35 research outputs found
Electronic Structure of LuRh2Si2: "Small" Fermi Surface Reference to YbRh2Si2
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
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Strong coupling superconductivity in a quasiperiodic host-guest structure.
We examine the low-temperature states supported by the quasiperiodic host-guest structure of elemental bismuth at high pressure, Bi-III. Our electronic transport and magnetization experiments establish Bi-III as a rare example of type II superconductivity in an element, with a record upper critical field of ~ 2.5 T, unusually strong electron-phonon coupling, and an anomalously large, linear temperature dependence of the electrical resistivity in the normal state. These properties may be attributed to the peculiar phonon spectrum of incommensurate host-guest structures, which exhibit additional quasi-acoustic sliding modes, suggesting a pathway toward strong coupling superconductivity with the potential for enhanced transition temperatures and high critical fields
Spectroscopic study of the magnetic ground state of NbFe
We have investigated single crystals and polycrystals from the series
NbFe, 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 (), Nb--rich and stoichiometric NbFe display spin
density wave order with small magnetic moment amplitudes of the order . This provides microscopic evidence for a
modulated magnetic state on the border of ferromagnetism in NbFe.Comment: 7 pages, 9 figure
Normal and intrinsic anomalous Hall effect in Nb1-yFe2+y
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}
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 -LuAlB
The origin of intrinsic quantum criticality in the heavy-fermion
superconductor -YbAlB 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 -LuAlB. Quantum oscillation measurements and DFT
calculations reveal a Fermi surface markedly different from that of
-YbAlB, 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 -YbAlB.Comment: 6 pages, 4 figure
Magnetic signatures of multicomponent superconductivity in pressurized UTe2
The heavy fermion material UTe 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 in high quality UTe single crystals. We resolve a
single superconducting transition in at low pressures 0.3 GPa. At
higher pressure, however, a second feature emerges in , 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 can be understood as a
consequence of the change in the London penetration depth, when UTe
switches from one superconducting phase into another
Superconductivity beyond the Pauli limit in high-pressure CeSb2
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
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Unconventional Superconductivity in the Layered Iron Germanide YFe(2)Ge(2).
The iron-based intermetallic YFe_{2}Ge_{2} stands out among transition metal compounds for its high Sommerfeld coefficient of the order of 100  mJ/(mol K^{2}), which signals strong electronic correlations. A new generation of high quality samples of YFe_{2}Ge_{2} show superconducting transition anomalies below 1.8 K in thermodynamic, magnetic, and transport measurements, establishing that superconductivity is intrinsic in this layered iron compound outside the known superconducting iron pnictide or chalcogenide families. The Fermi surface geometry of YFe_{2}Ge_{2} resembles that of KFe_{2}As_{2} in the high pressure collapsed tetragonal phase, in which superconductivity at temperatures as high as 10 K has recently been reported, suggesting an underlying connection between the two systems.The work was supported by the EPSRC of the UK and by Trinity College. Supporting data can be found at https://www.repository.cam.ac.uk/handle/1810/253875.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevLett.116.12700