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Abstract The interplay between a multitude of electronic, spin, and lattice degrees of freedom underlies the complex phase diagrams of quantum materials. Layer stacking in van der Waals (vdW) heterostructures is responsible for exotic electronic and magnetic properties, which inspires stacking control of two-dimensional magnetism. Beyond the interplay between stacking order and interlayer magnetism, we discover a spin-shear coupling mechanism in which a subtle shear of the atomic layers can have a profound effect on the intralayer magnetic order in a family of vdW antiferromagnets. Using time-resolved X-ray diffraction and optical linear dichroism measurements, interlayer shear is identified as the primary structural degree of freedom that couples with magnetic order. The recovery times of both shear and magnetic order upon optical excitation diverge at the magnetic ordering temperature with the same critical exponent. The time-dependent Ginzburg-Landau theory shows that this concurrent critical slowing down arises from a linear coupling of the interlayer shear to the magnetic order, which is dictated by the broken mirror symmetry intrinsic to the monoclinic stacking. Our results highlight the importance of interlayer shear in ultrafast control of magnetic order via spin-mechanical coupling. 

Understanding the pathways and time scales underlying electrically driven insulator-metal transitions is crucial for uncovering the fundamental limits of device operation. Using stroboscopic electron diffraction, we perform synchronized time-resolved measurements of atomic motions and electronic transport in operating vanadium dioxide (VO₂) switches. We discover an electrically triggered, isostructural state that forms transiently on microsecond time scales, which is shown by phase-field simulations to be stabilized by local heterogeneities and interfacial interactions between the equilibrium phases. This metastable phase is similar to that formed under photoexcitation within picoseconds, suggesting a universal transformation pathway. Our results establish electrical excitation as a route for uncovering nonequilibrium and metastable phases in correlated materials, opening avenues for engineering dynamical behavior in nanoelectronics.

 

On‐chip dynamic strain engineering requires efficient micro‐actuators that can generate large in‐plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (≈1 V) and produce considerable strains (≈1%). However, actuation speed and efficiency are limited by mass transport of ions. Minimizing the number of ions required to actuate is thus key to enabling useful “straintronic” devices. Here, it is shown that the electrochemical intercalation of exceptionally few lithium ions into WTe₂causes large anisotropic in‐plane strain: 5% in one in‐plane direction and 0.1% in the other. This efficient stretching of the 2D WTe₂layers contrasts to intercalation‐induced strains in related materials which are predominantly in the out‐of‐plane direction. The unusual actuation of Li_xWTe₂is linked to the formation of a newly discovered crystallographic phase, referred to as Td', with an exotic atomic arrangement. On‐chip low‐voltage (<0.2 V) control is demonstrated over the transition to the novel phase and its composition. Within the Td'‐Li_0.5−δWTe₂phase, a uniaxial in‐plane strain of 1.4% is achieved with a change of δ of only 0.075. This makes the in‐plane chemical expansion coefficient of Td'‐Li_0.5−δWTe₂far greater than of any other single‐phase material, enabling fast and efficient planar electrochemical actuation.