Crystal electric field splitting and f -electron hybridization in heavy-fermion CePt2In7

Abstract

We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is a member of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f 1 5/2 and 4f 1 7/2 states. Also, we find that the Fermi surface has a strongly three-dimensional topology, in agreement with density-functional theory calculations. PACS numbers: 74.25.Jb,71.18.+y,74.70.Tx, The physics underlying the formation of superconductivity from a coherent heavy fermion (HF) state has persisted as a central mystery despite more than four decades of intensive experimental and theoretical study [1,2]. HF superconductivity, similar to traditional Bardeen-Cooper-Schrieffer (BCS) superconductivity, is more likely to occur in compounds with particular crystal structures [3,4], and for magnetically mediated superconductivity, quasi-two-dimensional (2D) compounds are likely to have a higher transition temperature than a three-dimensional counterpart [5]. This expectation appears to be borne out in a family of tetragonal HF compounds Ce m M n In 3m+2n (M = Co, Rh, and Ir) in which the quasi-2D members with m=1, n=1 have T c 's [6] up to an order of magnitude higher than the maximum pressure-induced T c of 0.25 K found in cubic building block CeIn 3 [7]. Recent polarized soft x-ray absorption and nonresonant inelastic x-ray scattering experiments find that, in addition to the crystal structure, details of anisotropic hybridization of f and itinerant electrons play a nontrivial role in determining the ground state of the m=1, n=1 family members [8,9]. Understanding how superconductivity originates from a strongly correlated ground state which must be associated with structure, dimensionality, and orbital anisotropy requires detailed high-resolution techniques that allow studying quantitatively a system's electronic structure.Low-dimensional Ce-based systems hold a promise for the successful angle-resolved photoemission spectroscopy (ARPES) exploration of the HF electronic structure with high momentum and energy resolution. Most prior ARPES investigations of Ce-based HFs have been done on 3D systems but significant k z broadening [10-14] limits the intrinsic accuracy of 3D band measurement. Low photon energies produce high-energy and in-plane momentum resolutions; however, the 4f signal is quite low and sits atop a relatively large background. The part of the reciprocal-space spectrum where the nearly flat 4f bands, split by spin-orbit interaction, intersect with conduction bands is the site of interest for detailed inquiry. A Ce-based HF system, as close to 2D as possible, is needed to extract this information and that would provide a level of detail comparabl...

Angle-resolved photoemission spectroscopy study of crystal electric field in heavy fermion compound CePt2In7

“…We chose the AFM HF superconductor CePt 2 In 7 to study this concern. CePt 2 In 7 , discovered in 2008 [15], is a member of a widely-studied HF compound family Ce m M n In 3m+2n (M = Co, Rh, Ir, Pt) [10][11][12][13][16][17][18][19][20][21][22][23]. At ambient pressure CePt 2 In 7 undergoes an AFM phase transition at the Néel temperature T N = 5.2 K [24].…”

“…Nuclear quadrupolar resonance (NQR) and muon spin rotation/relaxation data reveal commensurate [28,29], or coexisting commensurate and incommensurate [8,30], AFM orders. A complex Fermi-surface (FS) topology composed of quasi-two-dimensional (quasi-2D) sheets or coexisting quasi-2D and three-dimensional (3D) character were revealed by quantum oscillation [31,32] and ARPES measurements [23,33]. Recently, weaker hybridization was revealed by optical spectroscopy [34] and ARPES [23].…”

“…A complex Fermi-surface (FS) topology composed of quasi-two-dimensional (quasi-2D) sheets or coexisting quasi-2D and three-dimensional (3D) character were revealed by quantum oscillation [31,32] and ARPES measurements [23,33]. Recently, weaker hybridization was revealed by optical spectroscopy [34] and ARPES [23]. Knight shift measurements return a T * ∼ 40 K [7], and NMR determines a T * ∼ 20 K [8].…”

“…Knight shift measurements return a T * ∼ 40 K [7], and NMR determines a T * ∼ 20 K [8]. BZ and calculated results are adopted from reference [23] In this study we varied the temperature between 10 and 136 K above the Néel temperature. CePt 2 In 7 FS topology along the k z (perpendicular) direction was mapped out using systematic photon energy dependence (hν = 76 -112 eV) and constant photon energy (hν = 85 and 92 eV) ARPES measurement.…”

“…CePt 2 In 7 FS topology along the k z (perpendicular) direction was mapped out using systematic photon energy dependence (hν = 76 -112 eV) and constant photon energy (hν = 85 and 92 eV) ARPES measurement. The FS measured topology was compared to density-functional theory (DFT) calculations [23]. The 4f electrons properties were investigated by comparing off-and on-resonance spectra.…”