A nodeless superconducting gap in Sr₂RuO₄from tunneling spectroscopy

Abstract

Abstract. We report on tunneling spectroscopy measurements using a scanning tunneling microscope (STM) on the spin triplet superconductor Sr 2 RuO 4 . A fully open gap, close to the Bardeen-Cooper-Schrieffer (BCS) value, is found, which disappears at the bulk T c = 1.5 K. The results are discussed in the framework of recent multigap scenarios for an unconventional spin triplet superconductor.

Impurity Effect as a Probe of the Pairing Symmetry in BiS2-Based Superconductors

“…As one can see, the LDOS spectrum in the bulk is also V-shaped with nodal characteristics. Previously, a fully nodeless SC gap was found in the Sr 2 RuO 4 superconductors from the scanning tunnelling microscopy experiments 57 , which is quite different from our result. This is most due to its complex paring symmetry without nodes at the Fermi surface, i.e., sinp x +isinp y wave or sin(p x +p y )+isin(−p x +p y ) wave 58 .…”

Is the anisotropy of the upper critical field of Sr2RuO4consistent with a helicalp-wave state?

“…Thus, the thermodynamic zero-field specific heat measurements appear to be in direct conflict with the field-dependent thermodynamic specific heat and magnetization measurements of the upper critical field [12][13][14]19]. Further calculations to try to fit the excellent scanning tunneling microscopy results of Suderow et al with a p-wave order parameter are also needed [25]. A point node in a helical p-wave order parameter might smear the sharp density of states walls they observed, but an accurate calculation is needed to quantify this possible disagreement.…”

“…Although introducing a multi-component order parameter seems rather unconvincing that it might apply to all cases [21,22], it might be relevant to the chiralnonchiral transition in vortex states [23,24] or even to the first-order transition to the normal state [14]. Further complicating matters, one set of scanning tunneling microscopy (STM) experiments was consistent with a single nodeless gap on all three Fermi surfaces of Sr 2 RuO 4 [25], but in another STM experiment, the tip was placed in a spot with substantial normal regions for T ≪ T c [26], completely disguising any possible superconducting order parameter form. To gain a possibly consistent interpretation to all pieces of experimental evidence, it appears indispensable to introduce a new mechanism to describe the nontrivial interaction between spin-triplet superconductivity and H. Beforehand, one could nevertheless assume that the Pauli limit was essential to determine the in-plane H c2,ab .…”

First-order chiral to non-chiral transition in the angular dependence of the upper critical induction of the Scharnberg–Klemmp-wave pair state

“…Since UCoGe is orthorhombic, the ellipsoidal FS model is the best that can be made without additional features such as magnetic pairing fluctuation effects and B dependencies of the pairing interactions 37 , or B-dependent interactions 38 , etc. For tetragonal Sr 2 RuO 4 , the lack of any detectable ferromagnetism strongly suggests weak coupling interactions, but there are three barrel shaped FSs, and the STM experiments strongly suggest nearly equal isotropic gaps on each 18 . Although one could envision a scenario in which one FS dominated B c2 (0 • , φ, T ) and another dominated B c2 (90…”

“…Recently, there has been a great deal of interest in pwave superconductivity [1][2][3][4][5][6][7][8][9][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . The most likely candidate p-wave superconductors are the ferromagnetic superconductors UGe 2 , UCoGe, and URhGe, which exhibit long-range ferromagnetism well above the superconducting transition temperature T c , and the same electrons participate in the ferromagnetism and the superconductivity [1][2][3][4][5][6][7] .…”