656 research outputs found
Orbital Multiferroicity in Pentalayer Rhombohedral Graphene
Ferroic orders describe spontaneous polarization of spin, charge, and lattice
degrees of freedom in materials. Materials featuring multiple ferroic orders,
known as multiferroics, play important roles in multi-functional electrical and
magnetic device applications. 2D materials with honeycomb lattices offer
exciting opportunities to engineer unconventional multiferroicity, where the
ferroic orders are driven purely by the orbital degrees of freedom but not
electron spin. These include ferro-valleytricity corresponding to the electron
valley and ferro-orbital-magnetism supported by quantum geometric effects. Such
orbital multiferroics could offer strong valley-magnetic couplings and large
responses to external fields-enabling device applications such as
multiple-state memory elements, and electric control of valley and magnetic
states. Here we report orbital multiferroicity in pentalayer rhombohedral
graphene using low temperature magneto-transport measurements. We observed
anomalous Hall signals Rxy with an exceptionally large Hall angle (tan{\Theta}H
> 0.6) and orbital magnetic hysteresis at hole doping. There are four such
states with different valley polarizations and orbital magnetizations, forming
a valley-magnetic quartet. By sweeping the gate electric field E we observed a
butterfly-shaped hysteresis of Rxy connecting the quartet. This hysteresis
indicates a ferro-valleytronic order that couples to the composite field E\cdot
B, but not the individual fields. Tuning E would switch each ferroic order
independently, and achieve non-volatile switching of them together. Our
observations demonstrate a new type of multiferroics and point to electrically
tunable ultra-low power valleytronic and magnetic devices
Microwave Spin Control of a Tin-Vacancy Qubit in Diamond
The negatively charged tin-vacancy (SnV-) center in diamond is a promising
solid-state qubit for applications in quantum networking due to its high
quantum efficiency, strong zero phonon emission, and reduced sensitivity to
electrical noise. The SnV- has a large spin-orbit coupling, which allows for
long spin lifetimes at elevated temperatures, but unfortunately suppresses the
magnetic dipole transitions desired for quantum control. Here, by use of a
naturally strained center, we overcome this limitation and achieve
high-fidelity microwave spin control. We demonstrate a pi-pulse fidelity of up
to 99.51+/0.03%$ and a Hahn-echo coherence time of T2echo = 170.0+/-2.8
microseconds, both the highest yet reported for SnV- platform. This performance
comes without compromise to optical stability, and is demonstrated at 1.7
Kelvin where ample cooling power is available to mitigate drive induced
heating. These results pave the way for SnV- spins to be used as a building
block for future quantum technologies
Recommended from our members
Controlled interlayer exciton ionization in an electrostatic trap in atomically thin heterostructures.
Atomically thin semiconductor heterostructures provide a two-dimensional (2D) device platform for creating high densities of cold, controllable excitons. Interlayer excitons (IEs), bound electrons and holes localized to separate 2D quantum well layers, have permanent out-of-plane dipole moments and long lifetimes, allowing their spatial distribution to be tuned on demand. Here, we employ electrostatic gates to trap IEs and control their density. By electrically modulating the IE Stark shift, electron-hole pair concentrations above 2 × 1012 cm-2 can be achieved. At this high IE density, we observe an exponentially increasing linewidth broadening indicative of an IE ionization transition, independent of the trap depth. This runaway threshold remains constant at low temperatures, but increases above 20 K, consistent with the quantum dissociation of a degenerate IE gas. Our demonstration of the IE ionization in a tunable electrostatic trap represents an important step towards the realization of dipolar exciton condensates in solid-state optoelectronic devices
Electrically Tunable Valley Dynamics in Twisted WSe₂/WSe₂ Bilayers
The twist degree of freedom provides a powerful new tool for engineering the electrical and optical properties of van der Waals heterostructures. Here, we show that the twist angle can be used to control the spin-valley properties of transition metal dichalcogenide bilayers by changing the momentum alignment of the valleys in the two layers. Specifically, we observe that the interlayer excitons in twisted WSe₂/WSe₂ bilayers exhibit a high (>60%) degree of circular polarization (DOCP) and long valley lifetimes (>40 ns) at zero electric and magnetic fields. The valley lifetime can be tuned by more than 3 orders of magnitude via electrostatic doping, enabling switching of the DOCP from ∼80% in the n-doped regime to <5% in the p-doped regime. These results open up new avenues for tunable chiral light-matter interactions, enabling novel device schemes that exploit the valley degree of freedom
Controlled Interlayer Exciton Ionization in an Electrostatic Trap in Atomically Thin Heterostructures
Atomically thin semiconductor heterostructures provide a two-dimensional (2D)
device platform for creating high densities of cold, controllable excitons.
Interlayer excitons (IEs), bound electrons and holes localized to separate 2D
quantum well layers, have permanent out-of-plane dipole moments and long
lifetimes, allowing their spatial distribution to be tuned on demand. Here, we
employ electrostatic gates to trap IEs and control their density. By
electrically modulating the IE Stark shift, electron-hole pair concentrations
above cm can be achieved. At this high IE density, we
observe an exponentially increasing linewidth broadening indicative of an IE
ionization transition, independent of the trap depth. This runaway threshold
remains constant at low temperatures, but increases above 20 K, consistent with
the quantum dissociation of a degenerate IE gas. Our demonstration of the IE
ionization in a tunable electrostatic trap represents an important step towards
the realization of dipolar exciton condensates in solid-state optoelectronic
devices.Comment: 14 pages, 4 main figures, 1 extended data figur
- …