237 research outputs found
Intrinsic spin Hall torque in a moire Chern magnet
In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-dimensional system
with intrinsic magnetism and strong Berry curvature. We study AB-stacked
MoTe2/WSe2, which hosts a magnetic Chern insulator at a carrier density of one
hole per moire superlattice site. We observe hysteretic switching of the
resistivity as a function of applied current. Magnetic imaging using a
superconducting quantum interference device reveals that current switches
correspond to reversals of individual magnetic domains. The real space pattern
of domain reversals aligns precisely with spin accumulation measured near the
high-Berry curvature Hubbard band edges. This suggests that intrinsic spin- or
valley-Hall torques drive the observed current-driven magnetic switching in
both MoTe2/WSe2 and other moire materials. The switching current density of
10^3 Amps per square centimeter is significantly less than reported in other
platforms paving the way for efficient control of magnetic order
Intervalley coherence and intrinsic spin-orbit coupling in rhombohedral trilayer graphene
Rhombohedral graphene multilayers provide a clean and highly reproducible
platform to explore the emergence of superconductivity and magnetism in a
strongly interacting electron system. Here, we use electronic compressibility
and local magnetometry to explore the phase diagram of this material class in
unprecedented detail. We focus on rhombohedral trilayer in the quarter metal
regime, where the electronic ground state is characterized by the occupation of
a single spin and valley isospin flavor. Our measurements reveal a subtle
competition between valley imbalanced (VI) orbital ferromagnets and intervalley
coherent (IVC) states in which electron wave functions in the two momentum
space valleys develop a macroscopically coherent relative phase. Contrasting
the in-plane spin susceptibility of the IVC and VI phases reveals the influence
of graphene's intrinsic spin-orbit coupling, which drives the emergence of a
distinct correlated phase with hybrid VI and IVC character. Spin-orbit also
suppresses the in-plane magnetic susceptibility of the VI phase, which allows
us to extract the spin-orbit coupling strength of eV for
our hexagonal boron nitride-encapsulated graphene system. We discuss the
implications of finite spin-orbit coupling on the spin-triplet superconductors
observed in both rhombohedral and twisted graphene multilayers
Search for the Rare Decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-
The KTeV E799 experiment has conducted a search for the rare decays
KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-, where the X0 is a possible new
neutral boson that was reported by the HyperCP experiment with a mass of (214.3
pm 0.5) MeV/c^{2}. We find no evidence for either decay. We obtain upper limits
of Br(KL->pi0pi0X0->pi0pi0mu+mu-) pi0pi0mu+mu-) <
9.2 x 10^{-11} at the 90% confidence level. This result rules out the
pseudoscalar X0 as an explanation of the HyperCP result under the scenario that
the \bar{d}sX0 coupling is completely real
Search for the Rare Decay K_{L}\to\pi^{0}\pi^{0}\gamma
The KTeV E799 experiment has conducted a search for the rare decay
via the topology
(where ). Due to Bose
statistics of the pair and the real nature of the photon, the
decay is restricted to proceed at lowest order
by the CP conserving direct emission (DE) of an E2 electric quadrupole photon.
The rate of this decay is interesting theoretically since chiral perturbation
theory predicts that this process vanishes at level . Therefore, this
mode probes chiral perturbation theory at . In this paper we report a
determination of an upper limit of (90% CL) for
. This is approximately a factor of 20 lower than
previous results.Comment: six pages and six figures in the submission. Reformatted for Physics
Review
Determination of the Parity of the Neutral Pion via the Four-Electron Decay
We present a new determination of the parity of the neutral pion via the
double Dalitz decay pi^0 -> e+ e- e+ e-. Our sample, which consists of 30511
candidate decays, was collected from K_L -> pi0 pi0 pi0 decays in flight at the
KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the
negative pi^0 parity, and place a limit on scalar contributions to the pi^0 ->
e+ e- e+ e- decay amplitude of less than 3.3% assuming CPT conservation. The
pi^0 gamma* gamma* form factor is well described by a momentum-dependent model
with a slope parameter fit to the final state phase space distribution.
Additionally, we have measured the branching ratio of this mode to be B(pi^0 ->
e+ e- e+ e-) = (3.26 +- 0.18) x 10^(-5).Comment: 5 pages, 4 figures. Typographical error in radiative branching ratio
(Eq. 6) correcte
A Measurement of the K0 Charge Radius and a CP Violating Asymmetry Together with a Search for CP Violating E1 Direct Photon Emission in the Rare Decay KL->pi+pi-e+e-
Using the complete KTeV data set of 5241 candidate KL->pi+pi-e+e- decays
(including an estimated background of 204+-14 events), we have measured the
coupling gCR=0.163+- 0.014(stat)+-0.023(syst) of the CP conserving charge
radius process and from it determined a K0 charge radius of
(K0)=(-0.077+-0.007(stat)+-0.011(syst)) fm**2. We have also determined a
first experimental upper limit of 0.04 (90% CL) for the ratio |g_{E1}|/|g_{M1}|
of the coupling for the E1 direct photon emission process relative to the
coupling for M1 direct photon emission process. We also report the measurement
of its associated vector form factor |gM1`|(1+
(a_1/a_2)/(M(rho)**2-M(K)**2)+2M(K)E(gamma*)) where |gM1`|=(1.11+-
0.12(stat)+-0.08(syst) and a_1/a_2 = (-0.744+-0.027(stat)0.032(syst))
GeV**2/c**2. In addition, a measurement of the manifestly CP violating
asymmetry of magnitude (13.6+- 1.4+-(stat)+-1.5(syst))% in the CP and T odd
angle phi between the decay planes of the e+e- and pi+pi- pairs in the KL
center of mass system is reported
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