36 research outputs found
Spin-orbit density wave induced hidden topological order in URu2Si2
The conventional order parameters in quantum matters are often characterized
by 'spontaneous' broken symmetries. However, sometimes the broken symmetries
may blend with the invariant symmetries to lead to mysterious emergent phases.
The heavy fermion metal URu2Si2 is one such example, where the order parameter
responsible for a second-order phase transition at Th = 17.5 K has remained a
long-standing mystery. Here we propose via ab-initio calculation and effective
model that a novel spin-orbit density wave in the f-states is responsible for
the hidden-order phase in URu2Si2. The staggered spin-orbit order 'spontaneous'
breaks rotational, and translational symmetries while time-reversal symmetry
remains intact. Thus it is immune to pressure, but can be destroyed by magnetic
field even at T = 0 K, that means at a quantum critical point. We compute
topological index of the order parameter to show that the hidden order is
topologically invariant. Finally, some verifiable predictions are presented.Comment: (v2) Substantially modified from v1, more calculation and comparison
with experiments are include
Möbius Kondo insulators
Heavy fermion materials have recently attracted attention for their potential
to combine topological protection with strongly correlated electron physics. To
date, the ideas of topological protection have been restricted to the heavy
fermion or "Kondo" insulators with the simplest point-group symmetries. Here we
argue that the presence of nonsymmorphic crystal symmetries in many heavy
fermion materials opens up a new family of topologically protected heavy
electron systems. Re-examination of archival resistivity measurements in
nonsymmorphic heavy fermion insulators CeBiPt and CeNiSn reveals
the presence of low temperature conductivity plateau, making them candidate
members of the new class of material. We illustrate our ideas with a specific
model for CeNiSn, showing how glide symmetries generate surface states with a
novel Mobius braiding that can be detected by ARPES or non-local conductivity
measurements. One of the interesting effects of strong correlation, is the
development of partially localization or "Kondo breakdown" on the surfaces,
which transforms Mobius surface states into quasi-one dimensional conductors,
with the potential for novel electronic phase transitions.Comment: Revised version. 24 pages, 9 figures, accepted by Nature Physic
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Photoemission from YbInCu4: Testing the single impurity model
The electronic properties of single crystal YbInCu4 and YbAgCu4 have been investigated by means of high resolution photoelectron spectroscopy. A first order, isostructural phase transition for YbInCu4 at 42 K leads to changes in the Kondo temperature, of more than an order of magnitude. This phase transition and accompanying Kondo temperature change provide the most direct test of the single impurity model to date. The photoemission results are incongruous with the single impurity model predictions for temperature dependence, binding energy and 4f occupancy, encouraging a re-evaluation of the single impurity model applicability. © 1999 Taylor & Francis Group, LLC
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Photoemission from YbInCu4: Testing the single impurity model
The electronic properties of single crystal YbInCu4 and YbAgCu4 have been investigated by means of high resolution photoelectron spectroscopy. A first order, isostructural phase transition for YbInCu4 at 42 K leads to changes in the Kondo temperature, of more than an order of magnitude. This phase transition and accompanying Kondo temperature change provide the most direct test of the single impurity model to date. The photoemission results are incongruous with the single impurity model predictions for temperature dependence, binding energy and 4f occupancy, encouraging a re-evaluation of the single impurity model applicability. © 1999 Taylor & Francis Group, LLC
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Photoemission spectra of CeAl3, CeBe13, CeSi2, and CeCu2Si2: Weights and widths of the 4f emission features.
We present valence-band photoemission spectra for CeAl3, CeBe13, CeSi2, CeCu2Si2, and related conventional rare-earth counterpart compounds, taken at photon energies corresponding to the giant 4d resonance with resolution ∼150 meV. We take into account the 5d emission, which comprises 30% of the valence-band emission at the 4d resonance. We compare the resulting 4f emission to the predictions of the Anderson impurity model calculated in a low-order 1/N expansion, and including spin-orbit, crystal-field, and finite Coulomb correlation effects. The calculation gives order-of-magnitude fits to the data, but underestimates the spectral weight near the Fermi level by a factor of 2 and overestimates the width of the main f emission at 2 eV by a factor of 4. We argue that Ce photoemission remains an open problem and discuss several experimental and theoretical issues which need to be resolved to make further progress. © 1993 The American Physical Society
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Photoemission spectra of CeAl3, CeBe13, CeSi2, and CeCu2Si2: Weights and widths of the 4f emission features.
We present valence-band photoemission spectra for CeAl3, CeBe13, CeSi2, CeCu2Si2, and related conventional rare-earth counterpart compounds, taken at photon energies corresponding to the giant 4d resonance with resolution ∼150 meV. We take into account the 5d emission, which comprises 30% of the valence-band emission at the 4d resonance. We compare the resulting 4f emission to the predictions of the Anderson impurity model calculated in a low-order 1/N expansion, and including spin-orbit, crystal-field, and finite Coulomb correlation effects. The calculation gives order-of-magnitude fits to the data, but underestimates the spectral weight near the Fermi level by a factor of 2 and overestimates the width of the main f emission at 2 eV by a factor of 4. We argue that Ce photoemission remains an open problem and discuss several experimental and theoretical issues which need to be resolved to make further progress. © 1993 The American Physical Society
4f bands in Ce heavy fermions and mixed valent compounds at T ≫ TK
We report evidence of 4f band character in Ce 4f states at T ≫ TK using high-resolution angle-resolved resonant photoemission. The Ce intermetallic compound CePt2+x was grown and studied in situ by the method of MBE and was characterized by LEED, XPS and XAS. These new findings suggest a need for a re-examination of 4f photoemission in Ce compounds. © 1995