Superconducting Diode Effect and Large Magnetochiral Anisotropy in Td_d-MoTe2_2 Thin Film

In the absence of time-reversal invariance, metals without inversion symmetry may exhibit nonreciprocal charge transport -- a magnetochiral anisotropy that manifests as unequal electrical resistance for opposite current flow directions. If superconductivity also sets in, the charge transmission may become dissipationless in one direction while remaining dissipative in the opposite, thereby realizing a superconducting diode. Through both direct-current and alternating-current measurements, we study the nonreciprocal effects in thin films of the noncentrosymmetric superconductor T$_d$-MoTe\textsubscript{2} with disorders. We observe nonreciprocal superconducting critical currents with a diode efficiency close to 20\%~, and a large magnetochiral anisotropy coefficient up to \SI{5.9e8}{\per\tesla\per\ampere}, under weak out-of-plane magnetic field in the millitesla range. The great enhancement of rectification efficiency under out-of-plane magnetic field is likely abscribed to the vortex ratchet effect, which naturally appears in the noncentrosymmetric superconductor with disorders. Intriguingly, unlike the finding in Rashba systems, the strongest in-plane nonreciprocal effect does not occur when the field is perpendicular to the current flow direction. We develop a phenomenological theory to demonstrate that this peculiar behavior can be attributed to the asymmetric structure of spin-orbit coupling in T$_d$-MoTe\textsubscript{2}. Our study highlights how the crystallographic symmetry critically impacts the nonreciprocal transport, and would further advance the research for designing the superconducting diode with the best performance.Comment: 7 pages, 5figure

Dimer rattling mode induced low thermal conductivity in an excellent acoustic conductor

A solid with larger sound speeds usually exhibits higher lattice thermal conductivity. Here, we report an exception that CuP2 has a quite large mean sound speed of 4155 m s −1, comparable to GaAs, but single crystals show very low lattice thermal conductivity of about 4 W m −1 K−1 at room temperature, one order of magnitude smaller than GaAs. To understand such a puzzling thermal transport behavior, we have thoroughly investigated the atomic structures and lattice dynamics by combining neutron scattering techniques with first-principles simulations. This compound crystallizes in a layered structure where Cu atoms forming dimers are sandwiched in between P atomic networks. In this work, we reveal that Cu atomic dimers vibrate as a rattling mode with frequency around 11 meV, which is manifested to be remarkably anharmonic and strongly scatters acoustic phonons to achieve the low lattice thermal conductivity.This work was supported by the National Natural Science Foundation of China (Grant nos. 11934007 and 11804346), the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (Grant no. ZDBS-LY-JSC002), and the Liaoning Revitalization Talents Program (Grant no. XLYC1807122). J.S.Z. was supported by an NSF grant (MRSEC DMR-1720595). We acknowledge beam time awarded by ANSTO (Proposal no. P7373), ORNL (Proposal no. IPTS-21435.1), and SPring-8 (Proposal no. 2019A1249). A portion of this research used resources at Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. We thank Dr. Richard Mole for the help on the onsite data reduction and crystal alignment at Pelican as well as Dr. Guochu Deng for pre-aligning the crystal at the Joey Neutron Laue Camera.Center for Dynamics and Control of Material

NanoMi - An Open Source Transmission Electron Microscope

NanoMi is a project towards an open source modular electron microscope. It will allow to assemble transmission electron microscope (TEM) column, scanning TEM (STEM) column or scanning electron microscope (SEM) column. The goal of the NanoMi project is to establish framework for a community development of an electron microscope. Perhaps most important aspect is the license that covers the development: CERN Open Hardware v2, weakly reciprocal for hardware components. https://cern-ohl.web.cern.ch/ and GPL v3 for software (see below