The temperature-induced structure variation and its effect on physical properties is pivotal in material preparation for devices application. Motivated by surface scanning tunnel microscope (STM) measurement of $T_d-{\mathrm{MoTe}}_2$ single crystal at low temperature, temperature dependent electronic structure, lattice dynamics, and topological properties are explored to understand the microscopic origin of the observed anisotropic negative thermal expansion and abnormal STM images below 70 K. Remarkably, we find that the nonequivalent Te atoms in $T_d-{\mathrm{MoTe}}_2$ have qualitatively different contributions to both phonon spectra and electronic structures. The in-plane longitudinal acoustic mode and the ${\mathrm{Te}}_{\left(2\right)}$ atoms are found to play an important role in uniaxial negative thermal expansion and the temperature dependent electronic phase transition, respectively. Interestingly, under the scalar relativistic approximation, a band renormalization occurs, accompanied by a Dirac phase transition from type II to type I, upon cooling below 70 K. Introducing spin-orbit coupling induces a temperature dependent semimetal–semiconductor transition. Our results explain the experimental phenomena very well: abnormal surface STM image below 70 K does not originate from the displacement of the Te atoms but the band renormalization owing to strong electron-lattice coupling.

This study introduces a novel multi-degree-of-freedom (MDOF) piezoelectric motor (PEM) for high precision and a 10 × 10 mm2 large travel range within a rigid and compact structure (33 × 33 × 30 mm3). The motor consists of four piezoelectric tubes (PTs) arranged and mounted parallel to each other to enable controlled movement along both the X and Y axes by using a sawtooth waveform with a time-delay control strategy. The design features a moving plate clamped between two upper and two lower sapphire balls, with the balls supported by CuBe springs, ensuring symmetric and precise movement. Applying individual driving signals to each PT induces bending deformation sequentially in the same direction, followed by simultaneous recovery to the original position, thereby enabling the movement of the moving plate. Experimental results demonstrated that the motor operated effectively at a signal frequency of 150 Hz, with a minimum driving voltage of 18 V required for detectable motion. The motor exhibited the capability to produce step sizes from 0.53 to 6.23 µm with a linear relationship between driving voltage (±30 to ±180 V) and step size, ensuring consistent performance. The hysteresis analysis revealed minimal energy loss, with hysteresis ratios of 5.2% on the X axis and 4.16% on the Y axis, indicating the motor’s high precision and efficiency. Additionally, the motor sustained a load of 120 g while traversing a 10 × 10 mm2 area, and continuous operation for 12 h revealed no significant performance degradation. The compact and reliable design of this novel MDOF PEM holds potential for applications in confined spaces, such as small-bore superconducting magnets, enabling precise large-area atomic resolution imaging and magnetic property measurements.

We present a novel homebuilt scanning tunneling microscope (STM) with atomic resolution integrated into a cryogen-free superconducting magnet system with a variable temperature insert. The STM head is designed as a nested structure of double piezoelectric tubes (PTs), which are connected coaxially through a sapphire frame whose top has a sample stage. A single shaft made of tantalum, with the STM tip on top, is held firmly by a spring strip inside the internal PT. The external PT drives the shaft to the tip–sample junction based on the SpiderDrive principle, and the internal PT completes the subsequent scanning and imaging work. The STM head is simple, compact, and easy to assemble. The excellent performance of the device was demonstrated by obtaining atomic-resolution images of graphite and low drift rates of 30.2 pm/min and 41.4 pm/min in the X–Y plane and Z direction, respectively, at 300K. In addition, we cooled the sample to 1.6 K and took atomic-resolution images of graphite and NbSe₂. Finally, we performed a magnetic field sweep test from 0 T to 9 T at 70 K, obtaining distinct graphite images with atomic resolution under varying magnetic fields. These experiments show our newly developed STM’s high stability, vibration resistance, and immunity to high magnetic fields.