28 research outputs found
Magnetic order and the electronic ground state in the pyrochlore iridate Nd2Ir2O7
We report a combined muon spin relaxation/rotation, bulk magnetization,
neutron scattering, and transport study of the electronic properties of the
pyrochlore iridate Nd2Ir2O7. We observe the onset of strongly hysteretic
behavior in the temperature dependent magnetization below 120 K, and an abrupt
increase in the temperature dependent resistivity below 8 K. Zero field muon
spin relaxation measurements show that the hysteretic magnetization is driven
by a transition to a magnetically disordered state, and that below 8 K a
complex magnetically ordered ground state sets in, as evidenced by the onset of
heavily damped spontaneous muon precession. Our measurements point toward the
absence of a true metal-to-insulator phase transition in this material and
suggest that Nd2Ir2O7 lies either within or on the metallic side of the
boundary of the Dirac semimetal regime within its topological phase diagram.Comment: 21 pages, 7 figure
Magnetic Order in the Pyrochlore Iridates A2Ir2O7 (A = Y, Yb)
We present results from muon spin relaxation/rotation, magnetization, neutron
scattering and transport measurements on polycrystalline samples of the
pyrochlore iridates Y2Ir2O7 (Y-227) and Yb2Ir2O7 (Yb-227). Well-defined
spontaneous oscillations of the muon asymmetry are observed together with
hysteretic behavior in magnetization below 130 K in Yb-227, indicative of
commensurate long-range magnetic order. Similar oscillations are observed in
Y-227 below 150 K; however the onset of hysteretic magnetization at T = 190 K
indicates a transition to an intermediate state lacking long-range order as
observed in Nd-227. Our results also show that insulating members of the
iridate family have nearly identical magnetic ground states, and that the
presence of magnetic A-site species does not play any significant role in
altering the ground state properties
Spin ordering and electronic texture in the bilayer iridate SrIrO
Through a neutron scattering, charge transport, and magnetization study, the
correlated ground state in the bilayer iridium oxide SrIrO is
explored. Our combined results resolve scattering consistent with a high
temperature magnetic phase that persists above 600 K, reorients at the
previously defined K, and coexists with an electronic ground state
whose phase behavior suggests the formation of a fluctuating charge or orbital
phase that freezes below K. Our study provides a window into
the emergence of multiple electronic order parameters near the boundary of the
metal to insulator phase transition of the 5d Mott phase.Comment: Revised text and figures. 4 pages, 4 figure
Optimizing for periodicity: a model-independent approach to flux crosstalk calibration for superconducting circuits
Flux tunability is an important engineering resource for superconducting
circuits. Large-scale quantum computers based on flux-tunable superconducting
circuits face the problem of flux crosstalk, which needs to be accurately
calibrated to realize high-fidelity quantum operations. Typical calibration
methods either assume that circuit elements can be effectively decoupled and
simple models can be applied, or require a large amount of data. Such methods
become ineffective as the system size increases and circuit interactions become
stronger. Here we propose a new method for calibrating flux crosstalk, which is
independent of the underlying circuit model. Using the fundamental property
that superconducting circuits respond periodically to external fluxes,
crosstalk calibration of N flux channels can be treated as N independent
optimization problems, with the objective functions being the periodicity of a
measured signal depending on the compensation parameters. We demonstrate this
method on a small-scale quantum annealing circuit based on superconducting flux
qubits, achieving comparable accuracy with previous methods. We also show that
the objective function usually has a nearly convex landscape, allowing
efficient optimization
Multiferroicity in doped hexagonal LuFeO3
The hexagonal phase of LuFeO3 is a rare example of a multiferroic material possessing a weak ferromagnetic moment, which is predicted to be switchable by an electric field. We stabilize this structure in bulk form though Mn and Sc doping, and determine the complete magnetic and crystallographic structures using neutron-scattering and magnetometry techniques. The ferroelectric P6(3)cm space group is found to be stable over a wide concentration range, ordering antiferromagnetically with Neel temperatures that smoothly increase following the ratio of c to a (c/a) lattice parameters up to 172 K, the highest found in this class of materials to date. The magnetic structure for a range of temperatures and dopings is consistent with recent studies of high quality epitaxial films of pure hexagonal LuFeO3 including a ferromagnetic moment parallel to the ferroelectric axis. We propose a mechanism by which room-temperature multiferroicity could be achieved in this class of materialsopen
Magnetization and Hall effect studies on the pyrochlore iridate Nd
We present magnetization and Hall effect measurements on the pyrochlore
iridate Nd2Ir2O7. Previous muon spin rotation measurements have shown that the
system undergoes an unusual transition at T = 110 K into a magnetic phase
lacking long-range order, followed by a transition at T = 6 K into a
state with long-range magnetic order. We observe a small remnant magnetization
when cycling through zero magnetic field at temperatures below T. Below
T, this remnant magnetization increases sharply, and new hysteresis
effects appear at a higher field B = 2.5 T, while the Hall resistance
develops a non-monotonic and hysteretic magnetic field dependence, with a
maximum at B and signatures of an anomalous Hall effect. The dependence on
field sweep direction demonstrates a non-trivial transition into a magnetically
ordered state with properties paralleling those of known spin-ice systems and
suggests a spin reorientation transition across the metal insulator transition
in the A-227 series
Magnetization and Hall effect studies on the pyrochlore iridate Nd2Ir2O7
We present magnetization and Hall effect measurements on the pyrochlore iridate Nd 2 Ir 2 O 7 . Previous muon spin rotation measurements have shown that the system undergoes an unusual transition at T M ≈110 K into a magnetic phase lacking long-range order, followed by a transition at T LRO ≈6 K into a state with long-range magnetic order. We observe a small remnant magnetization when cycling through a zero magnetic field at temperatures below T M . Below T LRO , this remnant magnetization increases sharply, and additional hysteresis effects appear at a higher field B c = 2.5 T, while the Hall resistance develops a nonmonotonic and hysteretic magnetic field dependence, with a maximum at B c and signatures of an anomalous Hall effect. The dependence on field sweep direction demonstrates a nontrivial transition into a magnetically ordered state with properties paralleling those of known spin-ice systems and suggests a spin reorientation transition across the metal-insulator transition in the A -227 series