{
  "id": "1904.07203",
  "version": "v1",
  "published": "2019-04-15T17:25:59.000Z",
  "updated": "2019-04-15T17:25:59.000Z",
  "title": "Anisotropic upper critical field of pristine and proton-irradiated single crystals of the magnetically ordered superconductor RbEuFe$_4$As$_4$",
  "authors": [
    "M. P. Smylie",
    "A. E. Koshelev",
    "K. Willa",
    "R. Willa",
    "W. -K. Kwok",
    "J. -K. Bao",
    "D. Y. Chung",
    "M. G. Kanatzidis",
    "J. Singleton",
    "F. F. Balakirev",
    "H. Hebbeker",
    "P. Niraula",
    "E. Bokari",
    "A. Kayani",
    "U. Welp"
  ],
  "comment": "10 pages (including references), 7 figures",
  "categories": [
    "cond-mat.supr-con"
  ],
  "abstract": "We present a study of the upper critical field, H$_{c2}$, of pristine and proton-irradiated RbEuFe$_4$As$_4$ crystals in pulsed magnetic fields of up to 65 T. The data for H$_{c2}$ reveal pronounced downwards curvature, particularly for the in-plane field orientation, and a superconducting anisotropy that decreases with decreasing temperature. These features are indicative of Pauli paramagnetic limiting. For the interpretation of these data, we use a model of a clean single-band superconductor with an open Fermi surface in the shape of a warped cylinder, which includes strong paramagnetic limiting. Fits to the data reveal that the in-plane upper critical field is Pauli paramagnetic limited, while the out-of-plane upper critical field is orbitally limited and that the orbital and paramagnetic fields have opposite anisotropies. A consequence of this particular combination is the unusual inversion of the anisotropy, $H_{c2}^{ab} < H_{c2}^c$, of the irradiated sample at temperatures below 10 K. The fits also yield an in-plane Maki parameter, $\\alpha_M^{110} \\approx$ 2.6, exceeding the critical value for the formation of the Fulde-Ferrell-Larkin-Ovchinnikov state. Nevertheless, the current measurements did not reveal direct evidence for the occurrence of this state.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2019-04-15T17:25:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "anisotropic upper critical field",
      "magnetically ordered superconductor rbeufe",
      "proton-irradiated single crystals",
      "pauli paramagnetic"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}