35 research outputs found

    Electronic Structure of LuRh2Si2: "Small" Fermi Surface Reference to YbRh2Si2

    Full text link
    We present band structure calculations and quantum oscillation measurements on LuRh2Si2, which is an ideal reference to the intensively studied quantum critical heavy-fermion system YbRh2Si2. Our band structure calculations show a strong sensitivity of the Fermi surface on the position of the silicon atoms zSi within the unit cell. Single crystal structure refinement and comparison of predicted and observed quantum oscillation frequencies and masses yield zSi = 0.379c in good agreement with numerical lattice relaxation. This value of zSi is suggested for future band structure calculations on LuRh2Si2 and YbRh2Si2. LuRh2Si2 with a full f electron shell represents the "small" Fermi surface configuration of YbRh2Si2. Our experimentally and ab initio derived quantum oscillation frequencies of LuRh2Si2 show strong differences with earlier measurements on YbRh2Si2. Consequently, our results confirm the contribution of the f electrons to the Fermi surface of YbRh2Si2 at high magnetic fields. Yet the limited agreement with refined fully itinerant local density approximation calculations highlights the need for more elaborated models to describe the Fermi surface of YbRh2Si2.Comment: 12 pages 10 figure

    Spectroscopic study of the magnetic ground state of Nb1−y_{1-y}Fe2+y_{2+y}

    Full text link
    We have investigated single crystals and polycrystals from the series Nb1−y_{1-y}Fe2+y_{2+y}, −0.004≤y≤0.018-0.004 \leq y \leq 0.018 by electron spin resonance, muon spin relaxation and M\"ossbauer spectroscopy. Our data establish that at lowest temperatures all samples exhibit bulk magnetic order. Slight Fe-excess induces low-moment ferromagnetism, consistent with bulk magnetometry (≃0.06 μB/Fe\simeq 0.06 ~\mu_B/{\rm Fe}), Nb--rich and stoichiometric NbFe2_2 display spin density wave order with small magnetic moment amplitudes of the order ∼0.001−0.01 μB/Fe\sim 0.001 - 0.01 ~\mu_B/{\rm Fe}. This provides microscopic evidence for a modulated magnetic state on the border of ferromagnetism in NbFe2_2.Comment: 7 pages, 9 figure

    Normal and intrinsic anomalous Hall effect in Nb1-yFe2+y

    Full text link
    The Hall effect on selected samples of the dilution series Nb1-yFe2+y is studied. Normal and anomalous contributions are observed, with positive normal Hall effect dominating at high temperatures. Consistent analysis of the anomalous contribution is only possible for Fe-rich Nb0.985Fe2.015 featuring a ferromagnetic ground state. Here, a positive normal Hall coefficient is found at all temperatures with a moderate maximum at the spin-density-wave transition. The anomalous Hall effect is consistent with an intrinsic (Berry-phase) contribution which is constant below the ordering temperature TC and continuously vanishes above TC. For stoichiometric NbFe2 and Nb-rich Nb1.01Fe1.99 - both having a spin-density-wave ground state - an additional contribution to the Hall resistivity impedes a complete analysis and indicates the need for more sophisticated models of the anomalous Hall effect in itinerant antiferromagnets.Comment: 6 pages 5 figure

    Pressure-induced and Composition-induced Structural Quantum Phase Transition in the Cubic Superconductor (Sr/Ca)_3Ir_4Sn_{13}

    Full text link
    We show that the quasi-skutterudite superconductor Sr_3Ir_4Sn_{13} undergoes a structural transition from a simple cubic parent structure, the I-phase, to a superlattice variant, the I'-phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T* can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.Comment: 4 figures, 5 pages (excluding supplementary material). To be published in Phys. Rev. Let

    Strong in-plane anisotropy in the electronic structure of fixed-valence β\beta-LuAlB4_4

    Full text link
    The origin of intrinsic quantum criticality in the heavy-fermion superconductor β\beta-YbAlB4_4 has been attributed to strong Yb valence fluctuations and its peculiar crystal structure. Here, we assess these contributions individually by studying the isostructural but fixed-valence compound β\beta-LuAlB4_4. Quantum oscillation measurements and DFT calculations reveal a Fermi surface markedly different from that of β\beta-YbAlB4_4, consistent with a `large' Fermi surface there. We also find an unexpected in-plane anisotropy of the electronic structure, in contrast to the isotropic Kondo hybridization in β\beta-YbAlB4_4.Comment: 6 pages, 4 figure

    Magnetic signatures of multicomponent superconductivity in pressurized UTe2

    Full text link
    The heavy fermion material UTe2_2 possesses a rich phase diagram with multiple superconducting phases, several of which exhibit characteristics of odd-parity pairing. Here, we report on the pressure dependence of signatures of the superconducting transition in the temperature dependent ac magnetic susceptibility χ(T)\chi(T) in high quality UTe2_2 single crystals. We resolve a single superconducting transition in χ(T)\chi(T) at low pressures << 0.3 GPa. At higher pressure, however, a second feature emerges in χ(T)\chi(T), which is located at the thermodynamic phase boundary between two separate superconducting states previously identified by specific heat studies. The observation of a two-step transition in χ(T)\chi(T) can be understood as a consequence of the change in the London penetration depth, when UTe2_2 switches from one superconducting phase into another

    Superconductivity beyond the Pauli limit in high-pressure CeSb2

    Full text link
    We report the discovery of superconductivity at a pressure-induced magnetic quantum critical point in the Kondo-lattice system CeSb2, sustained up to magnetic fields that exceed the conventional Pauli limit eight-fold. Like CeRh2As2, CeSb2 is locally non-centrosymmetric around the Ce-site, but the evolution of critical fields and normal state properties as CeSb2 is tuned through the quantum critical point motivates a fundamentally different explanation for its resilience to applied field.Comment: 5 pages, 3 figure
    corecore