Evidence of a structural quantum critical point in (CaxSr1-x)3Rh4Sn13 from a lattice dynamics study

Authors
Cheung, YW 
Hu, YJ 
Imai, M 
Tanioku, Y 
Kanagawa, H 

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Abstract

Approaching a quantum critical point (QCP) has been an effective route to stabilize superconductivity. While the role of magnetic QCPs has been extensively discussed, similar exploration of a structural QCP is scarce due to the lack of suitable systems with a continuous structural transition that can be conveniently tuned to 0~K. Using inelastic X-ray scattering, we examine the phonon spectrum of the nonmagnetic quasi-skutterudite (CaxSr1−x)3Rh4Sn13, which represents a precious system to explore the interplay between structural instabilities and superconductivity by tuning the Ca concentration x. We unambiguously detect the softening of phonon modes around the M point on cooling towards the structural transition. Intriguingly, at x=0.85, the soft mode energy squared at the M point extrapolates to zero at (−5.7±7.7)~K, providing the first compelling microscopic evidence of a structural QCP in (CaxSr1−x)3Rh4Sn13. The enhanced phonon density-of-states at low energy provides the essential ingredient for realizing strong-coupling superconductivity near the structural QCP.

Publication Date
2018
Online Publication Date
2018-10-04
Acceptance Date
2018-09-21
Keywords
cond-mat.supr-con, cond-mat.supr-con, cond-mat.str-el
Journal Title
Physical Review B
Journal ISSN
2469-9950
2469-9969
Volume Title
98
Publisher
American Physical Society (APS)
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