74 research outputs found
Anisotropic Zeeman Splitting in YbNi4P2
The electronic structure of heavy-fermion materials is highly renormalised at
low temperatures with localised moments contributing to the electronic
excitation spectrum via the Kondo effect. Thus, heavy-fermion materials are
very susceptible to Lifshitz transitions due to the small effective Fermi
energy arising on parts of the renormalised Fermi surface. Here, we study
Lifshitz transitions that have been discovered in YbNi4P2 in high magnetic
fields. We measure the angular dependence of the critical fields necessary to
induce a number of Lifshitz transitions and find it to follow a simple
Zeeman-shift model with anisotropic g-factor. This highlights the coherent
nature of the heavy quasiparticles forming a renormalised Fermi surface. We
extract information on the orientation of the Fermi surface parts giving rise
to the Lifshitz transitions and we determine the anisotropy of the effective
g-factor to be in good agreement with the crystal field
scheme of YbNi4P2.Comment: 10 pages, 5 figures, prepared for resubmission to SciPos
Cascade of magnetic field induced Lifshitz transitions in the ferromagnetic Kondo lattice material YbNi4P2
A ferromagnetic quantum critical point is thought not to exist in two and
three-dimensional metallic systems yet is realized in the Kondo lattice
compound YbNi4(P,As)2, possibly due to its one-dimensionality. It is crucial to
investigate the dimensionality of the Fermi surface of YbNi4P2 experimentally
but common probes such as ARPES and quantum oscillation measurements are
lacking. Here, we studied the magnetic field dependence of transport and
thermodynamic properties of YbNi4P2. The Kondo effect is continuously
suppressed and additionally we identify nine Lifshitz transitions between 0.4
and 18 T. We analyze the transport coefficients in detail and identify the type
of Lifshitz transitions as neck or void type to gain information on the Fermi
surface of YbNi4P2. The large number of Lifshitz transitions observed within
this small energy window is unprecedented and results from the particular flat
renormalized band structure with strong 4f-electron character shaped by the
Kondo lattice effect.Comment: 6 pages, 4 figure
Simultaneous loss of interlayer coherence and long-range magnetism in quasi-two-dimensional PdCrO\u3csub\u3e2\u3c/sub\u3e
Incoherent transport is an important feature of many anisotropic quantum materials but often its origin is not well understood. Here, the authors show that in a layered quantum magnet, incoherence is driven by the interaction of electrons with spin fluctuations after the
Measurement Of Magnetic Susceptibility In Pulsed Magnetic Fields Using A Proximity Detector Oscillator
We present a novel susceptometer with a particularly small spatial footprint and no moving parts. The susceptometer is suitable for use in systems with limited space where magnetic measurements may not have been previously possible, such as in pressure cells and rotators, as well as in extremely high pulsed fields. The susceptometer is based on the proximity detector oscillator, which has a broad dynamic resonant frequency range and has so far been used predominantly for transport measurements. We show that for insulating samples, the resonance frequency behavior as a function of field consists of a magnetoresistive and an inductive component, originating, respectively, from the sensor coil and the sample. The response of the coil is modeled, and upon subtraction of the magnetoresistive component the dynamic magnetic susceptibility and magnetization can be extracted. We successfully measure the magnetization of the organic molecular magnets Cu(H2O)(5)(VOF4)(H2O) and [Cu(HF2)(pyz)(2)]BF4 in pulsed magnetic fields and by comparing the results to that from a traditional extraction susceptometer confirm that the new system can be used to measure and observe magnetic susceptibilities and phase transitions. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3653395
Emergence of the nematic electronic state in FeSe
We present a comprehensive study of the evolution of the nematic electronic
structure of FeSe using high resolution angle-resolved photoemission
spectroscopy (ARPES), quantum oscillations in the normal state and
elastoresistance measurements. Our high resolution ARPES allows us to track the
Fermi surface deformation from four-fold to two-fold symmetry across the
structural transition at ~87 K which is stabilized as a result of the dramatic
splitting of bands associated with dxz and dyz character. The low temperature
Fermi surface is that a compensated metal consisting of one hole and two
electron bands and is fully determined by combining the knowledge from ARPES
and quantum oscillations. A manifestation of the nematic state is the
significant increase in the nematic susceptibility as approaching the
structural transition that we detect from our elastoresistance measurements on
FeSe. The dramatic changes in electronic structure cannot be explained by the
small lattice effects and, in the absence of magnetic fluctuations above the
structural transition, points clearly towards an electronically driven
transition in FeSe stabilized by orbital-charge ordering.Comment: Latex, 8 pages, 4 figure
Robustness of superconductivity to structural disorder in Sr0.3(NH2)y(NH3)1−yFe2Se2
The superconducting properties of a recently discovered high-Tc superconductor, Sr/ammonia-intercalated FeSe, have been measured using pulsed magnetic fields down to 4.2 K and muon spin spectroscopy down to 1.5 K. This compound exhibits intrinsic disorder resulting from random stacking of the FeSe layers along the c axis that is not present in other intercalates of the same family. This arises because the coordination requirements of the intercalated Sr and ammonia moieties imply that the interlayer stacking (along c) involves a translation of either a/2 or b/2 that locally breaks tetragonal symmetry. The result of this stacking arrangement is that the Fe ions in this compound describe a body-centered-tetragonal lattice in contrast to the primitive arrangement of Fe ions described in all other Fe-based superconductors. In pulsed magnetic fields, the upper critical field Hc2 was found to increase on cooling with an upward curvature that is commonly seen in type-II superconductors of a multiband nature. Fitting the data to a two-band model and extrapolation to absolute zero gave a maximum upper critical field μ0Hc2(0) of 33(2)T. A clear superconducting transition with a diamagnetic shift was also observed in transverse-field muon measurements at Tc≈36.3(2)K. These results demonstrate that robust superconductivity in these intercalated FeSe systems does not rely on perfect structural coherence along the c axis
Controlling magnetic order and quantum disorder in molecule-based magnets.
We investigate the structural and magnetic properties of two molecule-based magnets synthesized from the same starting components. Their different structural motifs promote contrasting exchange pathways and consequently lead to markedly different magnetic ground states. Through examination of their structural and magnetic properties we show that [Cu(pyz)(H 2 O)(gly) 2 ](ClO 4 ) 2 may be considered a quasi-one-dimensional quantum Heisenberg antiferromagnet whereas the related compound [Cu(pyz)(gly)](ClO 4 ) , which is formed from dimers of antiferromagnetically interacting Cu 2+ spins, remains disordered down to at least 0.03 K in zero field but shows a field-temperature phase diagram reminiscent of that seen in materials showing a Bose-Einstein condensation of magnons
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