27 research outputs found
The approach to a superconductor-to-Bose-insulator transition in disordered films
Through a detailed study of scaling near the magnetic field-tuned
superconductor-to-insulator transition in strongly disordered films, we find
that results for a variety of materials can be collapsed onto a single phase
diagram. The data display two clear branches, one with weak disorder and an
intervening metallic phase, the other with strong disorder. Along the strongly
disordered branch, the resistance at the critical point approaches and the scaling of the resistance is consistent with quantum
percolation, and therefore with the predictions of the dirty boson model.Comment: 4 pages, 4 figure
Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate -LiIrO
Honeycomb iridates such as -LiIrO are argued to realize
Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly
other couplings. While systems with pure Kitaev interactions are candidates to
realize a quantum spin liquid ground state, in -LiIrO it has
been shown that the balance of magnetic interactions leads to the
incommensurate spiral spin order at ambient pressure below 38 K. We study the
fragility of this state in single crystals of -LiIrO using
resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to
3.0 GPa. RXS is a direct probe of the underlying electronic order, and we
observe the abrupt disappearance of the =(0.57, 0, 0) spiral order at a
critical pressure GPa with no accompanying change in the symmetry
of the lattice. This dramatic disappearance is in stark contrast with recent
studies of -LiIrO that show continuous suppression of the spiral
order in magnetic field; under pressure, a new and possibly nonmagnetic ground
state emerges
Weak antilocalization and disorder-enhanced electron interactions in crystalline GeSbTe
Phase change materials can be reversibly switched between amorphous and
crystalline states and often show strong contrast in the optical and electrical
properties of these two phases. They are now in widespread use for optical data
storage, and their fast switching and a pronounced change of resistivity upon
crystallization are also very attractive for nonvolatile electronic data
storage. Nevertheless there are still several open questions regarding the
electronic states and charge transport in these compounds. In this work we
study electrical transport in thin metallic films of the disordered,
crystalline phase change material GeSbTe. We observe weak
antilocalization and disorder enhanced Coulomb interaction effects at low
temperatures, and separate the contributions of these two phenomena to the
temperature dependence of the resistivity, Hall effect, and magnetoresistance.
Strong spin-orbit scattering causes positive magnetoresistance at all
temperatures, and a careful analysis of the low-field magnetoresistance allows
us to extract the temperature dependent electron dephasing rate and study other
scattering phenomena. We find electron dephasing due to inelastic
electron-phonon scattering at higher temperatures, electron-electron scattering
dephasing at intermediate temperatures, and a crossover to weak temperature
dependence below 1 K
A new spin-anisotropic harmonic honeycomb iridate
The physics of Mott insulators underlies diverse phenomena ranging from high
temperature superconductivity to exotic magnetism. Although both the electron
spin and the structure of the local orbitals play a key role in this physics,
in most systems these are connected only indirectly --- via the Pauli exclusion
principle and the Coulomb interaction. Iridium-based oxides (iridates) open a
further dimension to this problem by introducing strong spin-orbit
interactions, such that the Mott physics has a strong orbital character. In the
layered honeycomb iridates this is thought to generate highly spin-anisotropic
interactions, coupling the spin orientation to a given spatial direction of
exchange and leading to strongly frustrated magnetism. The potential for new
physics emerging from such interactions has driven much scientific excitement,
most recently in the search for a new quantum spin liquid, first discussed by
Kitaev \cite{kitaev_anyons_2006}. Here we report a new iridate structure that
has the same local connectivity as the layered honeycomb, but in a
three-dimensional framework. The temperature dependence of the magnetic
susceptibility exhibits a striking reordering of the magnetic anisotropy,
giving evidence for highly spin-anisotropic exchange interactions. Furthermore,
the basic structural units of this material suggest the possibility of a new
family of structures, the `harmonic honeycomb' iridates. This compound thus
provides a unique and exciting glimpse into the physics of a new class of
strongly spin-orbit coupled Mott insulators.Comment: 12 pages including bibliography, 5 figure