Disorder-robust high-field superconducting phase of FeSe single crystals

Abstract

When exposed to high magnetic fields, certain materials manifest an exotic superconducting (SC) phase that has attracted considerable attention. A proposed explanation for the origin of the high-field SC phase is the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. This state is characterized by inhomogeneous superconductivity, where the Cooper pairs have finite center-of-mass momenta. Recently, the high-field SC phase was observed in FeSe, and it was deemed to originate from the FFLO state. Here, we synthesize FeSe single crystals with different levels of disorder. The level of disorder is expressed by the ratio of the mean free path to the coherence length and ranges between 35 and 1.2. The upper critical field \textit{B}${}_{\mathrm{c}2}$ was obtained by both resistivity and magnetic torque measurements over a wide range of temperatures, which went as low as $\sim$0.5 K, and magnetic fields, which went up to $\sim$38 T along the \textit{c} axis and in the \textit{ab} plane. In the high-field region parallel to the \textit{ab} plane, an unusual SC phase was confirmed in all the crystals, and the phase was found to be robust against disorder. This result suggests that the high-field SC phase in FeSe is not a conventional FFLO state.

11 pages, 11 figures

References in corpus (19)

• The Structural Phase Transition in FeSe (Fe1+dSe)
• Fulde-Ferrell-Larkin-Ovchinnikov State in Heavy Fermion Superconductors
• Nematic and meta-nematic transitions in the iron pnictides
• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• Calorimetric Evidence for a Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in the Layered Organic Superconductor κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$
• Anomalous Fermi surface in FeSe seen by Shubnikov-de Haas oscillation measurements
• Evidence of Andreev bound states as a hallmark of the FFLO phase in $\kappa$-(BEDT-TTF)${}_2$Cu(NCS)${}_2$
• Evidence for an FFLO state with segmented vortices in the BCS-BEC-crossover superconductor FeSe
• Phase Diagram and Spectroscopy of FFLO states of two-dimensional d-wave superconductors
• Thermodynamic evidence for the Fulde-Ferrell-Larkin-Ovchinnikov state in the KFe2As2 superconductor
• Upper critical field study in the organic superconductor ${\beta }^{\prime \prime }$-(ET)${}_2$SF${}_5$CH${}_2$CF${}_2$SO${}_3$ : Possibility of Fulde-Ferrell-Larkin-Ovchinnikov state
• Gap structure of FeSe determined by field-angle-resolved specific heat measurements
• Inherent spin density wave instability by vortices in superconductors with strong Pauli effects
• Impurity-induced configuration-transition in the Fulde-Ferrell-Larkin-Ovchinnikov state of a d-wave superconductor
• Controllable spin-orbit coupling and its influence on the upper critical field in the chemically doped quasi-one-dimensional Nb${}_2$PdS${}_5$ superconductor
• Strong Pauli paramagnetic effect in the upper critical field of KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Observation of the in-plane magnetic field-induced phase transitions in FeSe
• Impurity-induced bound states inside the superconducting gap of FeSe
• Vortex-lattice melting and paramagnetic depairing in the nematic superconductor FeSe

Cited by in corpus (1)

• Investigation of the Pauli paramagnetic effect in systematically tuned NbN thin films