems exhibits a phase separation which shows a ressemblance to that of a He 3– He 4 mixture. This could be the clue to the apparent dilemma of a Bose metal at zero temperature.

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