Nonmagnetic impurity resonance states as a test of superconducting pairing symmetry in CeCoIn5

Abstract

We theoretically study the effect of a nonmagnetic impurity in heavy fermion superconductor CeCoIn5 within a coherent three-dimensional Anderson lattice model and the T-matrix approximation approach. By considering two known possible pairing symmetry candidates d x 2 −y 2 and dxy, we find that although both total density of states exhibit a similar V-shaped gaplike feature, only d x 2 −y 2 -wave pairing symmetry gives rise to robust intragap impurity resonance states reflected by the resonance peaks near the Fermi energy in the local density of states. These features can be readily probed by scanning tunneling microscopy experiments, and are proposed to shed light on the pairing symmetry and provide hints on the microscopic mechanism of unconventional superconductivity in the Ce-based heavy fermion superconductors.PACS numbers: 74.25.Jb, 74.20.Pq, 74.50.+r, 74.62.En Recently, the interplay of antiferromagnetic (AF) order and unconventional superconductivity in Ce-based heavy fermion superconductors CeMIn 5 (M = Co, Rh, Ir) have been intensively studied 1-13 . For instance, CeCoIn 5 is a superconductor with the highest transition temperature T c ≈ 2.3K whereas CeRhIn 5 orders antiferromagnetically below T N ≈ 3.7K 9 . On the other hand, superconductivity is observed in the latter compound by application of pressure whereas unconventional superconductivity in CeCoIn 5 9 emerges in close proximity to an AF quantum critical point as in the cuprates and pnictides superconductors. Moreover, neutron scattering experiments indicate strong AF quasielastic excitations at wavevectors Q= ( 1 2 1 2 1 2 ) and equivalent positions in the paramagnetic regime. When entering the superconducting state, the magnetic excitations spectra by inelastic neutron scattering show the appearance of a sharp spin resonance 10 . These finding underline the analogy to the cuprate high-temperature superconductors 14,15 and the new iron superconductors 16,17 , where AF spin fluctuations may actually mediate unconventional superconductivity.So far, the superconducting pairing symmetry in CeCoIn 5 has been discussed from both experimental and theoretical sides, it has not yet been determined unambiguously. Soon after the discovery of CeCoIn 5 material, its Fermi surface (FS) has been studied in detail by quantum oscillation, which consists of nearly cylindrical one and small ellipsoidal ones. The cylindrical sheets reflect quasi-two-dimensional(2D) character, by analogy with cuprates. Then the pairing state in CeCoIn5 has been widely believed to be unconventional with d-wave symmetry with vertical line node. The early thermal conductivity and specific heat have been measured in a rotating magnetic field, and gave a controversial result on whether CeCoIn 5 has a superconducting gap with d Although the ideally field-angle resolved thermal conductivity and specific heat measurements can give the position of the nodes, they rely on the ability to accurately model the true electronic structure, which in fact is poorly understood in heavy fermi...

Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials

“…CeCoIn 5 [21] exhibits the largest = T 2.3 c K in this family of heavy fermion materials, and has long been considered the 'hydrogen atom' of heavy fermion superconductivity [26,[122][123][124][125][126][127]. While much experimental [22][23][24][128][129][130][131][132][133][134][135] and theoretical effort [10,114,[136][137][138][139][140][141] has focused on illuminating its unconventional properties [142][143][144][145][146], and the microscopic mechanism underlying the emergence of superconductivity, no consensus has been reached to-date. A major obstacle in providing a quantitative or even qualitative explanation for its properties in the superconducting state has been the lack of insight into the material's complex electronic bandstructure [132].…”

Merohedral disorder and impurity impacts on superconductivity of fullerenes

“…Disorder, impurities in an otherwise homogeneous superconductor, are often undesired aliens because they may hinder observations of intrinsic properties of the host material [1][2][3] . Yet dopant impurities could also be a double-edged sword by leading not only to emergent hightemperature (Tc) superconductivity in cuprates and iron pnictides 4,5 but also to uncovering the underlying mechanism of unconventional superconductivity [6][7][8][9][10] , especially as multiple unusual states are complexly intertwined in these correlated electron materials 11,12 . Whereas it has been well documented that non-magnetic impurities little affect Cooper pairs in conventional superconductors 13,14 , they turn out to induce local bound states inside the superconducting gap and suppress superconductivity via pair breaking for unconventional pairing symmetries, for example, in a d-wave or s± wave superconductor 7,[14][15][16][17] .…”

“…Recently, anomalous enhancement of superconductivity by disorder is another example of impurities revealing their fundamental significance for the low-dimensional supercondcutors [18][19][20] . It is therefore tempting to consider impurities as a blessing in disguise to understand the physics of candidate superconductors [4][5][6][7][8][9][10][11][12][13][14][15][16][17] , to strive for optimal superconductivity 21 , and to create electronic states that never emerge from pure superconducting systems 22 .…”